Swift: generate getParent implementation

By explicitly marking children in the `schema.yml` file, an internal
`getAChild` predicate is implemented, that is in turn used in `AstNode`
to implement `getParent`.

This is yet to be used in the control flow library to replace the
hand-rolled implementation.

A further, more complex step is to use the same information to fully
generate the core implementation of `PrintAst` (including the
accessor string). This will be done later.

The `parent` tests use the same swift code as the extractor tests, and
this is currently enforced by `sync-files.py`. Notice that `qltest.sh`
had to be modified to deal with multiple files, which was not working
yet.

.pre-commit-config.yaml

@@ -25,7 +25,7 @@ repos:
 
       - id: sync-files
         name: Fix files required to be identical
-        files: \.(qll?|qhelp)$
+        files: \.(qll?|qhelp|swift)$
         language: system
         entry: python3 config/sync-files.py --latest
         pass_filenames: false

config/identical-files.json

@@ -566,5 +566,21 @@
   "Typo database": [
     "javascript/ql/src/Expressions/TypoDatabase.qll",
     "ql/ql/src/codeql_ql/style/TypoDatabase.qll"
+  ],
+  "Swift declarations test file": [
+    "swift/ql/test/extractor-tests/declarations/declarations.swift",
+    "swift/ql/test/library-tests/parent/declarations.swift"
+  ],
+  "Swift statements test file": [
+    "swift/ql/test/extractor-tests/statements/statements.swift",
+    "swift/ql/test/library-tests/parent/statements.swift"
+  ],
+  "Swift expressions test file": [
+    "swift/ql/test/extractor-tests/expressions/expressions.swift",
+    "swift/ql/test/library-tests/parent/expressions.swift"
+  ],
+  "Swift patterns test file": [
+    "swift/ql/test/extractor-tests/patterns/patterns.swift",
+    "swift/ql/test/library-tests/parent/patterns.swift"
   ]
-}
+}

swift/codegen/generators/qlgen.py

@@ -19,6 +19,7 @@ def get_ql_property(cls: schema.Class, prop: schema.Property):
             type=prop.type,
             tablename=inflection.tableize(cls.name),
             tableparams=["this"] + ["result" if p is prop else "_" for p in cls.properties if p.is_single],
+            is_child=prop.is_child,
         )
     elif prop.is_repeated:
         return ql.Property(
@@ -28,6 +29,7 @@ def get_ql_property(cls: schema.Class, prop: schema.Property):
             tablename=inflection.tableize(f"{cls.name}_{prop.name}"),
             tableparams=["this", "index", "result"],
             is_optional=prop.is_optional,
+            is_child=prop.is_child,
         )
     elif prop.is_optional:
         return ql.Property(
@@ -36,6 +38,7 @@ def get_ql_property(cls: schema.Class, prop: schema.Property):
             tablename=inflection.tableize(f"{cls.name}_{prop.name}"),
             tableparams=["this", "result"],
             is_optional=True,
+            is_child=prop.is_child,
         )
     elif prop.is_predicate:
         return ql.Property(

swift/codegen/lib/ql.py

@@ -22,6 +22,7 @@ class Property:
     local_var: str = "x"
     is_optional: bool = False
     is_predicate: bool = False
+    is_child: bool = False
 
     def __post_init__(self):
         if self.tableparams:

swift/codegen/lib/schema.py

@@ -19,6 +19,7 @@ class Property:
 
     name: str
     type: str = None
+    is_child: bool = False
 
 
 @dataclass
@@ -62,17 +63,18 @@ class Schema:
     includes: Set[str] = field(default_factory=set)
 
 
-def _parse_property(name, type):
+def _parse_property(name: str, type: str, is_child: bool = False):
+    assert not (is_child and type[0].islower()), f"children must have class type, got {type} for {name}"
     if type.endswith("?*"):
-        return RepeatedOptionalProperty(name, type[:-2])
+        return RepeatedOptionalProperty(name, type[:-2], is_child=is_child)
     elif type.endswith("*"):
-        return RepeatedProperty(name, type[:-1])
+        return RepeatedProperty(name, type[:-1], is_child=is_child)
     elif type.endswith("?"):
-        return OptionalProperty(name, type[:-1])
+        return OptionalProperty(name, type[:-1], is_child=is_child)
     elif type == "predicate":
         return PredicateProperty(name)
     else:
-        return SingleProperty(name, type)
+        return SingleProperty(name, type, is_child=is_child)
 
 
 class _DirSelector:
@@ -109,6 +111,8 @@ def load(path):
                     classes[base].derived.add(name)
             elif k == "_dir":
                 cls.dir = pathlib.Path(v)
+            elif k == "_children":
+                cls.properties.extend(_parse_property(kk, vv, is_child=True) for kk, vv in v.items())
         if not cls.bases and cls.name != root_class_name:
             cls.bases.add(root_class_name)
             classes[root_class_name].derived.add(name)

swift/codegen/schema.yml

@@ -52,9 +52,10 @@ AstNode:
 
 ConditionElement:
   _extends: Locatable
-  boolean: Expr?
-  pattern: Pattern?
-  initializer: Expr?
+  _children:
+    boolean: Expr?
+    pattern: Pattern?
+    initializer: Expr?
   _dir: stmt
 
 AnyFunctionType:
@@ -247,7 +248,8 @@ TypeAliasType:
 
 EnumCaseDecl:
   _extends: Decl
-  elements: EnumElementDecl*
+  _children:
+    elements: EnumElementDecl*
 
 IfConfigDecl:
   _extends: Decl
@@ -264,8 +266,9 @@ OperatorDecl:
 
 PatternBindingDecl:
   _extends: Decl
-  inits: Expr?*
-  patterns: Pattern*
+  _children:
+    inits: Expr?*
+    patterns: Pattern*
 
 PoundDiagnosticDecl:
   _extends: Decl
@@ -275,7 +278,8 @@ PrecedenceGroupDecl:
 
 TopLevelCodeDecl:
   _extends: Decl
-  body: BraceStmt
+  _children:
+    body: BraceStmt
 
 ValueDecl:
   _extends: Decl
@@ -286,37 +290,43 @@ AbstractClosureExpr:
 
 AnyTryExpr:
   _extends: Expr
-  sub_expr: Expr
+  _children:
+    sub_expr: Expr
 
 AppliedPropertyWrapperExpr:
   _extends: Expr
 
 Argument:
   label: string
-  expr: Expr
+  _children:
+    expr: Expr
   _dir: expr
 
 ApplyExpr:
   _extends: Expr
-  function: Expr
-  arguments: Argument*
+  _children:
+    function: Expr
+    arguments: Argument*
 
 ArrowExpr:
   _extends: Expr
 
 AssignExpr:
   _extends: Expr
-  dest: Expr
-  source: Expr
+  _children:
+    dest: Expr
+    source: Expr
 
 BindOptionalExpr:
   _extends: Expr
-  sub_expr: Expr
+  _children:
+    sub_expr: Expr
 
 CaptureListExpr:
   _extends: Expr
-  binding_decls: PatternBindingDecl*
-  closure_body: ClosureExpr
+  _children:
+    binding_decls: PatternBindingDecl*
+    closure_body: ClosureExpr
 
 CodeCompletionExpr:
   _extends: Expr
@@ -343,103 +353,121 @@ DiscardAssignmentExpr:
 
 DotSyntaxBaseIgnoredExpr:
   _extends: Expr
-  qualifier: Expr
-  sub_expr: Expr
+  _children:
+    qualifier: Expr
+    sub_expr: Expr
 
 DynamicTypeExpr:
   _extends: Expr
-  base_expr: Expr
+  _children:
+    base_expr: Expr
 
 EditorPlaceholderExpr:
   _extends: Expr
 
 EnumIsCaseExpr:
   _extends: Expr
-  sub_expr: Expr
-  type_repr: TypeRepr
-  element: EnumElementDecl
+  _children:
+    sub_expr: Expr
+    type_repr: TypeRepr
+    element: EnumElementDecl
 
 ErrorExpr:
   _extends: Expr
 
 ExplicitCastExpr:
   _extends: Expr
-  sub_expr: Expr
+  _children:
+    sub_expr: Expr
 
 ForceValueExpr:
   _extends: Expr
-  sub_expr: Expr
+  _children:
+    sub_expr: Expr
 
 IdentityExpr:
   _extends: Expr
-  sub_expr: Expr
+  _children:
+    sub_expr: Expr
 
 IfExpr:
   _extends: Expr
-  condition: Expr
-  then_expr: Expr
-  else_expr: Expr
+  _children:
+    condition: Expr
+    then_expr: Expr
+    else_expr: Expr
 
 ImplicitConversionExpr:
   _extends: Expr
-  sub_expr: Expr
+  _children:
+    sub_expr: Expr
 
 InOutExpr:
   _extends: Expr
-  sub_expr: Expr
+  _children:
+    sub_expr: Expr
 
 KeyPathApplicationExpr:
   _extends: Expr
-  base: Expr
-  key_path: Expr
+  _children:
+    base: Expr
+    key_path: Expr
 
 KeyPathDotExpr:
   _extends: Expr
 
 KeyPathExpr:
   _extends: Expr
-  parsed_root: Expr?
-  parsed_path: Expr?
+  _children:
+    parsed_root: Expr?
+    parsed_path: Expr?
 
