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Sema: Fix isExported() for extension decls #42585

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Fix isExported() for extension decls in order to correct availability diagnostics when -target-min-inlining-version min is specified.

Previously, an extension decl was always considered exported (externally visible to module clients) as long as it extended an exported type. Extensions need to either contain some externally visible member (e.g. a public method) or implement a conformance to a public protcol, though, to actually be exported. Without this fix, the compiler incorrectly requires internal extensions to types that are always available at runtime to have declared availability which would be a nuisance for library authors.

As part of testing this change, I expanded the attr_inlinable_available.swift test case significantly and that prompted me to scrap the copy of the test specific to macCatalyst as it seemed like needing to keep the two tests in sync was going to be a liability going forward. I replaced the deleted test with a couple of more targeted tests that use -dump-type-refinement-contexts to verify the effect of -target-min-inlining-version min on the root refinement context. Again a macCatalyst version of the test is required because we don't have bots that are configured to make the macCatalyst runtime the "target" OS.

Resolves rdar://91382040

…lability diagnostics when `-target-min-inlining-version min` is specified.

Previously, an extension decl was always considered exported (externally visible to module clients) as long as it extended an exported type. Extensions need to either contain some externally visible member (e.g. a public method) or implement a conformance to a public protcol, though, to actually be exported. Without this fix, the compiler incorrectly requires internal extensions to types that are always available at runtime to have declared availability which would be a nuisance for library authors.

As part of testing this change, I expanded the attr_inlinable_available.swift test case significantly and that prompted me to scrap the copy of the test specific to macCatalyst as it seemed like needing to keep the two tests in sync was going to be a liability going forward. I replaced the deleted test with a couple of more targeted tests that use `-dump-type-refinement-contexts` to verify the effect of `-target-min-inlining-version min` on the root refinement context. Again a macCatalyst version of the test is required because we don't have bots that are configured to make the macCatalyst runtime the "target" OS.

Resolves rdar://91382040
@tshortli tshortli force-pushed the target-min-inlining-version-extension-availability branch from 7df3ffc to 00ac799 Compare April 22, 2022 21:33
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@swift-ci please test

@tshortli tshortli merged commit b806113 into swiftlang:main Apr 26, 2022
@tshortli tshortli deleted the target-min-inlining-version-extension-availability branch May 8, 2022 16:31
tshortli added a commit that referenced this pull request Jun 1, 2022
… min` (#59176)

Cherry-pick and squash of the following PRs to release/5.7:

#42585
#58417
#58654
#58680
#58707
#58870
#58963
#59040
#59065

* Sema: Fix `isExported()` for extension decls in order to correct availability diagnostics when `-target-min-inlining-version min` is specified.

Resolves rdar://91382040

* Sema: Avoid diagnosing potential unavailability of type components (extension nominal type, superclass, etc.) on declarations that are explicitly unavailable.

Resolves rdar://92179327

* Sema: Downgrade diagnostics about potential unavailability of the extended type in an extension declaration when the following conditions are met:

1. The extension is missing explicit availability.
2. The required availability is before the deployment target.

Resolves rdar://92621567

* NFC: Expand `-target-min-inlining-versiong` tests to cover a number of corner cases:

- unavailable declarations and unavailable containers
- SPI declarations and spi containers
- property initializer expressions
- property wrappers

* Sema: When computing potential unavailability of a decl, first check whether the decl is explicitly unavailable and the context is also unavailable. If those conditions are met, treat the decl as if it were always available since unavailable code is allowed to reference unavailable decls.

Resolves rdar://92551870

* Sema: Use the deployment target when checking availability for SPI and unavailable API declarations with `-target-min-inlining-version min` specified. There's not much benefit to more accurate enforcement of availability in these decls since API clients can't use them and there's a lot of existing code that would be needlessly diagnosed without these exceptions.

Resolves rdar://92716633

* Sema: Teach the compiler to refine `VarDecl` initializer expressions using the deployment target when the init would not be exposed to module clients. Without this, the initializers of public properties in API modules could be misdiagnosed as potentially unavailable to clients of the module, even though the expression will only ever execute on the deployment target or higher.

Resolves rdar://92713589

* Tests: Update `attr_inlinable_available.swift` to require macOS and remove the OS versions for other platforms from availability attributes.

* Tests: Add test cases for potential unavailability in class inheritance when  is specified.

* Sema: Reword diagnostics about potentially unavailable decls to improve clarity for authors of API libraries. When decls are diagnosed as potentially unavailable on an OS earlier than the deployment target, the message will now indicate that the issue would be faced by clients of the module.

Resolves rdar://93466875

* Sema: Use the availability of the extended nominal as a floor for the availability of extensions. The primary motivation for this change is to reduce unnecessary availability diagnostics for API library authors. Many API libraries contain existing extension decls that lack declared availability where the extension introduces additional members to the extended type in the same release that the extended type was declared. Others contain extensions where the extension itself does not have declared availability but each of the members do. In both cases, the code is safe as written so the extra diagnostics would be a nuisance.

Resolves rdar://93630782

* Sema: Downgrade diagnostics about inheritance from a less available type when `-target-min-inlining-version min` is specified.

As a concession to source compatibility for API libraries, downgrade diagnostics about inheritance from a less available type when the following conditions are met:
1. The inherited type is only potentially unavailable before the deployment target.
2. The inheriting type is `@usableFromInline`.

Resolves rdar://92747826
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