TypeScript: support syntax for optional tuple type elements

javascript/ql/src/semmle/javascript/TypeScript.qll

@@ -1073,6 +1073,14 @@ class IsTypeExpr extends @istypeexpr, TypeExpr {
   TypeExpr getPredicateType() { result = this.getChildTypeExpr(1) }
 }
 
+/**
+ * An optional type element in a tuple type, such as `number?` in `[string, number?]`.
+ */
+class OptionalTypeExpr extends @optionaltypeexpr, TypeExpr {
+  /** Gets the type `T` in `T?` */
+  TypeExpr getElementType() { result = getChildTypeExpr(0) }
+}
+
 /**
  * A possibly qualified name that refers to a variable from inside a type.
  *

javascript/ql/src/semmlecode.javascript.dbscheme

@@ -556,7 +556,9 @@ case @typeexpr.kind of
 | 29 = @infertypeexpr
 | 30 = @importtypeaccess
 | 31 = @importnamespaceaccess
-| 32 = @importvartypeaccess;
+| 32 = @importvartypeaccess
+| 33 = @optionaltypeexpr
+;
 
 @typeref = @typeaccess | @typedecl;
 @typeidentifier = @typedecl | @localtypeaccess | @typelabel | @localvartypeaccess | @localnamespaceaccess;

javascript/ql/test/library-tests/TypeScript/TypeAnnotations/TupleTypeExpr.expected

@@ -3,3 +3,6 @@
 | tst.ts:48:16:48:40 | [number ... oolean] | 2 | 3 | tst.ts:48:33:48:39 | boolean |
 | tst.ts:95:31:95:35 | [S,T] | 0 | 2 | tst.ts:95:32:95:32 | S |
 | tst.ts:95:31:95:35 | [S,T] | 1 | 2 | tst.ts:95:34:95:34 | T |
+| tst.ts:133:31:133:55 | [number ... umber?] | 0 | 3 | tst.ts:133:32:133:37 | number |
+| tst.ts:133:31:133:55 | [number ... umber?] | 1 | 3 | tst.ts:133:40:133:45 | string |
+| tst.ts:133:31:133:55 | [number ... umber?] | 2 | 3 | tst.ts:133:48:133:54 | number? |

javascript/ql/test/library-tests/TypeScript/TypeAnnotations/VariableTypes.expected

@@ -69,3 +69,5 @@
 | tst.ts:126:5:126:18 | importedTypeof | importedTypeof | tst.ts:126:21:126:42 | typeof  ... value") |
 | tst.ts:127:5:127:27 | importe ... dTypeof | importedQualifiedTypeof | tst.ts:127:30:127:53 | typeof  ... lue").x |
 | tst.ts:128:5:128:35 | importe ... tespace | importedQualifiedTypeWhitespace | tst.ts:131:4:131:6 | bar |
+| tst.ts:133:5:133:28 | tupleWi ... Element | tupleWithOptionalElement | tst.ts:133:31:133:55 | [number ... umber?] |
+| tst.ts:134:5:134:14 | emptyTuple | emptyTuple | tst.ts:134:17:134:18 | [] |

javascript/ql/test/library-tests/TypeScript/TypeAnnotations/tst.ts

@@ -129,3 +129,6 @@ var importedQualifiedTypeWhitespace: import(
   'awkard-namespace'
   )
   .bar;
+
+let tupleWithOptionalElement: [number, string, number?];
+let emptyTuple: [];