[Clang] Fix crash when building a module with CC_PRINT_HEADERS_FORMAT=json

[bob-wilson]

There is no main file when building a module, so the code in HeaderIncludesJSONCallback::EndOfMainFile() needs to check for that to avoid crashing.

[llvmbot]

@llvm/pr-subscribers-clang

Author: Bob Wilson (bob-wilson)

Changes

There is no main file when building a module, so the code in HeaderIncludesJSONCallback::EndOfMainFile() needs to check for that to avoid crashing.

---

Full diff: https://github.com/llvm/llvm-project/pull/136227.diff

2 Files Affected:

• (modified) clang/lib/Frontend/HeaderIncludeGen.cpp (+5-2)
• (added) clang/test/Preprocessor/print-header-crash.modulemap (+2)

diff --git a/clang/lib/Frontend/HeaderIncludeGen.cpp b/clang/lib/Frontend/HeaderIncludeGen.cpp
index 992c2670260e5..792526083b1e6 100644
--- a/clang/lib/Frontend/HeaderIncludeGen.cpp
+++ b/clang/lib/Frontend/HeaderIncludeGen.cpp
@@ -260,8 +260,11 @@ void HeaderIncludesCallback::FileSkipped(const FileEntryRef &SkippedFile, const
 
 void HeaderIncludesJSONCallback::EndOfMainFile() {
   OptionalFileEntryRef FE = SM.getFileEntryRefForID(SM.getMainFileID());
-  SmallString<256> MainFile(FE->getName());
-  SM.getFileManager().makeAbsolutePath(MainFile);
+  SmallString<256> MainFile;
+  if (FE) {
+    MainFile += FE->getName();
+    SM.getFileManager().makeAbsolutePath(MainFile);
+  }
 
   std::string Str;
   llvm::raw_string_ostream OS(Str);
diff --git a/clang/test/Preprocessor/print-header-crash.modulemap b/clang/test/Preprocessor/print-header-crash.modulemap
new file mode 100644
index 0000000000000..5919c70780a95
--- /dev/null
+++ b/clang/test/Preprocessor/print-header-crash.modulemap
@@ -0,0 +1,2 @@
+// RUN: %clang_cc1 -header-include-format=json -header-include-filtering=only-direct-system -header-include-file %t.txt -emit-module -x c -fmodules -fmodule-name=X %s -o /dev/null
+module X {}

[jansvoboda11]

Since this is trying to make CC_PRINT_HEADERS_FORMAT work for modules, I have to ask: should it report module map files too?

[bob-wilson]

I'm still investigating what to do for modules. It's not yet clear if that should be handled along with CC_PRINT_HEADERS_FORMAT=json or some new option. I figured it would be good to start by fixing the crashes.

[jansvoboda11]

Ok, LGTM as a targeted fix.