[clang] Correctly implement CWG 2672 (#75001)

clang/docs/ReleaseNotes.rst

@@ -723,7 +723,8 @@ Bug Fixes to C++ Support
 
 - Clang emits an error on substitution failure within lambda body inside a
   requires-expression. This fixes:
-  (`#64138 <https://github.com/llvm/llvm-project/issues/64138>`_).
+  (`#64138 <https://github.com/llvm/llvm-project/issues/64138>`_) and
+  (`#71684 <https://github.com/llvm/llvm-project/issues/71684>`_).
 
 - Update ``FunctionDeclBitfields.NumFunctionDeclBits``. This fixes:
   (`#64171 <https://github.com/llvm/llvm-project/issues/64171>`_).

clang/lib/Sema/SemaTemplateInstantiate.cpp

@@ -35,7 +35,6 @@
 #include "clang/Sema/Template.h"
 #include "clang/Sema/TemplateDeduction.h"
 #include "clang/Sema/TemplateInstCallback.h"
-#include "llvm/ADT/ScopeExit.h"
 #include "llvm/ADT/StringExtras.h"
 #include "llvm/Support/ErrorHandling.h"
 #include "llvm/Support/TimeProfiler.h"
@@ -1142,8 +1141,7 @@ std::optional<TemplateDeductionInfo *> Sema::isSFINAEContext() const {
     case CodeSynthesisContext::DeducedTemplateArgumentSubstitution:
       // We're either substituting explicitly-specified template arguments,
       // deduced template arguments. SFINAE applies unless we are in a lambda
-      // expression, see [temp.deduct]p9.
-      [[fallthrough]];
+      // body, see [temp.deduct]p9.
     case CodeSynthesisContext::ConstraintSubstitution:
     case CodeSynthesisContext::RequirementInstantiation:
     case CodeSynthesisContext::RequirementParameterInstantiation:
@@ -1445,13 +1443,6 @@ namespace {
       LocalInstantiationScope Scope(SemaRef, /*CombineWithOuterScope=*/true);
       Sema::ConstraintEvalRAII<TemplateInstantiator> RAII(*this);
 
-      Sema::CodeSynthesisContext C;
-      C.Kind = clang::Sema::CodeSynthesisContext::LambdaExpressionSubstitution;
-      C.PointOfInstantiation = E->getBeginLoc();
-      SemaRef.pushCodeSynthesisContext(C);
-      auto PopCtx =
-          llvm::make_scope_exit([this] { SemaRef.popCodeSynthesisContext(); });
-
       ExprResult Result = inherited::TransformLambdaExpr(E);
       if (Result.isInvalid())
         return Result;

clang/lib/Sema/TreeTransform.h

@@ -13685,10 +13685,17 @@ TreeTransform<Derived>::TransformLambdaExpr(LambdaExpr *E) {
   getSema().PushExpressionEvaluationContext(
       Sema::ExpressionEvaluationContext::PotentiallyEvaluated);
 
+  Sema::CodeSynthesisContext C;
+  C.Kind = clang::Sema::CodeSynthesisContext::LambdaExpressionSubstitution;
+  C.PointOfInstantiation = E->getBody()->getBeginLoc();
+  getSema().pushCodeSynthesisContext(C);
+
   // Instantiate the body of the lambda expression.
   StmtResult Body =
       Invalid ? StmtError() : getDerived().TransformLambdaBody(E, E->getBody());
 
+  getSema().popCodeSynthesisContext();
+
   // ActOnLambda* will pop the function scope for us.
   FuncScopeCleanup.disable();
 

clang/test/CXX/drs/dr26xx.cpp

@@ -211,7 +211,7 @@ void f(...);
 
 template <class T>
 void bar(T) requires requires {
-   decltype([]() -> T {})::foo();
+   []() -> decltype(T::foo()) {};
 };
 void bar(...);
 

clang/test/CXX/expr/expr.prim/expr.prim.lambda/default-arguments.cpp

@@ -35,8 +35,7 @@ struct NoDefaultCtor {
 template<typename T>
 void defargs_in_template_unused(T t) {
   auto l1 = [](const T& value = T()) { };  // expected-error{{no matching constructor for initialization of 'NoDefaultCtor'}} \
-                                           // expected-note {{in instantiation of default function argument expression for 'operator()<NoDefaultCtor>' required here}} \
-                                           // expected-note {{while substituting into a lambda expression here}}
+                                           // expected-note {{in instantiation of default function argument expression for 'operator()<NoDefaultCtor>' required here}}
   l1(t);
 }
 
