[clang] Construct ExprRequirement with SubstitutionDiagnostic on SubstFailure

We're expecting a SubstitutionDiagnostic in diagnoseUnsatisfiedRequirement
if the status of ExprRequirement is SubstFailure. Previously, the Requirement
was created with Expr on SubstFailure by mistake, which could lead to the
assertion failure in the subsequent diagnosis.

Fixes https://github.com/clangd/clangd/issues/1726
Fixes https://github.com/llvm/llvm-project/issues/64723
Fixes https://github.com/llvm/llvm-project/issues/64172

In addition, this patch also fixes an invalid test from D129499.

Reviewed By: erichkeane

Differential Revision: https://reviews.llvm.org/D158061

clang/docs/ReleaseNotes.rst

@@ -250,6 +250,10 @@ Bug Fixes to C++ Support
   (`#64962 <https://github.com/llvm/llvm-project/issues/64962>`_) and
   (`#28679 <https://github.com/llvm/llvm-project/issues/28679>`_).
 
+- Fix a crash caused by substitution failure in expression requirements.
+  (`#64172 <https://github.com/llvm/llvm-project/issues/64172>`_) and
+  (`#64723 <https://github.com/llvm/llvm-project/issues/64723>`_).
+
 Bug Fixes to AST Handling
 ^^^^^^^^^^^^^^^^^^^^^^^^^
 - Fixed an import failure of recursive friend class template.

clang/include/clang/AST/ExprConcepts.h

@@ -14,20 +14,21 @@
 #ifndef LLVM_CLANG_AST_EXPRCONCEPTS_H
 #define LLVM_CLANG_AST_EXPRCONCEPTS_H
 
-#include "clang/AST/ASTContext.h"
 #include "clang/AST/ASTConcept.h"
+#include "clang/AST/ASTContext.h"
 #include "clang/AST/Decl.h"
-#include "clang/AST/DeclarationName.h"
 #include "clang/AST/DeclTemplate.h"
+#include "clang/AST/DeclarationName.h"
 #include "clang/AST/Expr.h"
 #include "clang/AST/NestedNameSpecifier.h"
 #include "clang/AST/TemplateBase.h"
 #include "clang/AST/Type.h"
 #include "clang/Basic/SourceLocation.h"
+#include "llvm/ADT/STLFunctionalExtras.h"
 #include "llvm/Support/ErrorHandling.h"
 #include "llvm/Support/TrailingObjects.h"
-#include <utility>
 #include <string>
+#include <utility>
 
 namespace clang {
 class ASTStmtReader;
@@ -486,6 +487,13 @@ public:
   }
 };
 
+using EntityPrinter = llvm::function_ref<void(llvm::raw_ostream &)>;
+
+/// \brief create a Requirement::SubstitutionDiagnostic with only a
+/// SubstitutedEntity and DiagLoc using Sema's allocator.
+Requirement::SubstitutionDiagnostic *
+createSubstDiagAt(Sema &S, SourceLocation Location, EntityPrinter Printer);
+
 } // namespace concepts
 
 /// C++2a [expr.prim.req]:

clang/lib/Sema/SemaExprCXX.cpp

@@ -19,6 +19,7 @@
 #include "clang/AST/CharUnits.h"
 #include "clang/AST/DeclObjC.h"
 #include "clang/AST/ExprCXX.h"
+#include "clang/AST/ExprConcepts.h"
 #include "clang/AST/ExprObjC.h"
 #include "clang/AST/RecursiveASTVisitor.h"
 #include "clang/AST/Type.h"
@@ -9080,16 +9081,22 @@ Sema::BuildExprRequirement(
     MLTAL.addOuterRetainedLevels(TPL->getDepth());
     const TypeConstraint *TC = Param->getTypeConstraint();
     assert(TC && "Type Constraint cannot be null here");
-    ExprResult Constraint =
-        SubstExpr(TC->getImmediatelyDeclaredConstraint(), MLTAL);
+    auto *IDC = TC->getImmediatelyDeclaredConstraint();
+    assert(IDC && "ImmediatelyDeclaredConstraint can't be null here.");
+    ExprResult Constraint = SubstExpr(IDC, MLTAL);
     if (Constraint.isInvalid()) {
-      Status = concepts::ExprRequirement::SS_ExprSubstitutionFailure;
-    } else {
-      SubstitutedConstraintExpr =
-          cast<ConceptSpecializationExpr>(Constraint.get());
-      if (!SubstitutedConstraintExpr->isSatisfied())
-        Status = concepts::ExprRequirement::SS_ConstraintsNotSatisfied;
+      return new (Context) concepts::ExprRequirement(
+          concepts::createSubstDiagAt(*this, IDC->getExprLoc(),
+                                      [&](llvm::raw_ostream &OS) {
+                                        IDC->printPretty(OS, /*Helper=*/nullptr,
+                                                         getPrintingPolicy());
+                                      }),
+          IsSimple, NoexceptLoc, ReturnTypeRequirement);
     }
+    SubstitutedConstraintExpr =
+        cast<ConceptSpecializationExpr>(Constraint.get());
+    if (!SubstitutedConstraintExpr->isSatisfied())
+      Status = concepts::ExprRequirement::SS_ConstraintsNotSatisfied;
   }
   return new (Context) concepts::ExprRequirement(E, IsSimple, NoexceptLoc,
                                                  ReturnTypeRequirement, Status,

clang/lib/Sema/SemaTemplateInstantiate.cpp

@@ -2271,9 +2271,9 @@ QualType TemplateInstantiator::TransformSubstTemplateTypeParmPackType(
       getPackIndex(Pack), Arg, TL.getNameLoc());
 }
 
