[PATCH] D152002: [clang][wip] Better handling of dependent lambda.This is an attempt to fix GH62916.However, it breaks GH57960I seem unable to find something that works for both issues.

[Corentin Jabot via Phabricator via cfe-commits]

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Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D152002

Files:
  clang/lib/Sema/SemaTemplateInstantiate.cpp
  clang/lib/Sema/TreeTransform.h
  clang/test/SemaCXX/lambda-expressions.cpp


Index: clang/test/SemaCXX/lambda-expressions.cpp
===================================================================
--- clang/test/SemaCXX/lambda-expressions.cpp
+++ clang/test/SemaCXX/lambda-expressions.cpp
@@ -715,3 +715,23 @@
   // CHECK-NEXT: ConstantExpr
   // CHECK-NEXT: value: Int 2
 }
+
+#if __cplusplus > 201402L
+namespace GH62916 {
+
+template <class T, int U = []() -> int { return T(42); }()>
+struct P {
+    static constexpr int value = U;
+};
+
+template <class T>
+constexpr P<T> foo() {
+    return {};
+}
+
+void test() {
+  static_assert(foo<int>().value == 42);
+}
+
+}
+#endif
Index: clang/lib/Sema/TreeTransform.h
===================================================================
--- clang/lib/Sema/TreeTransform.h
+++ clang/lib/Sema/TreeTransform.h
@@ -761,6 +761,8 @@
   /// the body.
   StmtResult SkipLambdaBody(LambdaExpr *E, Stmt *Body);
 
+  bool LambdaExpressionShouldBeConsideredDependent(LambdaExpr *E) const;
+
   QualType TransformReferenceType(TypeLocBuilder &TLB, ReferenceTypeLoc TL);
 
   StmtResult TransformCompoundStmt(CompoundStmt *S, bool IsStmtExpr);
@@ -13294,18 +13296,9 @@
 
   // Create the local class that will describe the lambda.
 
-  // FIXME: DependencyKind below is wrong when substituting inside a templated
-  // context that isn't a DeclContext (such as a variable template), or when
-  // substituting an unevaluated lambda inside of a function's parameter's type
-  // - as parameter types are not instantiated from within a function's DC. We
-  // use evaluation contexts to distinguish the function parameter case.
   CXXRecordDecl::LambdaDependencyKind DependencyKind =
-      CXXRecordDecl::LDK_Unknown;
-  if ((getSema().isUnevaluatedContext() ||
-       getSema().isConstantEvaluatedContext()) &&
-      (getSema().CurContext->isFileContext() ||
-       !getSema().CurContext->getParent()->isDependentContext()))
-    DependencyKind = CXXRecordDecl::LDK_NeverDependent;
+      getDerived().LambdaExpressionShouldBeConsideredDependent(E) ?
+      CXXRecordDecl::LDK_AlwaysDependent : CXXRecordDecl::LDK_NeverDependent;
 
   CXXRecordDecl *OldClass = E->getLambdaClass();
   CXXRecordDecl *Class = getSema().createLambdaClosureType(
@@ -13578,6 +13571,12 @@
   return S;
 }
 
+template<typename Derived>
+bool TreeTransform<Derived>::LambdaExpressionShouldBeConsideredDependent(LambdaExpr *) const {
+  return false;
+}
+
+
 template<typename Derived>
 ExprResult
 TreeTransform<Derived>::TransformCXXUnresolvedConstructExpr(
Index: clang/lib/Sema/SemaTemplateInstantiate.cpp
===================================================================
--- clang/lib/Sema/SemaTemplateInstantiate.cpp
+++ clang/lib/Sema/SemaTemplateInstantiate.cpp
@@ -1435,6 +1435,20 @@
       return Result;
     }
 
+    bool LambdaExpressionShouldBeConsideredDependent(LambdaExpr * E) const {
+      if(E->getLambdaClass()->isNeverDependentLambda())
+        return false;
+
+      if(SemaRef.CurContext->isDependentContext())
+        return true;
+
+      return llvm::any_of(TemplateArgs.getInnermost(), [](const TemplateArgument & C) {
+        return C.isDependent();
+      });
+
+    }
+
+
     ExprResult TransformRequiresExpr(RequiresExpr *E) {
       LocalInstantiationScope Scope(SemaRef, /*CombineWithOuterScope=*/true);
       ExprResult TransReq = inherited::TransformRequiresExpr(E);


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