[Basic] Use std::optional in FileManager.cpp (NFC)

This is part of an effort to migrate from llvm::Optional to
std::optional:

https://discourse.llvm.org/t/deprecating-llvm-optional-x-hasvalue-getva

[Basic] Use std::optional in FileManager.cpp (NFC)

This is part of an effort to migrate from llvm::Optional to
std::optional:

https://discourse.llvm.org/t/deprecating-llvm-optional-x-hasvalue-getvalue-getvalueor/63716

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[Basic] Use std::nullopt instead of None (NFC)

This patch mechanically replaces None with std::nullopt where the
compiler would warn if None were deprecated. The intent is to reduce
the amount of m

[Basic] Use std::nullopt instead of None (NFC)

This patch mechanically replaces None with std::nullopt where the
compiler would warn if None were deprecated. The intent is to reduce
the amount of manual work required in migrating from Optional to
std::optional.

This is part of an effort to migrate from llvm::Optional to
std::optional:

https://discourse.llvm.org/t/deprecating-llvm-optional-x-hasvalue-getvalue-getvalueor/63716

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[clang] Fix redirection behaviour for cached FileEntryRef

In 6a79e2ff1989b we changed Filemanager::getEntryRef() to return the
redirecting FileEntryRef instead of looking through the redirection.
Th

[clang] Fix redirection behaviour for cached FileEntryRef

In 6a79e2ff1989b we changed Filemanager::getEntryRef() to return the
redirecting FileEntryRef instead of looking through the redirection.
This commit fixes the case when looking up a cached file path to also
return the redirecting FileEntryRef. This mainly affects the behaviour
of calling getNameAsRequested() on the resulting entry ref.

Differential Revision: https://reviews.llvm.org/D131273

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[clang] Add FileEntryRef::getNameAsRequested()

As progress towards having FileManager::getFileRef() return the path
as-requested by default, return a FileEntryRef that can use
getNameAsRequested() t

[clang] Add FileEntryRef::getNameAsRequested()

As progress towards having FileManager::getFileRef() return the path
as-requested by default, return a FileEntryRef that can use
getNameAsRequested() to retrieve this path, with the ultimate goal that
this should be the behaviour of getName() and clients should explicitly
request the "external" name if they need to (see comment in
FileManager::getFileRef). For now, getName() continues to return the
external path by looking through the redirects.

For now, the new function is only used in unit tests.

Differential Revision: https://reviews.llvm.org/D131004

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[clang] Only modify FileEntryRef names that are externally remapped

As progress towards having FileEntryRef contain the requested name of
the file, this commit narrows the "remap" hack to only apply

[clang] Only modify FileEntryRef names that are externally remapped

As progress towards having FileEntryRef contain the requested name of
the file, this commit narrows the "remap" hack to only apply to paths
that were remapped to an external contents path by a VFS. That was
always the original intent of this code, and the fact it was making
relative paths absolute was an unintended side effect.

Differential Revision: https://reviews.llvm.org/D130935

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[VFS] RedirectingFileSystem only replace path if not already mapped

If the `ExternalFS` has already remapped to an external path then
`RedirectingFileSystem` should not change it to the originally p

[VFS] RedirectingFileSystem only replace path if not already mapped

If the `ExternalFS` has already remapped to an external path then
`RedirectingFileSystem` should not change it to the originally provided
path. This fixes the original path always being used if multiple VFS
overlays were provided and the path wasn't found in the highest (ie.
first in the chain).

For now this is accomplished through the use of a new
`ExposesExternalVFSPath` field on `vfs::Status`. This flag is true when
the `Status` has an external path that's different from its virtual
path, ie. the contained path is the external path. See the plan in
`FileManager::getFileRef` for where this is going - eventually we won't
need `IsVFSMapped` any more and all returned paths should be virtual.

Resolves rdar://90578880 and llvm-project#53306.

Reviewed By: dexonsmith

Differential Revision: https://reviews.llvm.org/D123398

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Remove a few effectively-unused FileEntry APIs. NFC

- isValid: FileManager only ever returns valid FileEntries (see next point)

- construction from outside FileManager (both FileEntry and Directory

Remove a few effectively-unused FileEntry APIs. NFC

- isValid: FileManager only ever returns valid FileEntries (see next point)

- construction from outside FileManager (both FileEntry and DirectoryEntry).
It's not possible to create a useful FileEntry this way, there are no setters.
This was only used in FileEntryTest, added a friend to enable this.
A real constructor is cleaner but requires larger changes to FileManager.

