[clang] [clang-tools-extra] [Clang][AST] Introduce `ExplicitInstantiationDecl` to preserve source info and fix diagnostic locations (PR #191658)

[Chuanqi Xu via cfe-commits]

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@@ -651,6 +652,11 @@ class ASTReader
   llvm::DenseMap<std::pair<const Decl *, unsigned>, NamedDecl *>
       LambdaDeclarationsForMerging;
 
+  /// Map from canonical specialization to the corresponding explicit
+  /// instantiation declaration, for merging across modules.
+  llvm::DenseMap<const Decl *, ExplicitInstantiationDecl *>
+      ExplicitInstantiationDeclsForMerging;
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ChuanqiXu9 wrote:

Why can't we merge it with the table within ASTContext?

https://github.com/llvm/llvm-project/pull/191658