[clang] [Sema] Fix crash in Sema::FindInstantiatedDecl (PR #96509)

[via cfe-commits]

llvmbot wrote:


<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-clang

Author: Alejandro Álvarez Ayllón (alejandro-alvarez-sonarsource)

<details>
<summary>Changes</summary>

When looking for a template instantiation with a non-type parameter of unknown type and with a default value.

This can happen when a template non-type parameter has a broken expression that gets replaced by a `RecoveryExpr`.

---
Full diff: https://github.com/llvm/llvm-project/pull/96509.diff


2 Files Affected:

- (modified) clang/lib/Sema/SemaTemplateInstantiateDecl.cpp (+1-1) 
- (added) clang/test/SemaCXX/instantiate-template-broken-nontype-default.cpp (+12) 


``````````diff
diff --git a/clang/lib/Sema/SemaTemplateInstantiateDecl.cpp b/clang/lib/Sema/SemaTemplateInstantiateDecl.cpp
index 0681520764d9a..999fec0ebb259 100644
--- a/clang/lib/Sema/SemaTemplateInstantiateDecl.cpp
+++ b/clang/lib/Sema/SemaTemplateInstantiateDecl.cpp
@@ -6300,7 +6300,7 @@ NamedDecl *Sema::FindInstantiatedDecl(SourceLocation Loc, NamedDecl *D,
                   getTrivialTemplateArgumentLoc(UnpackedArg, QualType(), Loc));
           }
           QualType T = CheckTemplateIdType(TemplateName(TD), Loc, Args);
-          if (T.isNull())
+          if (T.isNull() || T->containsErrors())
             return nullptr;
           CXXRecordDecl *SubstRecord = T->getAsCXXRecordDecl();
 
diff --git a/clang/test/SemaCXX/instantiate-template-broken-nontype-default.cpp b/clang/test/SemaCXX/instantiate-template-broken-nontype-default.cpp
new file mode 100644
index 0000000000000..a644cc3d057cb
--- /dev/null
+++ b/clang/test/SemaCXX/instantiate-template-broken-nontype-default.cpp
@@ -0,0 +1,12 @@
+// RUN: %clang_cc1 -std=c++20 -fsyntax-only -verify %s
+
+constexpr Missing a = 0; // expected-error {{unknown type name 'Missing'}}
+
+template < typename T, Missing b = a> // expected-error {{unknown type name 'Missing'}}
+class Klass { // expected-note {{candidate template ignored: could not match 'Klass<T, b>' against 'int'}}
+  Klass(T);   // expected-note {{candidate template ignored: substitution failure [with T = int, b = <recovery-expr>()]}}
+};
+
+Klass foo{5}; // no-crash \
+                 expected-error {{no viable constructor or deduction guide for deduction of template arguments of 'Klass'}}
+

``````````

</details>


https://github.com/llvm/llvm-project/pull/96509