[clang] Fix crash when declaring invalid lambda member (#74110)

In valid code, there should only be a very specific set of members in a
lambda definition. If the user tries to define something inside the
lambda class, this assumption is violated and causes an assertion error.
This can be fixed by checking whether the members are valid, and if not,
ignore that the class members are potentially unexpected.

I've come across this while working on implementing lambdas in C++03.

Author: philnik777

clang/docs/ReleaseNotes.rst

@@ -258,6 +258,9 @@ Bug Fixes in This Version
   operator.
   Fixes (#GH83267).
 
+- Fixes an assertion failure on invalid code when trying to define member
+  functions in lambdas.
+
 Bug Fixes to Compiler Builtins
 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 
@@ -408,7 +411,7 @@ RISC-V Support
 CUDA/HIP Language Changes
 ^^^^^^^^^^^^^^^^^^^^^^^^^
 
-- PTX is no longer included by default when compiling for CUDA. Using 
+- PTX is no longer included by default when compiling for CUDA. Using
   ``--cuda-include-ptx=all`` will return the old behavior.
 
 CUDA Support

clang/lib/AST/DeclCXX.cpp

@@ -1567,10 +1567,9 @@ bool CXXRecordDecl::isGenericLambda() const {
 
 #ifndef NDEBUG
 static bool allLookupResultsAreTheSame(const DeclContext::lookup_result &R) {
-  for (auto *D : R)
-    if (!declaresSameEntity(D, R.front()))
-      return false;
-  return true;
+  return llvm::all_of(R, [&](NamedDecl *D) {
+    return D->isInvalidDecl() || declaresSameEntity(D, R.front());
+  });
 }
 #endif
 

clang/test/SemaCXX/lambda-expressions.cpp

@@ -1,3 +1,4 @@
+// RUN: %clang_cc1 -std=c++11 -Wno-unused-value -fsyntax-only -verify=expected,expected-cxx14,cxx11 -fblocks %s
 // RUN: %clang_cc1 -std=c++14 -Wno-unused-value -fsyntax-only -verify -verify=expected-cxx14 -fblocks %s
 // RUN: %clang_cc1 -std=c++17 -Wno-unused-value -verify -ast-dump -fblocks %s | FileCheck %s
 
@@ -558,8 +559,8 @@ struct B {
   int x;
   A a = [&] { int y = x; };
   A b = [&] { [&] { [&] { int y = x; }; }; };
-  A d = [&](auto param) { int y = x; };
-  A e = [&](auto param) { [&] { [&](auto param2) { int y = x; }; }; };
+  A d = [&](auto param) { int y = x; }; // cxx11-error {{'auto' not allowed in lambda parameter}}
+  A e = [&](auto param) { [&] { [&](auto param2) { int y = x; }; }; }; // cxx11-error 2 {{'auto' not allowed in lambda parameter}}
 };
 
 B<int> b;
@@ -589,6 +590,7 @@ struct S1 {
 void foo1() {
   auto s0 = S1{[name=]() {}}; // expected-error 2 {{expected expression}}
   auto s1 = S1{[name=name]() {}}; // expected-error {{use of undeclared identifier 'name'; did you mean 'name1'?}}
+                                  // cxx11-warning@-1 {{initialized lambda captures are a C++14 extension}}
 }
 }
 
@@ -604,7 +606,7 @@ namespace PR25627_dont_odr_use_local_consts {
 
 namespace ConversionOperatorDoesNotHaveDeducedReturnType {
   auto x = [](int){};
-  auto y = [](auto &v) -> void { v.n = 0; };
+  auto y = [](auto &v) -> void { v.n = 0; }; // cxx11-error {{'auto' not allowed in lambda parameter}} cxx11-note {{candidate function not viable}} cxx11-note {{conversion candidate}}
   using T = decltype(x);
   using U = decltype(y);
   using ExpectedTypeT = void (*)(int);
@@ -624,22 +626,22 @@ namespace ConversionOperatorDoesNotHaveDeducedReturnType {
     template<typename T>
       friend constexpr U::operator ExpectedTypeU<T>() const noexcept;
 #else
-    friend auto T::operator()(int) const;
+    friend auto T::operator()(int) const; // cxx11-error {{'auto' return without trailing return type; deduced return types are a C++14 extension}}
     friend T::operator ExpectedTypeT() const;
 
     template<typename T>
-      friend void U::operator()(T&) const;
+      friend void U::operator()(T&) const; // cxx11-error {{friend declaration of 'operator()' does not match any declaration}}
     // FIXME: This should not match, as above.
     template<typename T>
-      friend U::operator ExpectedTypeU<T>() const;
+      friend U::operator ExpectedTypeU<T>() const; // cxx11-error {{friend declaration of 'operator void (*)(type-parameter-0-0 &)' does not match any declaration}}
 #endif
 
   private:
     int n;
   };
 
-  // Should be OK: lambda's call operator is a friend.
-  void use(X &x) { y(x); }
+  // Should be OK in C++14 and later: lambda's call operator is a friend.
+  void use(X &x) { y(x); } // cxx11-error {{no matching function for call to object}}
 
   // This used to crash in return type deduction for the conversion opreator.
   struct A { int n; void f() { +[](decltype(n)) {}; } };