 LazyInitializerExpr:
   _extends: Expr
-  sub_expr: Expr
+  _children:
+    sub_expr: Expr
 
 LiteralExpr:
   _extends: Expr
 
 LookupExpr:
   _extends: Expr
-  base_expr: Expr
+  _children:
+    base_expr: Expr
   member: Decl
 
 MakeTemporarilyEscapableExpr:
   _extends: Expr
-  escaping_closure: OpaqueValueExpr
-  nonescaping_closure: Expr
-  sub_expr: Expr
+  _children:
+    escaping_closure: OpaqueValueExpr
+    nonescaping_closure: Expr
+    sub_expr: Expr
 
 ObjCSelectorExpr:
   _extends: Expr
-  sub_expr: Expr
+  _children:
+    sub_expr: Expr
   method: AbstractFunctionDecl
 
 OneWayExpr:
   _extends: Expr
-  sub_expr: Expr
+  _children:
+    sub_expr: Expr
 
 OpaqueValueExpr:
   _extends: Expr
 
 OpenExistentialExpr:
   _extends: Expr
-  sub_expr: Expr
-  existential: Expr
-  opaque_expr: OpaqueValueExpr
+  _children:
+    sub_expr: Expr
+    existential: Expr
+    opaque_expr: OpaqueValueExpr
 
 OptionalEvaluationExpr:
   _extends: Expr
-  sub_expr: Expr
+  _children:
+    sub_expr: Expr
 
 OtherConstructorDeclRefExpr:
   _extends: Expr
@@ -452,8 +480,9 @@ PropertyWrapperValuePlaceholderExpr:
 
 RebindSelfInConstructorExpr:
   _extends: Expr
-  sub_expr: Expr
-  self: VarDecl
+  _children:
+    sub_expr: Expr
+    self: VarDecl
 
 SequenceExpr:
   _extends: Expr
@@ -464,22 +493,26 @@ SuperRefExpr:
 
 TapExpr:
   _extends: Expr
-  sub_expr: Expr?
+  _children:
+    sub_expr: Expr?
+    body: BraceStmt
   var: VarDecl
-  body: BraceStmt
 
 TupleElementExpr:
   _extends: Expr
-  sub_expr: Expr
+  _children:
+    sub_expr: Expr
   index: int
 
 TupleExpr:
   _extends: Expr
-  elements: Expr*
+  _children:
+    elements: Expr*
 
 TypeExpr:
   _extends: Expr
-  type_repr: TypeRepr?
+  _children:
+    type_repr: TypeRepr?
 
 UnresolvedDeclRefExpr:
   _extends: Expr
@@ -498,14 +531,16 @@ UnresolvedSpecializeExpr:
 
 VarargExpansionExpr:
   _extends: Expr
-  sub_expr: Expr
+  _children:
+    sub_expr: Expr
 
 AnyPattern:
   _extends: Pattern
 
 BindingPattern:
   _extends: Pattern
-  sub_pattern: Pattern
+  _children:
+    sub_pattern: Pattern
 
 BoolPattern:
   _extends: Pattern
@@ -514,11 +549,13 @@ BoolPattern:
 EnumElementPattern:
   _extends: Pattern
   element: EnumElementDecl
-  sub_pattern: Pattern?
+  _children:
+    sub_pattern: Pattern?
 
 ExprPattern:
   _extends: Pattern
-  sub_expr: Expr
+  _children:
+    sub_expr: Expr
 
 IsPattern:
   _extends: Pattern
@@ -531,24 +568,29 @@ NamedPattern:
 
 OptionalSomePattern:
   _extends: Pattern
-  sub_pattern: Pattern
+  _children:
+    sub_pattern: Pattern
 
 ParenPattern:
   _extends: Pattern
-  sub_pattern: Pattern
+  _children:
+    sub_pattern: Pattern
 
 TuplePattern:
   _extends: Pattern
-  elements: Pattern*
+  _children:
+    elements: Pattern*
 
 TypedPattern:
   _extends: Pattern
-  sub_pattern: Pattern
-  type_repr: TypeRepr?
+  _children:
+    sub_pattern: Pattern
+    type_repr: TypeRepr?
 
 BraceStmt:
   _extends: Stmt
-  elements: AstNode*
+  _children:
+    elements: AstNode*
 
 BreakStmt:
   _extends: Stmt
@@ -557,14 +599,16 @@ BreakStmt:
 
 CaseStmt:
   _extends: Stmt
-  body: Stmt
-  labels: CaseLabelItem*
+  _children:
+    body: Stmt
+    labels: CaseLabelItem*
   variables: VarDecl*
 
 CaseLabelItem:
   _extends: AstNode
-  pattern: Pattern
-  guard: Expr?
+  _children:
+    pattern: Pattern
+    guard: Expr?
   _dir: stmt
 
 ContinueStmt:
@@ -574,7 +618,8 @@ ContinueStmt:
 
 DeferStmt:
   _extends: Stmt
-  body: BraceStmt
+  _children:
+    body: BraceStmt
 
 FailStmt:
   _extends: Stmt
@@ -593,15 +638,18 @@ PoundAssertStmt:
 
 ReturnStmt:
   _extends: Stmt
-  result: Expr?
+  _children:
+    result: Expr?
 
 ThrowStmt:
   _extends: Stmt
-  sub_expr: Expr
+  _children:
+    sub_expr: Expr
 
 YieldStmt:
   _extends: Stmt
-  results: Expr*
+  _children:
+    results: Expr*
 
 BoundGenericType:
   _extends: NominalOrBoundGenericNominalType
@@ -657,17 +705,20 @@ AbstractFunctionDecl:
     - GenericContext
     - ValueDecl
   name: string
-  body: BraceStmt?
-  params: ParamDecl*
+  _children:
+    body: BraceStmt?
+    params: ParamDecl*
 
 AbstractStorageDecl:
   _extends: ValueDecl
-  accessor_decls: AccessorDecl*
+  _children:
+    accessor_decls: AccessorDecl*
 
 EnumElementDecl:
   _extends: ValueDecl
   name: string
-  params: ParamDecl*
+  _children:
+    params: ParamDecl*
 
 TypeDecl:
   _extends: ValueDecl
@@ -676,11 +727,13 @@ TypeDecl:
 
 AutoClosureExpr:
   _extends: AbstractClosureExpr
-  body: BraceStmt
+  _children:
+    body: BraceStmt
 
 ClosureExpr:
   _extends: AbstractClosureExpr
-  body: BraceStmt
+  _children:
+    body: BraceStmt
 
 ForceTryExpr:
   _extends: AnyTryExpr
@@ -705,15 +758,18 @@ PrefixUnaryExpr:
 
 SelfApplyExpr:
   _extends: ApplyExpr
-  base_expr: Expr
+  _children:
+    base_expr: Expr
 
 ArrayExpr:
   _extends: CollectionExpr
-  elements: Expr*
+  _children:
+    elements: Expr*
 
 DictionaryExpr:
   _extends: CollectionExpr
-  elements: Expr*
+  _children:
+    elements: Expr*
 
 CheckedCastExpr:
   _extends: ExplicitCastExpr
@@ -832,9 +888,10 @@ BuiltinLiteralExpr:
 InterpolatedStringLiteralExpr:
   _extends: LiteralExpr
   interpolation_expr: OpaqueValueExpr?
-  interpolation_count_expr: Expr?
-  literal_capacity_expr: Expr?
-  appending_expr: TapExpr?
+  _children:
+    interpolation_count_expr: Expr?
+    literal_capacity_expr: Expr?
+    appending_expr: TapExpr?
 
 RegexLiteralExpr:
   _extends: LiteralExpr
@@ -857,7 +914,8 @@ MemberRefExpr:
 SubscriptExpr:
   _extends:
     - LookupExpr
-  arguments: Argument*
+  _children:
+    arguments: Argument*
   has_direct_to_storage_semantics: predicate
   has_direct_to_implementation_semantics: predicate
   has_ordinary_semantics: predicate
@@ -867,38 +925,45 @@ OverloadedDeclRefExpr:
 
 DoCatchStmt:
   _extends: LabeledStmt
-  body: Stmt
-  catches: CaseStmt*
+  _children:
+    body: Stmt
+    catches: CaseStmt*
 
 DoStmt:
   _extends: LabeledStmt
-  body: BraceStmt
+  _children:
+    body: BraceStmt
 
 ForEachStmt:
   _extends: LabeledStmt
-  pattern: Pattern
-  sequence: Expr
-  where: Expr?
-  body: BraceStmt
+  _children:
+    pattern: Pattern
+    sequence: Expr
+    where: Expr?
+    body: BraceStmt
 
 LabeledConditionalStmt:
   _extends: LabeledStmt
-  condition: StmtCondition
+  _children:
+    condition: StmtCondition
 
 StmtCondition:
   _extends: AstNode
-  elements: ConditionElement*
+  _children:
+    elements: ConditionElement*
   _dir: stmt
 
 RepeatWhileStmt:
   _extends: LabeledStmt
-  condition: Expr
-  body: Stmt
+  _children:
+    condition: Expr
+    body: Stmt
 
 SwitchStmt:
   _extends: LabeledStmt
-  expr: Expr
-  cases: CaseStmt*
+  _children:
+    expr: Expr
+    cases: CaseStmt*
 
 BoundGenericClassType:
   _extends: BoundGenericType
@@ -943,7 +1008,8 @@ SubscriptDecl:
   _extends:
     - AbstractStorageDecl
     - GenericContext
-  params: ParamDecl*
+  _children:
+    params: ParamDecl*
   element_type: Type
 
 VarDecl:
@@ -1006,16 +1072,19 @@ DynamicSubscriptExpr:
 
 GuardStmt:
   _extends: LabeledConditionalStmt
-  body: BraceStmt
+  _children:
+    body: BraceStmt
 
 IfStmt:
   _extends: LabeledConditionalStmt
-  then: Stmt
-  else: Stmt?
+  _children:
+    then: Stmt
+    else: Stmt?
 
