[clang] [clang][ASTImporter] set nonnull type for var specialized from lambda template (PR #105492)

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llvmbot wrote:


<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-clang

Author: Ding Fei (danix800)

<details>
<summary>Changes</summary>

There's circular deps here when importing btw VarTemplateSpecializationDecl (m) and its type.

VarDecl is created with a null type QualType(), and the importing of its type will leads to linkage computation (for the templated lambda) which depends on the var's type (not yet imported).

This fix uses a non-null type instead of a null one. But this seems still cannot ensure the computation is correct.

Fixes #<!-- -->104622 

---
Full diff: https://github.com/llvm/llvm-project/pull/105492.diff


2 Files Affected:

- (modified) clang/lib/AST/ASTImporter.cpp (+4-2) 
- (modified) clang/unittests/AST/ASTImporterTest.cpp (+13) 


``````````diff
diff --git a/clang/lib/AST/ASTImporter.cpp b/clang/lib/AST/ASTImporter.cpp
index 103235547f482e..cc1bd01f15bef6 100644
--- a/clang/lib/AST/ASTImporter.cpp
+++ b/clang/lib/AST/ASTImporter.cpp
@@ -6582,6 +6582,8 @@ ExpectedDecl ASTNodeImporter::VisitVarTemplateSpecializationDecl(
       return std::move(Err);
   }
 
+  QualType ToTmpTy = Importer.getToContext().IntTy;
+  ToTmpTy = ToTmpTy.withCVRQualifiers(D->getType().getCVRQualifiers());
   using PartVarSpecDecl = VarTemplatePartialSpecializationDecl;
   // Create a new specialization.
   if (auto *FromPartial = dyn_cast<PartVarSpecDecl>(D)) {
@@ -6592,7 +6594,7 @@ ExpectedDecl ASTNodeImporter::VisitVarTemplateSpecializationDecl(
     PartVarSpecDecl *ToPartial;
     if (GetImportedOrCreateDecl(ToPartial, D, Importer.getToContext(), DC,
                                 *BeginLocOrErr, *IdLocOrErr, *ToTPListOrErr,
-                                VarTemplate, QualType(), nullptr,
+                                VarTemplate, ToTmpTy, nullptr,
                                 D->getStorageClass(), TemplateArgs))
       return ToPartial;
 
@@ -6613,7 +6615,7 @@ ExpectedDecl ASTNodeImporter::VisitVarTemplateSpecializationDecl(
   } else { // Full specialization
     if (GetImportedOrCreateDecl(D2, D, Importer.getToContext(), DC,
                                 *BeginLocOrErr, *IdLocOrErr, VarTemplate,
-                                QualType(), nullptr, D->getStorageClass(),
+                                ToTmpTy, nullptr, D->getStorageClass(),
                                 TemplateArgs))
       return D2;
   }
diff --git a/clang/unittests/AST/ASTImporterTest.cpp b/clang/unittests/AST/ASTImporterTest.cpp
index 57242ff49fe3b8..06996268d1fb94 100644
--- a/clang/unittests/AST/ASTImporterTest.cpp
+++ b/clang/unittests/AST/ASTImporterTest.cpp
@@ -9919,6 +9919,19 @@ TEST_P(ImportTemplateParmDeclDefaultValue, ImportExistingVarTemplate) {
   testImport(FromLastD);
 }
 
+TEST_P(ASTImporterOptionSpecificTestBase, VarTemplatedLambdaInGlobalScope) {
+  Decl *FromTU = getTuDecl(
+      R"(
+        namespace { template <typename> auto m = [] {}; }
+        void bar() { auto n = m<int>; }
+      )",
+      Lang_CXX14, "input0.cc");
+  FunctionDecl *FromF = FirstDeclMatcher<FunctionDecl>().match(
+      FromTU, functionDecl(hasName("bar")));
+  FunctionDecl *ToF = Import(FromF, Lang_CXX14);
+  EXPECT_TRUE(ToF);
+}
+
 INSTANTIATE_TEST_SUITE_P(ParameterizedTests, ASTImporterLookupTableTest,
                          DefaultTestValuesForRunOptions);
 

``````````

</details>


https://github.com/llvm/llvm-project/pull/105492