[clang] [lldb] [clang] Honor ShowLevel for diagnostics without a source location (PR #203520)

[Yao Qi via cfe-commits]

https://github.com/qiyao updated https://github.com/llvm/llvm-project/pull/203520

>From 7bf6b93489cf436055479c1dd8818dff293e4571 Mon Sep 17 00:00:00 2001
From: Yao Qi <yao_qi at apple.com>
Date: Fri, 5 Jun 2026 14:59:19 +0100
Subject: [PATCH 1/2] [clang] Honor ShowLevel for diagnostics without a source
 location

When lldb evaluates expression and gets error, it prints double
`error: ` as below,
```
(lldb) expression v1::withImplicitTag(Simple{.mem = 6})

note: Ran expression as 'C++11'.
error: error: Multiple internal symbols found for 'v1'
```

The first `error:` is from lldb and the second `error:` is from
clang's diagnostic.  LLDB's `ClangDiagnosticManagerAdapter` sets
`ShowLevel=false`, so that its own rendering
layer (`RenderDiagnosticDetails`) can add the severity prefix with
color.  However, clang still adds "error:" in the output buffer means
the guard is missing.

`TextDiagnosticPrinter::HandleDiagnostic` has two paths: one for
diagnostics with a valid source location (delegating to
`TextDiagnostic::emitDiagnostic`) and a simpler path for diagnostics
without one. The with-location path already guarded `printDiagnosticLevel`
behind `DiagOpts.ShowLevel`; the no-location path called it unconditionally.

Add a parameterized unit test covering `ShowLevel=true` and `ShowLevel=false`
for no-location diagnostics to prevent regression.
---
 clang/lib/Frontend/TextDiagnosticPrinter.cpp  |  3 ++-
 .../unittests/Frontend/TextDiagnosticTest.cpp | 26 +++++++++++++++++++
 .../diagnostics/TestExprDiagnostics.py        |  2 +-
 .../Shell/Expr/TestObjCxxEnumConflict.test    |  4 +--
 4 files changed, 31 insertions(+), 4 deletions(-)

diff --git a/clang/lib/Frontend/TextDiagnosticPrinter.cpp b/clang/lib/Frontend/TextDiagnosticPrinter.cpp
index 83fd70e5f99f9..475f11e36977c 100644
--- a/clang/lib/Frontend/TextDiagnosticPrinter.cpp
+++ b/clang/lib/Frontend/TextDiagnosticPrinter.cpp
@@ -133,7 +133,8 @@ void TextDiagnosticPrinter::HandleDiagnostic(DiagnosticsEngine::Level Level,
   // diagnostics in a context that lacks language options, a source manager, or
   // other infrastructure necessary when emitting more rich diagnostics.
   if (!Info.getLocation().isValid()) {
-    TextDiagnostic::printDiagnosticLevel(OS, Level, DiagOpts.ShowColors);
+    if (DiagOpts.ShowLevel)
+      TextDiagnostic::printDiagnosticLevel(OS, Level, DiagOpts.ShowColors);
     TextDiagnostic::printDiagnosticMessage(
         OS, /*IsSupplemental=*/Level == DiagnosticsEngine::Note,
         DiagMessageStream.str(), OS.tell() - StartOfLocationInfo,
diff --git a/clang/unittests/Frontend/TextDiagnosticTest.cpp b/clang/unittests/Frontend/TextDiagnosticTest.cpp
index 622dbc5883067..20ab54379c7a4 100644
--- a/clang/unittests/Frontend/TextDiagnosticTest.cpp
+++ b/clang/unittests/Frontend/TextDiagnosticTest.cpp
@@ -10,6 +10,7 @@
 #include "clang/Basic/FileManager.h"
 #include "clang/Basic/LangOptions.h"
 #include "clang/Basic/SourceManager.h"
+#include "clang/Frontend/TextDiagnosticPrinter.h"
 #include "llvm/Support/SmallVectorMemoryBuffer.h"
 #include "gtest/gtest.h"
 
@@ -95,4 +96,29 @@ TEST(TextDiagnostic, ShowLine) {
   EXPECT_EQ("main.cpp:1: warning: message\n", PrintDiag(DiagOpts, Loc));
 }
 
