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

llvm-svn: 304515

1 files changed, 13 insertions, 1 deletions

diff --git a/clang/test/Modules/diagnostics.modulemap b/clang/test/Modules/diagnostics.modulemap
index 3b5b6a5c039..865892b53b2 100644
--- a/clang/test/Modules/diagnostics.modulemap
+++ b/clang/test/Modules/diagnostics.modulemap
@@ -1,4 +1,4 @@
-// RUN: not %clang_cc1 -fmodules -fmodules-cache-path=%t -fmodule-map-file=%S/Inputs/diagnostics-aux.modulemap -fmodule-map-file=%s -fsyntax-only -x c++ /dev/null 2>&1 | FileCheck %s
+// RUN: not %clang_cc1 -fmodules -fmodules-cache-path=%t -fmodule-map-file=%S/Inputs/diagnostics-aux.modulemap -fmodule-map-file=%s -fsyntax-only -x c++ /dev/null 2>&1 | FileCheck %s --implicit-check-not error:
 
 // CHECK: In file included from {{.*}}diagnostics-aux.modulemap:3:
 // CHECK: diagnostics-aux-2.modulemap:2:3: error: expected
@@ -15,3 +15,15 @@ module bad_use {
   // CHECK: diagnostics.modulemap:[[@LINE+1]]:22: error: use declarations are only allowed in top-level modules
   module submodule { use foo }
 }
+
+module header_attr {
+  // CHECK: diagnostics.modulemap:[[@LINE+1]]:20: error: expected a header attribute name
+  header "foo.h" { x }
+  // CHECK: diagnostics.modulemap:[[@LINE+1]]:27: error: header attribute 'size' specified multiple times
+  header "bar.h" { size 1 size 2 }
+  // CHECK: diagnostics.modulemap:[[@LINE+1]]:25: error: expected integer literal as value for header attribute 'size'
+  header "baz.h" { size "30 kilobytes" }
+
+  header "quux.h" { size 1 mtime 2 }
+  header "no_attrs.h" {}
+}