@@ -46,8 +45,7 @@ template void defargs_in_template_unused(NoDefaultCtor);  // expected-note{{in i
 template<typename T>
 void defargs_in_template_used() {
   auto l1 = [](const T& value = T()) { }; // expected-error{{no matching constructor for initialization of 'NoDefaultCtor'}} \
-                                          // expected-note {{in instantiation of default function argument expression for 'operator()<NoDefaultCtor>' required here}} \
-                                          // expected-note {{while substituting into a lambda expression here}}
+                                          // expected-note {{in instantiation of default function argument expression for 'operator()<NoDefaultCtor>' required here}}
   l1();
 }
 

clang/test/CXX/expr/expr.prim/expr.prim.lambda/p11-1y.cpp

@@ -35,7 +35,6 @@ auto init_kind_2 = [ec = ExplicitCopy()] {}; // expected-error {{no matching con
 template<typename T> void init_kind_template() {
   auto init_kind_1 = [ec(T())] {};
   auto init_kind_2 = [ec = T()] {}; // expected-error {{no matching constructor}}
-                                    // expected-note@-1 {{while substituting into a lambda expression here}}
 }
 template void init_kind_template<int>();
 template void init_kind_template<ExplicitCopy>(); // expected-note {{instantiation of}}
@@ -53,7 +52,6 @@ auto bad_init_6 = [a{overload_fn}] {}; // expected-error {{cannot deduce type fo
 auto bad_init_7 = [a{{1}}] {}; // expected-error {{cannot deduce type for lambda capture 'a' from nested initializer list}}
 
 template<typename...T> void pack_1(T...t) { (void)[a(t...)] {}; } // expected-error {{initializer missing for lambda capture 'a'}}
-                                                                  // expected-note@-1 {{while substituting into a lambda expression here}}
 template void pack_1<>(); // expected-note {{instantiation of}}
 
 // No lifetime-extension of the temporary here.

clang/test/CXX/expr/expr.prim/expr.prim.lambda/p23.cpp

@@ -85,7 +85,6 @@ void init_capture_pack_err(Args ...args) {
 template<typename ...Args>
 void init_capture_pack_multi(Args ...args) {
   [as(args...)] {} (); // expected-error {{initializer missing for lambda capture 'as'}} expected-error {{multiple}}
-                       // expected-note@-1 2{{while substituting into a lambda expression}}
 }
 template void init_capture_pack_multi(); // expected-note {{instantiation}}
 template void init_capture_pack_multi(int);

clang/test/CXX/expr/expr.prim/expr.prim.lambda/p4.cpp

@@ -55,12 +55,11 @@ void test_result_type(int N) {  // expected-note {{declared here}}
 template <typename T>
 void test_result_type_tpl(int N) { // expected-note 2{{declared here}}
   auto l1 = []() -> T {}; // expected-error{{incomplete result type 'Incomplete' in lambda expression}}
-                          // expected-note@-1{{while substituting into a lambda expression here}}
   typedef int vla[N]; // expected-warning 2{{variable length arrays in C++ are a Clang extension}} \
                          expected-note 2{{function parameter 'N' with unknown value cannot be used in a constant expression}}
   auto l2 = []() -> vla {}; // expected-error{{function cannot return array type 'vla' (aka 'int[N]')}}
 }
 
 void test_result_type_call() {
-  test_result_type_tpl<Incomplete>(10); // expected-note 2{{requested here}}
+  test_result_type_tpl<Incomplete>(10); // expected-note {{requested here}}
 }

