[PATCH] D51568: [modules] Add `-fno-absolute-module-directory` flag for relocatable modules

[Richard Smith - zygoloid via Phabricator via cfe-commits]

rsmith added a comment.

I don't think we need to change the serialization format for this: a serialized path beginning with / is already treated as absolute and any other path is already treated as relative, so we don't need a flag to carry that information.

I'm also not convinced we need to put this behind a flag. It would seem reasonable to me to simply always emit the `MODULE_DIRECTORY` as relative (if we found the module via a relative path), at least for an explicitly-built module. (For an implicitly built module, we probably need to track the absolute path so we can detect whether we found the right PCM file.)



================
Comment at: lib/Serialization/ASTWriter.cpp:4524-4546
+bool ASTWriter::PreparePathForOutput(SmallVectorImpl<char> &Path,
+                                     bool &IsRelativeModuleDirectory) {
   assert(Context && "should have context when outputting path");
 
   bool Changed =
-      cleanPathForOutput(Context->getSourceManager().getFileManager(), Path);
+      cleanPathForOutput(Context->getSourceManager().getFileManager(), Path,
+                         llvm::sys::path::is_absolute(BaseDirectory));
----------------
The intent of this function is to use an absolute form of both the file path and `BaseDirectory` so that we can strip off `BaseDirectory` even if the file path ends up absolute somehow.  Rather than changing `BaseDirectory` above and then changing the code here to compensate, could you only change the code that writes out the `MODULE_DIRECTORY` record to write a relative path?


Repository:
  rC Clang

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  https://reviews.llvm.org/D51568/new/

https://reviews.llvm.org/D51568