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Partially implement the proposed resolution to CWG2569.
D119136 <https://reviews.llvm.org/D119136> broke some libstdc++ code, as
P2036R3, implemented as a DR to
C++11 made ill-formed some previously valid and innocuous code.
We resolve this issue to allow decltype(x) - but not decltype((x)
to appear in the parameter list of a lambda that capture x by copy.
Unlike CWG2569, we do not extend that special treatment to
sizeof/noexcept yet, as the resolution has not been approved yet
and keeping the review small allows a quicker fix of impacted code.
Repository:
rG LLVM Github Monorepo
https://reviews.llvm.org/D123909
Files:
clang/include/clang/Parse/Parser.h
clang/include/clang/Sema/Sema.h
clang/lib/Parse/ParseDeclCXX.cpp
clang/lib/Parse/ParseExprCXX.cpp
clang/lib/Sema/SemaExpr.cpp
clang/test/SemaCXX/lambda-capture-type-deduction.cpp
Index: clang/test/SemaCXX/lambda-capture-type-deduction.cpp
===================================================================
--- clang/test/SemaCXX/lambda-capture-type-deduction.cpp
+++ clang/test/SemaCXX/lambda-capture-type-deduction.cpp
@@ -87,23 +87,23 @@
int y, z; // expected-note 2{{declared here}}
auto implicit_tpl = [=]( // expected-note {{variable 'y' is captured here}}
decltype(
- [&]<decltype(y)> { return 0; }) y) { //expected-error{{captured variable 'y' cannot appear here}}
+ [&]<decltype((y))> { return 0; }) y) { // expected-error{{captured variable 'y' cannot appear here}}
return y;
};
- auto init_tpl = [x = 1]( // expected-note{{explicitly captured here}}
- decltype([&]<decltype(x)> { return 0; }) y) { // expected-error {{captured variable 'x' cannot appear here}}
+ auto init_tpl = [x = 1]( // expected-note{{explicitly captured here}}
+ decltype([&]<decltype((x))> { return 0; }) y) { // expected-error {{captured variable 'x' cannot appear here}}
return x;
};
auto implicit = [=]( // expected-note {{variable 'z' is captured here}}
decltype(
- [&](decltype(z)) { return 0; }) z) { //expected-error{{captured variable 'z' cannot appear here}}
+ [&](decltype((z))) { return 0; }) z) { // expected-error{{captured variable 'z' cannot appear here}}
return z;
};
- auto init = [x = 1]( // expected-note{{explicitly captured here}}
- decltype([&](decltype(x)) { return 0; }) y) { // expected-error {{captured variable 'x' cannot appear here}}
+ auto init = [x = 1]( // expected-note{{explicitly captured here}}
+ decltype([&](decltype((x))) { return 0; }) y) { // expected-error {{captured variable 'x' cannot appear here}}
return x;
};
@@ -141,20 +141,20 @@
decltype([&](
decltype([=]( // expected-note {{variable 'x' is captured here}}
decltype([&](
- decltype([&](decltype(x)) {}) // expected-error{{captured variable 'x' cannot appear here}}
+ decltype([&](decltype((x))) {}) // expected-error{{captured variable 'x' cannot appear here}}
) {})) {})) {})){};
(void)[&](
decltype([&](
decltype([&](
decltype([&](
- decltype([&](decltype(y)) {})) {})) {})) {})){};
+ decltype([&](decltype((y))) {})) {})) {})) {})){};
(void)[=](
decltype([=](
decltype([=](
- decltype([=]( // expected-note {{variable 'z' is captured here}}
- decltype([&]<decltype(z)> {}) // expected-error{{captured variable 'z' cannot appear here}}
+ decltype([=]( // expected-note {{variable 'z' is captured here}}
+ decltype([&]<decltype((z))> {}) // expected-error{{captured variable 'z' cannot appear here}}
) {})) {})) {})){};
}
@@ -171,3 +171,13 @@
dependent<int&>(r);
dependent<const int&>(cr);
}
+
+void test_CWG2569_tpl(auto a) {
+ (void)[=]<typename T = decltype(a)>(decltype(a) b = decltype(a)()){};
+}
+
+void test_CWG2569() {
+ int a = 0;
+ (void)[=]<typename T = decltype(a)>(decltype(a) b = decltype(a)()){};
+ test_CWG2569_tpl(0);
+}
Index: clang/lib/Sema/SemaExpr.cpp
===================================================================
--- clang/lib/Sema/SemaExpr.cpp
+++ clang/lib/Sema/SemaExpr.cpp
@@ -2698,6 +2698,21 @@
return BuildDeclarationNameExpr(SS, R, ADL);
}
+ExprResult Sema::ActOnMutableAgnosticIdExpression(Scope *S, CXXScopeSpec &SS,
+ UnqualifiedId &Id,
+ SourceLocation TemplateKwLoc,
+ bool HasTrailingLParen) {
+ InMutableAgnosticContext = true;
+ ExprResult Res =
+ ActOnIdExpression(S, SS, TemplateKwLoc, Id, HasTrailingLParen,
+ /*IsAddressOfOperand*/ false,
+ /*CorrectionCandidateCallback*/ nullptr,
+ /*IsInlineAsmIdentifier*/ false,
+ /*KeywordReplacement*/ nullptr);
+ InMutableAgnosticContext = false;
+ return Res;
+}
+
/// BuildQualifiedDeclarationNameExpr - Build a C++ qualified
/// declaration name, generally during template instantiation.
