[Lldb-commits] [lldb] [lldb][ObjC] Don't query objective-c runtime for decls in C++ contexts (PR #95963)

[Michael Buch via lldb-commits]

https://github.com/Michael137 created https://github.com/llvm/llvm-project/pull/95963

When LLDB isn't able to find a `clang::Decl` in response to a `FindExternalVisibleDeclsByName`, it will fall-back to looking into the Objective-C runtime for that decl. This ends up doing a lot of work which isn't necessary when we're debugging a C++ program. This patch makes the ObjC lookup conditional on the language that the ExpressionParser deduced (which can be explicitly set using the `expr --language` option or is set implicitly if we're stopped in an ObjC frame or a C++ frame without debug-info).

rdar://96236519

>From 25e64a8a622496cbde447d0d5185f0e7ef06586d Mon Sep 17 00:00:00 2001
From: Michael Buch <michaelbuch12 at gmail.com>
Date: Tue, 18 Jun 2024 18:04:03 +0100
Subject: [PATCH] [lldb][ObjC] Don't query objective-c runtime for decls in C++
 contexts

When LLDB isn't able to find a `clang::Decl` in response
to a `FindExternalVisibleDeclsByName`, it will fall-back
to looking into the Objective-C runtime for that decl. This
ends up doing a lot of work which isn't necessary when we're
debugging a C++ program. This patch makes the ObjC lookup
conditional on the language that the ExpressionParser deduced
(which can be explicitly set using the `expr --language` option
or is set implicitly if we're stopped in an ObjC frame or a
C++ frame without debug-info).

rdar://96236519
---
 .../ExpressionParser/Clang/ClangASTSource.cpp |  2 +-
 .../TestObjCFromCppFramesWithoutDebugInfo.py  |  5 +++++
 .../test/Shell/Expr/TestObjCInCXXContext.test | 21 +++++++++++++++++++
 3 files changed, 27 insertions(+), 1 deletion(-)
 create mode 100644 lldb/test/Shell/Expr/TestObjCInCXXContext.test

diff --git a/lldb/source/Plugins/ExpressionParser/Clang/ClangASTSource.cpp b/lldb/source/Plugins/ExpressionParser/Clang/ClangASTSource.cpp
index 82a7a2cc3f1ef..1fdd272dcbece 100644
--- a/lldb/source/Plugins/ExpressionParser/Clang/ClangASTSource.cpp
+++ b/lldb/source/Plugins/ExpressionParser/Clang/ClangASTSource.cpp
@@ -637,7 +637,7 @@ void ClangASTSource::FindExternalVisibleDecls(
     FindDeclInModules(context, name);
   }
 
-  if (!context.m_found_type) {
+  if (!context.m_found_type && m_ast_context->getLangOpts().ObjC) {
     FindDeclInObjCRuntime(context, name);
   }
 }
diff --git a/lldb/test/API/lang/objcxx/objc-from-cpp-frames-without-debuginfo/TestObjCFromCppFramesWithoutDebugInfo.py b/lldb/test/API/lang/objcxx/objc-from-cpp-frames-without-debuginfo/TestObjCFromCppFramesWithoutDebugInfo.py
index ef8d5540fa4ef..2c2e072bba686 100644
--- a/lldb/test/API/lang/objcxx/objc-from-cpp-frames-without-debuginfo/TestObjCFromCppFramesWithoutDebugInfo.py
+++ b/lldb/test/API/lang/objcxx/objc-from-cpp-frames-without-debuginfo/TestObjCFromCppFramesWithoutDebugInfo.py
@@ -15,4 +15,9 @@ def test(self):
         (_, process, _, _) = lldbutil.run_to_name_breakpoint(self, "main")
 
         self.assertState(process.GetState(), lldb.eStateStopped)
+
+        # Tests that we can use builtin Objective-C identifiers.
         self.expect("expr id", error=False)
+
+        # Tests that we can lookup Objective-C decls in the ObjC runtime plugin.
+        self.expect_expr("NSString *c; c == nullptr", result_value="true", result_type="bool")
diff --git a/lldb/test/Shell/Expr/TestObjCInCXXContext.test b/lldb/test/Shell/Expr/TestObjCInCXXContext.test
new file mode 100644
index 0000000000000..8537799bdeb67
--- /dev/null
+++ b/lldb/test/Shell/Expr/TestObjCInCXXContext.test
@@ -0,0 +1,21 @@
+// UNSUPPORTED: system-linux, system-windows
+
+// Tests that we don't consult the the Objective-C runtime
+// plugin when in a purely C++ context.
+//
+// RUN: %clangxx_host %p/Inputs/objc-cast.cpp -g -o %t
+// RUN: %lldb %t \
+// RUN:   -o "b main" -o run \
+// RUN:   -o "expression --language objective-c -- NSString * a; a" \
+// RUN:   -o "expression --language objective-c++ -- NSString * b; b" \
+// RUN:   -o "expression NSString" \
+// RUN:   2>&1 | FileCheck %s
+
+// CHECK:      (lldb) expression --language objective-c -- NSString * a; a
+// CHECK-NEXT: (NSString *){{.*}}= nil
+
+// CHECK:      (lldb) expression --language objective-c++ -- NSString * b; b
+// CHECK-NEXT: (NSString *){{.*}}= nil
+
+// CHECK:      (lldb) expression NSString
+// CHECK-NEXT: error:{{.*}} use of undeclared identifier 'NSString'