[clang] [clang] Bailout when the substitution of template parameter mapping is invalid. (PR #86869)

[Haojian Wu via cfe-commits]

https://github.com/hokein created https://github.com/llvm/llvm-project/pull/86869

Fixes #86757

We missed to handle the invalid case when substituting into the parameter mapping of an constraint during normalization.

>From 85eba887cf6d253ff041b23cd4d8d5506aa1c674 Mon Sep 17 00:00:00 2001
From: Haojian Wu <hokein.wu at gmail.com>
Date: Wed, 27 Mar 2024 21:29:47 +0100
Subject: [PATCH] [clang] Bailout when the substitution of template parameter
 mapping is invalid.

Fixes #86757

We missed to handle the invalid case when substituting into the parameter
mapping of an constraint during normalization.
---
 clang/docs/ReleaseNotes.rst                  |  1 +
 clang/lib/Sema/SemaConcept.cpp               |  2 ++
 clang/test/SemaTemplate/concepts-GH86757.cpp | 13 +++++++++++++
 3 files changed, 16 insertions(+)
 create mode 100644 clang/test/SemaTemplate/concepts-GH86757.cpp

diff --git a/clang/docs/ReleaseNotes.rst b/clang/docs/ReleaseNotes.rst
index 0fdd9e3fb3eee2..1411e15a649ae0 100644
--- a/clang/docs/ReleaseNotes.rst
+++ b/clang/docs/ReleaseNotes.rst
@@ -455,6 +455,7 @@ Bug Fixes to C++ Support
 - Fix an issue where a namespace alias could be defined using a qualified name (all name components
   following the first `::` were ignored).
 - Fix an out-of-bounds crash when checking the validity of template partial specializations. (part of #GH86757).
+- Fix an issue caused by not handling invalid cases when substituting into the parameter mapping of a constraint. Fixes (#GH86757).
 
 Bug Fixes to AST Handling
 ^^^^^^^^^^^^^^^^^^^^^^^^^
diff --git a/clang/lib/Sema/SemaConcept.cpp b/clang/lib/Sema/SemaConcept.cpp
index b6c4d3d540ef50..a2d8ba9a96d7a4 100644
--- a/clang/lib/Sema/SemaConcept.cpp
+++ b/clang/lib/Sema/SemaConcept.cpp
@@ -1281,6 +1281,8 @@ substituteParameterMappings(Sema &S, NormalizedConstraint &N,
       S, InstLocBegin,
       Sema::InstantiatingTemplate::ParameterMappingSubstitution{}, Concept,
       {InstLocBegin, InstLocEnd});
+  if (Inst.isInvalid())
+    return true;
   if (S.SubstTemplateArguments(*Atomic.ParameterMapping, MLTAL, SubstArgs))
     return true;
 
diff --git a/clang/test/SemaTemplate/concepts-GH86757.cpp b/clang/test/SemaTemplate/concepts-GH86757.cpp
new file mode 100644
index 00000000000000..3122381b20359e
--- /dev/null
+++ b/clang/test/SemaTemplate/concepts-GH86757.cpp
@@ -0,0 +1,13 @@
+// RUN: %clang_cc1 -std=c++20 -Wfatal-errors -verify %s
+
+template <typename> int a;
+template <typename... b> concept c = a<b...>;
+template <typename> concept e = c<>;
+
+// must be a fatal error to trigger the crash
+undefined; // expected-error {{a type specifier is required for all declarations}}
+
+template <typename d> concept g = e<d>;
+template <g> struct h
+template <g d>
+struct h<d>;