[llvm-branch-commits] [clang] release/19.x: [Clang][Sema] Revisit the fix for the lambda within a type alias template decl (#89934) (PR #106166)
Tobias Hieta via llvm-branch-commits
llvm-branch-commits at lists.llvm.org
Sun Sep 1 01:10:48 PDT 2024
https://github.com/tru updated https://github.com/llvm/llvm-project/pull/106166
>From 52ab956704050302926e8afe1c7dbda4578acb9d Mon Sep 17 00:00:00 2001
From: Younan Zhang <zyn7109 at gmail.com>
Date: Tue, 27 Aug 2024 09:25:53 +0800
Subject: [PATCH] [Clang][Sema] Revisit the fix for the lambda within a type
alias template decl (#89934)
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In the last patch #82310, we used template depths to tell if such alias
decls contain lambdas, which is wrong because the lambda can also appear
as a part of the default argument, and that would make
`getTemplateInstantiationArgs` provide extra template arguments in
undesired contexts. This leads to issue #89853.
Moreover, our approach
for https://github.com/llvm/llvm-project/issues/82104 was sadly wrong.
We tried to teach `DeduceReturnType` to consider alias template
arguments; however, giving these arguments in the context where they
should have been substituted in a `TransformCallExpr` call is never
correct.
This patch addresses such problems by using a `RecursiveASTVisitor` to
check if the lambda is contained by an alias `Decl`, as well as
twiddling the lambda dependencies - we should also build a dependent
lambda expression if the surrounding alias template arguments were
dependent.
Fixes #89853
Fixes #102760
Fixes #105885
(cherry picked from commit b412ec5d3924c7570c2c96106f95a92403a4e09b)
---
clang/lib/Sema/SemaTemplateInstantiate.cpp | 73 +++++++++---------
.../alias-template-with-lambdas.cpp | 75 ++++++++++++++++++-
2 files changed, 110 insertions(+), 38 deletions(-)
diff --git a/clang/lib/Sema/SemaTemplateInstantiate.cpp b/clang/lib/Sema/SemaTemplateInstantiate.cpp
index 8995d461362d70..a09e3be83c4544 100644
--- a/clang/lib/Sema/SemaTemplateInstantiate.cpp
+++ b/clang/lib/Sema/SemaTemplateInstantiate.cpp
@@ -20,6 +20,7 @@
#include "clang/AST/Expr.h"
#include "clang/AST/ExprConcepts.h"
#include "clang/AST/PrettyDeclStackTrace.h"
+#include "clang/AST/RecursiveASTVisitor.h"
#include "clang/AST/Type.h"
#include "clang/AST/TypeLoc.h"
#include "clang/AST/TypeVisitor.h"
@@ -87,12 +88,19 @@ struct Response {
// than lambda classes.
const FunctionDecl *
getPrimaryTemplateOfGenericLambda(const FunctionDecl *LambdaCallOperator) {
+ if (!isLambdaCallOperator(LambdaCallOperator))
+ return LambdaCallOperator;
while (true) {
if (auto *FTD = dyn_cast_if_present<FunctionTemplateDecl>(
LambdaCallOperator->getDescribedTemplate());
FTD && FTD->getInstantiatedFromMemberTemplate()) {
LambdaCallOperator =
FTD->getInstantiatedFromMemberTemplate()->getTemplatedDecl();
+ } else if (LambdaCallOperator->getPrimaryTemplate()) {
+ // Cases where the lambda operator is instantiated in
+ // TemplateDeclInstantiator::VisitCXXMethodDecl.
+ LambdaCallOperator =
+ LambdaCallOperator->getPrimaryTemplate()->getTemplatedDecl();
} else if (auto *Prev = cast<CXXMethodDecl>(LambdaCallOperator)
->getInstantiatedFromMemberFunction())
LambdaCallOperator = Prev;
@@ -138,22 +146,28 @@ getEnclosingTypeAliasTemplateDecl(Sema &SemaRef) {
// Check if we are currently inside of a lambda expression that is
// surrounded by a using alias declaration. e.g.
// template <class> using type = decltype([](auto) { ^ }());
-// By checking if:
-// 1. The lambda expression and the using alias declaration share the
-// same declaration context.