-template<typename EntityPrinter>
 static concepts::Requirement::SubstitutionDiagnostic *
-createSubstDiag(Sema &S, TemplateDeductionInfo &Info, EntityPrinter Printer) {
+createSubstDiag(Sema &S, TemplateDeductionInfo &Info,
+                concepts::EntityPrinter Printer) {
   SmallString<128> Message;
   SourceLocation ErrorLoc;
   if (Info.hasSFINAEDiagnostic()) {
@@ -2297,6 +2297,19 @@ createSubstDiag(Sema &S, TemplateDeductionInfo &Info, EntityPrinter Printer) {
       StringRef(MessageBuf, Message.size())};
 }
 
+concepts::Requirement::SubstitutionDiagnostic *
+concepts::createSubstDiagAt(Sema &S, SourceLocation Location,
+                            EntityPrinter Printer) {
+  SmallString<128> Entity;
+  llvm::raw_svector_ostream OS(Entity);
+  Printer(OS);
+  char *EntityBuf = new (S.Context) char[Entity.size()];
+  llvm::copy(Entity, EntityBuf);
+  return new (S.Context) concepts::Requirement::SubstitutionDiagnostic{
+      /*SubstitutedEntity=*/StringRef(EntityBuf, Entity.size()),
+      /*DiagLoc=*/Location, /*DiagMessage=*/StringRef()};
+}
+
 ExprResult TemplateInstantiator::TransformRequiresTypeParams(
     SourceLocation KWLoc, SourceLocation RBraceLoc, const RequiresExpr *RE,
     RequiresExprBodyDecl *Body, ArrayRef<ParmVarDecl *> Params,

clang/test/SemaCXX/concept-crash-on-diagnostic.cpp

@@ -0,0 +1,37 @@
+// RUN: %clang_cc1 -fsyntax-only -std=c++20 -verify %s
+
+template <typename Iterator> class normal_iterator {};
+
+template <typename From, typename To> struct is_convertible {};
+
+template <typename From, typename To>
+inline constexpr bool is_convertible_v = is_convertible<From, To>::value; // expected-error {{no member named 'value' in 'is_convertible<bool, bool>'}}
+
+template <typename From, typename To>
+concept convertible_to = is_convertible_v<From, To>; // #1
+
+template <typename IteratorL, typename IteratorR>
+  requires requires(IteratorL lhs, IteratorR rhs) { // #2
+    { lhs == rhs } -> convertible_to<bool>; // #3
+  }
+constexpr bool compare(normal_iterator<IteratorL> lhs, normal_iterator<IteratorR> rhs) { // #4
+  return false;
+}
+
+class Object;
+
+void function() {
+  normal_iterator<Object *> begin, end;
+  compare(begin, end); // expected-error {{no matching function for call to 'compare'}} #5
+}
+
+// expected-note@#1 {{in instantiation of variable template specialization 'is_convertible_v<bool, bool>' requested here}}
+// expected-note@#1 {{substituting template arguments into constraint expression here}}
+// expected-note@#3 {{checking the satisfaction of concept 'convertible_to<bool, bool>'}}
+// expected-note@#2 {{substituting template arguments into constraint expression here}}
+// expected-note@#5 {{checking constraint satisfaction for template 'compare<Object *, Object *>'}}
+// expected-note@#5 {{in instantiation of function template specialization 'compare<Object *, Object *>' requested here}}
+
+// expected-note@#4 {{candidate template ignored: constraints not satisfied [with IteratorL = Object *, IteratorR = Object *]}}
+// We don't know exactly the substituted type for `lhs == rhs`, thus a placeholder 'expr-type' is emitted.
+// expected-note@#3 {{because 'convertible_to<expr-type, bool>' would be invalid}}

clang/test/SemaCXX/concept-fatal-error.cpp

@@ -1,4 +1,4 @@
-// RUN: not %clang_cc1 -fsyntax-only -std=c++20 -ferror-limit 1 -verify %s
+// RUN: %clang_cc1 -fsyntax-only -std=c++20 -ferror-limit 1 -verify %s
 
 template <class>
 concept f = requires { 42; };
@@ -6,5 +6,5 @@ struct h {
   // The missing semicolon will trigger an error and -ferror-limit=1 will make it fatal
   // We test that we do not crash in such cases (#55401)
   int i = requires { { i } f } // expected-error {{expected ';' at end of declaration list}}
-                               // expected-error@* {{too many errros emitted}}
+                               // expected-error@* {{too many errors emitted}}
 };