 WhileStmt:
   _extends: LabeledConditionalStmt
-  body: Stmt
+  _children:
+    body: Stmt
 
 AccessorDecl:
   _extends: FuncDecl

swift/codegen/templates/ql_class.mustache

@@ -1,5 +1,8 @@
 // generated by {{generator}}
 
+{{^root}}
+import codeql.swift.elements.Element
+{{/root}}
 {{#imports}}
 import {{.}}
 {{/imports}}
@@ -19,10 +22,26 @@ class {{name}}Base extends {{db_id}}{{#bases}}, {{.}}{{/bases}} {
     or
     result = getResolveStep().resolve()
   }
+
+  {{name}}Base getAChild() { none() } // overridden by subclasses, internal use only
   {{/root}}
   {{#final}}
   override string getAPrimaryQlClass() { result = "{{name}}" }
   {{/final}}
+  {{^root}}
+
+  cached override Element getAChild() {
+    none()
+    {{#bases}}
+    or result = {{.}}.super.getAChild()
+    {{/bases}}
+    {{#properties}}
+    {{#is_child}}
+    or result = {{getter}}({{#is_repeated}}_{{/is_repeated}})
+    {{/is_child}}
+    {{/properties}}
+  }
+  {{/root}}
   {{#properties}}
 
   {{type}} {{getter}}({{#is_repeated}}int index{{/is_repeated}}) {

swift/codegen/test/test_qlgen.py

@@ -99,44 +99,47 @@ def test_single_properties(opts, input, renderer):
     }
 
 
-def test_optional_property(opts, input, renderer):
+@pytest.mark.parametrize("is_child", [False, True])
+def test_optional_property(opts, input, renderer, is_child):
     input.classes = [
-        schema.Class("MyObject", properties=[schema.OptionalProperty("foo", "bar")]),
+        schema.Class("MyObject", properties=[schema.OptionalProperty("foo", "bar", is_child=is_child)]),
     ]
     assert generate(opts, renderer) == {
         import_file(): ql.ImportList([stub_import_prefix + "MyObject"]),
         stub_path() / "MyObject.qll": ql.Stub(name="MyObject", base_import=gen_import_prefix + "MyObject"),
         ql_output_path() / "MyObject.qll": ql.Class(name="MyObject", final=True, properties=[
             ql.Property(singular="Foo", type="bar", tablename="my_object_foos", tableparams=["this", "result"],
-                        is_optional=True),
+                        is_optional=True, is_child=is_child),
         ])
     }
 
 
-def test_repeated_property(opts, input, renderer):
+@pytest.mark.parametrize("is_child", [False, True])
+def test_repeated_property(opts, input, renderer, is_child):
     input.classes = [
-        schema.Class("MyObject", properties=[schema.RepeatedProperty("foo", "bar")]),
+        schema.Class("MyObject", properties=[schema.RepeatedProperty("foo", "bar", is_child=is_child)]),
     ]
     assert generate(opts, renderer) == {
         import_file(): ql.ImportList([stub_import_prefix + "MyObject"]),
         stub_path() / "MyObject.qll": ql.Stub(name="MyObject", base_import=gen_import_prefix + "MyObject"),
         ql_output_path() / "MyObject.qll": ql.Class(name="MyObject", final=True, properties=[
             ql.Property(singular="Foo", plural="Foos", type="bar", tablename="my_object_foos",
-                        tableparams=["this", "index", "result"]),
+                        tableparams=["this", "index", "result"], is_child=is_child),
         ])
     }
 
 
-def test_repeated_optional_property(opts, input, renderer):
+@pytest.mark.parametrize("is_child", [False, True])
+def test_repeated_optional_property(opts, input, renderer, is_child):
     input.classes = [
-        schema.Class("MyObject", properties=[schema.RepeatedOptionalProperty("foo", "bar")]),
+        schema.Class("MyObject", properties=[schema.RepeatedOptionalProperty("foo", "bar", is_child=is_child)]),
     ]
     assert generate(opts, renderer) == {
         import_file(): ql.ImportList([stub_import_prefix + "MyObject"]),
         stub_path() / "MyObject.qll": ql.Stub(name="MyObject", base_import=gen_import_prefix + "MyObject"),
         ql_output_path() / "MyObject.qll": ql.Class(name="MyObject", final=True, properties=[
             ql.Property(singular="Foo", plural="Foos", type="bar", tablename="my_object_foos",
-                        tableparams=["this", "index", "result"], is_optional=True),
+                        tableparams=["this", "index", "result"], is_optional=True, is_child=is_child),
         ])
     }
 
@@ -155,9 +158,10 @@ def test_predicate_property(opts, input, renderer):
     }
 
 
-def test_single_class_property(opts, input, renderer):
+@pytest.mark.parametrize("is_child", [False, True])
+def test_single_class_property(opts, input, renderer, is_child):
     input.classes = [
-        schema.Class("MyObject", properties=[schema.SingleProperty("foo", "Bar")]),
+        schema.Class("MyObject", properties=[schema.SingleProperty("foo", "Bar", is_child=is_child)]),
         schema.Class("Bar"),
     ]
     assert generate(opts, renderer) == {
@@ -166,7 +170,8 @@ def test_single_class_property(opts, input, renderer):
         stub_path() / "Bar.qll": ql.Stub(name="Bar", base_import=gen_import_prefix + "Bar"),
         ql_output_path() / "MyObject.qll": ql.Class(
             name="MyObject", final=True, imports=[stub_import_prefix + "Bar"], properties=[
-                ql.Property(singular="Foo", type="Bar", tablename="my_objects", tableparams=["this", "result"]),
+                ql.Property(singular="Foo", type="Bar", tablename="my_objects", tableparams=["this", "result"],
+                            is_child=is_child),
             ],
         ),
         ql_output_path() / "Bar.qll": ql.Class(name="Bar", final=True)

swift/codegen/test/test_schema.py

@@ -1,5 +1,7 @@
 import sys
 
+import pytest
+
 from swift.codegen.test.utils import *
 
 root_name = schema.root_class_name
@@ -163,9 +165,43 @@ Element:
     assert ret.classes == [
         schema.Class(root_name, properties=[
             schema.SingleProperty('x', 'string'),
-         ]),
+        ]),
     ]
 
 
+def test_children(load):
+    ret = load("""
+A:
+    a: string
+    b: B*
+    _children:
+        c: C
+        d: D*
+        e: E?
+        f: F?*
+""")
+    assert ret.classes == [
+        schema.Class(root_name, derived={'A'}),
+        schema.Class('A', bases={root_name}, properties=[
+            schema.SingleProperty('a', 'string'),
+            schema.RepeatedProperty('b', 'B'),
+            schema.SingleProperty('c', 'C', is_child=True),
+            schema.RepeatedProperty('d', 'D', is_child=True),
+            schema.OptionalProperty('e', 'E', is_child=True),
+            schema.RepeatedOptionalProperty('f', 'F', is_child=True),
+        ]),
+    ]
+
+
+@pytest.mark.parametrize("type", ["string", "int", "boolean", "predicate"])
+def test_builtin_and_predicate_children_not_allowed(load, type):
+    with pytest.raises(AssertionError):
+        load(f"""
+A:
+    _children:
+        x: {type}
+""")
+
+
 if __name__ == '__main__':
     sys.exit(pytest.main([__file__] + sys.argv[1:]))

swift/extractor/visitors/ExprVisitor.h

@@ -313,7 +313,7 @@ class ExprVisitor : public AstVisitorBase<ExprVisitor> {
     auto varLabel = dispatcher_.fetchLabel(expr->getVar());
     auto bodyLabel = dispatcher_.fetchLabel(expr->getBody());
 
-    dispatcher_.emit(TapExprsTrap{label, varLabel, bodyLabel});
+    dispatcher_.emit(TapExprsTrap{label, bodyLabel, varLabel});
     if (auto subExpr = expr->getSubExpr()) {
       dispatcher_.emit(TapExprSubExprsTrap{label, dispatcher_.fetchLabel(subExpr)});
     }

swift/ql/lib/codeql/swift/elements/AstNode.qll

@@ -1,4 +1,7 @@
-// generated by codegen/codegen.py, remove this comment if you wish to edit this file
 private import codeql.swift.generated.AstNode
 
-class AstNode extends AstNodeBase { }
+class AstNode extends AstNodeBase {
+  AstNode getParent() {
+    result = unique(AstNode x | this = x.getAChild() and not exists(x.getResolveStep()) | x)
+  }
+}

swift/ql/lib/codeql/swift/elements/Element.qll

@@ -1,15 +1,15 @@
 private import codeql.swift.generated.Element
 
 class Element extends ElementBase {
-  private predicate resolvesTo(Element e) { e.getResolveStep() = this }
+  private predicate resolvesFrom(Element e) { e.getResolveStep() = this }
 
   override string toString() { result = getPrimaryQlClasses() }
 
   Element getFullyUnresolved() {
-    not this.resolvesTo(_) and result = this
+    not this.resolvesFrom(_) and result = this
     or
     exists(Element e |
-      this.resolvesTo(e) and
+      this.resolvesFrom(e) and
       result = e.getFullyUnresolved()
     )
   }

swift/ql/lib/codeql/swift/generated/AstNode.qll

@@ -1,4 +1,11 @@
 // generated by codegen/codegen.py
+import codeql.swift.elements.Element
 import codeql.swift.elements.Locatable
 
-class AstNodeBase extends @ast_node, Locatable { }
+class AstNodeBase extends @ast_node, Locatable {
+  cached
+  override Element getAChild() {
+    none() or
+    result = Locatable.super.getAChild()
+  }
+}

swift/ql/lib/codeql/swift/generated/Element.qll

@@ -14,5 +14,7 @@ class ElementBase extends @element {
     result = getResolveStep().resolve()
   }
 
+  ElementBase getAChild() { none() } // overridden by subclasses, internal use only
+
   predicate isUnknown() { element_is_unknown(this) }
 }

swift/ql/lib/codeql/swift/generated/File.qll

@@ -1,8 +1,15 @@
 // generated by codegen/codegen.py
 import codeql.swift.elements.Element
+import codeql.swift.elements.Element
 
 class FileBase extends @file, Element {
   override string getAPrimaryQlClass() { result = "File" }
 
+  cached
+  override Element getAChild() {
+    none() or
+    result = Element.super.getAChild()
+  }
+
   string getName() { files(this, result) }
 }

swift/ql/lib/codeql/swift/generated/Locatable.qll

@@ -1,8 +1,15 @@
 // generated by codegen/codegen.py
 import codeql.swift.elements.Element
+import codeql.swift.elements.Element
 import codeql.swift.elements.Location
 
 class LocatableBase extends @locatable, Element {
+  cached
+  override Element getAChild() {
+    none() or
+    result = Element.super.getAChild()
+  }
+
   Location getLocation() {
     exists(Location x |
       locatables(this, x) and

swift/ql/lib/codeql/swift/generated/Location.qll

@@ -1,10 +1,17 @@
 // generated by codegen/codegen.py
 import codeql.swift.elements.Element
+import codeql.swift.elements.Element
 import codeql.swift.elements.File
 
 class LocationBase extends @location, Element {
   override string getAPrimaryQlClass() { result = "Location" }
 