/// There's a large number of things which don't need to be done along
@@ -18545,6 +18560,11 @@
static bool CheckCaptureUseBeforeLambdaQualifiers(Sema &S, VarDecl *Var,
SourceLocation ExprLoc,
LambdaScopeInfo *LSI) {
+
+ // Allow `[a = 1](decltype(a)) {}` as per CWG2569.
+ if (S.InMutableAgnosticContext)
+ return true;
+
if (Var->isInvalidDecl())
return false;
@@ -18627,7 +18647,7 @@
LSI = dyn_cast_or_null<LambdaScopeInfo>(
FunctionScopes[FunctionScopesIndex]);
if (LSI && LSI->BeforeLambdaQualifiersScope) {
- if (isa<ParmVarDecl>(Var))
+ if (isa<ParmVarDecl>(Var) && !Var->getDeclContext()->isFunctionOrMethod())
return true;
IsInLambdaBeforeQualifiers = true;
if (!CheckCaptureUseBeforeLambdaQualifiers(*this, Var, ExprLoc, LSI)) {
Index: clang/lib/Parse/ParseExprCXX.cpp
===================================================================
--- clang/lib/Parse/ParseExprCXX.cpp
+++ clang/lib/Parse/ParseExprCXX.cpp
@@ -685,6 +685,36 @@
return Result;
}
+/// ParseCXXMaybeMutableAgnosticExpression - Handle Expressions inside of
+/// sizeof, decltype, noexcepr
+/// - unqualified-id
+/// - expression
+/// This serves to silence errors about captured variable refered in lambda
+/// parameter list, if they aree used as the unqualified-id of a decltype,
+/// sizeof, or noexcept expression
+ExprResult Parser::ParseCXXMaybeMutableAgnosticExpression() {
+
+ if (!getLangOpts().CPlusPlus11)
+ return ParseExpression();
+
+ if (Tok.is(tok::identifier) && NextToken().is(tok::r_paren)) {
+ SourceLocation TemplateKWLoc;
+ UnqualifiedId Name;
+ CXXScopeSpec SS;
+ if (!ParseUnqualifiedId(SS, /*ObjectType=*/nullptr,
+ /*ObjectHadErrors=*/false,
+ /*EnteringContext=*/false,
+ /*AllowDestructorName=*/false,
+ /*AllowConstructorName=*/false,
+ /*AllowDeductionGuide=*/false, &TemplateKWLoc,
+ Name)) {
+ return Actions.ActOnMutableAgnosticIdExpression(getCurScope(), SS, Name,
+ TemplateKWLoc, false);
+ }
+ }
+ return ParseExpression();
+}
+
/// ParseLambdaExpression - Parse a C++11 lambda expression.
///
/// lambda-expression:
Index: clang/lib/Parse/ParseDeclCXX.cpp
===================================================================
--- clang/lib/Parse/ParseDeclCXX.cpp
+++ clang/lib/Parse/ParseDeclCXX.cpp
@@ -1054,7 +1054,7 @@
Actions, Sema::ExpressionEvaluationContext::Unevaluated, nullptr,
Sema::ExpressionEvaluationContextRecord::EK_Decltype);
Result = Actions.CorrectDelayedTyposInExpr(
- ParseExpression(), /*InitDecl=*/nullptr,
+ ParseCXXMaybeMutableAgnosticExpression(), /*InitDecl=*/nullptr,
/*RecoverUncorrectedTypos=*/false,
[](Expr *E) { return E->hasPlaceholderType() ? ExprError() : E; });
if (Result.isInvalid()) {
Index: clang/include/clang/Sema/Sema.h
===================================================================
--- clang/include/clang/Sema/Sema.h
+++ clang/include/clang/Sema/Sema.h
@@ -787,6 +787,11 @@
/// context.
unsigned FunctionScopesStart = 0;
+ /// Whether we are currently in the context of a mutable agnostic identifier
+ /// as described by CWG2569.
+ /// We are handling the unqualified-id of a decltype or noexcept expression.
+ bool InMutableAgnosticContext = false;
+
ArrayRef<sema::FunctionScopeInfo*> getFunctionScopes() const {
return llvm::makeArrayRef(FunctionScopes.begin() + FunctionScopesStart,
FunctionScopes.end());
@@ -5270,6 +5275,11 @@
CorrectionCandidateCallback *CCC = nullptr,
bool IsInlineAsmIdentifier = false, Token *KeywordReplacement = nullptr);
+ ExprResult ActOnMutableAgnosticIdExpression(Scope *S, CXXScopeSpec &SS,
+ UnqualifiedId &Id,
+ SourceLocation TemplateKwLoc,
+ bool HasTrailingLParen);
+
void DecomposeUnqualifiedId(const UnqualifiedId &Id,
TemplateArgumentListInfo &Buffer,
DeclarationNameInfo &NameInfo,
Index: clang/include/clang/Parse/Parser.h
===================================================================
--- clang/include/clang/Parse/Parser.h
+++ clang/include/clang/Parse/Parser.h
@@ -1861,6 +1861,8 @@
Token &Replacement);
ExprResult ParseCXXIdExpression(bool isAddressOfOperand = false);
+ ExprResult ParseCXXMaybeMutableAgnosticExpression();
+
bool areTokensAdjacent(const Token &A, const Token &B);
void CheckForTemplateAndDigraph(Token &Next, ParsedType ObjectTypePtr,
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