[clang] [Clang] Don't form a type constraint if the concept is invalid (PR #122065)

[Younan Zhang via cfe-commits]

https://github.com/zyn0217 updated https://github.com/llvm/llvm-project/pull/122065

>From 312776183068b84ddfea38ea7158c44c1926160a Mon Sep 17 00:00:00 2001
From: Younan Zhang <zyn7109 at gmail.com>
Date: Wed, 8 Jan 2025 15:40:23 +0800
Subject: [PATCH 1/3] [Clang] Don't form a type constraint if the concept is
 invalid

After 0dedd6fe1 and 03229e7c0, invalid concept declarations might
lack expressions for evaluation and normalization. This could make
it crash in certain scenarios, apart from the one of evaluation
concepts showed in 03229e7c0, there's also an issue when checking
specializations where the normalization also relies on a non-null expression.

This patch prevents that by avoiding building up a type constraint
in such situations, thereafter the template parameter wouldn't
have a concept specialization of a null expression.

With this patch, the assumption in ASTWriterDecl is no longer valid.
Namely, HasConstraint and TypeConstraintInitialized must now represent
different meanings for both source fidelity and semantic requirements.
---
 clang/lib/Sema/SemaTemplate.cpp           |  3 +++
 clang/lib/Serialization/ASTWriterDecl.cpp |  1 -
 clang/test/SemaTemplate/concepts.cpp      | 12 ++++++++++++
 3 files changed, 15 insertions(+), 1 deletion(-)

diff --git a/clang/lib/Sema/SemaTemplate.cpp b/clang/lib/Sema/SemaTemplate.cpp
index 20ec2fbeaa6a8b..ce672b00893b0d 100644
--- a/clang/lib/Sema/SemaTemplate.cpp
+++ b/clang/lib/Sema/SemaTemplate.cpp
@@ -4557,6 +4557,9 @@ Sema::CheckConceptTemplateId(const CXXScopeSpec &SS,
                              const TemplateArgumentListInfo *TemplateArgs) {
   assert(NamedConcept && "A concept template id without a template?");
 
+  if (NamedConcept->isInvalidDecl())
+    return ExprError();
+
   llvm::SmallVector<TemplateArgument, 4> SugaredConverted, CanonicalConverted;
   if (CheckTemplateArgumentList(
           NamedConcept, ConceptNameInfo.getLoc(),
diff --git a/clang/lib/Serialization/ASTWriterDecl.cpp b/clang/lib/Serialization/ASTWriterDecl.cpp
index 75c1d9a6d438ce..c7b8759916f421 100644
--- a/clang/lib/Serialization/ASTWriterDecl.cpp
+++ b/clang/lib/Serialization/ASTWriterDecl.cpp
@@ -1951,7 +1951,6 @@ void ASTDeclWriter::VisitTemplateTypeParmDecl(TemplateTypeParmDecl *D) {
   Record.push_back(D->wasDeclaredWithTypename());
 
   const TypeConstraint *TC = D->getTypeConstraint();
-  assert((bool)TC == D->hasTypeConstraint());
   if (TC) {
     auto *CR = TC->getConceptReference();
     Record.push_back(CR != nullptr);
diff --git a/clang/test/SemaTemplate/concepts.cpp b/clang/test/SemaTemplate/concepts.cpp
index 312469313fc535..f335ca3bd22bc3 100644
--- a/clang/test/SemaTemplate/concepts.cpp
+++ b/clang/test/SemaTemplate/concepts.cpp
@@ -1165,3 +1165,15 @@ concept C = invalid; // expected-error {{use of undeclared identifier 'invalid'}
 bool val2 = C<int>;
 
 } // namespace GH109780
+
+namespace GH121980 {
+
+template <class>
+concept has_member_difference_type; // expected-error {{expected '='}}
+
+template <has_member_difference_type> struct incrementable_traits; // expected-note {{declared here}}
+
+template <has_member_difference_type Tp>
+struct incrementable_traits<Tp>; // expected-error {{not more specialized than the primary}}
+
+}

>From 202196262cc0864b9cbeb91ea6df6e0cd299fe5d Mon Sep 17 00:00:00 2001
From: Younan Zhang <zyn7109 at gmail.com>
Date: Wed, 8 Jan 2025 18:43:02 +0800
Subject: [PATCH 2/3] Fix the serialization for invalid constraints

