[Clang] [NFC] Introduce DynamicRecursiveASTVisitor (#110040)

See #105195 as well as the big comment in DynamicRecursiveASTVisitor.cpp
for more context.

clang/include/clang/AST/DynamicRecursiveASTVisitor.h

@@ -0,0 +1,276 @@
+//===--- DynamicRecursiveASTVisitor.h - Virtual AST Visitor -----*- C++ -*-===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+//
+//  This file defines the DynamicRecursiveASTVisitor interface, which acts
+//  identically to RecursiveASTVisitor, except that it uses virtual dispatch
+//  instead of CRTP, which greatly improves compile times and binary size.
+//
+//  Prefer to use this over RecursiveASTVisitor whenever possible.
+//
+//===----------------------------------------------------------------------===//
+#ifndef LLVM_CLANG_AST_DYNAMIC_RECURSIVE_AST_VISITOR_H
+#define LLVM_CLANG_AST_DYNAMIC_RECURSIVE_AST_VISITOR_H
+
+#include "clang/AST/Attr.h"
+#include "clang/AST/ExprConcepts.h"
+#include "clang/AST/TypeLoc.h"
+
+namespace clang {
+class ASTContext;
+
+/// Recursive AST visitor that supports extension via dynamic dispatch.
+///
+/// Like RecursiveASTVisitor, this class allows for traversal of arbitrarily
+/// complex ASTs. The main difference is that this uses virtual functions
+/// instead of CRTP, which greatly improves compile times of Clang itself,
+/// as well as binary size.
+///
+/// Instead of functions (e.g. shouldVisitImplicitCode()), this class
+/// uses member variables (e.g. ShouldVisitImplicitCode) to control
+/// visitation behaviour.
+///
+/// However, there is no support for overriding some of the less commonly
+/// used features of the RAV, such as WalkUpFromX or attribute traversal
+/// (attributes can still be traversed, but you can't change what happens
+/// when we traverse one).
+///
+/// The following is a list of RAV features that are NOT customisable:
+///
+///   - Visiting attributes,
+///   - Overriding WalkUpFromX,
+///   - Overriding getStmtChildren().
+///
+/// Furthermore, post-order traversal is not supported at all.
+///
+/// Prefer to use this over RecursiveASTVisitor unless you absolutely
+/// need to use one of the features listed above (e.g. overriding
+/// WalkUpFromX or post-order traversal).
+///
+/// \see RecursiveASTVisitor.
+class DynamicRecursiveASTVisitor {
+public:
+  /// Whether this visitor should recurse into template instantiations.
+  bool ShouldVisitTemplateInstantiations = false;
+
+  /// Whether this visitor should recurse into the types of TypeLocs.
+  bool ShouldWalkTypesOfTypeLocs = true;
+
+  /// Whether this visitor should recurse into implicit code, e.g.
+  /// implicit constructors and destructors.
+  bool ShouldVisitImplicitCode = false;
+
+  /// Whether this visitor should recurse into lambda body.
+  bool ShouldVisitLambdaBody = true;
+
+protected:
+  DynamicRecursiveASTVisitor() = default;
+  DynamicRecursiveASTVisitor(DynamicRecursiveASTVisitor &&) = default;
+  DynamicRecursiveASTVisitor(const DynamicRecursiveASTVisitor &) = default;
+  DynamicRecursiveASTVisitor &
+  operator=(DynamicRecursiveASTVisitor &&) = default;
+  DynamicRecursiveASTVisitor &
+  operator=(const DynamicRecursiveASTVisitor &) = default;
+
+public:
+  virtual void anchor();
+  virtual ~DynamicRecursiveASTVisitor() = default;
+
+  /// Recursively visits an entire AST, starting from the TranslationUnitDecl.
+  /// \returns false if visitation was terminated early.
+  virtual bool TraverseAST(ASTContext &AST);
+
+  /// Recursively visit an attribute, by dispatching to
+  /// Traverse*Attr() based on the argument's dynamic type.
+  ///
+  /// \returns false if the visitation was terminated early, true
+  /// otherwise (including when the argument is a Null type location).
+  virtual bool TraverseAttr(Attr *At);
+
+  /// Recursively visit a constructor initializer.  This
+  /// automatically dispatches to another visitor for the initializer
+  /// expression, but not for the name of the initializer, so may
+  /// be overridden for clients that need access to the name.
+  ///
+  /// \returns false if the visitation was terminated early, true otherwise.
