[clang] [clang]Fix name lookup crash (PR #190484)

[via cfe-commits]

https://github.com/Serosh-commits updated https://github.com/llvm/llvm-project/pull/190484

>From b718513c1c1617f2b0f3fd941fc4cba68083cb8c Mon Sep 17 00:00:00 2001
From: Serosh-commits <janmejayapanda400 at gmail.com>
Date: Sat, 25 Apr 2026 18:36:59 +0530
Subject: [PATCH 1/3] [Clang] Fix a name lookup crash when parsing invalid
 template parameters (#GH189344)

---
 clang/docs/ReleaseNotes.rst     |  2 ++
 clang/lib/Sema/SemaLookup.cpp   |  5 +----
 clang/test/SemaCXX/gh189344.cpp | 12 ++++++++++++
 3 files changed, 15 insertions(+), 4 deletions(-)
 create mode 100644 clang/test/SemaCXX/gh189344.cpp

diff --git a/clang/docs/ReleaseNotes.rst b/clang/docs/ReleaseNotes.rst
index f8508ebefb199..752e37765a484 100644
--- a/clang/docs/ReleaseNotes.rst
+++ b/clang/docs/ReleaseNotes.rst
@@ -520,6 +520,8 @@ Bug Fixes to Attribute Support
 
 Bug Fixes to C++ Support
 ^^^^^^^^^^^^^^^^^^^^^^^^
+
+- Fixed a name lookup crash when parsing invalid template parameters. (#GH189344)
 - Fixed a crash when a function template is defined as a non-template friend with a global scope qualifier. (#GH185341)
 - Clang now rejects constant template parameters with block pointer types, since these are not implemented anyway and would lead to crashes. (#GH189247)
 - Fixed a crash on error recovery when dealing with invalid templates. (#GH183075)
diff --git a/clang/lib/Sema/SemaLookup.cpp b/clang/lib/Sema/SemaLookup.cpp
index b96065f8619d2..9ce64ed85540b 100644
--- a/clang/lib/Sema/SemaLookup.cpp
+++ b/clang/lib/Sema/SemaLookup.cpp
@@ -1528,10 +1528,7 @@ bool Sema::CppLookupName(LookupResult &R, Scope *S) {
         // If we have a context, and it's not a context stashed in the
         // template parameter scope for an out-of-line definition, also
         // look into that context.
-        if (!(Found && S->isTemplateParamScope())) {
-          assert(Ctx->isFileContext() &&
-              "We should have been looking only at file context here already.");
-
+        if (Ctx->isFileContext() && !(Found && S->isTemplateParamScope())) {
           // Look into context considering using-directives.
           if (CppNamespaceLookup(*this, R, Context, Ctx, UDirs))
             Found = true;
diff --git a/clang/test/SemaCXX/gh189344.cpp b/clang/test/SemaCXX/gh189344.cpp
new file mode 100644
index 0000000000000..f656c1173c2ac
--- /dev/null
+++ b/clang/test/SemaCXX/gh189344.cpp
@@ -0,0 +1,12 @@
+// RUN: %clang_cc1 -fsyntax-only -verify %s
+
+template <union { } alignas ( union  a { c ) ( a :: ) ( :: (b
+// expected-error at -1 {{cannot be defined in a type specifier}}
+// expected-error at -2 {{'a' cannot be defined in a type specifier}}
+// expected-error at -3 {{unknown type name 'b'}}
+// expected-error at -4 2{{parameter declarator cannot be qualified}}
+// expected-error at -5 {{a type specifier is required for all declarations}}
+// expected-note at -6 2{{to match this '('}}
+// expected-error@* 3{{expected unqualified-id}}
+// expected-error@* 2{{expected ')'}}
+// expected-error@* {{expected ',' or '>' in template-parameter-list}}

>From 5e70ddf052e37fcc2fa4755e06270fd2c73d760c Mon Sep 17 00:00:00 2001
From: Serosh-commits <janmejayapanda400 at gmail.com>
Date: Mon, 25 May 2026 16:34:00 +0530
Subject: [PATCH 2/3] address feedback