+  cached
+  override Element getAChild() {
+    none() or
+    result = Element.super.getAChild()
+  }
+
   File getFile() {
     exists(File x |
       locations(this, x, _, _, _, _) and

swift/ql/lib/codeql/swift/generated/decl/AbstractFunctionDecl.qll

@@ -1,10 +1,20 @@
 // generated by codegen/codegen.py
+import codeql.swift.elements.Element
 import codeql.swift.elements.stmt.BraceStmt
 import codeql.swift.elements.decl.GenericContext
 import codeql.swift.elements.decl.ParamDecl
 import codeql.swift.elements.decl.ValueDecl
 
 class AbstractFunctionDeclBase extends @abstract_function_decl, GenericContext, ValueDecl {
+  cached
+  override Element getAChild() {
+    none() or
+    result = GenericContext.super.getAChild() or
+    result = ValueDecl.super.getAChild() or
+    result = getBody() or
+    result = getParam(_)
+  }
+
   string getName() { abstract_function_decls(this, result) }
 
   BraceStmt getBody() {

swift/ql/lib/codeql/swift/generated/decl/AbstractStorageDecl.qll

@@ -1,8 +1,16 @@
 // generated by codegen/codegen.py
+import codeql.swift.elements.Element
 import codeql.swift.elements.decl.AccessorDecl
 import codeql.swift.elements.decl.ValueDecl
 
 class AbstractStorageDeclBase extends @abstract_storage_decl, ValueDecl {
+  cached
+  override Element getAChild() {
+    none() or
+    result = ValueDecl.super.getAChild() or
+    result = getAccessorDecl(_)
+  }
+
   AccessorDecl getAccessorDecl(int index) {
     exists(AccessorDecl x |
       abstract_storage_decl_accessor_decls(this, index, x) and

swift/ql/lib/codeql/swift/generated/decl/AbstractTypeParamDecl.qll

@@ -1,4 +1,11 @@
 // generated by codegen/codegen.py
+import codeql.swift.elements.Element
 import codeql.swift.elements.decl.TypeDecl
 
-class AbstractTypeParamDeclBase extends @abstract_type_param_decl, TypeDecl { }
+class AbstractTypeParamDeclBase extends @abstract_type_param_decl, TypeDecl {
+  cached
+  override Element getAChild() {
+    none() or
+    result = TypeDecl.super.getAChild()
+  }
+}

swift/ql/lib/codeql/swift/generated/decl/AccessorDecl.qll

@@ -1,9 +1,16 @@
 // generated by codegen/codegen.py
+import codeql.swift.elements.Element
 import codeql.swift.elements.decl.FuncDecl
 
 class AccessorDeclBase extends @accessor_decl, FuncDecl {
   override string getAPrimaryQlClass() { result = "AccessorDecl" }
 
+  cached
+  override Element getAChild() {
+    none() or
+    result = FuncDecl.super.getAChild()
+  }
+
   predicate isGetter() { accessor_decl_is_getter(this) }
 
   predicate isSetter() { accessor_decl_is_setter(this) }

swift/ql/lib/codeql/swift/generated/decl/AssociatedTypeDecl.qll

@@ -1,6 +1,13 @@
 // generated by codegen/codegen.py
+import codeql.swift.elements.Element
 import codeql.swift.elements.decl.AbstractTypeParamDecl
 
 class AssociatedTypeDeclBase extends @associated_type_decl, AbstractTypeParamDecl {
   override string getAPrimaryQlClass() { result = "AssociatedTypeDecl" }
+
+  cached
+  override Element getAChild() {
+    none() or
+    result = AbstractTypeParamDecl.super.getAChild()
+  }
 }

swift/ql/lib/codeql/swift/generated/decl/ClassDecl.qll

@@ -1,6 +1,13 @@
 // generated by codegen/codegen.py
+import codeql.swift.elements.Element
 import codeql.swift.elements.decl.NominalTypeDecl
 
 class ClassDeclBase extends @class_decl, NominalTypeDecl {
   override string getAPrimaryQlClass() { result = "ClassDecl" }
+
+  cached
+  override Element getAChild() {
+    none() or
+    result = NominalTypeDecl.super.getAChild()
+  }
 }

swift/ql/lib/codeql/swift/generated/decl/ConcreteFuncDecl.qll

@@ -1,6 +1,13 @@
 // generated by codegen/codegen.py
+import codeql.swift.elements.Element
 import codeql.swift.elements.decl.FuncDecl
 
 class ConcreteFuncDeclBase extends @concrete_func_decl, FuncDecl {
   override string getAPrimaryQlClass() { result = "ConcreteFuncDecl" }
+
+  cached
+  override Element getAChild() {
+    none() or
+    result = FuncDecl.super.getAChild()
+  }
 }

swift/ql/lib/codeql/swift/generated/decl/ConcreteVarDecl.qll

@@ -1,8 +1,15 @@
 // generated by codegen/codegen.py
+import codeql.swift.elements.Element
 import codeql.swift.elements.decl.VarDecl
 
 class ConcreteVarDeclBase extends @concrete_var_decl, VarDecl {
   override string getAPrimaryQlClass() { result = "ConcreteVarDecl" }
 
+  cached
+  override Element getAChild() {
+    none() or
+    result = VarDecl.super.getAChild()
+  }
+
   int getIntroducerInt() { concrete_var_decls(this, result) }
 }

swift/ql/lib/codeql/swift/generated/decl/ConstructorDecl.qll

@@ -1,6 +1,13 @@
 // generated by codegen/codegen.py
+import codeql.swift.elements.Element
 import codeql.swift.elements.decl.AbstractFunctionDecl
 
 class ConstructorDeclBase extends @constructor_decl, AbstractFunctionDecl {
   override string getAPrimaryQlClass() { result = "ConstructorDecl" }
+
+  cached
+  override Element getAChild() {
+    none() or
+    result = AbstractFunctionDecl.super.getAChild()
+  }
 }

swift/ql/lib/codeql/swift/generated/decl/Decl.qll

@@ -1,4 +1,11 @@
 // generated by codegen/codegen.py
+import codeql.swift.elements.Element
 import codeql.swift.elements.AstNode
 
-class DeclBase extends @decl, AstNode { }
+class DeclBase extends @decl, AstNode {
+  cached
+  override Element getAChild() {
+    none() or
+    result = AstNode.super.getAChild()
+  }
+}

swift/ql/lib/codeql/swift/generated/decl/DestructorDecl.qll

@@ -1,6 +1,13 @@
 // generated by codegen/codegen.py
+import codeql.swift.elements.Element
 import codeql.swift.elements.decl.AbstractFunctionDecl
 
 class DestructorDeclBase extends @destructor_decl, AbstractFunctionDecl {
   override string getAPrimaryQlClass() { result = "DestructorDecl" }
+
+  cached
+  override Element getAChild() {
+    none() or
+    result = AbstractFunctionDecl.super.getAChild()
+  }
 }

swift/ql/lib/codeql/swift/generated/decl/EnumCaseDecl.qll

@@ -1,10 +1,18 @@
 // generated by codegen/codegen.py
+import codeql.swift.elements.Element
 import codeql.swift.elements.decl.Decl
 import codeql.swift.elements.decl.EnumElementDecl
 
 class EnumCaseDeclBase extends @enum_case_decl, Decl {
   override string getAPrimaryQlClass() { result = "EnumCaseDecl" }
 
+  cached
+  override Element getAChild() {
+    none() or
+    result = Decl.super.getAChild() or
+    result = getElement(_)
+  }
+
   EnumElementDecl getElement(int index) {
     exists(EnumElementDecl x |
       enum_case_decl_elements(this, index, x) and

swift/ql/lib/codeql/swift/generated/decl/EnumDecl.qll

@@ -1,6 +1,13 @@
 // generated by codegen/codegen.py
+import codeql.swift.elements.Element
 import codeql.swift.elements.decl.NominalTypeDecl
 
 class EnumDeclBase extends @enum_decl, NominalTypeDecl {
   override string getAPrimaryQlClass() { result = "EnumDecl" }
+
+  cached
+  override Element getAChild() {
+    none() or
+    result = NominalTypeDecl.super.getAChild()
+  }
 }

swift/ql/lib/codeql/swift/generated/decl/EnumElementDecl.qll

@@ -1,10 +1,18 @@
 // generated by codegen/codegen.py
+import codeql.swift.elements.Element
 import codeql.swift.elements.decl.ParamDecl
 import codeql.swift.elements.decl.ValueDecl
 
 class EnumElementDeclBase extends @enum_element_decl, ValueDecl {
   override string getAPrimaryQlClass() { result = "EnumElementDecl" }
 
+  cached
+  override Element getAChild() {
+    none() or
+    result = ValueDecl.super.getAChild() or
+    result = getParam(_)
+  }
+
   string getName() { enum_element_decls(this, result) }
 
   ParamDecl getParam(int index) {

swift/ql/lib/codeql/swift/generated/decl/ExtensionDecl.qll

@@ -1,8 +1,17 @@
 // generated by codegen/codegen.py
+import codeql.swift.elements.Element
 import codeql.swift.elements.decl.Decl
 import codeql.swift.elements.decl.GenericContext
 import codeql.swift.elements.decl.IterableDeclContext
 
 class ExtensionDeclBase extends @extension_decl, Decl, GenericContext, IterableDeclContext {
   override string getAPrimaryQlClass() { result = "ExtensionDecl" }
+
+  cached
+  override Element getAChild() {
+    none() or
+    result = Decl.super.getAChild() or
+    result = GenericContext.super.getAChild() or
+    result = IterableDeclContext.super.getAChild()
+  }
 }

swift/ql/lib/codeql/swift/generated/decl/FuncDecl.qll

@@ -1,4 +1,11 @@
 // generated by codegen/codegen.py
+import codeql.swift.elements.Element
 import codeql.swift.elements.decl.AbstractFunctionDecl
 