Differential Revision: https://reviews.llvm.org/D123197

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Revert "[VFS] RedirectingFileSystem only replace path if not already mapped"

This reverts commit 3fda0edc51fd68192a30e302d45db081bb02d7f9, which
breaks crash reproducers in very specific circumstanc

Revert "[VFS] RedirectingFileSystem only replace path if not already mapped"

This reverts commit 3fda0edc51fd68192a30e302d45db081bb02d7f9, which
breaks crash reproducers in very specific circumstances. Specifically,
since crash reproducers have `UseExternalNames` set to false, the
`File->getFileEntry().getDir()->getName()` call in `DoFrameworkLookup`
would use the *cached* directory name instead of the directory of the
looked-up file.

The plan is to re-commit this patch but to *add*
`ExposesExternalVFSPath` rather than replace `IsVFSMapped`.

Differential Revision: https://reviews.llvm.org/D123103

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FileManager: std::map => BumpPtrAllocator + DenseMap of pointers. NFC

This is both smaller and faster.

Differential Revision: https://reviews.llvm.org/D123144

[VFS] RedirectingFileSystem only replace path if not already mapped

If the `ExternalFS` has already remapped a path then the
`RedirectingFileSystem` should not change it to the originally provided
p

[VFS] RedirectingFileSystem only replace path if not already mapped

If the `ExternalFS` has already remapped a path then the
`RedirectingFileSystem` should not change it to the originally provided
path. This fixes the original path always being used if multiple VFS
overlays were provided and the path wasn't found in the highest (ie.
first in the chain).

This also renames `IsVFSMapped` to `ExposesExternalVFSPath` and only
sets it if `UseExternalName` is true. This flag then represents that the
`Status` has an external path that's different from its virtual path.
Right now the contained path is still the external path, but further PRs
will change this to *always* be the virtual path. Clients that need the
external can then request it specifically.

Note that even though `ExposesExternalVFSPath` isn't set for all
VFS-mapped paths, `IsVFSMapped` was only being used by a hack in
`FileManager` that was specific to module searching. In that case
`UseExternalNames` is always `true` and so that hack still applies.

Resolves rdar://90578880 and llvm-project#53306.

Differential Revision: https://reviews.llvm.org/D122549

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Fix a use-after-scope from 99023627010bbfefb71e25a2b4d056de1cbd354e

Support: Use sys::path::is_style_{posix,windows}() in a few places

Use the new sys::path::is_style_posix() and is_style_windows() in a few
places that need to detect the system's native path style.

Support: Use sys::path::is_style_{posix,windows}() in a few places

Use the new sys::path::is_style_posix() and is_style_windows() in a few
places that need to detect the system's native path style.

In llvm/lib/Support/Path.cpp, this patch removes most uses of the
private `real_style()`, where is_style_posix() and is_style_windows()
are just a little tidier.

Elsewhere, this removes `_WIN32` macro checks. Added a FIXME to a
FileManagerTest that seemed fishy, but maintained the existing
behaviour.

Differential Revision: https://reviews.llvm.org/D112289

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VFS: Document goals of 'use-external-name' and related logic, NFC

Document 'use-external-name' and the various bits of logic that make it
work, to avoid others having to repeat the archival work (gi

VFS: Document goals of 'use-external-name' and related logic, NFC

Document 'use-external-name' and the various bits of logic that make it
work, to avoid others having to repeat the archival work (given that I
added getFileRefReturnsCorrectNameForDifferentStatPath to
FileManagerTest, seems possible I understood this once before!).

- b59cf679e81483cbb3a9252056b7528f4c49586c added 'use-external-name' to
RedirectingFileSystem. This causes `stat`s to return the external
name for a redirected file instead of the name it was accessed by,
leaking it through the VFS.
- d066d4c849be06a01c0d17e8dc206913f4e7bfe3 propagated the external name
further through clang::FileManager.
- 4dc5573acc0d2e7c59d8bac2543eb25cb4b32984, which added
clang::FileEntryRef to clang::FileManager, has complicated concession
to account for this as well (since refactored a bit).

The goal of 'use-external-name' is to enable Clang to report "real" file
paths to users (via diagnostics) and to external tools (such as
debuggers reading debug info and build systems reading `.d` files).

I've added FIXMEs to look at other channels for communicating the
external names, since the current implementation adds complexity to
FileManager and exposes an inconsistent interface to clients.

Besides that, the FileManager logic appears to be kicking in outside of
'use-external-name'. Seems that *some* vfs::FileSystem implementations
canonicalize some paths returned by `stat` in *some* cases (the bug
isn't fully understood yet). Volodymyr Sapsai is investigating, this at
least better documents what *is* understood.