---
 clang/lib/Sema/SemaDecl.cpp   | 5 ++++-
 clang/lib/Sema/SemaLookup.cpp | 5 ++++-
 2 files changed, 8 insertions(+), 2 deletions(-)

diff --git a/clang/lib/Sema/SemaDecl.cpp b/clang/lib/Sema/SemaDecl.cpp
index 36538e18f297c..2f9f03d2c34b0 100644
--- a/clang/lib/Sema/SemaDecl.cpp
+++ b/clang/lib/Sema/SemaDecl.cpp
@@ -1489,6 +1489,7 @@ void Sema::EnterTemplatedContext(Scope *S, DeclContext *DC) {
   unsigned ScopeDepth = getTemplateDepth(S);
   for (; S && S->isTemplateParamScope(); S = S->getParent(), --ScopeDepth) {
     DeclContext *SearchDCAfterScope = DC;
+    bool SetLookupEntity = false;
     for (; DC; DC = DC->getLookupParent()) {
       if (const TemplateParameterList *TPL =
               cast<Decl>(DC)->getDescribedTemplateParams()) {
@@ -1497,10 +1498,12 @@ void Sema::EnterTemplatedContext(Scope *S, DeclContext *DC) {
           continue;
         if (ScopeDepth == DCDepth)
           SearchDCAfterScope = DC = DC->getLookupParent();
+        SetLookupEntity = true;
         break;
       }
     }
-    S->setLookupEntity(SearchDCAfterScope);
+    if (SetLookupEntity)
+      S->setLookupEntity(SearchDCAfterScope);
   }
 }
 
diff --git a/clang/lib/Sema/SemaLookup.cpp b/clang/lib/Sema/SemaLookup.cpp
index 9ce64ed85540b..b96065f8619d2 100644
--- a/clang/lib/Sema/SemaLookup.cpp
+++ b/clang/lib/Sema/SemaLookup.cpp
@@ -1528,7 +1528,10 @@ bool Sema::CppLookupName(LookupResult &R, Scope *S) {
         // If we have a context, and it's not a context stashed in the
         // template parameter scope for an out-of-line definition, also
         // look into that context.
-        if (Ctx->isFileContext() && !(Found && S->isTemplateParamScope())) {
+        if (!(Found && S->isTemplateParamScope())) {
+          assert(Ctx->isFileContext() &&
+              "We should have been looking only at file context here already.");
+
           // Look into context considering using-directives.
           if (CppNamespaceLookup(*this, R, Context, Ctx, UDirs))
             Found = true;

>From 83d2d3095703304570ca6abe7690d913eabaae39 Mon Sep 17 00:00:00 2001
From: Serosh-commits <janmejayapanda400 at gmail.com>
Date: Mon, 25 May 2026 18:12:25 +0530
Subject: [PATCH 3/3] fix the mecha properly to prevent the bad union stash

---
 clang/lib/Sema/SemaDecl.cpp | 15 +++++++++++----
 1 file changed, 11 insertions(+), 4 deletions(-)

diff --git a/clang/lib/Sema/SemaDecl.cpp b/clang/lib/Sema/SemaDecl.cpp
index 2f9f03d2c34b0..410ba470b3834 100644
--- a/clang/lib/Sema/SemaDecl.cpp
+++ b/clang/lib/Sema/SemaDecl.cpp
@@ -1489,7 +1489,7 @@ void Sema::EnterTemplatedContext(Scope *S, DeclContext *DC) {
   unsigned ScopeDepth = getTemplateDepth(S);
   for (; S && S->isTemplateParamScope(); S = S->getParent(), --ScopeDepth) {
     DeclContext *SearchDCAfterScope = DC;
-    bool SetLookupEntity = false;
+    bool FoundTemplateContext = false;
     for (; DC; DC = DC->getLookupParent()) {
       if (const TemplateParameterList *TPL =
               cast<Decl>(DC)->getDescribedTemplateParams()) {
@@ -1498,12 +1498,19 @@ void Sema::EnterTemplatedContext(Scope *S, DeclContext *DC) {
           continue;
         if (ScopeDepth == DCDepth)
           SearchDCAfterScope = DC = DC->getLookupParent();
-        SetLookupEntity = true;
+        FoundTemplateContext = true;
         break;
       }
     }
-    if (SetLookupEntity)
-      S->setLookupEntity(SearchDCAfterScope);
+    if (!SearchDCAfterScope)
+      continue;
+
+    if (!FoundTemplateContext && !SearchDCAfterScope->isFileContext()) {
+      if (const auto *RD = dyn_cast<RecordDecl>(SearchDCAfterScope))
+        if (RD->isUnion() && !RD->isTemplateDecl())
+          continue;
+    }
+    S->setLookupEntity(SearchDCAfterScope);
   }
 }