[clang] [clang][Lex] add -Wnonportable-include-path-separator (PR #186770)
Rose Hudson via cfe-commits
cfe-commits at lists.llvm.org
Tue Apr 7 05:56:15 PDT 2026
https://github.com/rosefromthedead updated https://github.com/llvm/llvm-project/pull/186770
>From e2294efaabcc745bf6beacbefbd371595cf3e87f Mon Sep 17 00:00:00 2001
From: Rose Hudson <rose.hudson at sony.com>
Date: Wed, 25 Mar 2026 10:15:01 +0000
Subject: [PATCH] [clang][Lex] add -Wnonportable-include-path-separator
Emit a warning when #include paths contain backslashes, with a fixit to
convert them all to '/'. This can help users that build only on Windows
to automatically make their #includes more portable. The warning is off
by default due to being noisy and not always desirable.
---
clang/docs/ReleaseNotes.rst | 6 +++++
clang/include/clang/Basic/DiagnosticGroups.td | 3 +++
.../include/clang/Basic/DiagnosticLexKinds.td | 5 ++++-
clang/include/clang/Basic/SourceManager.h | 9 ++++++++
clang/lib/Lex/PPDirectives.cpp | 11 ++++++++++
clang/test/Lexer/backslash-include-win.c | 22 +++++++++++++++++++
6 files changed, 55 insertions(+), 1 deletion(-)
create mode 100644 clang/test/Lexer/backslash-include-win.c
diff --git a/clang/docs/ReleaseNotes.rst b/clang/docs/ReleaseNotes.rst
index 08d7ffd826b41..bb83847d240c2 100644
--- a/clang/docs/ReleaseNotes.rst
+++ b/clang/docs/ReleaseNotes.rst
@@ -360,6 +360,12 @@ Improvements to Clang's diagnostics
- Clang now emits an error when implicitly casting a complex type to a built-in vector type. (#GH186805)
+- Added ``-Wnonportable-include-path-separator`` (off by default) to catch
+ #include directives that use backslashes as a path separator. The warning
+ includes a FixIt to change all the backslashes to forward slashes, so that the
+ code can automatically be made portable to other host platforms that don't
+ support backslashes.
+
Improvements to Clang's time-trace
----------------------------------
diff --git a/clang/include/clang/Basic/DiagnosticGroups.td b/clang/include/clang/Basic/DiagnosticGroups.td
index dc7280c66ea79..cc5626b76ad5f 100644
--- a/clang/include/clang/Basic/DiagnosticGroups.td
+++ b/clang/include/clang/Basic/DiagnosticGroups.td
@@ -176,6 +176,9 @@ def NullConversion : DiagGroup<"null-conversion">;
def ImplicitConversionFloatingPointToBool :
DiagGroup<"implicit-conversion-floating-point-to-bool">;
def ObjCLiteralConversion : DiagGroup<"objc-literal-conversion">;
+def NonportableIncludePathSeparator : DiagGroup<"nonportable-include-path-separator">;
+def NonportableIncludePath : DiagGroup<"nonportable-include-path",
+ [NonportableIncludePathSeparator]>;
def MacroRedefined : DiagGroup<"macro-redefined">;
def BuiltinMacroRedefined : DiagGroup<"builtin-macro-redefined">;
def BuiltinRequiresHeader : DiagGroup<"builtin-requires-header">;
diff --git a/clang/include/clang/Basic/DiagnosticLexKinds.td b/clang/include/clang/Basic/DiagnosticLexKinds.td
index bea0aafac98cf..07afc69793499 100644
--- a/clang/include/clang/Basic/DiagnosticLexKinds.td
+++ b/clang/include/clang/Basic/DiagnosticLexKinds.td
@@ -377,9 +377,12 @@ class NonportablePath : Warning<
"non-portable path to file '%0'; specified path differs in case from file"
" name on disk">;
def pp_nonportable_path : NonportablePath,
- InGroup<DiagGroup<"nonportable-include-path">>;
+ InGroup<NonportableIncludePath>;
def pp_nonportable_system_path : NonportablePath, DefaultIgnore,
InGroup<DiagGroup<"nonportable-system-include-path">>;
+def pp_nonportable_path_separator : Warning<
+ "non-portable path to file '%0'; specified path contains backslashes">,
+ DefaultIgnore, InGroup<NonportableIncludePathSeparator>;
def pp_pragma_once_in_main_file : Warning<"#pragma once in main file">,
InGroup<DiagGroup<"pragma-once-outside-header">>;
diff --git a/clang/include/clang/Basic/SourceManager.h b/clang/include/clang/Basic/SourceManager.h
index bc9e97863556d..4217b8683da1e 100644
--- a/clang/include/clang/Basic/SourceManager.h
+++ b/clang/include/clang/Basic/SourceManager.h
@@ -1526,6 +1526,15 @@ class SourceManager : public RefCountedBase<SourceManager> {
return Filename == "<scratch space>";
}
+ /// Returns whether \p Loc is located in a <module-includes> file.