clang/test/CXX/temp/temp.deduct/p9.cpp

@@ -28,18 +28,14 @@ template <class T>
 auto h(T) -> decltype([x = T::invalid]() { });
 void h(...);
 void test_h() {
-  h(0); // expected-error@-3 {{type 'int' cannot be used prior to '::'}}
-        // expected-note@-1 {{while substituting deduced template arguments}}
-        // expected-note@-5 {{while substituting into a lambda expression here}}
+  h(0);
 }
 
 template <class T>
 auto i(T) -> decltype([]() -> typename T::invalid { });
 void i(...);
 void test_i() {
-  i(0); // expected-error@-3 {{type 'int' cannot be used prior to '::'}}
-        // expected-note@-1 {{while substituting deduced template arguments}}
-        // expected-note@-5 {{while substituting into a lambda expression here}}
+  i(0);
 }
 
 

clang/test/SemaCXX/cxx1y-init-captures.cpp

@@ -21,17 +21,17 @@ namespace variadic_expansion {
                     return a;
                   }() ...);
                 };                 
-    auto N2 = [x = y, //expected-note3{{begins here}} expected-note 6 {{default capture by}} expected-note 2 {{substituting into a lambda}}
+    auto N2 = [x = y, //expected-note3{{begins here}} expected-note 6 {{default capture by}}
                 &z = y, n = f(t...), 
-                o = f([&a(t)](T& ... t)->decltype(auto) { return a; }(t...)...)](T& ... s) { // expected-note 6 {{capture 't' by}}
-                fv([&a(t)]()->decltype(auto) { //expected-error 3{{captured}} expected-note 2{{substituting into a lambda}}
+                o = f([&a(t)](T& ... t)->decltype(auto) { return a; }(t...)...)](T& ... s) { // expected-note 6 {{capture 't' by}} expected-note {{substituting into a lambda}}
+                fv([&a(t)]()->decltype(auto) { //expected-error 3{{captured}}
                     return a;
                   }() ...);
                 };                 
 
   }
 
-  void h(int i, char c) { g(i, c); } //expected-note 2{{in instantiation}}
+  void h(int i, char c) { g(i, c); } // expected-note {{requested here}}
 }
 
 namespace odr_use_within_init_capture {

clang/test/SemaCXX/cxx1z-lambda-star-this.cpp

@@ -46,7 +46,7 @@ class B {
   template <class T = int>
   void foo() {
     (void)[this] { return x; };
-    (void)[*this] { return x; }; //expected-error2{{call to deleted}} expected-note {{while substituting into a lambda}}
+    (void)[*this] { return x; }; //expected-error2{{call to deleted}}
   }
 
   B() = default;
@@ -63,7 +63,7 @@ class B {
 public:
   template <class T = int>
   auto foo() {
-    const auto &L = [*this](auto a) mutable { //expected-error{{call to deleted}} expected-note {{while substituting into a lambda}}
+    const auto &L = [*this](auto a) mutable { //expected-error{{call to deleted}}
       d += a;
       return [this](auto b) { return d += b; };
     };

clang/test/SemaCXX/lambda-expressions.cpp

@@ -393,7 +393,7 @@ struct S {
 namespace PR18473 {
   template<typename T> void f() {
     T t(0);
-    (void) [=]{ int n = t; }; // expected-error {{deleted}} expected-note {{while substituting into a lambda}}
+    (void) [=]{ int n = t; }; // expected-error {{deleted}}
   }
 
   template void f<int>();
@@ -476,7 +476,7 @@ namespace error_in_transform_prototype {
   void f(T t) {
     // expected-error@+2 {{type 'int' cannot be used prior to '::' because it has no members}}
     // expected-error@+1 {{no member named 'ns' in 'error_in_transform_prototype::S'}}
-    auto x = [](typename T::ns::type &k) {}; // expected-note 2 {{while substituting into a lambda}}
+    auto x = [](typename T::ns::type &k) {};
   }
   class S {};
   void foo() {