-// 2. They have the same template depth.
// We have to do so since a TypeAliasTemplateDecl (or a TypeAliasDecl) is never
// a DeclContext, nor does it have an associated specialization Decl from which
// we could collect these template arguments.
bool isLambdaEnclosedByTypeAliasDecl(
- const FunctionDecl *PrimaryLambdaCallOperator,
+ const FunctionDecl *LambdaCallOperator,
const TypeAliasTemplateDecl *PrimaryTypeAliasDecl) {
- return cast<CXXRecordDecl>(PrimaryLambdaCallOperator->getDeclContext())
- ->getTemplateDepth() ==
- PrimaryTypeAliasDecl->getTemplateDepth() &&
- getLambdaAwareParentOfDeclContext(
- const_cast<FunctionDecl *>(PrimaryLambdaCallOperator)) ==
- PrimaryTypeAliasDecl->getDeclContext();
+ struct Visitor : RecursiveASTVisitor<Visitor> {
+ Visitor(const FunctionDecl *CallOperator) : CallOperator(CallOperator) {}
+ bool VisitLambdaExpr(const LambdaExpr *LE) {
+ // Return true to bail out of the traversal, implying the Decl contains
+ // the lambda.
+ return getPrimaryTemplateOfGenericLambda(LE->getCallOperator()) !=
+ CallOperator;
+ }
+ const FunctionDecl *CallOperator;
+ };
+
+ QualType Underlying =
+ PrimaryTypeAliasDecl->getTemplatedDecl()->getUnderlyingType();
+
+ return !Visitor(getPrimaryTemplateOfGenericLambda(LambdaCallOperator))
+ .TraverseType(Underlying);
}
// Add template arguments from a variable template instantiation.
@@ -290,23 +304,8 @@ Response HandleFunction(Sema &SemaRef, const FunctionDecl *Function,
// If this function is a generic lambda specialization, we are done.
if (!ForConstraintInstantiation &&
- isGenericLambdaCallOperatorOrStaticInvokerSpecialization(Function)) {
- // TypeAliasTemplateDecls should be taken into account, e.g.
- // when we're deducing the return type of a lambda.
- //
- // template <class> int Value = 0;
- // template <class T>
- // using T = decltype([]<int U = 0>() { return Value<T>; }());
- //
- if (auto TypeAlias = getEnclosingTypeAliasTemplateDecl(SemaRef)) {
- if (isLambdaEnclosedByTypeAliasDecl(
- /*PrimaryLambdaCallOperator=*/getPrimaryTemplateOfGenericLambda(
- Function),
- /*PrimaryTypeAliasDecl=*/TypeAlias.PrimaryTypeAliasDecl))
- return Response::UseNextDecl(Function);
- }
+ isGenericLambdaCallOperatorOrStaticInvokerSpecialization(Function))
return Response::Done();
- }
} else if (Function->getDescribedFunctionTemplate()) {
assert(
@@ -418,10 +417,9 @@ Response HandleRecordDecl(Sema &SemaRef, const CXXRecordDecl *Rec,
// Retrieve the template arguments for a using alias declaration.
// This is necessary for constraint checking, since we always keep
// constraints relative to the primary template.
