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@beccadax beccadax commented Nov 3, 2020

This pull request begins to implement "module selectors", which allow references to declarations to be unambiguously prefixed with a module they can be found through:

class MyClass: ObjectiveC::NSObject {}  // OK, ObjectiveC defines NSObject
class MyClass: Foundation::NSObject {}  // OK, Foundation re-exports NSObject
class MyClass: Swift::NSObject {}       // error, Swift does not re-export or define NSObject
class MyClass: MyModule::NSObject {}    // error, MyModule does not re-export or define NSObject

This PR parses module selectors and partially implements lookup and diagnostics for them. The new functionality is hidden behind an -enable-experimental-module-selector frontend flag. There is one diagnostic regression with that flag enabled, but I've made sure that it keeps working when the diagnostic is disabled.

This work was previously in PR #28834, which was closed during the master-to-main transition. I've updated it to work on modern compilers, including removing some FIXMEs for bad diagnostics that have improved since December 2019.

Makes progress on rdar://problem/19481048.

@beccadax beccadax changed the title Module selectors Implement experimental module selectors (MyMod::someName) feature Nov 3, 2020
@beccadax beccadax force-pushed the mod-squad-2 branch 3 times, most recently from eb8ecdf to b6d41f6 Compare July 21, 2021 20:18
@nkcsgexi
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Woohoo! Thank you for reviving this, Becca!

A PatternBindingEntry formed from a MissingPatternSyntax has no valid SourceLocs in it, and a PatternBindingDecl containing only PatternBindingEntries with no valid SourceLocs trips an assertion during availability checking. (Generating dummy SourceLocs can cause invalid overlaps between AvailabilityScopes, so that’s not a workable solution.) The fix is to:

• Refuse to generate a PatternBindingEntry from a PatternBindingSyntax with a MissingPatternSyntax (MissingPatternSyntaxes at nested positions don’t have this problem)
• Refuse to generate a PatternBindingDecl with no PatternBindingEntries

This ensures that the invalid AST nodes are never formed.

No current test cases hit this problem, but certain invalid module selector tests can run into this situation when run with ASTGen.
The diagnostics in this test will evolve as we implement pieces of the feature.
Adds comments explaining why these conversions aren’t lossy.
Lookups like Builtin::Int64 were failing because BuiltinUnit rejected all unqualified lookups. Make it allow unqualified lookups with a module selector.
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@swift-ci please smoke test

This support is currently opt-in and has several modes.
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@swift-ci please build toolchain

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@swift-ci build toolchain Windows platform

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@swift-ci please test

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@swift-ci build toolchain Windows platform

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@beccadax
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@swift-ci build toolchain Windows platform

@beccadax
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@swift-ci build toolchain Windows platform

@beccadax
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@swift-ci build toolchain Windows platform

@beccadax
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@swift-ci build toolchain Windows platform

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