[all-commits] [llvm/llvm-project] b1867e: [Attributes] Support Attributes being declared as ...

[Dan Liew via All-commits]

  Branch: refs/heads/main
  Home:   https://github.com/llvm/llvm-project
  Commit: b1867e18c346e9621e14270bea2d1acb7d2a9ce0
      https://github.com/llvm/llvm-project/commit/b1867e18c346e9621e14270bea2d1acb7d2a9ce0
  Author: Dan Liew <delcypher at gmail.com>
  Date:   2024-04-29 (Mon, 29 Apr 2024)

  Changed paths:
    M clang/docs/ReleaseNotes.rst
    M clang/include/clang/Basic/Attr.td
    M clang/include/clang/Basic/LangOptions.def
    M clang/include/clang/Driver/Options.td
    M clang/include/clang/Parse/Parser.h
    M clang/lib/Driver/ToolChains/Clang.cpp
    M clang/lib/Parse/ParseDecl.cpp
    A clang/test/Driver/experimental-late-parse-attributes.c
    M clang/utils/TableGen/ClangAttrEmitter.cpp

  Log Message:
  -----------
  [Attributes] Support Attributes being declared as supporting an experimental late parsing mode "extension" (#88596)

This patch changes the `LateParsed` field of `Attr` in `Attr.td` to be
an instantiation of the new `LateAttrParseKind` class. The instation can be one of the following:

* `LateAttrParsingNever` - Corresponds with the false value of `LateParsed` prior to this patch (the default for an attribute).
* `LateAttrParseStandard` - Corresponds with the true value of `LateParsed` prior to this patch.
* `LateAttrParseExperimentalExt` - A new mode described below.

`LateAttrParseExperimentalExt` is an experimental extension to
`LateAttrParseStandard`. Essentially this allows
`Parser::ParseGNUAttributes(...)` to distinguish between these cases:

1. Only `LateAttrParseExperimentalExt` attributes should be late parsed.
2. Both `LateAttrParseExperimentalExt` and `LateAttrParseStandard`
  attributes should be late parsed.

Callers (and indirect callers) of `Parser::ParseGNUAttributes(...)`
indicate the desired behavior by setting a flag in the
`LateParsedAttrList` object that is passed to the function.

In addition to the above, a new driver and frontend flag
(`-fexperimental-late-parse-attributes`) with a corresponding LangOpt
(`ExperimentalLateParseAttributes`) is added that changes how
`LateAttrParseExperimentalExt` attributes are parsed.

* When the flag is disabled (default), in cases where only
  `LateAttrParsingExperimentalOnly` late parsing is requested, the
  attribute will be parsed immediately (i.e. **NOT** late parsed). This
  allows the attribute to act just like a `LateAttrParseStandard`
  attribute when the flag is disabled.

* When the flag is enabled, in cases where only
  `LateAttrParsingExperimentalOnly` late parsing is requested, the
  attribute will be late parsed.

The motivation behind this change is to allow the new `counted_by`
attribute (part of `-fbounds-safety`) to support late parsing but
**only** when `-fexperimental-late-parse-attributes` is enabled. This
attribute needs to support late parsing to allow it to refer to fields
later in a struct definition (or function parameters declared later).
However, there isn't a precedent for supporting late attribute parsing
in C so this flag allows the new behavior to exist in Clang but not be
on by default. This behavior was requested as part of the
`-fbounds-safety` RFC process
(https://discourse.llvm.org/t/rfc-enforcing-bounds-safety-in-c-fbounds-safety/70854/68).

This patch doesn't introduce any uses of `LateAttrParseExperimentalExt`.
This will be added for the `counted_by` attribute in a future patch
(https://github.com/llvm/llvm-project/pull/87596). A consequence is the
new behavior added in this patch is not yet testable. Hence, the lack of
tests covering the new behavior.

rdar://125400257



To unsubscribe from these emails, change your notification settings at https://github.com/llvm/llvm-project/settings/notifications