+ bool isWrittenInModuleIncludes(SourceLocation Loc) const {
+ PresumedLoc Presumed = getPresumedLoc(Loc);
+ if (Presumed.isInvalid())
+ return false;
+ StringRef Filename(Presumed.getFilename());
+ return Filename == "<module-includes>";
+ }
+
/// Returns whether \p Loc is located in a built-in or command line source.
bool isInPredefinedFile(SourceLocation Loc) const {
PresumedLoc Presumed = getPresumedLoc(Loc);
diff --git a/clang/lib/Lex/PPDirectives.cpp b/clang/lib/Lex/PPDirectives.cpp
index b90c04776ff9e..172c2fa57db00 100644
--- a/clang/lib/Lex/PPDirectives.cpp
+++ b/clang/lib/Lex/PPDirectives.cpp
@@ -2731,6 +2731,17 @@ Preprocessor::ImportAction Preprocessor::HandleHeaderIncludeOrImport(
Diag(FilenameTok, DiagId) << Path <<
FixItHint::CreateReplacement(FilenameRange, Path);
}
+
+ bool SuppressBackslashDiag =
+ FilenameLoc.isMacroID() ||
+ SourceMgr.isWrittenInBuiltinFile(FilenameLoc) ||
+ SourceMgr.isWrittenInModuleIncludes(FilenameLoc);
+ if (!SuppressBackslashDiag && OriginalFilename.contains('\\')) {
+ std::string SuggestedPath = OriginalFilename.str();
+ llvm::replace(SuggestedPath, '\\', '/');
+ Diag(FilenameTok, diag::pp_nonportable_path_separator)
+ << Name << FixItHint::CreateReplacement(FilenameRange, SuggestedPath);
+ }
}
switch (Action) {
diff --git a/clang/test/Lexer/backslash-include-win.c b/clang/test/Lexer/backslash-include-win.c
new file mode 100644
index 0000000000000..a07325550093f
--- /dev/null
+++ b/clang/test/Lexer/backslash-include-win.c
@@ -0,0 +1,22 @@
+// REQUIRES: system-windows
+// RUN: mkdir -p %t/backslash
+// RUN: cp %S/Inputs/case-insensitive-include.h %t/backslash/case-insensitive-include.h
+// RUN: %clang_cc1 -fsyntax-only -Wnonportable-include-path-separator -I%t %s 2>&1 | FileCheck --check-prefixes=CHECK-ENABLED,CHECK-ALL %s
+// RUN: %clang_cc1 -fsyntax-only -Wnonportable-include-path -Wno-nonportable-include-path-separator -I%t %s 2>&1 | FileCheck --check-prefix=CHECK-DISABLED,CHECK-ALL %s
+
+#include "backslash\case-insensitive-include.h"
+// CHECK-ENABLED: non-portable path to file
+// CHECK-ENABLED: specified path contains backslashes
+// CHECK-ENABLED: "backslash/case-insensitive-include.h"
+// CHECK-DISABLED-NOT: non-portable path to file
+
+// Despite fixing the same span, nonportable-include-path is still a separate diagnostic
+// that can fire at the same time.
+#include "backslash\CASE-insensitive-include.h"
+// CHECK-ALL: non-portable path to file
+// CHECK-ALL: specified path differs in case from file name on disk
+// CHECK-ALL: "backslash\case-insensitive-include.h"
+// CHECK-ENABLED: non-portable path to file
+// CHECK-ENABLED: specified path contains backslashes
+// CHECK-ENABLED: "backslash/CASE-insensitive-include.h"
+// CHECK-DISABLED-NOT: non-portable path to file
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