[clang] [Clang][Sema] Fix crash in CheckNonTypeTemplateParameterType with invalid type (PR #186200)

[via cfe-commits]

llvmbot wrote:


<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-clang

Author: Krystian Stasiowski (sdkrystian)

<details>
<summary>Changes</summary>

When a non-type template parameter has a type containing an undeduced placeholder type that is invalid (e.g., a function returning a function), `SubstAutoTypeSourceInfoDependent` can return null if the type is invalid. `CheckNonTypeTemplateParameterType` was not handling this case and would dereference the null pointer.

Fixes #<!-- -->177545

---
Full diff: https://github.com/llvm/llvm-project/pull/186200.diff


3 Files Affected:

- (modified) clang/docs/ReleaseNotes.rst (+1) 
- (modified) clang/lib/Sema/SemaTemplate.cpp (+4-1) 
- (modified) clang/test/SemaTemplate/deduction-crash.cpp (+5) 


``````````diff
diff --git a/clang/docs/ReleaseNotes.rst b/clang/docs/ReleaseNotes.rst
index 3617786f09595..35e637e7290cc 100644
--- a/clang/docs/ReleaseNotes.rst
+++ b/clang/docs/ReleaseNotes.rst
@@ -322,6 +322,7 @@ Bug Fixes in This Version
 - Fixed a crash when parsing ``#pragma clang attribute`` arguments for attributes that forbid arguments. (#GH182122)
 - Fixed a bug with multiple-include optimization (MIOpt) state not being preserved in some cases during lexing, which could suppress header-guard mismatch diagnostics and interfere with include-guard optimization. (#GH180155)
 - Fixed a crash when normalizing constraints involving concept template parameters whose index coincided with non-concept template parameters in the same parameter mapping.
+- Fixed a crash when substituting into a non-type template parameter that has a type containing an undeduced placeholder type.
 
 Bug Fixes to Compiler Builtins
 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
diff --git a/clang/lib/Sema/SemaTemplate.cpp b/clang/lib/Sema/SemaTemplate.cpp
index 9b0bec20618a0..9194ee5e2bee9 100644
--- a/clang/lib/Sema/SemaTemplate.cpp
+++ b/clang/lib/Sema/SemaTemplate.cpp
@@ -1342,7 +1342,10 @@ QualType Sema::CheckNonTypeTemplateParameterType(TypeSourceInfo *&TSI,
     //    - an identifier associated by name lookup with a non-type
     //      template-parameter declared with a type that contains a
     //      placeholder type (7.1.7.4),
-    TSI = SubstAutoTypeSourceInfoDependent(TSI);
+    TypeSourceInfo *NewTSI = SubstAutoTypeSourceInfoDependent(TSI);
+    if (!NewTSI)
+      return QualType();
+    TSI = NewTSI;
   }
 
   return CheckNonTypeTemplateParameterType(TSI->getType(), Loc);
diff --git a/clang/test/SemaTemplate/deduction-crash.cpp b/clang/test/SemaTemplate/deduction-crash.cpp
index 99ca0b365ff6f..7c3e92af068e9 100644
--- a/clang/test/SemaTemplate/deduction-crash.cpp
+++ b/clang/test/SemaTemplate/deduction-crash.cpp
@@ -172,3 +172,8 @@ namespace PR51872_part1 {
   // expected-error at -1 {{no viable constructor or deduction guide for deduction of template arguments of 'T1'}}
   // expected-note at -7  {{candidate template ignored: could not match 'PR51872_part1::T1<value-parameter-0-0>' against 'int'}}
 }
+
+namespace GH177545 {
+  template<decltype(auto)()() volatile throw() -> char> // expected-error {{'decltype(auto)' can only be used as a return type in a function declaration}}
+  struct T2;                                            // expected-error at -1 {{function cannot return function type 'auto () volatile throw() -> decltype(auto)'}}
+}

``````````

</details>


https://github.com/llvm/llvm-project/pull/186200