-class FuncDeclBase extends @func_decl, AbstractFunctionDecl { }
+class FuncDeclBase extends @func_decl, AbstractFunctionDecl {
+  cached
+  override Element getAChild() {
+    none() or
+    result = AbstractFunctionDecl.super.getAChild()
+  }
+}

swift/ql/lib/codeql/swift/generated/decl/GenericContext.qll

@@ -1,8 +1,15 @@
 // generated by codegen/codegen.py
 import codeql.swift.elements.Element
+import codeql.swift.elements.Element
 import codeql.swift.elements.decl.GenericTypeParamDecl
 
 class GenericContextBase extends @generic_context, Element {
+  cached
+  override Element getAChild() {
+    none() or
+    result = Element.super.getAChild()
+  }
+
   GenericTypeParamDecl getGenericTypeParam(int index) {
     exists(GenericTypeParamDecl x |
       generic_context_generic_type_params(this, index, x) and

swift/ql/lib/codeql/swift/generated/decl/GenericTypeDecl.qll

@@ -1,5 +1,13 @@
 // generated by codegen/codegen.py
+import codeql.swift.elements.Element
 import codeql.swift.elements.decl.GenericContext
 import codeql.swift.elements.decl.TypeDecl
 
-class GenericTypeDeclBase extends @generic_type_decl, GenericContext, TypeDecl { }
+class GenericTypeDeclBase extends @generic_type_decl, GenericContext, TypeDecl {
+  cached
+  override Element getAChild() {
+    none() or
+    result = GenericContext.super.getAChild() or
+    result = TypeDecl.super.getAChild()
+  }
+}

swift/ql/lib/codeql/swift/generated/decl/GenericTypeParamDecl.qll

@@ -1,6 +1,13 @@
 // generated by codegen/codegen.py
+import codeql.swift.elements.Element
 import codeql.swift.elements.decl.AbstractTypeParamDecl
 
 class GenericTypeParamDeclBase extends @generic_type_param_decl, AbstractTypeParamDecl {
   override string getAPrimaryQlClass() { result = "GenericTypeParamDecl" }
+
+  cached
+  override Element getAChild() {
+    none() or
+    result = AbstractTypeParamDecl.super.getAChild()
+  }
 }

swift/ql/lib/codeql/swift/generated/decl/IfConfigDecl.qll

@@ -1,6 +1,13 @@
 // generated by codegen/codegen.py
+import codeql.swift.elements.Element
 import codeql.swift.elements.decl.Decl
 
 class IfConfigDeclBase extends @if_config_decl, Decl {
   override string getAPrimaryQlClass() { result = "IfConfigDecl" }
+
+  cached
+  override Element getAChild() {
+    none() or
+    result = Decl.super.getAChild()
+  }
 }

swift/ql/lib/codeql/swift/generated/decl/ImportDecl.qll

@@ -1,6 +1,13 @@
 // generated by codegen/codegen.py
+import codeql.swift.elements.Element
 import codeql.swift.elements.decl.Decl
 
 class ImportDeclBase extends @import_decl, Decl {
   override string getAPrimaryQlClass() { result = "ImportDecl" }
+
+  cached
+  override Element getAChild() {
+    none() or
+    result = Decl.super.getAChild()
+  }
 }

swift/ql/lib/codeql/swift/generated/decl/InfixOperatorDecl.qll

@@ -1,10 +1,17 @@
 // generated by codegen/codegen.py
+import codeql.swift.elements.Element
 import codeql.swift.elements.decl.OperatorDecl
 import codeql.swift.elements.decl.PrecedenceGroupDecl
 
 class InfixOperatorDeclBase extends @infix_operator_decl, OperatorDecl {
   override string getAPrimaryQlClass() { result = "InfixOperatorDecl" }
 
+  cached
+  override Element getAChild() {
+    none() or
+    result = OperatorDecl.super.getAChild()
+  }
+
   PrecedenceGroupDecl getPrecedenceGroup() {
     exists(PrecedenceGroupDecl x |
       infix_operator_decl_precedence_groups(this, x) and

swift/ql/lib/codeql/swift/generated/decl/IterableDeclContext.qll

@@ -1,8 +1,15 @@
 // generated by codegen/codegen.py
+import codeql.swift.elements.Element
 import codeql.swift.elements.decl.Decl
 import codeql.swift.elements.Element
 
 class IterableDeclContextBase extends @iterable_decl_context, Element {
+  cached
+  override Element getAChild() {
+    none() or
+    result = Element.super.getAChild()
+  }
+
   Decl getMember(int index) {
     exists(Decl x |
       iterable_decl_context_members(this, index, x) and

swift/ql/lib/codeql/swift/generated/decl/MissingMemberDecl.qll

@@ -1,6 +1,13 @@
 // generated by codegen/codegen.py
+import codeql.swift.elements.Element
 import codeql.swift.elements.decl.Decl
 
 class MissingMemberDeclBase extends @missing_member_decl, Decl {
   override string getAPrimaryQlClass() { result = "MissingMemberDecl" }
+
+  cached
+  override Element getAChild() {
+    none() or
+    result = Decl.super.getAChild()
+  }
 }

swift/ql/lib/codeql/swift/generated/decl/ModuleDecl.qll

@@ -1,6 +1,13 @@
 // generated by codegen/codegen.py
+import codeql.swift.elements.Element
 import codeql.swift.elements.decl.TypeDecl
 
 class ModuleDeclBase extends @module_decl, TypeDecl {
   override string getAPrimaryQlClass() { result = "ModuleDecl" }
+
+  cached
+  override Element getAChild() {
+    none() or
+    result = TypeDecl.super.getAChild()
+  }
 }

swift/ql/lib/codeql/swift/generated/decl/NominalTypeDecl.qll

@@ -1,9 +1,17 @@
 // generated by codegen/codegen.py
+import codeql.swift.elements.Element
 import codeql.swift.elements.decl.GenericTypeDecl
 import codeql.swift.elements.decl.IterableDeclContext
 import codeql.swift.elements.type.Type
 
 class NominalTypeDeclBase extends @nominal_type_decl, GenericTypeDecl, IterableDeclContext {
+  cached
+  override Element getAChild() {
+    none() or
+    result = GenericTypeDecl.super.getAChild() or
+    result = IterableDeclContext.super.getAChild()
+  }
+
   Type getType() {
     exists(Type x |
       nominal_type_decls(this, x) and

swift/ql/lib/codeql/swift/generated/decl/OpaqueTypeDecl.qll

@@ -1,6 +1,13 @@
 // generated by codegen/codegen.py
+import codeql.swift.elements.Element
 import codeql.swift.elements.decl.GenericTypeDecl
 
 class OpaqueTypeDeclBase extends @opaque_type_decl, GenericTypeDecl {
   override string getAPrimaryQlClass() { result = "OpaqueTypeDecl" }
+
+  cached
+  override Element getAChild() {
+    none() or
+    result = GenericTypeDecl.super.getAChild()
+  }
 }

swift/ql/lib/codeql/swift/generated/decl/OperatorDecl.qll

@@ -1,6 +1,13 @@
 // generated by codegen/codegen.py
+import codeql.swift.elements.Element
 import codeql.swift.elements.decl.Decl
 
 class OperatorDeclBase extends @operator_decl, Decl {
+  cached
+  override Element getAChild() {
+    none() or
+    result = Decl.super.getAChild()
+  }
+
   string getName() { operator_decls(this, result) }
 }

swift/ql/lib/codeql/swift/generated/decl/ParamDecl.qll

@@ -1,6 +1,13 @@
 // generated by codegen/codegen.py
+import codeql.swift.elements.Element
 import codeql.swift.elements.decl.VarDecl
 
 class ParamDeclBase extends @param_decl, VarDecl {
   override string getAPrimaryQlClass() { result = "ParamDecl" }
+
+  cached
+  override Element getAChild() {
+    none() or
+    result = VarDecl.super.getAChild()
+  }
 }

swift/ql/lib/codeql/swift/generated/decl/PatternBindingDecl.qll

@@ -1,4 +1,5 @@
 // generated by codegen/codegen.py
+import codeql.swift.elements.Element
 import codeql.swift.elements.decl.Decl
 import codeql.swift.elements.expr.Expr
 import codeql.swift.elements.pattern.Pattern
@@ -6,6 +7,14 @@ import codeql.swift.elements.pattern.Pattern
 class PatternBindingDeclBase extends @pattern_binding_decl, Decl {
   override string getAPrimaryQlClass() { result = "PatternBindingDecl" }
 
+  cached
+  override Element getAChild() {
+    none() or
+    result = Decl.super.getAChild() or
+    result = getInit(_) or
+    result = getPattern(_)
+  }
+
   Expr getInit(int index) {
     exists(Expr x |
       pattern_binding_decl_inits(this, index, x) and

swift/ql/lib/codeql/swift/generated/decl/PostfixOperatorDecl.qll

@@ -1,6 +1,13 @@
 // generated by codegen/codegen.py
+import codeql.swift.elements.Element
 import codeql.swift.elements.decl.OperatorDecl
 
 class PostfixOperatorDeclBase extends @postfix_operator_decl, OperatorDecl {
   override string getAPrimaryQlClass() { result = "PostfixOperatorDecl" }
+
+  cached
+  override Element getAChild() {
+    none() or
+    result = OperatorDecl.super.getAChild()
+  }
 }

swift/ql/lib/codeql/swift/generated/decl/PoundDiagnosticDecl.qll

@@ -1,6 +1,13 @@
 // generated by codegen/codegen.py
+import codeql.swift.elements.Element
 import codeql.swift.elements.decl.Decl
 
 class PoundDiagnosticDeclBase extends @pound_diagnostic_decl, Decl {
   override string getAPrimaryQlClass() { result = "PoundDiagnosticDecl" }
+
+  cached
+  override Element getAChild() {
+    none() or
+    result = Decl.super.getAChild()
+  }
 }

swift/ql/lib/codeql/swift/generated/decl/PrecedenceGroupDecl.qll

@@ -1,6 +1,13 @@
 // generated by codegen/codegen.py
+import codeql.swift.elements.Element
 import codeql.swift.elements.decl.Decl
 
 class PrecedenceGroupDeclBase extends @precedence_group_decl, Decl {
   override string getAPrimaryQlClass() { result = "PrecedenceGroupDecl" }
+
+  cached
+  override Element getAChild() {
+    none() or
+    result = Decl.super.getAChild()
+  }
 }

swift/ql/lib/codeql/swift/generated/decl/PrefixOperatorDecl.qll

@@ -1,6 +1,13 @@
 // generated by codegen/codegen.py
+import codeql.swift.elements.Element
 import codeql.swift.elements.decl.OperatorDecl
 