+  virtual bool TraverseConstructorInitializer(CXXCtorInitializer *Init);
+
+  /// Recursively visit a base specifier. This can be overridden by a
+  /// subclass.
+  ///
+  /// \returns false if the visitation was terminated early, true otherwise.
+  virtual bool TraverseCXXBaseSpecifier(const CXXBaseSpecifier &Base);
+
+  /// Recursively visit a declaration, by dispatching to
+  /// Traverse*Decl() based on the argument's dynamic type.
+  ///
+  /// \returns false if the visitation was terminated early, true
+  /// otherwise (including when the argument is NULL).
+  virtual bool TraverseDecl(Decl *D);
+
+  /// Recursively visit a name with its location information.
+  ///
+  /// \returns false if the visitation was terminated early, true otherwise.
+  virtual bool TraverseDeclarationNameInfo(DeclarationNameInfo NameInfo);
+
+  /// Recursively visit a lambda capture. \c Init is the expression that
+  /// will be used to initialize the capture.
+  ///
+  /// \returns false if the visitation was terminated early, true otherwise.
+  virtual bool TraverseLambdaCapture(LambdaExpr *LE, const LambdaCapture *C,
+                                     Expr *Init);
+
+  /// Recursively visit a C++ nested-name-specifier.
+  ///
+  /// \returns false if the visitation was terminated early, true otherwise.
+  virtual bool TraverseNestedNameSpecifier(NestedNameSpecifier *NNS);
+
+  /// Recursively visit a C++ nested-name-specifier with location
+  /// information.
+  ///
+  /// \returns false if the visitation was terminated early, true otherwise.
+  virtual bool TraverseNestedNameSpecifierLoc(NestedNameSpecifierLoc NNS);
+
+  /// Recursively visit a statement or expression, by
+  /// dispatching to Traverse*() based on the argument's dynamic type.
+  ///
+  /// \returns false if the visitation was terminated early, true
+  /// otherwise (including when the argument is nullptr).
+  virtual bool TraverseStmt(Stmt *S);
+
+  /// Recursively visit a template argument and dispatch to the
+  /// appropriate method for the argument type.
+  ///
+  /// \returns false if the visitation was terminated early, true otherwise.
+  // FIXME: migrate callers to TemplateArgumentLoc instead.
+  virtual bool TraverseTemplateArgument(const TemplateArgument &Arg);
+
+  /// Recursively visit a template argument location and dispatch to the
+  /// appropriate method for the argument type.
+  ///
+  /// \returns false if the visitation was terminated early, true otherwise.
+  virtual bool TraverseTemplateArgumentLoc(const TemplateArgumentLoc &ArgLoc);
+
+  /// Recursively visit a set of template arguments.
+  ///
+  /// \returns false if the visitation was terminated early, true otherwise.
+  // FIXME: take a TemplateArgumentLoc* (or TemplateArgumentListInfo) instead.
+  // Not virtual for now because no-one overrides it.
+  bool TraverseTemplateArguments(ArrayRef<TemplateArgument> Args);
+
+  /// Recursively visit a template name and dispatch to the
+  /// appropriate method.
+  ///
+  /// \returns false if the visitation was terminated early, true otherwise.
+  virtual bool TraverseTemplateName(TemplateName Template);
+
+  /// Recursively visit a type, by dispatching to
+  /// Traverse*Type() based on the argument's getTypeClass() property.
+  ///
+  /// \returns false if the visitation was terminated early, true
+  /// otherwise (including when the argument is a Null type).
+  virtual bool TraverseType(QualType T);
+
+  /// Recursively visit a type with location, by dispatching to
+  /// Traverse*TypeLoc() based on the argument type's getTypeClass() property.
+  ///
+  /// \returns false if the visitation was terminated early, true
+  /// otherwise (including when the argument is a Null type location).
+  virtual bool TraverseTypeLoc(TypeLoc TL);
+
+  /// Recursively visit an Objective-C protocol reference with location
+  /// information.
+  ///
+  /// \returns false if the visitation was terminated early, true otherwise.
+  virtual bool TraverseObjCProtocolLoc(ObjCProtocolLoc ProtocolLoc);
+
