Merge pull request #9454 from swiftlang/lldb/warn-on-mapimported-conflict-to-20240723

[lldb][ClangASTImporter][NFC] Emit a log message when we break MapImported invariant

Author: Michael137

lldb/source/Plugins/ExpressionParser/Clang/ClangASTImporter.cpp

@@ -1230,6 +1230,30 @@ ClangASTImporter::ASTImporterDelegate::ImportImpl(Decl *From) {
 
 void ClangASTImporter::ASTImporterDelegate::ImportDefinitionTo(
     clang::Decl *to, clang::Decl *from) {
+  Log *log = GetLog(LLDBLog::Expressions);
+
+  auto getDeclName = [](Decl const *decl) {
+    std::string name_string;
+    if (auto const *from_named_decl = dyn_cast<clang::NamedDecl>(decl)) {
+      llvm::raw_string_ostream name_stream(name_string);
+      from_named_decl->printName(name_stream);
+      name_stream.flush();
+    }
+
+    return name_string;
+  };
+
+  if (log) {
+    if (auto *D = GetAlreadyImportedOrNull(from); D && D != to) {
+      LLDB_LOG(
+          log,
+          "[ClangASTImporter] ERROR: overwriting an already imported decl "
+          "'{0:x}' ('{1}') from '{2:x}' with '{3:x}'. Likely due to a name "
+          "conflict when importing '{1}'.",
+          D, getDeclName(from), from, to);
+    }
+  }
+
   // We might have a forward declaration from a shared library that we
   // gave external lexical storage so that Clang asks us about the full
   // definition when it needs it. In this case the ASTImporter isn't aware
@@ -1239,8 +1263,6 @@ void ClangASTImporter::ASTImporterDelegate::ImportDefinitionTo(
   // tell the ASTImporter that 'to' was imported from 'from'.
   MapImported(from, to);
 
-  Log *log = GetLog(LLDBLog::Expressions);
-
   if (llvm::Error err = ImportDefinition(from)) {
     LLDB_LOG_ERROR(log, std::move(err),
                    "[ClangASTImporter] Error during importing definition: {0}");
@@ -1252,19 +1274,13 @@ void ClangASTImporter::ASTImporterDelegate::ImportDefinitionTo(
       to_tag->setCompleteDefinition(from_tag->isCompleteDefinition());
 
       if (Log *log_ast = GetLog(LLDBLog::AST)) {
-        std::string name_string;
-        if (NamedDecl *from_named_decl = dyn_cast<clang::NamedDecl>(from)) {
-          llvm::raw_string_ostream name_stream(name_string);
-          from_named_decl->printName(name_stream);
-          name_stream.flush();
-        }
         LLDB_LOG(log_ast,
                  "==== [ClangASTImporter][TUDecl: {0:x}] Imported "
                  "({1}Decl*){2:x}, named {3} (from "
                  "(Decl*){4:x})",
                  static_cast<void *>(to->getTranslationUnitDecl()),
-                 from->getDeclKindName(), static_cast<void *>(to), name_string,
-                 static_cast<void *>(from));
+                 from->getDeclKindName(), static_cast<void *>(to),
+                 getDeclName(from), static_cast<void *>(from));
 
         // Log the AST of the TU.
         std::string ast_string;