[Modules] Improve error message when cannot find parent module for submodule definition.

Before the change the diagnostic for

module unknown.submodule {}

was "error: expected module name" whic

[Modules] Improve error message when cannot find parent module for submodule definition.

Before the change the diagnostic for

module unknown.submodule {}

was "error: expected module name" which is incorrect and misleading
because both "unknown" and "submodule" are valid module names.

We already have a better error message when a parent module is a
submodule itself and is missing. Make the error for a missing top-level
module more like the one for a submodule.

rdar://problem/64424407

Reviewed By: bruno

Differential Revision: https://reviews.llvm.org/D84458

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Make AST reading work better with LLVM_APPEND_VC_REV=NO

With LLVM_APPEND_VC_REV=NO, Modules/merge-lifetime-extended-temporary.cpp
would fail if it ran before a0f50d731639350c7a7 (which changed
the s

Make AST reading work better with LLVM_APPEND_VC_REV=NO

With LLVM_APPEND_VC_REV=NO, Modules/merge-lifetime-extended-temporary.cpp
would fail if it ran before a0f50d731639350c7a7 (which changed
the serialization format) and then after, for these reasons:

1. With LLVM_APPEND_VC_REV=NO, the module hash before and after the
change was the same.

2. Modules/merge-lifetime-extended-temporary.cpp is the only test
we have that uses -fmodule-cache-path=%t that
a) actually writes to the cache path
b) doesn't do `rm -rf %t` at the top of the test

So the old run would write a module file, and then the new run would
try to load it, but the serialized format changed.

Do several things to fix this:

1. Include clang::serialization::VERSION_MAJOR/VERSION_MINOR in
the module hash, so that when the AST format changes (...and
we remember to bump these), we use a different module cache dir.
2. Bump VERSION_MAJOR, since a0f50d731639350c7a7 changed the
on-disk format in a way that a gch file written before that change
can't be read after that change.
3. Add `rm -rf %t` to all tests that pass -fmodule-cache-path=%t.
This is unnecessary from a correctness PoV after 1 and 2,
but makes it so that we don't amass many cache dirs over time.
(Arguably, it also makes it so that the test suite doesn't catch
when we change the serialization format but don't bump
clang::serialization::VERSION_MAJOR/VERSION_MINOR; oh well.)

Differential Revision: https://reviews.llvm.org/D73202

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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 t

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

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[modules] When diagnosing errors in module map files found by 'extern module' declarations, show how we got to that module map file.

llvm-svn: 242105

[modules] Restrict the module use-declaration to only appear in top-level
modules, and allow sub-modules of a module with a use-declaration to make use
of the nominated modules.

llvm-svn: 233323

[modules] Accept //-style comments in module maps on purpose rather than by
accident, and accept them even when they begin '//*'.

llvm-svn: 229240

PR22299: Relocate code for handling -fmodule-map-file= so that we don't try to
produce diagnostics with source locations before the diagnostics system is
ready for them.

llvm-svn: 226882