[clang] Insert headers in global module fragment (PR #151624)

[Mythreya Kuricheti via cfe-commits]

https://github.com/MythreyaK updated https://github.com/llvm/llvm-project/pull/151624

>From b4c0f290cf9b74813c015afc1167d016b78049cf Mon Sep 17 00:00:00 2001
From: Mythreya Kuricheti <git at mythreya.dev>
Date: Fri, 1 Aug 2025 01:19:18 -0700
Subject: [PATCH] [libtooling] Insert headers in global module fragment

---
 .../lib/Tooling/Inclusions/HeaderIncludes.cpp | 22 ++++-
 .../unittests/Tooling/HeaderIncludesTest.cpp  | 81 +++++++++++++++++++
 2 files changed, 102 insertions(+), 1 deletion(-)

diff --git a/clang/lib/Tooling/Inclusions/HeaderIncludes.cpp b/clang/lib/Tooling/Inclusions/HeaderIncludes.cpp
index 2b5a293b35841..2ad0c8b1ff135 100644
--- a/clang/lib/Tooling/Inclusions/HeaderIncludes.cpp
+++ b/clang/lib/Tooling/Inclusions/HeaderIncludes.cpp
@@ -74,6 +74,15 @@ void skipComments(Lexer &Lex, Token &Tok) {
       return;
 }
 
+bool checkAndConsumeModuleDecl(const SourceManager &SM, Lexer &Lex,
+                               Token &Tok) {
+  bool Matched = Tok.is(tok::raw_identifier) &&
+                 Tok.getRawIdentifier() == "module" &&
+                 !Lex.LexFromRawLexer(Tok) && Tok.is(tok::semi) &&
+                 !Lex.LexFromRawLexer(Tok);
+  return Matched;
+}
+
 // Returns the offset after header guard directives and any comments
 // before/after header guards (e.g. #ifndef/#define pair, #pragma once). If no
 // header guard is present in the code, this will return the offset after
@@ -95,7 +104,17 @@ unsigned getOffsetAfterHeaderGuardsAndComments(StringRef FileName,
               return std::max(InitialOffset, Consume(SM, Lex, Tok));
             });
       };
-  return std::max(
+
+  auto ModuleDecl = ConsumeHeaderGuardAndComment(
+      [](const SourceManager &SM, Lexer &Lex, Token Tok) -> unsigned {
+        if (checkAndConsumeModuleDecl(SM, Lex, Tok)) {
+          skipComments(Lex, Tok);
+          return SM.getFileOffset(Tok.getLocation());
+        }
+        return 0;
+      });
+
+  auto HeaderAndPPOffset = std::max(
       // #ifndef/#define
       ConsumeHeaderGuardAndComment(
           [](const SourceManager &SM, Lexer &Lex, Token Tok) -> unsigned {
@@ -115,6 +134,7 @@ unsigned getOffsetAfterHeaderGuardsAndComments(StringRef FileName,
               return SM.getFileOffset(Tok.getLocation());
             return 0;
           }));
+  return std::max(HeaderAndPPOffset, ModuleDecl);
 }
 
 // Check if a sequence of tokens is like
diff --git a/clang/unittests/Tooling/HeaderIncludesTest.cpp b/clang/unittests/Tooling/HeaderIncludesTest.cpp
index 929156a11d0d9..9308513225d9a 100644
--- a/clang/unittests/Tooling/HeaderIncludesTest.cpp
+++ b/clang/unittests/Tooling/HeaderIncludesTest.cpp
@@ -594,6 +594,87 @@ TEST_F(HeaderIncludesTest, CanDeleteAfterCode) {
   EXPECT_EQ(Expected, remove(Code, "\"b.h\""));
 }
 
+TEST_F(HeaderIncludesTest, InsertInGlobalModuleFragment) {
+  // Ensure header insertions go only in the global module fragment
+  std::string Code = R"cpp(// comments
+
+// more comments
+
+module;
+export module foo;
+
+int main() {
+    std::vector<int> ints {};
+})cpp";
+  std::string Expected = R"cpp(// comments
+
+// more comments
+
+module;
+#include <vector>
+export module foo;
+
+int main() {
+    std::vector<int> ints {};
+})cpp";
+
+  auto InsertedCode = insert(Code, "<vector>");
+  EXPECT_EQ(Expected, insert(Code, "<vector>"));
+}
+
+TEST_F(HeaderIncludesTest, InsertInGlobalModuleFragmentWithPP) {
+  // Ensure header insertions go only in the global module fragment
+  std::string Code = R"cpp(// comments
+
+// more comments
+
+// some more comments
+
+module;
+
+#ifndef MACRO_NAME
+#define MACRO_NAME
+#endif
+
+// comment
+
+#ifndef MACRO_NAME
+#define MACRO_NAME
+#endif
+
+// more comment
+
+int main() {
+    std::vector<int> ints {};
+})cpp";
+  std::string Expected = R"cpp(// comments
+
+// more comments
+
+// some more comments
+
+module;
+
+#include <vector>
+#ifndef MACRO_NAME
+#define MACRO_NAME
+#endif
+
+// comment
+
+#ifndef MACRO_NAME
+#define MACRO_NAME
+#endif
+
+// more comment
+
+int main() {
+    std::vector<int> ints {};
+})cpp";
+
+  EXPECT_EQ(Expected, insert(Code, "<vector>"));
+}
+
 } // namespace
 } // namespace tooling
 } // namespace clang