[clang] [clang] Improve diagnostics for invalid named-universal-characters (PR #206326)

Wed Jul 1 04:34:11 PDT 2026

llvm-ci wrote:

LLVM Buildbot has detected a new failure on builder `llvm-clang-x86_64-win-fast` running on `as-builder-3` while building `clang` at step 8 "test-build-unified-tree-check-clang-unit".

Full details are available at: https://lab.llvm.org/buildbot/#/builders/2/builds/55137

<details>
<summary>Here is the relevant piece of the build log for the reference</summary>

```
Step 8 (test-build-unified-tree-check-clang-unit) failure: test (failure)
...
[336/440] Building CXX object tools\clang\unittests\ScalableStaticAnalysis\CMakeFiles\ClangScalableAnalysisTests.dir\ErrorBuilderTest.cpp.obj
[337/440] Building CXX object tools\clang\unittests\CMakeFiles\AllClangUnitTests.dir\Frontend\FrontendActionTest.cpp.obj
[338/440] Building CXX object tools\clang\unittests\CMakeFiles\AllClangUnitTests.dir\Frontend\SearchPathTest.cpp.obj
[339/440] Building CXX object tools\clang\unittests\ScalableStaticAnalysis\CMakeFiles\ClangScalableAnalysisTests.dir\Registries\FancyAnalysisData.cpp.obj
[340/440] Building CXX object tools\clang\unittests\ScalableStaticAnalysis\CMakeFiles\ClangScalableAnalysisTests.dir\Serialization\JSONFormatTest\LUSummaryTest.cpp.obj
[341/440] Building CXX object tools\clang\unittests\ScalableStaticAnalysis\CMakeFiles\ClangScalableAnalysisTests.dir\SourceTransformation\EmitterTest.cpp.obj
[342/440] Building CXX object tools\clang\unittests\ScalableStaticAnalysis\CMakeFiles\ClangScalableAnalysisTests.dir\Registries\MockSerializationFormat.cpp.obj
[343/440] Building CXX object tools\clang\unittests\CMakeFiles\AllClangUnitTests.dir\Tooling\RecursiveASTVisitorTests\CallbacksUnaryOperator.cpp.obj
[344/440] Building CXX object tools\clang\unittests\ScalableStaticAnalysis\CMakeFiles\ClangScalableAnalysisTests.dir\Registries\SerializationFormatRegistryTest.cpp.obj
[345/440] Building CXX object tools\clang\unittests\Basic\CMakeFiles\BasicTests.dir\DiagnosticTest.cpp.obj
FAILED: tools/clang/unittests/Basic/CMakeFiles/BasicTests.dir/DiagnosticTest.cpp.obj 
C:\ninja\ccache.exe C:\PROGRA~1\MICROS~2\2022\COMMUN~1\VC\Tools\MSVC\1444~1.352\bin\Hostx64\x64\cl.exe  /nologo /TP -DCLANG_BUILD_STATIC -DLLVM_BUILD_STATIC -DUNICODE -D_CRT_NONSTDC_NO_DEPRECATE -D_CRT_NONSTDC_NO_WARNINGS -D_CRT_SECURE_NO_DEPRECATE -D_CRT_SECURE_NO_WARNINGS -D_HAS_EXCEPTIONS=0 -D_SCL_SECURE_NO_DEPRECATE -D_SCL_SECURE_NO_WARNINGS -D_UNICODE -D__STDC_CONSTANT_MACROS -D__STDC_FORMAT_MACROS -D__STDC_LIMIT_MACROS -IC:\buildbot\as-builder-3\llvm-clang-x86_64-win-fast\build\tools\clang\unittests\Basic -IC:\buildbot\as-builder-3\llvm-clang-x86_64-win-fast\llvm-project\clang\unittests\Basic -IC:\buildbot\as-builder-3\llvm-clang-x86_64-win-fast\llvm-project\clang\include -IC:\buildbot\as-builder-3\llvm-clang-x86_64-win-fast\build\tools\clang\include -IC:\buildbot\as-builder-3\llvm-clang-x86_64-win-fast\build\include -IC:\buildbot\as-builder-3\llvm-clang-x86_64-win-fast\llvm-project\llvm\include -IC:\buildbot\as-builder-3\llvm-clang-x86_64-win-fast\llvm-project\third-party\unittest\googletest\include -IC:\buildbot\as-builder-3\llvm-clang-x86_64-win-fast\llvm-project\third-party\unittest\googlemock\include /DWIN32 /D_WINDOWS   /Zc:inline /Zc:preprocessor /Zc:__cplusplus /Oi /bigobj /permissive- /W4 -wd4146 -wd4244 -wd4267 -wd4456 -wd4457 -wd4458 -wd4459 -wd4624 -wd4100 -wd4127 -wd4505 -wd4702 -wd4245 -wd4310 -wd4701 -wd4703 -wd4389 -wd4805 -wd4577 -wd4319 -wd4324 -wd4251 -wd4275 -w14062 -we4238 /Gw /O2 /Ob2 /DNDEBUG -MD /EHs-c- /GR- -std:c++17 /showIncludes /Fotools\clang\unittests\Basic\CMakeFiles\BasicTests.dir\DiagnosticTest.cpp.obj /Fdtools\clang\unittests\Basic\CMakeFiles\BasicTests.dir\ /FS -c C:\buildbot\as-builder-3\llvm-clang-x86_64-win-fast\llvm-project\clang\unittests\Basic\DiagnosticTest.cpp
C:\buildbot\as-builder-3\llvm-clang-x86_64-win-fast\llvm-project\clang\unittests\Basic\DiagnosticTest.cpp(454): error C2015: too many characters in constant
[346/440] Building CXX object tools\clang\unittests\ScalableStaticAnalysis\CMakeFiles\ClangScalableAnalysisTests.dir\Serialization\JSONFormatTest\JSONFormatTest.cpp.obj
[347/440] Building CXX object tools\clang\unittests\ScalableStaticAnalysis\CMakeFiles\ClangScalableAnalysisTests.dir\SourceTransformation\RegistryTest.cpp.obj
[348/440] Building CXX object tools\clang\unittests\ScalableStaticAnalysis\CMakeFiles\ClangScalableAnalysisTests.dir\Serialization\JSONFormatTest\TUSummaryTest.cpp.obj
[349/440] Building CXX object tools\clang\unittests\ScalableStaticAnalysis\CMakeFiles\ClangScalableAnalysisTests.dir\SummaryNameTest.cpp.obj
[350/440] Building CXX object tools\clang\unittests\CMakeFiles\AllClangUnitTests.dir\Tooling\RecursiveASTVisitorTests\Attr.cpp.obj
[351/440] Building CXX object tools\clang\unittests\CMakeFiles\AllClangUnitTests.dir\Tooling\Syntax\MutationsTest.cpp.obj
[352/440] Building CXX object tools\clang\unittests\CMakeFiles\AllClangUnitTests.dir\Tooling\RefactoringCallbacksTest.cpp.obj
[353/440] Building CXX object tools\clang\unittests\CMakeFiles\AllClangUnitTests.dir\Frontend\PCHPreambleTest.cpp.obj
[354/440] Building CXX object tools\clang\unittests\CMakeFiles\AllClangUnitTests.dir\Tooling\RecursiveASTVisitorTests\InitListExprPostOrder.cpp.obj
[355/440] Building CXX object tools\clang\unittests\CMakeFiles\AllClangUnitTests.dir\Tooling\ToolingTest.cpp.obj
[356/440] Building CXX object tools\clang\unittests\CMakeFiles\AllClangUnitTests.dir\Tooling\ReplacementsYamlTest.cpp.obj
[357/440] Building CXX object tools\clang\unittests\Basic\CMakeFiles\BasicTests.dir\LineOffsetMappingTest.cpp.obj
[358/440] Building CXX object tools\clang\unittests\Format\CMakeFiles\FormatTests.dir\FormatReplacementTest.cpp.obj
