[clang] [clang] Fix an out-of-bound crash when checking template partial specializations. (PR #86794)

[Haojian Wu via cfe-commits]

https://github.com/hokein created https://github.com/llvm/llvm-project/pull/86794

I found this issue (a separate one) during the investigation of #86757, the crash is similar in substituteParameterMappings, but at different inner places.

This was an out-of-bound issue where we access front element in an empty written template argument list to get the instantiation source range. This patch fixes it by adding a proper guard.

>From 9d3eaab5efce82024dfcd4338b4cf03feb3a5966 Mon Sep 17 00:00:00 2001
From: Haojian Wu <hokein.wu at gmail.com>
Date: Wed, 27 Mar 2024 13:04:13 +0100
Subject: [PATCH] [clang] Fix an out-of-bound crash when checking class
 template partial specialization.

I found this issue (a separate one) during the investigation of #86757,
the crash is similar in substituteParameterMappings, but at different
inner places.

This was an out-of-bound issue where we access front element in an empty
written template argument list to get the instantiation source range.
This patch fix it by adding a proper guard.
---
 clang/docs/ReleaseNotes.rst          |  1 +
 clang/lib/Sema/SemaConcept.cpp       | 12 ++++++++++--
 clang/test/SemaTemplate/concepts.cpp | 10 +++++++++-
 3 files changed, 20 insertions(+), 3 deletions(-)

diff --git a/clang/docs/ReleaseNotes.rst b/clang/docs/ReleaseNotes.rst
index 0dd026a5de5c6f..0fdd9e3fb3eee2 100644
--- a/clang/docs/ReleaseNotes.rst
+++ b/clang/docs/ReleaseNotes.rst
@@ -454,6 +454,7 @@ Bug Fixes to C++ Support
 - Fix a crash when instantiating a lambda that captures ``this`` outside of its context. Fixes (#GH85343).
 - 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).
 
 Bug Fixes to AST Handling
 ^^^^^^^^^^^^^^^^^^^^^^^^^
diff --git a/clang/lib/Sema/SemaConcept.cpp b/clang/lib/Sema/SemaConcept.cpp
index 1c546e9f5894f0..b6c4d3d540ef50 100644
--- a/clang/lib/Sema/SemaConcept.cpp
+++ b/clang/lib/Sema/SemaConcept.cpp
@@ -1269,10 +1269,18 @@ substituteParameterMappings(Sema &S, NormalizedConstraint &N,
                     : SourceLocation()));
     Atomic.ParameterMapping.emplace(TempArgs,  OccurringIndices.count());
   }
+  SourceLocation InstLocBegin =
+      ArgsAsWritten->arguments().empty()
+          ? ArgsAsWritten->getLAngleLoc()
+          : ArgsAsWritten->arguments().front().getSourceRange().getBegin();
+  SourceLocation InstLocEnd =
+      ArgsAsWritten->arguments().empty()
+          ? ArgsAsWritten->getRAngleLoc()
+          : ArgsAsWritten->arguments().front().getSourceRange().getEnd();
   Sema::InstantiatingTemplate Inst(
-      S, ArgsAsWritten->arguments().front().getSourceRange().getBegin(),
+      S, InstLocBegin,
       Sema::InstantiatingTemplate::ParameterMappingSubstitution{}, Concept,
-      ArgsAsWritten->arguments().front().getSourceRange());
+      {InstLocBegin, InstLocEnd});
   if (S.SubstTemplateArguments(*Atomic.ParameterMapping, MLTAL, SubstArgs))
     return true;
 
diff --git a/clang/test/SemaTemplate/concepts.cpp b/clang/test/SemaTemplate/concepts.cpp
index b7ea0d003a52d7..787cc809e25353 100644
--- a/clang/test/SemaTemplate/concepts.cpp
+++ b/clang/test/SemaTemplate/concepts.cpp
@@ -1,4 +1,4 @@
-// RUN: %clang_cc1 -std=c++20 -verify %s
+// RUN: %clang_cc1 -std=c++20 -ferror-limit 0 -verify %s
 
 namespace PR47043 {
   template<typename T> concept True = true;
@@ -1114,3 +1114,11 @@ void foo() {
 }
 
 } // namespace GH64808
+
+namespace GH86757_1 {
+template <typename...> concept b = false;
+template <typename> concept c = b<>;
+template <typename d> concept f = c< d >;
+template <f> struct e; // expected-note {{}}
+template <f d> struct e<d>; // expected-error {{class template partial specialization is not more specialized than the primary template}}
+}