introduce FieldDecl in the ast

ql/src/codeql_ql/ast/Ast.qll

@@ -563,8 +563,10 @@ class VarDecl extends TVarDecl, VarDef, Declaration {
     )
   }
 
-  /** If this is a field, returns the class type that declares it. */
-  ClassType getDeclaringType() { result.getDeclaration().getAField() = this }
+  /** If this is declared in a field, returns the class type that declares it. */
+  ClassType getDeclaringType() {
+    exists(FieldDecl f | f.getVarDecl() = this and result = f.getParent().(Class).getType())
+  }
 
   /**
    * Holds if this is a class field that overrides the field `other`.
@@ -580,6 +582,32 @@ class VarDecl extends TVarDecl, VarDef, Declaration {
   override string toString() { result = this.getName() }
 }
 
+/**
+ * A field declaration;
+ */
+class FieldDecl extends TFieldDecl, AstNode {
+  QL::Field f;
+
+  FieldDecl() { this = TFieldDecl(f) }
+
+  VarDecl getVarDecl() { toQL(result) = f.getChild() }
+
+  override AstNode getAChild(string pred) {
+    result = super.getAChild(pred)
+    or
+    pred = directMember("getVarDecl") and result = this.getVarDecl()
+  }
+
+  override string getAPrimaryQlClass() { result = "FieldDecl" }
+
+  /** Holds if this field is annotated as overriding another field. */
+  predicate isOverride() { this.hasAnnotation("override") }
+
+  string getName() { result = getVarDecl().getName() }
+
+  override QLDoc getQLDoc() { result = any(Class c).getQLDocFor(this) }
+}
+
 /**
  * A type reference, such as `DataFlow::Node`.
  */
@@ -716,10 +744,7 @@ class Class extends TClass, TypeDeclaration, ModuleDeclaration {
    */
   CharPred getCharPred() { toQL(result) = cls.getChild(_).(QL::ClassMember).getChild(_) }
 
-  AstNode getMember(int i) {
-    toQL(result) = cls.getChild(i).(QL::ClassMember).getChild(_) or
-    toQL(result) = cls.getChild(i).(QL::ClassMember).getChild(_).(QL::Field).getChild()
-  }
+  AstNode getMember(int i) { toQL(result) = cls.getChild(i).(QL::ClassMember).getChild(_) }
 
   QLDoc getQLDocFor(AstNode m) {
     exists(int i | result = this.getMember(i) and m = this.getMember(i + 1))
@@ -743,9 +768,7 @@ class Class extends TClass, TypeDeclaration, ModuleDeclaration {
   /**
    * Gets a field in this class.
    */
-  VarDecl getAField() {
-    toQL(result) = cls.getChild(_).(QL::ClassMember).getChild(_).(QL::Field).getChild()
-  }
+  FieldDecl getAField() { result = getMember(_) }
 
   /**
    * Gets a super-type referenced in the `extends` part of the class declaration.

ql/src/codeql_ql/ast/internal/AstNodes.qll

@@ -8,6 +8,7 @@ newtype TAstNode =
   TQLDoc(QL::Qldoc qldoc) or
   TClasslessPredicate(QL::ClasslessPredicate pred) or
   TVarDecl(QL::VarDecl decl) or
+  TFieldDecl(QL::Field field) or
   TClass(QL::Dataclass dc) or
   TCharPred(QL::Charpred pred) or
   TClassPredicate(QL::MemberPredicate pred) or
@@ -150,6 +151,8 @@ QL::AstNode toQL(AST::AstNode n) {
   or
   n = TVarDecl(result)
   or
+  n = TFieldDecl(result)
+  or
   n = TClass(result)
   or
   n = TCharPred(result)

ql/src/codeql_ql/ast/internal/Type.qll

@@ -134,7 +134,7 @@ predicate predOverrides(ClassPredicate sub, ClassPredicate sup) {
 }
 
 private VarDecl declaredField(ClassType ty, string name) {
-  result = ty.getDeclaration().getAField() and
+  result = ty.getDeclaration().getAField().getVarDecl() and
   result.getName() = name
 }
 

ql/src/codeql_ql/ast/internal/Variable.qll

@@ -37,7 +37,7 @@ class VariableScope extends TScope, AstNode {
   predicate containsField(VarDef decl, string name) {
     name = decl.getName() and
     (
-      decl = this.(Class).getAField()
+      decl = this.(Class).getAField().getVarDecl()
       or
       this.getOuterScope().containsField(decl, name) and
       not exists(this.getADefinition(name))