[all-commits] [llvm/llvm-project] 2b26ee: [libcxx] Handle windows system error code mapping ...

[James Y Knight via All-commits]

  Branch: refs/heads/main
  Home:   https://github.com/llvm/llvm-project
  Commit: 2b26ee6e790574e05c3c9a562bc37897daf0f384
      https://github.com/llvm/llvm-project/commit/2b26ee6e790574e05c3c9a562bc37897daf0f384
  Author: James Y Knight <jyknight at google.com>
  Date:   2025-01-08 (Wed, 08 Jan 2025)

  Changed paths:
    M libcxx/docs/ReleaseNotes/20.rst
    M libcxx/include/__filesystem/directory_entry.h
    M libcxx/include/__system_error/system_error.h
    M libcxx/src/filesystem/directory_iterator.cpp
    M libcxx/src/filesystem/error.h
    M libcxx/src/filesystem/file_descriptor.h
    M libcxx/src/filesystem/operations.cpp
    M libcxx/src/filesystem/posix_compat.h
    M libcxx/src/print.cpp
    M libcxx/src/system_error.cpp
    A libcxx/test/libcxx/diagnostics/system_error_win_codes.pass.cpp
    M libcxx/test/std/diagnostics/syserr/syserr.compare/eq_error_code_error_code.pass.cpp
    M libcxx/test/std/diagnostics/syserr/syserr.errcat/syserr.errcat.derived/message.pass.cpp
    M libcxx/test/std/diagnostics/syserr/syserr.errcat/syserr.errcat.objects/system_category.pass.cpp
    M libcxx/test/std/input.output/filesystems/class.directory_entry/directory_entry.obs/file_type_obs.pass.cpp
    M libcxx/test/std/input.output/filesystems/class.directory_entry/directory_entry.obs/status.pass.cpp
    M libcxx/test/std/input.output/filesystems/class.directory_entry/directory_entry.obs/symlink_status.pass.cpp
    M libcxx/test/support/filesystem_test_helper.h

  Log Message:
  -----------
  [libcxx] Handle windows system error code mapping in std::error_code. (#93101)

The `std::error_code`/`std::error_category` functionality is designed to
support multiple error domains. On Unix, both system calls and libc
functions return the same error codes, and thus, libc++ today treats
`generic_category()` and `system_category()` as being equivalent.

However, on Windows, libc functions return `errno.h` error codes in the
`errno` global, but system calls return the very different `winerror.h`
error codes via `GetLastError()`.

As such, there is a need to map the winerror.h error codes into generic
errno codes. In libc++, however, the system_error facility does not
implement this mapping; instead the mapping is hidden inside libc++,
used directly by the std::filesystem implementation.

That has a few problems:

1. For std::filesystem APIs, the concrete windows error number is lost,
before users can see it. The intent of the distinction between
std::error_code and std::error_condition is that the error_code return
has the original (potentially more detailed) error code.

2. User-written code which calls Windows system APIs requires this same
mapping, so it also can also return error_code objects that other
(cross-platform) code can understand.

After this commit, an `error_code` with `generic_category()` is used to
report an error from `errno`, and, on Windows only, an `error_code` with
`system_category()` is used to report an error from `GetLastError()`. On
Unix, system_category remains identity-mapped to generic_category, but
is never used by libc++ itself.

The windows error code mapping is moved into system_error, so that
conversion of an `error_code` to `error_condition` correctly translates
the `system_category()` code into a `generic_category()` code, when
appropriate.

This allows code like:
`error_code(GetLastError(), system_category()) == errc::invalid_argument`
to work as expected -- as it does with MSVC STL.

(Continued from old phabricator review [D151493](https://reviews.llvm.org/D151493))



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