+  /// Traverse a concept (requirement).
+  virtual bool TraverseTypeConstraint(const TypeConstraint *C);
+  virtual bool TraverseConceptRequirement(concepts::Requirement *R);
+  virtual bool TraverseConceptTypeRequirement(concepts::TypeRequirement *R);
+  virtual bool TraverseConceptExprRequirement(concepts::ExprRequirement *R);
+  virtual bool TraverseConceptNestedRequirement(concepts::NestedRequirement *R);
+  virtual bool TraverseConceptReference(ConceptReference *CR);
+  virtual bool VisitConceptReference(ConceptReference *CR) { return true; }
+
+  /// Visit a node.
+  virtual bool VisitAttr(Attr *A) { return true; }
+  virtual bool VisitDecl(Decl *D) { return true; }
+  virtual bool VisitStmt(Stmt *S) { return true; }
+  virtual bool VisitType(Type *T) { return true; }
+  virtual bool VisitTypeLoc(TypeLoc TL) { return true; }
+
+  /// Walk up from a node.
+  bool WalkUpFromDecl(Decl *D) { return VisitDecl(D); }
+  bool WalkUpFromStmt(Stmt *S) { return VisitStmt(S); }
+  bool WalkUpFromType(Type *T) { return VisitType(T); }
+  bool WalkUpFromTypeLoc(TypeLoc TL) { return VisitTypeLoc(TL); }
+
+  /// Invoked before visiting a statement or expression via data recursion.
+  ///
+  /// \returns false to skip visiting the node, true otherwise.
+  virtual bool dataTraverseStmtPre(Stmt *S) { return true; }
+
+  /// Invoked after visiting a statement or expression via data recursion.
+  /// This is not invoked if the previously invoked \c dataTraverseStmtPre
+  /// returned false.
+  ///
+  /// \returns false if the visitation was terminated early, true otherwise.
+  virtual bool dataTraverseStmtPost(Stmt *S) { return true; }
+  virtual bool dataTraverseNode(Stmt *S);
+
+#define DEF_TRAVERSE_TMPL_INST(kind)                                           \
+  virtual bool TraverseTemplateInstantiations(kind##TemplateDecl *D);
+  DEF_TRAVERSE_TMPL_INST(Class)
+  DEF_TRAVERSE_TMPL_INST(Var)
+  DEF_TRAVERSE_TMPL_INST(Function)
+#undef DEF_TRAVERSE_TMPL_INST
+
+  // Decls.
+#define ABSTRACT_DECL(DECL)
+#define DECL(CLASS, BASE) virtual bool Traverse##CLASS##Decl(CLASS##Decl *D);
+#include "clang/AST/DeclNodes.inc"
+
+#define DECL(CLASS, BASE)                                                      \
+  bool WalkUpFrom##CLASS##Decl(CLASS##Decl *D);                                \
+  virtual bool Visit##CLASS##Decl(CLASS##Decl *D) { return true; }
+#include "clang/AST/DeclNodes.inc"
+
+  // Stmts.
+#define ABSTRACT_STMT(STMT)
+#define STMT(CLASS, PARENT) virtual bool Traverse##CLASS(CLASS *S);
+#include "clang/AST/StmtNodes.inc"
+
+#define STMT(CLASS, PARENT)                                                    \
+  bool WalkUpFrom##CLASS(CLASS *S);                                            \
+  virtual bool Visit##CLASS(CLASS *S) { return true; }
+#include "clang/AST/StmtNodes.inc"
+
+  // Types.
+#define ABSTRACT_TYPE(CLASS, BASE)
+#define TYPE(CLASS, BASE) virtual bool Traverse##CLASS##Type(CLASS##Type *T);
+#include "clang/AST/TypeNodes.inc"
+
+#define TYPE(CLASS, BASE)                                                      \
+  bool WalkUpFrom##CLASS##Type(CLASS##Type *T);                                \
+  virtual bool Visit##CLASS##Type(CLASS##Type *T) { return true; }
+#include "clang/AST/TypeNodes.inc"
+
+  // TypeLocs.
+#define ABSTRACT_TYPELOC(CLASS, BASE)
+#define TYPELOC(CLASS, BASE)                                                   \
+  virtual bool Traverse##CLASS##TypeLoc(CLASS##TypeLoc TL);
+#include "clang/AST/TypeLocNodes.def"
+
+#define TYPELOC(CLASS, BASE)                                                   \
+  bool WalkUpFrom##CLASS##TypeLoc(CLASS##TypeLoc TL);                          \
+  virtual bool Visit##CLASS##TypeLoc(CLASS##TypeLoc TL) { return true; }
+#include "clang/AST/TypeLocNodes.def"
+};
+} // namespace clang
+
+#endif // LLVM_CLANG_AST_DYNAMIC_RECURSIVE_AST_VISITOR_H

clang/lib/AST/CMakeLists.txt

@@ -53,6 +53,7 @@ add_clang_library(clangAST
   DeclOpenMP.cpp
   DeclPrinter.cpp
   DeclTemplate.cpp
+  DynamicRecursiveASTVisitor.cpp
   ParentMapContext.cpp
   Expr.cpp
   ExprClassification.cpp