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PR51018: Remove explicit conversions from SmallString to StringRef to future-proof against C++23

C++23 will make these conversions ambiguous - so fix them to make the
codebase forward-compatible wit

PR51018: Remove explicit conversions from SmallString to StringRef to future-proof against C++23

C++23 will make these conversions ambiguous - so fix them to make the
codebase forward-compatible with C++23 (& a follow-up change I've made
will make this ambiguous/invalid even in <C++23 so we don't regress
this & it generally improves the code anyway)

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[clang] Rename StringRef _lower() method calls to _insensitive()

This is mostly a mechanical change, but a testcase that contains
parts of the StringRef class (clang/test/Analysis/llvm-conventions.c

[clang] Rename StringRef _lower() method calls to _insensitive()

This is mostly a mechanical change, but a testcase that contains
parts of the StringRef class (clang/test/Analysis/llvm-conventions.cpp)
isn't touched.

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[clang][FileManager] Support empty file name in getVirtualFileRef for serialized diagnostics

After https://reviews.llvm.org/D90484 libclang is unable to read a serialized diagnostic file
which conta

[clang][FileManager] Support empty file name in getVirtualFileRef for serialized diagnostics

After https://reviews.llvm.org/D90484 libclang is unable to read a serialized diagnostic file
which contains a diagnostic which came from a file with an empty filename. The reason being is
that the serialized diagnostic reader is creating a virtual file for the "" filename, which now
fails after the changes in https://reviews.llvm.org/D90484. This patch restores the previous
behavior in getVirtualFileRef by allowing it to construct a file entry ref with an empty name by
pretending its name is "." so that the directory entry can be created.

Differential Revision: https://reviews.llvm.org/D100428

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Basic: Add native support for stdin to SourceManager and FileManager

Add support for stdin to SourceManager and FileManager. Adds
FileManager::getSTDIN, which adds a FileEntryRef for `<stdin>` and r

Basic: Add native support for stdin to SourceManager and FileManager

Add support for stdin to SourceManager and FileManager. Adds
FileManager::getSTDIN, which adds a FileEntryRef for `<stdin>` and reads
the MemoryBuffer, which is stored as `FileEntry::Content`.

Eventually the other buffers in `ContentCache` will sink to here as well
-- we probably usually want to load/save a MemoryBuffer eagerly -- but
it's happening early for stdin to get rid of
CompilerInstance::InitializeSourceManager's final call to
`SourceManager::overrideFileContents`.

clang/test/CXX/modules-ts/dcl.dcl/dcl.module/dcl.module.export/p1.cpp
relies on building a module from stdin; supporting that requires setting
ContentCache::BufferOverridden.

Differential Revision: https://reviews.llvm.org/D93148

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Basic: Support named pipes natively in SourceManager and FileManager

Handle named pipes natively in SourceManager and FileManager, removing a
call to `SourceManager::overrideFileContents` in
`Compil

Basic: Support named pipes natively in SourceManager and FileManager

Handle named pipes natively in SourceManager and FileManager, removing a
call to `SourceManager::overrideFileContents` in
`CompilerInstance::InitializeSourceManager` (removing a blocker for
sinking the content cache to FileManager (which will incidently sink
this new named pipe logic with it)).

SourceManager usually checks if the file entry's size matches the
eventually loaded buffer, but that's now skipped for named pipes since
the `stat` won't reflect the full size. Since we can't trust
`ContentsEntry->getSize()`, we also need shift the check for files that
are too large until after the buffer is loaded... and load the buffer
immediately in `createFileID` so that no client gets a bad value from
`ContentCache::getSize`. `FileManager::getBufferForFile` also needs to
treat these files as volatile when loading the buffer.

Native support in SourceManager / FileManager means that named pipes can
also be `#include`d, and clang/test/Misc/dev-fd-fs.c was expanded to
check for that.

This is a new version of 3b18a594c7717a328c33b9c1eba675e9f4bd367c, which
was reverted in b34632201987eed369bb7ef4646f341b901c95b8 since it was
missing the `SourceManager` changes.

Differential Revision: https://reviews.llvm.org/D92531

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Revert "Frontend: Sink named pipe logic from CompilerInstance down to FileManager"

This reverts commit 3b18a594c7717a328c33b9c1eba675e9f4bd367c, since
apparently this doesn't work everywhere. E.g.,

Revert "Frontend: Sink named pipe logic from CompilerInstance down to FileManager"

This reverts commit 3b18a594c7717a328c33b9c1eba675e9f4bd367c, since
apparently this doesn't work everywhere. E.g.,
clang-x86_64-debian-fast/3889
(http://lab.llvm.org:8011/#/builders/109/builds/3889) gives me:
```
+ : 'RUN: at line 8'
+ /b/1/clang-x86_64-debian-fast/llvm.obj/bin/clang -x c /dev/fd/0 -E
+ cat /b/1/clang-x86_64-debian-fast/llvm.src/clang/test/Misc/dev-fd-fs.c
fatal error: file '/dev/fd/0' modified since it was first processed
1 error generated.
```

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Frontend: Sink named pipe logic from CompilerInstance down to FileManager

Remove compilicated logic from CompilerInstance::InitializeSourceManager
to deal with named pipes, updating FileManager::get

Frontend: Sink named pipe logic from CompilerInstance down to FileManager

Remove compilicated logic from CompilerInstance::InitializeSourceManager
to deal with named pipes, updating FileManager::getBufferForFile to
handle it in a more straightforward way. The existing test at
clang/test/Misc/dev-fd-fs.c covers the new behaviour (just like it did
the old behaviour).

