[clang] Fix main header matching for headers with special characters. (PR #211934)

[via cfe-commits]

https://github.com/dmaclach created https://github.com/llvm/llvm-project/pull/211934

In Clang Tooling, escape HeaderStem before constructing MainIncludeRegex to prevent special characters (such as '+') from being interpreted as regex operators. Useful for Objective-C where "Foo+Bar.h" headers are very common for categories.

>From 826a4c5f0e7b9d1bd06e5734128ea0a9ea789aaf Mon Sep 17 00:00:00 2001
From: Dave MacLachlan <dmaclach at gmail.com>
Date: Fri, 24 Jul 2026 14:51:11 -0700
Subject: [PATCH] Fix main header matching for headers with special characters.

In Clang Tooling, escape HeaderStem before constructing MainIncludeRegex to prevent special characters (such as '+') from being interpreted as regex operators.
Useful for Objective-C where "Foo+Bar.h" headers are very common for categories.
---
 clang/lib/Tooling/Inclusions/HeaderIncludes.cpp |  3 ++-
 clang/unittests/Tooling/HeaderIncludesTest.cpp  | 14 ++++++++++++++
 2 files changed, 16 insertions(+), 1 deletion(-)

diff --git a/clang/lib/Tooling/Inclusions/HeaderIncludes.cpp b/clang/lib/Tooling/Inclusions/HeaderIncludes.cpp
index 1212af52e1490..34f21faa8e342 100644
--- a/clang/lib/Tooling/Inclusions/HeaderIncludes.cpp
+++ b/clang/lib/Tooling/Inclusions/HeaderIncludes.cpp
@@ -340,7 +340,8 @@ bool IncludeCategoryManager::isMainHeader(StringRef IncludeName) const {
   else if (FileStem.equals_insensitive(HeaderStem))
     Matching = FileStem; // example 3)
   if (!Matching.empty()) {
-    llvm::Regex MainIncludeRegex(HeaderStem.str() + Style.IncludeIsMainRegex,
+    llvm::Regex MainIncludeRegex(llvm::Regex::escape(HeaderStem) +
+                                     Style.IncludeIsMainRegex,
                                  llvm::Regex::IgnoreCase);
     if (MainIncludeRegex.match(Matching))
       return true;
diff --git a/clang/unittests/Tooling/HeaderIncludesTest.cpp b/clang/unittests/Tooling/HeaderIncludesTest.cpp
index 95fb05885a0b9..bc2ac3a97e97d 100644
--- a/clang/unittests/Tooling/HeaderIncludesTest.cpp
+++ b/clang/unittests/Tooling/HeaderIncludesTest.cpp
@@ -144,6 +144,20 @@ TEST_F(HeaderIncludesTest, InsertAfterMainHeader) {
   EXPECT_NE(Expected, insert(Code, "<a>")) << "Not main header";
 }
 
+TEST_F(HeaderIncludesTest, InsertAfterMainHeaderWithSpecialChars) {
+  std::string Code = "#include \"fix+bar.h\"\n"
+                     "\n"
+                     "int main() {}";
+  std::string Expected = "#include \"fix+bar.h\"\n"
+                         "#include <a>\n"
+                         "\n"
+                         "int main() {}";
+  Style = format::getGoogleStyle(format::FormatStyle::LanguageKind::LK_Cpp)
+              .IncludeStyle;
+  FileName = "fix+bar.cpp";
+  EXPECT_EQ(Expected, insert(Code, "<a>"));
+}
+
 TEST_F(HeaderIncludesTest, InsertMainHeader) {
   Style = format::getGoogleStyle(format::FormatStyle::LanguageKind::LK_Cpp)
               .IncludeStyle;