---
 clang/lib/Serialization/ASTReaderDecl.cpp | 6 +++++-
 clang/lib/Serialization/ASTWriterDecl.cpp | 4 +++-
 2 files changed, 8 insertions(+), 2 deletions(-)

diff --git a/clang/lib/Serialization/ASTReaderDecl.cpp b/clang/lib/Serialization/ASTReaderDecl.cpp
index 719bc0d06f5b11..9671492f0d6544 100644
--- a/clang/lib/Serialization/ASTReaderDecl.cpp
+++ b/clang/lib/Serialization/ASTReaderDecl.cpp
@@ -2663,7 +2663,11 @@ void ASTDeclReader::VisitTemplateTypeParmDecl(TemplateTypeParmDecl *D) {
 
   D->setDeclaredWithTypename(Record.readInt());
 
-  if (D->hasTypeConstraint()) {
+  bool TypeConstraintInitialized = false;
+  if (D->hasTypeConstraint())
+    TypeConstraintInitialized = Record.readBool();
+
+  if (D->hasTypeConstraint() && TypeConstraintInitialized) {
     ConceptReference *CR = nullptr;
     if (Record.readBool())
       CR = Record.readConceptReference();
diff --git a/clang/lib/Serialization/ASTWriterDecl.cpp b/clang/lib/Serialization/ASTWriterDecl.cpp
index c7b8759916f421..f8ed155ca389d7 100644
--- a/clang/lib/Serialization/ASTWriterDecl.cpp
+++ b/clang/lib/Serialization/ASTWriterDecl.cpp
@@ -1951,6 +1951,8 @@ void ASTDeclWriter::VisitTemplateTypeParmDecl(TemplateTypeParmDecl *D) {
   Record.push_back(D->wasDeclaredWithTypename());
 
   const TypeConstraint *TC = D->getTypeConstraint();
+  if (D->hasTypeConstraint())
+    Record.push_back(/*TypeConstraintInitialized=*/TC != nullptr);
   if (TC) {
     auto *CR = TC->getConceptReference();
     Record.push_back(CR != nullptr);
@@ -1968,7 +1970,7 @@ void ASTDeclWriter::VisitTemplateTypeParmDecl(TemplateTypeParmDecl *D) {
   if (OwnsDefaultArg)
     Record.AddTemplateArgumentLoc(D->getDefaultArgument());
 
-  if (!TC && !OwnsDefaultArg &&
+  if (!D->hasTypeConstraint() && !OwnsDefaultArg &&
       D->getDeclContext() == D->getLexicalDeclContext() &&
       !D->isInvalidDecl() && !D->hasAttrs() &&
       !D->isTopLevelDeclInObjCContainer() && !D->isImplicit() &&

>From 6b59c7a8c8a5d06208e49622d68dd671032ed951 Mon Sep 17 00:00:00 2001
From: Younan Zhang <zyn7109 at gmail.com>
Date: Wed, 8 Jan 2025 18:48:39 +0800
Subject: [PATCH 3/3] fixup! Fix the serialization for invalid constraints

---
 clang/lib/Serialization/ASTReaderDecl.cpp | 7 ++-----
 1 file changed, 2 insertions(+), 5 deletions(-)

diff --git a/clang/lib/Serialization/ASTReaderDecl.cpp b/clang/lib/Serialization/ASTReaderDecl.cpp
index 9671492f0d6544..8c60e85c93d70e 100644
--- a/clang/lib/Serialization/ASTReaderDecl.cpp
+++ b/clang/lib/Serialization/ASTReaderDecl.cpp
@@ -2663,11 +2663,8 @@ void ASTDeclReader::VisitTemplateTypeParmDecl(TemplateTypeParmDecl *D) {
 
   D->setDeclaredWithTypename(Record.readInt());
 
-  bool TypeConstraintInitialized = false;
-  if (D->hasTypeConstraint())
-    TypeConstraintInitialized = Record.readBool();
-
-  if (D->hasTypeConstraint() && TypeConstraintInitialized) {
+  bool TypeConstraintInitialized = D->hasTypeConstraint() && Record.readBool();
+  if (TypeConstraintInitialized) {
     ConceptReference *CR = nullptr;
     if (Record.readBool())
       CR = Record.readConceptReference();