[ModuleInterface] Save -public-autolink-library module option

[kateinoigakukun]

Serialize the -public-autolink-library <name> option to the moduleinterface file because it can affect the LINK_LIBRARY entries in a swiftmodule file. Without saving the option being saved, specified libraries won't be linked when a module compiled from the moduleinterface is used.

This change marks the -public-autolink-library option as a module interface option and reads it when building a swiftmodule by module loader.

Close swiftwasm#5580

[kateinoigakukun]

@swift-ci smoke test

[kateinoigakukun]

@swift-ci build toolchain

[MaxDesiatov]

Should we be concerned about the macOS toolchain failure?

[kateinoigakukun]

curl: (55) Send failure: Broken pipe

The macOS failure is just a networking problem, and the toolchain build itself is fine 👍

[MaxDesiatov]

That failure should be intermittent then

[MaxDesiatov]

@swift-ci build toolchain macos

[artemcm]

We already use -autolink-force-load in .swiftinterface files to indicate that the module corresponds to a library which must be auto-linked by clients. Combined with -module-link-name <name> to set link library name.

Why is this new mechanism required?

[kateinoigakukun]

@artemcm This -public-autolink-library option is usually used to tell transitive public dependencies of private dependencies to module clients when static linking. (Usually not used for dynamic linking cases because a .so/.dylib itself can have their library dependencies.)

For example, we have a dependency relationship: Foundation -> CoreFoundation -> icu4c where:

• Foundation imports CoreFoundation with @_implementationOnly as a private dependency.
• libFoundation.a includes all object files of both Foundation and CoreFoundation, but not icu4c.
• libicu4c.a can be pulled by other libraries, so cannot be merged into libFoundation.a.

In this case, we use -public-autolink-library icu4c to construct Foundation.swiftmodule for static-linking version. Then importing Foundation module emits licu4c auto-link entry into the module client.

https://github.com/apple/swift-corelibs-foundation/blob/ca3669eb9ac282c649e71824d9357dbe140c8251/Sources/Foundation/CMakeLists.txt#L201-L206
swiftlang/swift-corelibs-foundation#2996

module-link-name <name> is something to set a library name of the module itself, but -public-autolink-library is something to set library names of the transitive public dependencies (e.g. libicu4c.a) of private dependencies (e.g. CoreFoundation).

At least, swiftmodules with and without -public-autolink-library are different and it leads pre-compiled swiftmodule installed in a toolchain and swiftmodule re-compiled from swiftinterface can be inconsistent.

[artemcm]

Makes sense. Thank you for the explanation.

[kateinoigakukun]

Thank you for your review!