[359/440] Building CXX object tools\clang\unittests\CMakeFiles\AllClangUnitTests.dir\Frontend\UtilsTest.cpp.obj
[360/440] Building CXX object tools\clang\unittests\CMakeFiles\AllClangUnitTests.dir\Tooling\RefactoringTest.cpp.obj
[361/440] Building CXX object tools\clang\unittests\Format\CMakeFiles\FormatTests.dir\CleanupTest.cpp.obj
[362/440] Building CXX object tools\clang\unittests\CMakeFiles\AllClangUnitTests.dir\CodeGen\TBAAMetadataTest.cpp.obj
[363/440] Building CXX object tools\clang\unittests\CMakeFiles\AllClangUnitTests.dir\Frontend\CompilerInvocationTest.cpp.obj
[364/440] Building CXX object tools\clang\unittests\Format\CMakeFiles\FormatTests.dir\MacroExpanderTest.cpp.obj
[365/440] Building CXX object tools\clang\unittests\CMakeFiles\AllClangUnitTests.dir\Tooling\SourceCodeTest.cpp.obj
[366/440] Building CXX object tools\clang\unittests\CMakeFiles\AllClangUnitTests.dir\Frontend\ReparseWorkingDirTest.cpp.obj
[367/440] Building CXX object tools\clang\unittests\Format\CMakeFiles\FormatTests.dir\MacroCallReconstructorTest.cpp.obj
[368/440] Building CXX object tools\clang\unittests\Format\CMakeFiles\FormatTests.dir\ObjCPropertyAttributeOrderFixerTest.cpp.obj
[369/440] Building CXX object tools\clang\unittests\Format\CMakeFiles\FormatTests.dir\FormatTokenSourceTest.cpp.obj
[370/440] Building CXX object tools\clang\unittests\CMakeFiles\AllClangUnitTests.dir\Rewrite\RewriterTest.cpp.obj
[371/440] Building CXX object tools\clang\unittests\Basic\CMakeFiles\BasicTests.dir\SourceManagerTest.cpp.obj
[372/440] Building CXX object tools\clang\unittests\Basic\CMakeFiles\BasicTests.dir\SarifTest.cpp.obj
[373/440] Building CXX object tools\clang\unittests\ScalableStaticAnalysis\CMakeFiles\ClangScalableAnalysisTests.dir\Analyses\PointerFlow\PointerFlowWPATest.cpp.obj
[374/440] Building CXX object tools\clang\unittests\CMakeFiles\AllClangUnitTests.dir\Tooling\Syntax\BuildTreeTest.cpp.obj
[375/440] Building CXX object tools\clang\unittests\CMakeFiles\AllClangUnitTests.dir\Tooling\RecursiveASTVisitorTests\CallbacksLeaf.cpp.obj
[376/440] Building CXX object tools\clang\unittests\CMakeFiles\AllClangUnitTests.dir\Frontend\CodeGenActionTest.cpp.obj
[377/440] Building CXX object tools\clang\unittests\ScalableStaticAnalysis\CMakeFiles\ClangScalableAnalysisTests.dir\Registries\MockSummaryExtractor1.cpp.obj
[378/440] Building CXX object tools\clang\unittests\Format\CMakeFiles\FormatTests.dir\FormatTestRawStrings.cpp.obj
[379/440] Building CXX object tools\clang\unittests\CMakeFiles\AllClangUnitTests.dir\Tooling\StencilTest.cpp.obj
[380/440] Building CXX object tools\clang\unittests\ScalableStaticAnalysis\CMakeFiles\ClangScalableAnalysisTests.dir\Analyses\UnsafeBufferUsage\UnsafeBufferUsageWPATest.cpp.obj
[381/440] Building CXX object tools\clang\unittests\CMakeFiles\AllClangUnitTests.dir\CodeGen\BufferSourceTest.cpp.obj

```

</details>

https://github.com/llvm/llvm-project/pull/206326