 class PrefixOperatorDeclBase extends @prefix_operator_decl, OperatorDecl {
   override string getAPrimaryQlClass() { result = "PrefixOperatorDecl" }
+
+  cached
+  override Element getAChild() {
+    none() or
+    result = OperatorDecl.super.getAChild()
+  }
 }

swift/ql/lib/codeql/swift/generated/decl/ProtocolDecl.qll

@@ -1,6 +1,13 @@
 // generated by codegen/codegen.py
+import codeql.swift.elements.Element
 import codeql.swift.elements.decl.NominalTypeDecl
 
 class ProtocolDeclBase extends @protocol_decl, NominalTypeDecl {
   override string getAPrimaryQlClass() { result = "ProtocolDecl" }
+
+  cached
+  override Element getAChild() {
+    none() or
+    result = NominalTypeDecl.super.getAChild()
+  }
 }

swift/ql/lib/codeql/swift/generated/decl/StructDecl.qll

@@ -1,6 +1,13 @@
 // generated by codegen/codegen.py
+import codeql.swift.elements.Element
 import codeql.swift.elements.decl.NominalTypeDecl
 
 class StructDeclBase extends @struct_decl, NominalTypeDecl {
   override string getAPrimaryQlClass() { result = "StructDecl" }
+
+  cached
+  override Element getAChild() {
+    none() or
+    result = NominalTypeDecl.super.getAChild()
+  }
 }

swift/ql/lib/codeql/swift/generated/decl/SubscriptDecl.qll

@@ -1,4 +1,5 @@
 // generated by codegen/codegen.py
+import codeql.swift.elements.Element
 import codeql.swift.elements.decl.AbstractStorageDecl
 import codeql.swift.elements.decl.GenericContext
 import codeql.swift.elements.decl.ParamDecl
@@ -7,6 +8,14 @@ import codeql.swift.elements.type.Type
 class SubscriptDeclBase extends @subscript_decl, AbstractStorageDecl, GenericContext {
   override string getAPrimaryQlClass() { result = "SubscriptDecl" }
 
+  cached
+  override Element getAChild() {
+    none() or
+    result = AbstractStorageDecl.super.getAChild() or
+    result = GenericContext.super.getAChild() or
+    result = getParam(_)
+  }
+
   ParamDecl getParam(int index) {
     exists(ParamDecl x |
       subscript_decl_params(this, index, x) and

swift/ql/lib/codeql/swift/generated/decl/TopLevelCodeDecl.qll

@@ -1,10 +1,18 @@
 // generated by codegen/codegen.py
+import codeql.swift.elements.Element
 import codeql.swift.elements.stmt.BraceStmt
 import codeql.swift.elements.decl.Decl
 
 class TopLevelCodeDeclBase extends @top_level_code_decl, Decl {
   override string getAPrimaryQlClass() { result = "TopLevelCodeDecl" }
 
+  cached
+  override Element getAChild() {
+    none() or
+    result = Decl.super.getAChild() or
+    result = getBody()
+  }
+
   BraceStmt getBody() {
     exists(BraceStmt x |
       top_level_code_decls(this, x) and

swift/ql/lib/codeql/swift/generated/decl/TypeAliasDecl.qll

@@ -1,6 +1,13 @@
 // generated by codegen/codegen.py
+import codeql.swift.elements.Element
 import codeql.swift.elements.decl.GenericTypeDecl
 
 class TypeAliasDeclBase extends @type_alias_decl, GenericTypeDecl {
   override string getAPrimaryQlClass() { result = "TypeAliasDecl" }
+
+  cached
+  override Element getAChild() {
+    none() or
+    result = GenericTypeDecl.super.getAChild()
+  }
 }

swift/ql/lib/codeql/swift/generated/decl/TypeDecl.qll

@@ -1,8 +1,15 @@
 // generated by codegen/codegen.py
+import codeql.swift.elements.Element
 import codeql.swift.elements.type.Type
 import codeql.swift.elements.decl.ValueDecl
 
 class TypeDeclBase extends @type_decl, ValueDecl {
+  cached
+  override Element getAChild() {
+    none() or
+    result = ValueDecl.super.getAChild()
+  }
+
   string getName() { type_decls(this, result) }
 
   Type getBaseType(int index) {

swift/ql/lib/codeql/swift/generated/decl/ValueDecl.qll

@@ -1,8 +1,15 @@
 // generated by codegen/codegen.py
+import codeql.swift.elements.Element
 import codeql.swift.elements.decl.Decl
 import codeql.swift.elements.type.Type
 
 class ValueDeclBase extends @value_decl, Decl {
+  cached
+  override Element getAChild() {
+    none() or
+    result = Decl.super.getAChild()
+  }
+
   Type getInterfaceType() {
     exists(Type x |
       value_decls(this, x) and

swift/ql/lib/codeql/swift/generated/decl/VarDecl.qll

@@ -1,10 +1,17 @@
 // generated by codegen/codegen.py
+import codeql.swift.elements.Element
 import codeql.swift.elements.decl.AbstractStorageDecl
 import codeql.swift.elements.expr.Expr
 import codeql.swift.elements.pattern.Pattern
 import codeql.swift.elements.type.Type
 
 class VarDeclBase extends @var_decl, AbstractStorageDecl {
+  cached
+  override Element getAChild() {
+    none() or
+    result = AbstractStorageDecl.super.getAChild()
+  }
+
   string getName() { var_decls(this, result, _) }
 
   Type getType() {

swift/ql/lib/codeql/swift/generated/expr/AbstractClosureExpr.qll

@@ -1,4 +1,11 @@
 // generated by codegen/codegen.py
+import codeql.swift.elements.Element
 import codeql.swift.elements.expr.Expr
 
-class AbstractClosureExprBase extends @abstract_closure_expr, Expr { }
+class AbstractClosureExprBase extends @abstract_closure_expr, Expr {
+  cached
+  override Element getAChild() {
+    none() or
+    result = Expr.super.getAChild()
+  }
+}

swift/ql/lib/codeql/swift/generated/expr/AnyHashableErasureExpr.qll

@@ -1,6 +1,13 @@
 // generated by codegen/codegen.py
+import codeql.swift.elements.Element
 import codeql.swift.elements.expr.ImplicitConversionExpr
 
 class AnyHashableErasureExprBase extends @any_hashable_erasure_expr, ImplicitConversionExpr {
   override string getAPrimaryQlClass() { result = "AnyHashableErasureExpr" }
+
+  cached
+  override Element getAChild() {
+    none() or
+    result = ImplicitConversionExpr.super.getAChild()
+  }
 }

swift/ql/lib/codeql/swift/generated/expr/AnyTryExpr.qll

@@ -1,7 +1,15 @@
 // generated by codegen/codegen.py
+import codeql.swift.elements.Element
 import codeql.swift.elements.expr.Expr
 
 class AnyTryExprBase extends @any_try_expr, Expr {
+  cached
+  override Element getAChild() {
+    none() or
+    result = Expr.super.getAChild() or
+    result = getSubExpr()
+  }
+
   Expr getSubExpr() {
     exists(Expr x |
       any_try_exprs(this, x) and

swift/ql/lib/codeql/swift/generated/expr/AppliedPropertyWrapperExpr.qll

@@ -1,6 +1,13 @@
 // generated by codegen/codegen.py
+import codeql.swift.elements.Element
 import codeql.swift.elements.expr.Expr
 
 class AppliedPropertyWrapperExprBase extends @applied_property_wrapper_expr, Expr {
   override string getAPrimaryQlClass() { result = "AppliedPropertyWrapperExpr" }
+
+  cached
+  override Element getAChild() {
+    none() or
+    result = Expr.super.getAChild()
+  }
 }

swift/ql/lib/codeql/swift/generated/expr/ApplyExpr.qll

@@ -1,8 +1,17 @@
 // generated by codegen/codegen.py
+import codeql.swift.elements.Element
 import codeql.swift.elements.expr.Argument
 import codeql.swift.elements.expr.Expr
 
 class ApplyExprBase extends @apply_expr, Expr {
+  cached
+  override Element getAChild() {
+    none() or
+    result = Expr.super.getAChild() or
+    result = getFunction() or
+    result = getArgument(_)
+  }
+
   Expr getFunction() {
     exists(Expr x |
       apply_exprs(this, x) and

swift/ql/lib/codeql/swift/generated/expr/ArchetypeToSuperExpr.qll

@@ -1,6 +1,13 @@
 // generated by codegen/codegen.py
+import codeql.swift.elements.Element
 import codeql.swift.elements.expr.ImplicitConversionExpr
 
 class ArchetypeToSuperExprBase extends @archetype_to_super_expr, ImplicitConversionExpr {
   override string getAPrimaryQlClass() { result = "ArchetypeToSuperExpr" }
+
+  cached
+  override Element getAChild() {
+    none() or
+    result = ImplicitConversionExpr.super.getAChild()
+  }
 }

swift/ql/lib/codeql/swift/generated/expr/Argument.qll

@@ -1,10 +1,18 @@
 // generated by codegen/codegen.py
 import codeql.swift.elements.Element
+import codeql.swift.elements.Element
 import codeql.swift.elements.expr.Expr
 
 class ArgumentBase extends @argument, Element {
   override string getAPrimaryQlClass() { result = "Argument" }
 
+  cached
+  override Element getAChild() {
+    none() or
+    result = Element.super.getAChild() or
+    result = getExpr()
+  }
+
   string getLabel() { arguments(this, result, _) }
 
   Expr getExpr() {

swift/ql/lib/codeql/swift/generated/expr/ArrayExpr.qll

@@ -1,10 +1,18 @@
 // generated by codegen/codegen.py
+import codeql.swift.elements.Element
 import codeql.swift.elements.expr.CollectionExpr
 import codeql.swift.elements.expr.Expr
 
 class ArrayExprBase extends @array_expr, CollectionExpr {
   override string getAPrimaryQlClass() { result = "ArrayExpr" }
 