- if (auto TypeAlias = getEnclosingTypeAliasTemplateDecl(SemaRef)) {
- const FunctionDecl *PrimaryLambdaCallOperator =
- getPrimaryTemplateOfGenericLambda(Rec->getLambdaCallOperator());
- if (isLambdaEnclosedByTypeAliasDecl(PrimaryLambdaCallOperator,
+ if (auto TypeAlias = getEnclosingTypeAliasTemplateDecl(SemaRef);
+ ForConstraintInstantiation && TypeAlias) {
+ if (isLambdaEnclosedByTypeAliasDecl(Rec->getLambdaCallOperator(),
TypeAlias.PrimaryTypeAliasDecl)) {
Result.addOuterTemplateArguments(TypeAlias.Template,
TypeAlias.AssociatedTemplateArguments,
@@ -1642,12 +1640,17 @@ namespace {
CXXRecordDecl::LambdaDependencyKind
ComputeLambdaDependency(LambdaScopeInfo *LSI) {
- auto &CCS = SemaRef.CodeSynthesisContexts.back();
- if (CCS.Kind ==
- Sema::CodeSynthesisContext::TypeAliasTemplateInstantiation) {
- unsigned TypeAliasDeclDepth = CCS.Entity->getTemplateDepth();
+ if (auto TypeAlias =
+ TemplateInstArgsHelpers::getEnclosingTypeAliasTemplateDecl(
+ getSema());
+ TypeAlias && TemplateInstArgsHelpers::isLambdaEnclosedByTypeAliasDecl(
+ LSI->CallOperator, TypeAlias.PrimaryTypeAliasDecl)) {
+ unsigned TypeAliasDeclDepth = TypeAlias.Template->getTemplateDepth();
if (TypeAliasDeclDepth >= TemplateArgs.getNumSubstitutedLevels())
return CXXRecordDecl::LambdaDependencyKind::LDK_AlwaysDependent;
+ for (const TemplateArgument &TA : TypeAlias.AssociatedTemplateArguments)
+ if (TA.isDependent())
+ return CXXRecordDecl::LambdaDependencyKind::LDK_AlwaysDependent;
}
return inherited::ComputeLambdaDependency(LSI);
}
diff --git a/clang/test/SemaTemplate/alias-template-with-lambdas.cpp b/clang/test/SemaTemplate/alias-template-with-lambdas.cpp
index ff94031e4d86f1..5ec93163e4d188 100644
--- a/clang/test/SemaTemplate/alias-template-with-lambdas.cpp
+++ b/clang/test/SemaTemplate/alias-template-with-lambdas.cpp
@@ -91,15 +91,84 @@ void bar() {
namespace GH82104 {
-template <typename, typename...> int Zero = 0;
+template <typename, typename... D> constexpr int Value = sizeof...(D);
-template <typename T, typename...U>
-using T14 = decltype([]<int V = 0>() { return Zero<T, U...>; }());
+template <typename T, typename... U>
+using T14 = decltype([]<int V = 0>(auto Param) {
+ return Value<T, U...> + V + (int)sizeof(Param);
+}("hello"));
template <typename T> using T15 = T14<T, T>;
static_assert(__is_same(T15<char>, int));
+// FIXME: This still crashes because we can't extract template arguments T and U
+// outside of the instantiation context of T16.
+#if 0
+template <typename T, typename... U>
+using T16 = decltype([](auto Param) requires (sizeof(Param) != 1 && sizeof...(U) > 0) {
+ return Value<T, U...> + sizeof(Param);
+});
+static_assert(T16<int, char, float>()(42) == 2 + sizeof(42));
+#endif
} // namespace GH82104
+namespace GH89853 {
+
+template <typename = void>
+static constexpr auto innocuous = []<int m> { return m; };
+
+template <auto Pred = innocuous<>>
+using broken = decltype(Pred.template operator()<42>());
+
+broken<> *boom;
+
+template <auto Pred =
+ []<char c> {
+ (void)static_cast<char>(c);
+ }>
+using broken2 = decltype(Pred.template operator()<42>());
+
+broken2<> *boom2;
+
+template <auto Pred = []<char m> { return m; }>
+using broken3 = decltype(Pred.template operator()<42>());
+
+broken3<> *boom3;
+
+static constexpr auto non_default = []<char c>(True auto) {
+ (void) static_cast<char>(c);
+};
+
+template<True auto Pred>
+using broken4 = decltype(Pred.template operator()<42>(Pred));
+
+broken4<non_default>* boom4;
+
+} // namespace GH89853
+
+namespace GH105885 {
+
+template<int>
+using test = decltype([](auto...) {
+}());
+
+static_assert(__is_same(test<0>, void));
+
+} // namespace GH105885
+
+namespace GH102760 {
+
+auto make_tuple = []< class Tag, class... Captures>(Tag, Captures...) {
+ return []< class _Fun >( _Fun) -> void requires requires { 0; }
+ {};
+};
+
+template < class, class... _As >
+using Result = decltype(make_tuple(0)(_As{}...));
+
+using T = Result<int, int>;
+
+} // namespace GH102760
+
} // namespace lambda_calls
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