[clang-tidy] Fix llvm-header-guard so that it works with Windows paths

Fixes pr40372 (https://bugs.llvm.org/show_bug.cgi?id=40372).

The llvm-header-guard check does not take into account that the path
separator on Windows is `\`, not `/`.

This means that instead of suggesting a header guard in the form of:
LLVM_CLANG_TOOLS_EXTRA_CLANG_TIDY_FOO_H

it incorrectly suggests:
C:\LLVM_PROJECT\CLANG_TOOLS_EXTRA\CLANG_TIDY\FOO_H

Differential Revision: https://reviews.llvm.org/D113450

1 files changed, 5 insertions, 0 deletions

diff --git a/clang-tools-extra/clang-tidy/llvm/HeaderGuardCheck.cpp b/clang-tools-extra/clang-tidy/llvm/HeaderGuardCheck.cpp
index 8f8bd7a..53c1e3c 100644
--- a/clang-tools-extra/clang-tidy/llvm/HeaderGuardCheck.cpp
+++ b/clang-tools-extra/clang-tidy/llvm/HeaderGuardCheck.cpp
@@ -8,6 +8,7 @@
 
 #include "HeaderGuardCheck.h"
 #include "clang/Tooling/Tooling.h"
+#include "llvm/Support/Path.h"
 
 namespace clang {
 namespace tidy {
@@ -21,6 +22,10 @@ std::string LLVMHeaderGuardCheck::getHeaderGuard(StringRef Filename,
                                                  StringRef OldGuard) {
   std::string Guard = tooling::getAbsolutePath(Filename);
 
+  // When running under Windows, need to convert the path separators from
+  // `\` to `/`.
+  Guard = llvm::sys::path::convert_to_slash(Guard);
+
   // Sanitize the path. There are some rules for compatibility with the historic
   // style in include/llvm and include/clang which we want to preserve.