Differential Revision: https://reviews.llvm.org/D90733

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FileManager: Add FileEntryRef::getDir, returning DirectoryEntryRef

Add `FileEntryRef::getDir`, which returns a `DirectoryEntryRef`. This
includes a few changes:

- Customize `OptionalStorage` so tha

FileManager: Add FileEntryRef::getDir, returning DirectoryEntryRef

Add `FileEntryRef::getDir`, which returns a `DirectoryEntryRef`. This
includes a few changes:

- Customize `OptionalStorage` so that `Optional<DirectoryEntryRef>` is
pointer-sized (like the change made to `Optional<FileEntryRef>`).
Factored out a common class, `FileMgr::MapEntryOptionalStorage`, to
reduce the code duplication.
- Store an `Optional<DirectoryEntryRef>` in `FileEntryRef::MapValue`.
This is set if and only if `MapValue` has a real `FileEntry`.
- Change `FileManager::getFileRef` and `getVirtualFileRef` to use
`getDirectoryRef` and store it in the `StringMap` for `FileEntryRef`.

Differential Revision: https://reviews.llvm.org/D90484

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Serialization: Change InputFile to use FileEntryRef and add getVirtualFileRef, NFC

Change the `InputFile` class to store `Optional<FileEntryRef>` instead
of `FileEntry*`. This paged in a few API cha

Serialization: Change InputFile to use FileEntryRef and add getVirtualFileRef, NFC

Change the `InputFile` class to store `Optional<FileEntryRef>` instead
of `FileEntry*`. This paged in a few API changes:

- Added `FileManager::getVirtualFileRef`, and converted `getVirtualFile`
to a wrapper of it.
- Updated `SourceManager::bypassFileContentsOverride` to take
`FileEntryRef` and return `Optional<FileEntryRef>`
(`ASTReader::getInputFile` is the only caller).

Differential Revision: https://reviews.llvm.org/D90053

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Unbreak build with gcc5.3 after 917acac

FileManager: Shrink FileEntryRef to the size of a pointer

Shrink `FileEntryRef` to the size of a pointer, by having it directly
reference the `StringMapEntry` the same way that `DirectoryEntryRef`
d

FileManager: Shrink FileEntryRef to the size of a pointer

Shrink `FileEntryRef` to the size of a pointer, by having it directly
reference the `StringMapEntry` the same way that `DirectoryEntryRef`
does. This makes `FileEntryRef::FileEntryRef` private as a side effect
(`FileManager` is a friend!).

There are two helper types added within `FileEntryRef`:

- `FileEntryRef::MapValue` is the type stored in
`FileManager::SeenFileEntries`. It's a replacement for
`SeenFileEntryOrRedirect`, where the second pointer type has been
changed from `StringRef*` to `MapEntry*` (see next bullet).
- `FileEntryRef::MapEntry` is the instantiation of `StringMapEntry<>`
where `MapValue` is stored. This is what `FileEntryRef` has a pointer
to, in order to grab the name in addition to the value.

Differential Revision: https://reviews.llvm.org/D89488

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[Clang] Expose RequiresNullTerminator in FileManager.

This is needed to fix the reason
0a2be46cfdb698fe (Modules: Invalidate out-of-date PCMs as they're
discovered) and 5b44a4b07fc1d ([modules] Do n

[Clang] Expose RequiresNullTerminator in FileManager.

This is needed to fix the reason
0a2be46cfdb698fe (Modules: Invalidate out-of-date PCMs as they're
discovered) and 5b44a4b07fc1d ([modules] Do not cache invalid state for
modules that we attempted to load.) were reverted.

These patches changed Clang to use `isVolatile` when loading modules.
This had the side effect of not using mmap when loading modules, and
thus greatly increased memory usage.

The reason it wasn't using mmap is because `MemoryBuffer` plays some
games with file size when you request null termination, and it has to
disable these when `isVolatile` is set as the size may change by the
time it's mmapped. Clang by default passes
`RequiresNullTerminator = true`, and `shouldUseMmap` ignored if
`RequiresNullTerminator` was even requested.

This patch adds `RequiresNullTerminator` to the `FileManager` interface
so Clang can use it when loading modules, and changes `shouldUseMmap` to
only take volatility into account if `RequiresNullTerminator` is true.
This is fine as both `mmap` and a `read` loop are vulnerable to
modifying the file while reading, but are immune to the rename Clang
does when replacing a module file.

Differential Revision: https://reviews.llvm.org/D77772

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