clang/test/SemaCXX/lambda-pack-expansion.cpp

@@ -8,7 +8,6 @@ struct X {
 
 void take_by_copy(auto &...args) {
   [...args = args] {}(); // expected-error {{call to deleted constructor}}
-                         // expected-note@-1 {{substituting into a lambda}}
 }
 
 void take_by_ref(auto &...args) {

clang/test/SemaCXX/vartemplate-lambda.cpp

@@ -8,7 +8,6 @@ template<typename T> auto v1 = [](int a = T()) { return a; }();
 // expected-error@-1{{cannot initialize a parameter of type 'int' with an rvalue of type 'int *'}}
 // expected-note@-2{{in instantiation of default function argument expression for 'operator()<int *>' required here}}
 // expected-note@-3{{passing argument to parameter 'a' here}}
-// expected-note@-4{{substituting into a lambda}}
 
 struct S {
   template<class T>

clang/test/SemaCXX/warn-unused-lambda-capture.cpp

@@ -145,38 +145,38 @@ void test_templated() {
   auto explicit_by_value_used_generic = [i](auto c) { return i + 1; };
   auto explicit_by_value_used_void = [i] { (void)i; };
 
-  auto explicit_by_value_unused = [i] {}; // expected-warning{{lambda capture 'i' is not used}} expected-note {{substituting into a lambda}}
-  auto explicit_by_value_unused_sizeof = [i] { return sizeof(i); }; // expected-warning{{lambda capture 'i' is not required to be captured for this use}} expected-note {{substituting into a lambda}}
-  auto explicit_by_value_unused_decltype = [i] { decltype(i) j = 0; }; // expected-warning{{lambda capture 'i' is not used}} expected-note {{substituting into a lambda}}
-  auto explicit_by_value_unused_const = [k] { return k + 1; };         // expected-warning{{lambda capture 'k' is not required to be captured for this use}} expected-note {{substituting into a lambda}}
-  auto explicit_by_value_unused_const_generic = [k](auto c) { return k + 1; }; // expected-warning{{lambda capture 'k' is not required to be captured for this use}} expected-note {{substituting into a lambda}}
+  auto explicit_by_value_unused = [i] {}; // expected-warning{{lambda capture 'i' is not used}}
+  auto explicit_by_value_unused_sizeof = [i] { return sizeof(i); }; // expected-warning{{lambda capture 'i' is not required to be captured for this use}}
+  auto explicit_by_value_unused_decltype = [i] { decltype(i) j = 0; }; // expected-warning{{lambda capture 'i' is not used}}
+  auto explicit_by_value_unused_const = [k] { return k + 1; };         // expected-warning{{lambda capture 'k' is not required to be captured for this use}}
+  auto explicit_by_value_unused_const_generic = [k](auto c) { return k + 1; }; // expected-warning{{lambda capture 'k' is not required to be captured for this use}}
 
   auto explicit_by_reference_used = [&i] { i++; };
-  auto explicit_by_reference_unused = [&i] {}; // expected-warning{{lambda capture 'i' is not used}} expected-note {{substituting into a lambda}}
+  auto explicit_by_reference_unused = [&i] {}; // expected-warning{{lambda capture 'i' is not used}}
 
   auto explicit_initialized_reference_used = [&j = i] { return j + 1; };
-  auto explicit_initialized_reference_unused = [&j = i]{}; // expected-warning{{lambda capture 'j' is not used}} expected-note {{substituting into a lambda}}
+  auto explicit_initialized_reference_unused = [&j = i]{}; // expected-warning{{lambda capture 'j' is not used}}
 
