[all-commits] [llvm/llvm-project] e1600d: [AST] Add UsingType: a sugar type for types found ...

[Sam McCall via All-commits]

  Branch: refs/heads/main
  Home:   https://github.com/llvm/llvm-project
  Commit: e1600db19d6303f84b995acb9340459694e06ea9
      https://github.com/llvm/llvm-project/commit/e1600db19d6303f84b995acb9340459694e06ea9
  Author: Sam McCall <sam.mccall at gmail.com>
  Date:   2021-12-20 (Mon, 20 Dec 2021)

  Changed paths:
    M clang-tools-extra/clang-tidy/google/UpgradeGoogletestCaseCheck.cpp
    M clang-tools-extra/clang-tidy/misc/UnusedUsingDeclsCheck.cpp
    M clang-tools-extra/clang-tidy/modernize/UseTrailingReturnTypeCheck.cpp
    M clang-tools-extra/clangd/FindTarget.cpp
    M clang-tools-extra/clangd/IncludeCleaner.cpp
    M clang-tools-extra/clangd/unittests/IncludeCleanerTests.cpp
    M clang-tools-extra/clangd/unittests/XRefsTests.cpp
    M clang/docs/ReleaseNotes.rst
    M clang/include/clang/AST/ASTContext.h
    M clang/include/clang/AST/PropertiesBase.td
    M clang/include/clang/AST/RecursiveASTVisitor.h
    M clang/include/clang/AST/TextNodeDumper.h
    M clang/include/clang/AST/Type.h
    M clang/include/clang/AST/TypeLoc.h
    M clang/include/clang/AST/TypeProperties.td
    M clang/include/clang/ASTMatchers/ASTMatchers.h
    M clang/include/clang/ASTMatchers/ASTMatchersInternal.h
    M clang/include/clang/Basic/TypeNodes.td
    M clang/include/clang/Serialization/TypeBitCodes.def
    M clang/lib/AST/ASTContext.cpp
    M clang/lib/AST/ASTDiagnostic.cpp
    M clang/lib/AST/ASTImporter.cpp
    M clang/lib/AST/ASTStructuralEquivalence.cpp
    M clang/lib/AST/ItaniumMangle.cpp
    M clang/lib/AST/QualTypeNames.cpp
    M clang/lib/AST/TextNodeDumper.cpp
    M clang/lib/AST/Type.cpp
    M clang/lib/AST/TypePrinter.cpp
    M clang/lib/ASTMatchers/ASTMatchersInternal.cpp
    M clang/lib/ASTMatchers/Dynamic/Registry.cpp
    M clang/lib/CodeGen/CGDebugInfo.cpp
    M clang/lib/CodeGen/CodeGenFunction.cpp
    M clang/lib/Sema/SemaCXXScopeSpec.cpp
    M clang/lib/Sema/SemaDecl.cpp
    M clang/lib/Sema/SemaExpr.cpp
    M clang/lib/Sema/TreeTransform.h
    M clang/lib/Serialization/ASTReader.cpp
    M clang/lib/Serialization/ASTWriter.cpp
    A clang/test/AST/ast-dump-using.cpp
    M clang/tools/libclang/CIndex.cpp
    M clang/unittests/AST/ASTImporterTest.cpp
    M lldb/source/Plugins/TypeSystem/Clang/TypeSystemClang.cpp

  Log Message:
  -----------
  [AST] Add UsingType: a sugar type for types found via UsingDecl

Currently there's no way to find the UsingDecl that a typeloc found its
underlying type through. Compare to DeclRefExpr::getFoundDecl().

Design decisions:
- a sugar type, as there are many contexts this type of use may appear in
- UsingType is a leaf like TypedefType, the underlying type has no TypeLoc
- not unified with UnresolvedUsingType: a single name is appealing,
  but being sometimes-sugar is often fiddly.
- not unified with TypedefType: the UsingShadowDecl is not a TypedefNameDecl or
  even a TypeDecl, and users think of these differently.
- does not cover other rarer aliases like objc @compatibility_alias,
  in order to be have a concrete API that's easy to understand.
- implicitly desugared by the hasDeclaration ASTMatcher, to avoid
  breaking existing patterns and following the precedent of ElaboratedType.

Scope:
- This does not cover types associated with template names introduced by
  using declarations. A future patch should introduce a sugar TemplateName
  variant for this. (CTAD deduced types fall under this)
- There are enough AST matchers to fix the in-tree clang-tidy tests and
  probably any other matchers, though more may be useful later.

Caveats:
- This changes a fairly common pattern in the AST people may depend on matching.
  Previously, typeLoc(loc(recordType())) matched whether a struct was
  referred to by its original scope or introduced via using-decl.
  Now, the using-decl case is not matched, and needs a separate matcher.
  This is similar to the case of typedefs but nevertheless both adds
  complexity and breaks existing code.

Differential Revision: https://reviews.llvm.org/D114251