+  cached
+  override Element getAChild() {
+    none() or
+    result = CollectionExpr.super.getAChild() or
+    result = getElement(_)
+  }
+
   Expr getElement(int index) {
     exists(Expr x |
       array_expr_elements(this, index, x) and

swift/ql/lib/codeql/swift/generated/expr/ArrayToPointerExpr.qll

@@ -1,6 +1,13 @@
 // generated by codegen/codegen.py
+import codeql.swift.elements.Element
 import codeql.swift.elements.expr.ImplicitConversionExpr
 
 class ArrayToPointerExprBase extends @array_to_pointer_expr, ImplicitConversionExpr {
   override string getAPrimaryQlClass() { result = "ArrayToPointerExpr" }
+
+  cached
+  override Element getAChild() {
+    none() or
+    result = ImplicitConversionExpr.super.getAChild()
+  }
 }

swift/ql/lib/codeql/swift/generated/expr/ArrowExpr.qll

@@ -1,6 +1,13 @@
 // generated by codegen/codegen.py
+import codeql.swift.elements.Element
 import codeql.swift.elements.expr.Expr
 
 class ArrowExprBase extends @arrow_expr, Expr {
   override string getAPrimaryQlClass() { result = "ArrowExpr" }
+
+  cached
+  override Element getAChild() {
+    none() or
+    result = Expr.super.getAChild()
+  }
 }

swift/ql/lib/codeql/swift/generated/expr/AssignExpr.qll

@@ -1,9 +1,18 @@
 // generated by codegen/codegen.py
+import codeql.swift.elements.Element
 import codeql.swift.elements.expr.Expr
 
 class AssignExprBase extends @assign_expr, Expr {
   override string getAPrimaryQlClass() { result = "AssignExpr" }
 
+  cached
+  override Element getAChild() {
+    none() or
+    result = Expr.super.getAChild() or
+    result = getDest() or
+    result = getSource()
+  }
+
   Expr getDest() {
     exists(Expr x |
       assign_exprs(this, x, _) and

swift/ql/lib/codeql/swift/generated/expr/AutoClosureExpr.qll

@@ -1,10 +1,18 @@
 // generated by codegen/codegen.py
+import codeql.swift.elements.Element
 import codeql.swift.elements.expr.AbstractClosureExpr
 import codeql.swift.elements.stmt.BraceStmt
 
 class AutoClosureExprBase extends @auto_closure_expr, AbstractClosureExpr {
   override string getAPrimaryQlClass() { result = "AutoClosureExpr" }
 
+  cached
+  override Element getAChild() {
+    none() or
+    result = AbstractClosureExpr.super.getAChild() or
+    result = getBody()
+  }
+
   BraceStmt getBody() {
     exists(BraceStmt x |
       auto_closure_exprs(this, x) and

swift/ql/lib/codeql/swift/generated/expr/AwaitExpr.qll

@@ -1,6 +1,13 @@
 // generated by codegen/codegen.py
+import codeql.swift.elements.Element
 import codeql.swift.elements.expr.IdentityExpr
 
 class AwaitExprBase extends @await_expr, IdentityExpr {
   override string getAPrimaryQlClass() { result = "AwaitExpr" }
+
+  cached
+  override Element getAChild() {
+    none() or
+    result = IdentityExpr.super.getAChild()
+  }
 }

swift/ql/lib/codeql/swift/generated/expr/BinaryExpr.qll

@@ -1,6 +1,13 @@
 // generated by codegen/codegen.py
+import codeql.swift.elements.Element
 import codeql.swift.elements.expr.ApplyExpr
 
 class BinaryExprBase extends @binary_expr, ApplyExpr {
   override string getAPrimaryQlClass() { result = "BinaryExpr" }
+
+  cached
+  override Element getAChild() {
+    none() or
+    result = ApplyExpr.super.getAChild()
+  }
 }

swift/ql/lib/codeql/swift/generated/expr/BindOptionalExpr.qll

@@ -1,9 +1,17 @@
 // generated by codegen/codegen.py
+import codeql.swift.elements.Element
 import codeql.swift.elements.expr.Expr
 
 class BindOptionalExprBase extends @bind_optional_expr, Expr {
   override string getAPrimaryQlClass() { result = "BindOptionalExpr" }
 
+  cached
+  override Element getAChild() {
+    none() or
+    result = Expr.super.getAChild() or
+    result = getSubExpr()
+  }
+
   Expr getSubExpr() {
     exists(Expr x |
       bind_optional_exprs(this, x) and

swift/ql/lib/codeql/swift/generated/expr/BooleanLiteralExpr.qll

@@ -1,8 +1,15 @@
 // generated by codegen/codegen.py
+import codeql.swift.elements.Element
 import codeql.swift.elements.expr.BuiltinLiteralExpr
 
 class BooleanLiteralExprBase extends @boolean_literal_expr, BuiltinLiteralExpr {
   override string getAPrimaryQlClass() { result = "BooleanLiteralExpr" }
 
+  cached
+  override Element getAChild() {
+    none() or
+    result = BuiltinLiteralExpr.super.getAChild()
+  }
+
   boolean getValue() { boolean_literal_exprs(this, result) }
 }

swift/ql/lib/codeql/swift/generated/expr/BridgeFromObjCExpr.qll

@@ -1,6 +1,13 @@
 // generated by codegen/codegen.py
+import codeql.swift.elements.Element
 import codeql.swift.elements.expr.ImplicitConversionExpr
 
 class BridgeFromObjCExprBase extends @bridge_from_obj_c_expr, ImplicitConversionExpr {
   override string getAPrimaryQlClass() { result = "BridgeFromObjCExpr" }
+
+  cached
+  override Element getAChild() {
+    none() or
+    result = ImplicitConversionExpr.super.getAChild()
+  }
 }

swift/ql/lib/codeql/swift/generated/expr/BridgeToObjCExpr.qll

@@ -1,6 +1,13 @@
 // generated by codegen/codegen.py
+import codeql.swift.elements.Element
 import codeql.swift.elements.expr.ImplicitConversionExpr
 
 class BridgeToObjCExprBase extends @bridge_to_obj_c_expr, ImplicitConversionExpr {
   override string getAPrimaryQlClass() { result = "BridgeToObjCExpr" }
+
+  cached
+  override Element getAChild() {
+    none() or
+    result = ImplicitConversionExpr.super.getAChild()
+  }
 }

swift/ql/lib/codeql/swift/generated/expr/BuiltinLiteralExpr.qll

@@ -1,4 +1,11 @@
 // generated by codegen/codegen.py
+import codeql.swift.elements.Element
 import codeql.swift.elements.expr.LiteralExpr
 
-class BuiltinLiteralExprBase extends @builtin_literal_expr, LiteralExpr { }
+class BuiltinLiteralExprBase extends @builtin_literal_expr, LiteralExpr {
+  cached
+  override Element getAChild() {
+    none() or
+    result = LiteralExpr.super.getAChild()
+  }
+}

swift/ql/lib/codeql/swift/generated/expr/CallExpr.qll

@@ -1,6 +1,13 @@
 // generated by codegen/codegen.py
+import codeql.swift.elements.Element
 import codeql.swift.elements.expr.ApplyExpr
 
 class CallExprBase extends @call_expr, ApplyExpr {
   override string getAPrimaryQlClass() { result = "CallExpr" }
+
+  cached
+  override Element getAChild() {
+    none() or
+    result = ApplyExpr.super.getAChild()
+  }
 }

swift/ql/lib/codeql/swift/generated/expr/CaptureListExpr.qll

@@ -1,4 +1,5 @@
 // generated by codegen/codegen.py
+import codeql.swift.elements.Element
 import codeql.swift.elements.expr.ClosureExpr
 import codeql.swift.elements.expr.Expr
 import codeql.swift.elements.decl.PatternBindingDecl
@@ -6,6 +7,14 @@ import codeql.swift.elements.decl.PatternBindingDecl
 class CaptureListExprBase extends @capture_list_expr, Expr {
   override string getAPrimaryQlClass() { result = "CaptureListExpr" }
 
+  cached
+  override Element getAChild() {
+    none() or
+    result = Expr.super.getAChild() or
+    result = getBindingDecl(_) or
+    result = getClosureBody()
+  }
+
   PatternBindingDecl getBindingDecl(int index) {
     exists(PatternBindingDecl x |
       capture_list_expr_binding_decls(this, index, x) and

swift/ql/lib/codeql/swift/generated/expr/CheckedCastExpr.qll

@@ -1,4 +1,11 @@
 // generated by codegen/codegen.py
+import codeql.swift.elements.Element
 import codeql.swift.elements.expr.ExplicitCastExpr
 
-class CheckedCastExprBase extends @checked_cast_expr, ExplicitCastExpr { }
+class CheckedCastExprBase extends @checked_cast_expr, ExplicitCastExpr {
+  cached
+  override Element getAChild() {
+    none() or
+    result = ExplicitCastExpr.super.getAChild()
+  }
+}

swift/ql/lib/codeql/swift/generated/expr/ClassMetatypeToObjectExpr.qll

@@ -1,6 +1,13 @@
 // generated by codegen/codegen.py
+import codeql.swift.elements.Element
 import codeql.swift.elements.expr.ImplicitConversionExpr
 
 class ClassMetatypeToObjectExprBase extends @class_metatype_to_object_expr, ImplicitConversionExpr {
   override string getAPrimaryQlClass() { result = "ClassMetatypeToObjectExpr" }
+
+  cached
+  override Element getAChild() {
+    none() or
+    result = ImplicitConversionExpr.super.getAChild()
+  }
 }

swift/ql/lib/codeql/swift/generated/expr/ClosureExpr.qll

@@ -1,10 +1,18 @@
 // generated by codegen/codegen.py
+import codeql.swift.elements.Element
 import codeql.swift.elements.expr.AbstractClosureExpr
 import codeql.swift.elements.stmt.BraceStmt
 
 class ClosureExprBase extends @closure_expr, AbstractClosureExpr {
   override string getAPrimaryQlClass() { result = "ClosureExpr" }
 
