Support lazy stat'ing of files referenced by module maps.

This patch adds support for a `header` declaration in a module map to specify
certain `stat` information (currently, size and mtime) about that header file.
This has two purposes:

- It removes the need to eagerly `stat` every file referenced by a module map.
  Instead, we track a list of unresolved header files with each size / mtime
  (actually, for simplicity, we track submodules with such headers), and when
  attempting to look up a header file based on a `FileEntry`, we check if there
  are any unresolved header directives with that `FileEntry`'s size / mtime and
  perform deferred `stat`s if so.

- It permits a preprocessed module to be compiled without the original files
  being present on disk. The only reason we used to need those files was to get
  the `stat` information in order to do header -> module lookups when using the
  module. If we're provided with the `stat` information in the preprocessed
  module, we can avoid requiring the files to exist.

Unlike most `header` directives, if a `header` directive with `stat`
information has no corresponding on-disk file the enclosing module is *not*
marked unavailable (so that behavior is consistent regardless of whether we've
resolved a header directive, and so that preprocessed modules don't get marked
unavailable). We could actually do this for all `header` directives: the only
reason we mark the module unavailable if headers are missing is to give a
diagnostic slightly earlier (rather than waiting until we actually try to build
the module / load and validate its .pcm file).

Differential Revision: https://reviews.llvm.org/D33703


git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@304515 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 6 insertions, 0 deletions

diff --git a/include/clang/Basic/DiagnosticLexKinds.td b/include/clang/Basic/DiagnosticLexKinds.td
index b393ce5f15..447f069456 100644
--- a/include/clang/Basic/DiagnosticLexKinds.td
+++ b/include/clang/Basic/DiagnosticLexKinds.td
@@ -664,6 +664,12 @@ def warn_mmap_mismatched_top_level_private : Warning<
   InGroup<PrivateModule>;
 def note_mmap_rename_top_level_private_as_submodule : Note<
   "make '%0' a submodule of '%1' to ensure it can be found by name">;
+def err_mmap_duplicate_header_attribute : Error<
+  "header attribute '%0' specified multiple times">;
+def err_mmap_invalid_header_attribute_value : Error<
+  "expected integer literal as value for header attribute '%0'">;
+def err_mmap_expected_header_attribute : Error<
+  "expected a header attribute name ('size' or 'mtime')">;
 
 def warn_auto_module_import : Warning<
   "treating #%select{include|import|include_next|__include_macros}0 as an "