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Update raw-dylib documentation for stabilization #1345

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May 14, 2023
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Update raw-dylib documentation for stabilization #1345

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36 changes: 33 additions & 3 deletions src/items/external-blocks.md
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Expand Up @@ -231,9 +231,38 @@ resolution logic to find that import library. Alternatively, specifying
`kind = "raw-dylib"` instructs the compiler to generate an import library
during compilation and provide that to the linker instead.

`raw-dylib` is only supported on Windows and not supported on 32-bit x86
(`target_arch="x86"`). Using it when targeting other platforms or
x86 on Windows will result in a compiler error.
`raw-dylib` is only supported on Windows. Using it when targeting other
platforms will result in a compiler error.

#### The `import_name_type` key

On x86 Windows, names of functions are "decorated" (i.e., have a specific prefix
and/or suffix added) to indicate their calling convention. For example, a
`stdcall` calling convention function with the name `fn1` that has no arguments
would be decorated as `_fn1@0`. However, the [PE Format] does also permit names
to have no prefix or be undecorated. Additionally, the MSVC and GNU toolchains
use different decorations for the same calling conventions which means, by
default, some Win32 functions cannot be called using the `raw-dylib` link kind
via the GNU toolchain.

To allow for these differences, when using the `raw-dylib` link kind you may
also specify the `import_name_type` key with one of the following values to
change how functions are named in the generated import library:

* `decorated`: The function name will be fully-decorated using the MSVC
toolchain format.
* `noprefix`: The function name will be decorated using the MSVC toolchain
format, but skipping the leading `?`, `@`, or optionally `_`.
* `undecorated`: The function name will not be decorated.

If the `import_name_type` key is not specified, then the function name will be
fully-decorated using the target toolchain's format.

Variables are never decorated and so the `import_name_type` key has no effect on
how they are named in the generated import library.

The `import_name_type` key is only supported on x86 Windows. Using it when
targeting other platforms will result in a compiler error.

### The `link_name` attribute

Expand Down Expand Up @@ -308,3 +337,4 @@ restrictions as [regular function parameters].
[`whole-archive` documentation for rustc]: ../../rustc/command-line-arguments.html#linking-modifiers-whole-archive
[`verbatim` documentation for rustc]: ../../rustc/command-line-arguments.html#linking-modifiers-verbatim
[`dylib` versus `raw-dylib`]: #dylib-versus-raw-dylib
[PE Format]: https://learn.microsoft.com/windows/win32/debug/pe-format#import-name-type