+  cached
+  override Element getAChild() {
+    none() or
+    result = AbstractClosureExpr.super.getAChild() or
+    result = getBody()
+  }
+
   BraceStmt getBody() {
     exists(BraceStmt x |
       closure_exprs(this, x) and

swift/ql/lib/codeql/swift/generated/expr/CodeCompletionExpr.qll

@@ -1,6 +1,13 @@
 // generated by codegen/codegen.py
+import codeql.swift.elements.Element
 import codeql.swift.elements.expr.Expr
 
 class CodeCompletionExprBase extends @code_completion_expr, Expr {
   override string getAPrimaryQlClass() { result = "CodeCompletionExpr" }
+
+  cached
+  override Element getAChild() {
+    none() or
+    result = Expr.super.getAChild()
+  }
 }

swift/ql/lib/codeql/swift/generated/expr/CoerceExpr.qll

@@ -1,6 +1,13 @@
 // generated by codegen/codegen.py
+import codeql.swift.elements.Element
 import codeql.swift.elements.expr.ExplicitCastExpr
 
 class CoerceExprBase extends @coerce_expr, ExplicitCastExpr {
   override string getAPrimaryQlClass() { result = "CoerceExpr" }
+
+  cached
+  override Element getAChild() {
+    none() or
+    result = ExplicitCastExpr.super.getAChild()
+  }
 }

swift/ql/lib/codeql/swift/generated/expr/CollectionExpr.qll

@@ -1,4 +1,11 @@
 // generated by codegen/codegen.py
+import codeql.swift.elements.Element
 import codeql.swift.elements.expr.Expr
 
-class CollectionExprBase extends @collection_expr, Expr { }
+class CollectionExprBase extends @collection_expr, Expr {
+  cached
+  override Element getAChild() {
+    none() or
+    result = Expr.super.getAChild()
+  }
+}

swift/ql/lib/codeql/swift/generated/expr/CollectionUpcastConversionExpr.qll

@@ -1,7 +1,14 @@
 // generated by codegen/codegen.py
+import codeql.swift.elements.Element
 import codeql.swift.elements.expr.ImplicitConversionExpr
 
 class CollectionUpcastConversionExprBase extends @collection_upcast_conversion_expr,
   ImplicitConversionExpr {
   override string getAPrimaryQlClass() { result = "CollectionUpcastConversionExpr" }
+
+  cached
+  override Element getAChild() {
+    none() or
+    result = ImplicitConversionExpr.super.getAChild()
+  }
 }

swift/ql/lib/codeql/swift/generated/expr/ConditionalBridgeFromObjCExpr.qll

@@ -1,7 +1,14 @@
 // generated by codegen/codegen.py
+import codeql.swift.elements.Element
 import codeql.swift.elements.expr.ImplicitConversionExpr
 
 class ConditionalBridgeFromObjCExprBase extends @conditional_bridge_from_obj_c_expr,
   ImplicitConversionExpr {
   override string getAPrimaryQlClass() { result = "ConditionalBridgeFromObjCExpr" }
+
+  cached
+  override Element getAChild() {
+    none() or
+    result = ImplicitConversionExpr.super.getAChild()
+  }
 }

swift/ql/lib/codeql/swift/generated/expr/ConditionalCheckedCastExpr.qll

@@ -1,6 +1,13 @@
 // generated by codegen/codegen.py
+import codeql.swift.elements.Element
 import codeql.swift.elements.expr.CheckedCastExpr
 
 class ConditionalCheckedCastExprBase extends @conditional_checked_cast_expr, CheckedCastExpr {
   override string getAPrimaryQlClass() { result = "ConditionalCheckedCastExpr" }
+
+  cached
+  override Element getAChild() {
+    none() or
+    result = CheckedCastExpr.super.getAChild()
+  }
 }

swift/ql/lib/codeql/swift/generated/expr/ConstructorRefCallExpr.qll

@@ -1,6 +1,13 @@
 // generated by codegen/codegen.py
+import codeql.swift.elements.Element
 import codeql.swift.elements.expr.SelfApplyExpr
 
 class ConstructorRefCallExprBase extends @constructor_ref_call_expr, SelfApplyExpr {
   override string getAPrimaryQlClass() { result = "ConstructorRefCallExpr" }
+
+  cached
+  override Element getAChild() {
+    none() or
+    result = SelfApplyExpr.super.getAChild()
+  }
 }

swift/ql/lib/codeql/swift/generated/expr/CovariantFunctionConversionExpr.qll

@@ -1,7 +1,14 @@
 // generated by codegen/codegen.py
+import codeql.swift.elements.Element
 import codeql.swift.elements.expr.ImplicitConversionExpr
 
 class CovariantFunctionConversionExprBase extends @covariant_function_conversion_expr,
   ImplicitConversionExpr {
   override string getAPrimaryQlClass() { result = "CovariantFunctionConversionExpr" }
+
+  cached
+  override Element getAChild() {
+    none() or
+    result = ImplicitConversionExpr.super.getAChild()
+  }
 }

swift/ql/lib/codeql/swift/generated/expr/CovariantReturnConversionExpr.qll

@@ -1,7 +1,14 @@
 // generated by codegen/codegen.py
+import codeql.swift.elements.Element
 import codeql.swift.elements.expr.ImplicitConversionExpr
 
 class CovariantReturnConversionExprBase extends @covariant_return_conversion_expr,
   ImplicitConversionExpr {
   override string getAPrimaryQlClass() { result = "CovariantReturnConversionExpr" }
+
+  cached
+  override Element getAChild() {
+    none() or
+    result = ImplicitConversionExpr.super.getAChild()
+  }
 }

swift/ql/lib/codeql/swift/generated/expr/DeclRefExpr.qll

@@ -1,4 +1,5 @@
 // generated by codegen/codegen.py
+import codeql.swift.elements.Element
 import codeql.swift.elements.decl.Decl
 import codeql.swift.elements.expr.Expr
 import codeql.swift.elements.type.Type
@@ -6,6 +7,12 @@ import codeql.swift.elements.type.Type
 class DeclRefExprBase extends @decl_ref_expr, Expr {
   override string getAPrimaryQlClass() { result = "DeclRefExpr" }
 
+  cached
+  override Element getAChild() {
+    none() or
+    result = Expr.super.getAChild()
+  }
+
   Decl getDecl() {
     exists(Decl x |
       decl_ref_exprs(this, x) and

swift/ql/lib/codeql/swift/generated/expr/DefaultArgumentExpr.qll

@@ -1,10 +1,17 @@
 // generated by codegen/codegen.py
+import codeql.swift.elements.Element
 import codeql.swift.elements.expr.Expr
 import codeql.swift.elements.decl.ParamDecl
 
 class DefaultArgumentExprBase extends @default_argument_expr, Expr {
   override string getAPrimaryQlClass() { result = "DefaultArgumentExpr" }
 
+  cached
+  override Element getAChild() {
+    none() or
+    result = Expr.super.getAChild()
+  }
+
   ParamDecl getParamDecl() {
     exists(ParamDecl x |
       default_argument_exprs(this, x, _) and

swift/ql/lib/codeql/swift/generated/expr/DerivedToBaseExpr.qll

@@ -1,6 +1,13 @@
 // generated by codegen/codegen.py
+import codeql.swift.elements.Element
 import codeql.swift.elements.expr.ImplicitConversionExpr
 
 class DerivedToBaseExprBase extends @derived_to_base_expr, ImplicitConversionExpr {
   override string getAPrimaryQlClass() { result = "DerivedToBaseExpr" }
+
+  cached
+  override Element getAChild() {
+    none() or
+    result = ImplicitConversionExpr.super.getAChild()
+  }
 }

swift/ql/lib/codeql/swift/generated/expr/DestructureTupleExpr.qll

@@ -1,6 +1,13 @@
 // generated by codegen/codegen.py
+import codeql.swift.elements.Element
 import codeql.swift.elements.expr.ImplicitConversionExpr
 
 class DestructureTupleExprBase extends @destructure_tuple_expr, ImplicitConversionExpr {
   override string getAPrimaryQlClass() { result = "DestructureTupleExpr" }
+
+  cached
+  override Element getAChild() {
+    none() or
+    result = ImplicitConversionExpr.super.getAChild()
+  }
 }

swift/ql/lib/codeql/swift/generated/expr/DictionaryExpr.qll

@@ -1,10 +1,18 @@
 // generated by codegen/codegen.py
+import codeql.swift.elements.Element
 import codeql.swift.elements.expr.CollectionExpr
 import codeql.swift.elements.expr.Expr
 
 class DictionaryExprBase extends @dictionary_expr, CollectionExpr {
   override string getAPrimaryQlClass() { result = "DictionaryExpr" }
 
+  cached
+  override Element getAChild() {
+    none() or
+    result = CollectionExpr.super.getAChild() or
+    result = getElement(_)
+  }
+
   Expr getElement(int index) {
     exists(Expr x |
       dictionary_expr_elements(this, index, x) and

swift/ql/lib/codeql/swift/generated/expr/DifferentiableFunctionExpr.qll

@@ -1,6 +1,13 @@
 // generated by codegen/codegen.py
+import codeql.swift.elements.Element
 import codeql.swift.elements.expr.ImplicitConversionExpr
 
 class DifferentiableFunctionExprBase extends @differentiable_function_expr, ImplicitConversionExpr {
   override string getAPrimaryQlClass() { result = "DifferentiableFunctionExpr" }
+
+  cached
+  override Element getAChild() {
+    none() or
+    result = ImplicitConversionExpr.super.getAChild()
+  }
 }

swift/ql/lib/codeql/swift/generated/expr/DifferentiableFunctionExtractOriginalExpr.qll

@@ -1,7 +1,14 @@
 // generated by codegen/codegen.py
+import codeql.swift.elements.Element
 import codeql.swift.elements.expr.ImplicitConversionExpr
 
 class DifferentiableFunctionExtractOriginalExprBase extends @differentiable_function_extract_original_expr,
   ImplicitConversionExpr {
   override string getAPrimaryQlClass() { result = "DifferentiableFunctionExtractOriginalExpr" }
+
+  cached
+  override Element getAChild() {
+    none() or
+    result = ImplicitConversionExpr.super.getAChild()
+  }
 }

swift/ql/lib/codeql/swift/generated/expr/DiscardAssignmentExpr.qll

@@ -1,6 +1,13 @@
 // generated by codegen/codegen.py
+import codeql.swift.elements.Element
 import codeql.swift.elements.expr.Expr
 
 class DiscardAssignmentExprBase extends @discard_assignment_expr, Expr {
   override string getAPrimaryQlClass() { result = "DiscardAssignmentExpr" }
+
+  cached
+  override Element getAChild() {
+    none() or
+    result = Expr.super.getAChild()
+  }
 }