[PATCH] D133500: [clang] Correct handling of lambdas in lambda default arguments in dependent contexts.

[Tom Honermann via Phabricator via cfe-commits]

tahonermann created this revision.
tahonermann added reviewers: erichkeane, aaron.ballman, shafik.
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Previously, a lambda expression in a dependent context with a default argument containing an immediately invoked lambda expression would produce a closure class object that, if invoked such that the default argument was used, resulted in a compiler crash or one of the following assertion failures during code generation. The failures occurred regardless of whether the lambda expressions were dependent.

  clang/lib/CodeGen/CGCall.cpp:
  Assertion `(isGenericMethod || Ty->isVariablyModifiedType() || Ty.getNonReferenceType()->isObjCRetainableType() || getContext() .getCanonicalType(Ty.getNonReferenceType()) .getTypePtr() == getContext().getCanonicalType((*Arg)->getType()).getTypePtr()) && "type mismatch in call argument!"' failed.
  
  clang/lib/AST/Decl.cpp:
  Assertion `!Init->isValueDependent()' failed.

Default arguments in declarations in local context are instantiated along with their enclosing function or variable template (since such declarations can't be explicitly specialized). Previously, such instantiations were performed at the same time that their associated parameters were instantiated. However, that approach fails in cases like the following in which the context for the inner lambda is the outer lambda, but construction of the outer lambda is dependent on the parameters of the inner lambda. This change resolves this dependency by delaying instantiation of default arguments in local contexts until after construction of the enclosing context.

  template <typename T>
  auto f() {
    return [](T = []{ return T{}; }()) { return 0; };
  }

Refactoring included with this change results in the same code now being used to instantiate default arguments that appear in local context and those that are only instantiated when used at a call site; previously, such code was duplicated and out of sync.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D133500

Files:
  clang/include/clang/Sema/Sema.h
  clang/lib/AST/DeclBase.cpp
  clang/lib/Sema/SemaTemplateInstantiate.cpp
  clang/lib/Sema/SemaTemplateInstantiateDecl.cpp
  clang/test/CXX/expr/expr.prim/expr.prim.lambda/default-arguments.cpp
  clang/test/CodeGenCXX/mangle-lambdas-cxx14.cpp
  clang/test/CodeGenCXX/mangle-lambdas-cxx20.cpp
  clang/test/CodeGenCXX/mangle-lambdas.cpp
  clang/test/SemaCXX/vartemplate-lambda.cpp
  clang/test/SemaTemplate/default-arguments.cpp
  clang/test/SemaTemplate/instantiate-local-class.cpp

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