From 440fffad7e7231fab766c6e00e47a39ad5a9b95e Mon Sep 17 00:00:00 2001
From: Younan Zhang <zyn7109@gmail.com>
Date: Wed, 17 Jul 2024 19:17:01 +0800
Subject: [PATCH] [Clang][Concepts] Avoid substituting into constraints for
 invalid TemplateDecls (#75697)

Fixes https://github.com/llvm/llvm-project/issues/73885.

Substituting into constraints for invalid TemplateDecls might still
yield dependent expressions and end up crashing later in evaluation.
---
 clang/docs/ReleaseNotes.rst                           |  1 +
 clang/lib/Sema/SemaConcept.cpp                        |  6 ++++++
 clang/test/SemaTemplate/instantiate-requires-expr.cpp | 10 ++++++++++
 3 files changed, 17 insertions(+)

diff --git a/clang/docs/ReleaseNotes.rst b/clang/docs/ReleaseNotes.rst
index 8c0d1635d27568..6dc45956a9afba 100644
--- a/clang/docs/ReleaseNotes.rst
+++ b/clang/docs/ReleaseNotes.rst
@@ -1042,6 +1042,7 @@ Bug Fixes to C++ Support
 - Fixed failed assertion when resolving context of defaulted comparison method outside of struct. (#GH96043).
 - Clang now diagnoses explicit object parameters in member pointers and other contexts where they should not appear.
   Fixes (#GH85992).
+- Fixed a crash-on-invalid bug involving extraneous template parameter with concept substitution. (#GH73885)
 
 Bug Fixes to AST Handling
 ^^^^^^^^^^^^^^^^^^^^^^^^^
diff --git a/clang/lib/Sema/SemaConcept.cpp b/clang/lib/Sema/SemaConcept.cpp
index 84c5753a46ac35..9e16b67284be45 100644
--- a/clang/lib/Sema/SemaConcept.cpp
+++ b/clang/lib/Sema/SemaConcept.cpp
@@ -625,6 +625,12 @@ bool Sema::CheckConstraintSatisfaction(
         *this, nullptr, ConstraintExprs, ConvertedConstraints,
         TemplateArgsLists, TemplateIDRange, OutSatisfaction);
   }
+  // Invalid templates could make their way here. Substituting them could result
+  // in dependent expressions.
+  if (Template->isInvalidDecl()) {
+    OutSatisfaction.IsSatisfied = false;
+    return true;
+  }
 
   // A list of the template argument list flattened in a predictible manner for
   // the purposes of caching. The ConstraintSatisfaction type is in AST so it
diff --git a/clang/test/SemaTemplate/instantiate-requires-expr.cpp b/clang/test/SemaTemplate/instantiate-requires-expr.cpp
index 516708bf4c875a..20a19d731ae169 100644
--- a/clang/test/SemaTemplate/instantiate-requires-expr.cpp
+++ b/clang/test/SemaTemplate/instantiate-requires-expr.cpp
@@ -227,3 +227,13 @@ struct r6 {};
 
 using r6i = r6<int>;
 // expected-error@-1 {{constraints not satisfied for class template 'r6' [with T = int]}}
+
+namespace GH73885 {
+
+template <class> // expected-error {{extraneous}}
+template <class T> requires(T{})
+constexpr bool e_v = true;
+
+static_assert(e_v<bool>);
+
+} // namespace GH73885