+// Parameterized fixture for ShowLevel tests: bool param = ShowLevel value.
+struct ShowLevelNoLocationTest : public ::testing::TestWithParam<bool> {};
+
+TEST_P(ShowLevelNoLocationTest, LevelPrefixRespected) {
+  bool ShowLevel = GetParam();
+  DiagnosticOptions DiagOpts;
+  DiagOpts.ShowLevel = ShowLevel;
+  std::string Output;
+  llvm::raw_string_ostream OS(Output);
+  TextDiagnosticPrinter Printer(OS, DiagOpts);
+  DiagnosticsEngine Diags(DiagnosticIDs::create(), DiagOpts, &Printer,
+                          /*ShouldOwnClient=*/false);
+  // Report without a SourceLocation, exercises the no-location path in
+  // TextDiagnosticPrinter::HandleDiagnostic.
+  unsigned ID = Diags.getCustomDiagID(DiagnosticsEngine::Error, "%0");
+  Diags.Report(ID) << "message";
+  if (ShowLevel)
+    EXPECT_EQ(Output, "error: message\n");
+  else
+    EXPECT_EQ(Output, "message\n");
+}
+
+INSTANTIATE_TEST_SUITE_P(ShowLevelNoLocation, ShowLevelNoLocationTest,
+                         ::testing::Bool());
+
 } // anonymous namespace
diff --git a/lldb/test/API/commands/expression/diagnostics/TestExprDiagnostics.py b/lldb/test/API/commands/expression/diagnostics/TestExprDiagnostics.py
index 1f87a6918bb21..03851924aba45 100644
--- a/lldb/test/API/commands/expression/diagnostics/TestExprDiagnostics.py
+++ b/lldb/test/API/commands/expression/diagnostics/TestExprDiagnostics.py
@@ -140,7 +140,7 @@ def test_source_and_caret_printing(self):
             """
     1 | foo(1, 2)
       | ^~~
-note: candidate function not viable: requires single argument 'x', but 2 arguments were provided
+candidate function not viable: requires single argument 'x', but 2 arguments were provided
 """,
             value.GetError().GetCString(),
         )
diff --git a/lldb/test/Shell/Expr/TestObjCxxEnumConflict.test b/lldb/test/Shell/Expr/TestObjCxxEnumConflict.test
index cf1f2c67e3880..2cbe13280a6b6 100644
--- a/lldb/test/Shell/Expr/TestObjCxxEnumConflict.test
+++ b/lldb/test/Shell/Expr/TestObjCxxEnumConflict.test
@@ -50,5 +50,5 @@ expression -l objective-c -- (MyInt)5
 
 # CHECK: error: reference to 'MyInt' is ambiguous 
 # CHECK: error: reference to 'MyInt' is ambiguous 
-# CHECK: note: note: candidate found by name lookup is 'MyInt' 
-# CHECK: note: note: candidate found by name lookup is 'MyInt' 
+# CHECK: note: candidate found by name lookup is 'MyInt'
+# CHECK: note: candidate found by name lookup is 'MyInt'

>From 204bcb8fa84e7cca743b205876ea8a714d650abd Mon Sep 17 00:00:00 2001
From: Yao Qi <qiyaoltc at gmail.com>
Date: Fri, 12 Jun 2026 16:54:16 +0100
Subject: [PATCH 2/2] Update clang/unittests/Frontend/TextDiagnosticTest.cpp

Co-authored-by: Michael Buch <michaelbuch12 at gmail.com>
---
 clang/unittests/Frontend/TextDiagnosticTest.cpp | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/clang/unittests/Frontend/TextDiagnosticTest.cpp b/clang/unittests/Frontend/TextDiagnosticTest.cpp
index 20ab54379c7a4..d99d3aef4caa2 100644
--- a/clang/unittests/Frontend/TextDiagnosticTest.cpp
+++ b/clang/unittests/Frontend/TextDiagnosticTest.cpp
@@ -96,8 +96,7 @@ TEST(TextDiagnostic, ShowLine) {
   EXPECT_EQ("main.cpp:1: warning: message\n", PrintDiag(DiagOpts, Loc));
 }
 
-// Parameterized fixture for ShowLevel tests: bool param = ShowLevel value.
-struct ShowLevelNoLocationTest : public ::testing::TestWithParam<bool> {};
+struct ShowLevelNoLocationTest : public ::testing::TestWithParam<bool /* ShowLevel */> {};
 
 TEST_P(ShowLevelNoLocationTest, LevelPrefixRespected) {
   bool ShowLevel = GetParam();