[clang-format] Skip line splices when sorting C++ includes

Fixes #109864.

Author: owenca

clang/lib/Format/Format.cpp

@@ -3247,7 +3247,14 @@ tooling::Replacements sortCppIncludes(const FormatStyle &Style, StringRef Code,
   std::string RawStringTermination = ")\"";
 
   for (;;) {
-    auto Pos = Code.find('\n', SearchFrom);
+    size_t Pos = SearchFrom;
+    if (Code[SearchFrom] != '\n') {
+      do { // Search for the first newline while skipping line splices.
+        ++Pos;
+        Pos = Code.find('\n', Pos);
+      } while (Pos != StringRef::npos && Code[Pos - 1] == '\\');
+    }
+
     StringRef Line =
         Code.substr(Prev, (Pos != StringRef::npos ? Pos : Code.size()) - Prev);
 

clang/unittests/Format/SortIncludesTest.cpp

@@ -984,6 +984,18 @@ TEST_F(SortIncludesTest, SortAndDeduplicateIncludes) {
                     "#include <c>\n"
                     "#include <b>"));
 
+  verifyFormat("/* COPYRIGHT *\\\n"
+               "\\* (C) 2024  */\n"
+               "\n"
+               "#include <a>\n"
+               "#include <b>",
+               sort("/* COPYRIGHT *\\\n"
+                    "\\* (C) 2024  */\n"
+                    "\n"
+                    "#include <b>\n"
+                    "#include <a>\n"
+                    "#include <b>"));
+
   Style.IncludeBlocks = tooling::IncludeStyle::IBS_Merge;
   verifyFormat("#include <a>\n"
                "#include <b>\n"