   auto explicit_initialized_value_used = [j = 1] { return j + 1; };
-  auto explicit_initialized_value_unused = [j = 1] {}; // expected-warning{{lambda capture 'j' is not used}} expected-note {{substituting into a lambda}}
+  auto explicit_initialized_value_unused = [j = 1] {}; // expected-warning{{lambda capture 'j' is not used}}
   auto explicit_initialized_value_non_trivial_constructor = [j = NonTrivialConstructor()]{};
   auto explicit_initialized_value_non_trivial_destructor = [j = NonTrivialDestructor()]{};
-  auto explicit_initialized_value_trivial_init = [j = Trivial()]{}; // expected-warning{{lambda capture 'j' is not used}} expected-note {{substituting into a lambda}}
+  auto explicit_initialized_value_trivial_init = [j = Trivial()]{}; // expected-warning{{lambda capture 'j' is not used}}
   auto explicit_initialized_value_non_trivial_init = [j = Trivial(42)]{};
   auto explicit_initialized_value_with_side_effect = [j = side_effect()]{};
   auto explicit_initialized_value_generic_used = [i = 1](auto c) mutable { i++; };
-  auto explicit_initialized_value_generic_unused = [i = 1](auto c) mutable {}; // expected-warning{{lambda capture 'i' is not used}} expected-note {{substituting into a lambda}}
+  auto explicit_initialized_value_generic_unused = [i = 1](auto c) mutable {}; // expected-warning{{lambda capture 'i' is not used}}
 
   auto nested = [&i] { // expected-note {{substituting into a lambda}}
     auto explicit_by_value_used = [i] { return i + 1; };
-    auto explicit_by_value_unused = [i] {}; // expected-warning{{lambda capture 'i' is not used}} expected-note {{substituting into a lambda}}
+    auto explicit_by_value_unused = [i] {}; // expected-warning{{lambda capture 'i' is not used}}
   };
 
   Trivial trivial;
-  auto explicit_by_value_trivial = [trivial] {}; // expected-warning{{lambda capture 'trivial' is not used}} expected-note {{substituting into a lambda}}
+  auto explicit_by_value_trivial = [trivial] {}; // expected-warning{{lambda capture 'trivial' is not used}}
 
   NonTrivialConstructor cons;
-  auto explicit_by_value_non_trivial_constructor = [cons] {}; // expected-warning{{lambda capture 'cons' is not used}} expected-note {{substituting into a lambda}}
+  auto explicit_by_value_non_trivial_constructor = [cons] {}; // expected-warning{{lambda capture 'cons' is not used}}
 
   NonTrivialCopyConstructor copy_cons;
   auto explicit_by_value_non_trivial_copy_constructor = [copy_cons] {};
@@ -189,7 +189,7 @@ void test_templated() {
 }
 
 void test_use_template() {
-  test_templated<int>(); // expected-note 13{{in instantiation of function template specialization 'test_templated<int>' requested here}}
+  test_templated<int>(); // expected-note 3 {{requested here}}
 }
 
 namespace pr35555 {

clang/test/SemaTemplate/instantiate-local-class.cpp

@@ -473,8 +473,7 @@ namespace rdar23721638 {
   template <typename T> void bar() {
     auto lambda = [](T a = "") {}; // expected-error {{conversion function from 'const char[1]' to 'rdar23721638::A' invokes a deleted function}} \
                                    // expected-note  {{in instantiation of default function argument expression for 'operator()<rdar23721638::A>' required here}} \
-                                   // expected-note  {{passing argument to parameter 'a' here}} \
-                                   // expected-note {{while substituting into a lambda}}
+                                   // expected-note  {{passing argument to parameter 'a' here}}
     lambda();
   }
   template void bar<A>(); // expected-note {{in instantiation}}
@@ -497,7 +496,6 @@ namespace PR45000 {
   // expected-error@-1 {{cannot initialize a parameter of type 'int' with an rvalue of type 'std::nullptr_t'}}
   // expected-note@-2  {{in instantiation of default function argument expression for 'operator()<int>' required here}}
   // expected-note@-3  {{passing argument to parameter 'x' here}}
-  // expected-note@-4  {{while substituting into a lambda}}
 
   void g() { f<int>(); }
   // expected-note@-1 {{in instantiation of default function argument expression for 'f<int>' required here}}