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Sema: Don't complain about internal type aliases referenced from @inlinable functions in Swift < 4.2 #17493

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Merged
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Jun 26, 2018
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Sema: Don't complain about internal type aliases referenced from @inlinable functions in Swift < 4.2 #17493

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9 changes: 6 additions & 3 deletions lib/Sema/ResilienceDiagnostics.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -129,9 +129,12 @@ bool TypeChecker::diagnoseInlinableDeclRef(SourceLoc loc,
DowngradeToWarning downgradeToWarning = DowngradeToWarning::No;

// Swift 4.2 did not perform any checks for type aliases.
if (!Context.isSwiftVersionAtLeast(5) &&
isa<TypeAliasDecl>(D))
downgradeToWarning = DowngradeToWarning::Yes;
if (isa<TypeAliasDecl>(D)) {
if (!Context.isSwiftVersionAtLeast(4, 2))
return false;
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Hm. :-/ What happens in Swift 4.0 mode when Swift 5 come out?

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I’m not sure I follow?

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I thought the reason we were adding these warnings is because they could lead to linker errors in Swift 5. Maybe I'm misremembering.

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They can lead to linker errors in any release. Here is a test case:

struct Internal {}
typealias Alias = Internal
@inlinable func f() {
  print(Alias.self)
}

In 4.1, this produced no warning and failed to link when another module inlined f(). In Swift 5 mode this is an error. In 4.2 it's just a warning.

The reason it's just a warning is because there are valid code patterns you can write too, eg the underlying type of the Alias is @usableFromInline:

@usableFromInline struct Internal {}
typealias Alias = Internal
@inlinable func f() {
  print(Alias.self)
}

The correct way to write the above is to write, the following, which is the only variant that compiles without errors in Swift 5 mode:

@usableFromInline struct Internal {}
@usableFromInline typealias Alias = Internal
@inlinable func f() {
  print(Alias.self)
}

However, in Swift 4.1, @usableFromInline was not allowed on type aliases at all. SwiftNIO wants to have the same source compile warning-free on both 4.1 and 4.2. So they're just not declaring their type aliases as @usableFromInline and promising to ensure the underlying type has the right visibility.

Once 4.2 is GM, I expect they will drop support for 4.1, and I will go back to emitting these warnings unconditionally. (And in Swift 5 mode it's an error as always).

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Thanks for the explanation.

if (!Context.isSwiftVersionAtLeast(5))
downgradeToWarning = DowngradeToWarning::Yes;
}

auto diagID = diag::resilience_decl_unavailable;
if (downgradeToWarning == DowngradeToWarning::Yes)
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21 changes: 21 additions & 0 deletions test/Compatibility/attr_inlinable_typealias_swift4.swift
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@@ -0,0 +1,21 @@
// RUN: %target-typecheck-verify-swift -swift-version 4

// No diagnostics at all in Swift 4.0 mode.

private typealias PrivateAlias = Int

internal typealias InternalAlias = Int

@usableFromInline typealias UsableFromInlineAlias = Int

public typealias PublicAlias = Int

@inlinable public func f() {
_ = PrivateAlias.self

_ = InternalAlias.self

_ = UsableFromInlineAlias.self

_ = PublicAlias.self
}
4 changes: 3 additions & 1 deletion ...patibility/attr_inlinable_typealias.swift → ...ty/attr_inlinable_typealias_swift42.swift
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@@ -1,4 +1,6 @@
// RUN: %target-typecheck-verify-swift -swift-version 4
// RUN: %target-typecheck-verify-swift -swift-version 4.2

// Only warnings in Swift 4.2 mode.

private typealias PrivateAlias = Int
// expected-note@-1 {{type alias 'PrivateAlias' is not '@usableFromInline' or public}}
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