[WIP] Forward matching of trailing closure arguments. #32644

DougGregor · 2020-07-01T07:03:30Z

Introduce an experimental attribute and command-line flag to replace
the "backward" matching algorithm for unlabeled trailing closure
arguments with a simpler "forward" algorithm. In this new algorithm,
unlabeled trailing closure arguments match the next parameter in the
parameter list that can accept an unlabeled trailing closure.

The "can accept an unlabeled trailing closure" criteria looks at the
parameter itself. The parameter accepts an unlabeled trailing closure
if all of the following are true:

The parameter is not variadic
The parameter is not inout
The adjusted type of the parameter (defined below) is a function type

The adjusted type of the parameter is the parameter's type as
declared, after performing two adjustments:

If the parameter is an @autoclosure, use the result type of the
parameter's declared (function) type, before performing the second
adjustment.
Remove all outer "optional" types.

For example, the following function illustrates both adjustments to
determine that the parameter "body" accepts an unlabeled trailing
closure:

func doSomething(body: @autoclosure () -> (((Int) -> String)?))

This source-breaking change is accessible in one of two ways. The new attribute

@_trailingClosureMatching(.forward)

can be applied to a function, initializer, or subscript to enable the
new forward matching algorithm for direct calls to that function. This
allows specific APIs to opt in to forward matching while leaving all
other calls unaffected.

The command-line parameter -enable-experimental-trailing-closure-matching
enables forward matching as the default algorithm. It is most useful
for experimenting with the source-compatibility effects of forward
matching.

Specific APIs can also explicitly request to use the current, backward
matching algorithm to maintain their existing behavior even under the
new command-line parameter, by using the other form of the new
trailing closure matching attribute:

@_trailingClosureMatching(.backward)

DougGregor · 2020-07-02T06:57:06Z

@swift-ci please test source compatibility

If we're matching the trailing closure at the end but haven't seen any mismatches yet, consider the trailing closure to be a mismatch. This function probably needs to be rewritten in terms of matchCallArguments(), because it is performing an incorrect approximation of label matching that doesn't work for multiple trailing closures.

@autoclosure

Introduce an experimental attribute and command-line flag to replace the "backward" matching algorithm for unlabeled trailing closure arguments with a simpler "forward" algorithm. In this new algorithm, unlabeled trailing closure arguments match the next parameter in the parameter list that can accept an unlabeled trailing closure. The "can accept an unlabeled trailing closure" criteria looks at the parameter itself. The parameter accepts an unlabeled trailing closure if all of the following are true: * The parameter is not variadic * The parameter is not 'inout' * The adjusted type of the parameter (defined below) is a function type The adjusted type of the parameter is the parameter's type as declared, after performing two adjustments: * If the parameter is an @autoclosure, use the result type of the parameter's declared (function) type, before performing the second adjustment. * Remove all outer "optional" types. For example, the following function illustrates both adjustments to determine that the parameter "body" accepts an unlabeled trailing closure: func doSomething(body: @autoclosure () -> (((Int) -> String)?)) This source-breaking change is accessible in one of two ways. The new attribute @_trailingClosureMatching(.forward) can be applied to a function, initializer, or subscript to enable the new forward matching algorithm for direct calls to that function. This allows specific APIs to opt in to forward matching while leaving all other calls unaffected. The command-line parameter `-enable-experimental-trailing-closure-matching` enables forward matching as the default algorithm. It is most useful for experimenting with the source-compatibility effects of forward matching. Specific APIs can also explicitly request to use the current, backward matching algorithm to maintain their existing behavior even under the new command-line parameter, by using the other form of the new trailing closure matching attribute: @_trailingClosureMatching(.backward)

DougGregor · 2020-07-02T21:00:25Z

@swift-ci test source compatibility

DougGregor · 2020-07-02T21:03:14Z

@swift-ci test source compatibility

DougGregor · 2020-07-03T03:58:33Z

We're missing a lot of data here because of the current SwiftPM issue. However, there are only 3 failures that are clearly attributable to this new rule:

ACHNBrowserUI and MovieSwift fail because SwiftUI.View.sheet(isPresented:onDismiss:content:) only works properly with the backward rule.
ModelAssistant has its own API that only works properly with the backward rule.

DougGregor · 2020-07-03T03:58:43Z

@swift-ci build toolchain

DougGregor · 2020-07-03T03:59:31Z

@swift-ci please build toolchain

DougGregor · 2020-07-03T17:35:36Z

@swift-ci please build toolchain

DougGregor · 2020-07-03T17:35:42Z

@swift-ci please test

DougGregor · 2020-07-03T17:35:54Z

@swift-ci please test source compatibility

DougGregor · 2020-07-03T17:36:09Z

@swift-ci please build toolchain

DougGregor · 2020-07-03T17:36:19Z

@swift-ci please test source compatibility

DougGregor · 2020-07-03T17:36:24Z

@swift-ci please test

swift-ci · 2020-07-03T17:49:17Z

Build failed
Swift Test OS X Platform
Git Sha - f0b8eb1

DougGregor · 2020-07-03T18:15:04Z

@swift-ci please test platform macOS

DougGregor · 2020-07-03T18:19:28Z

@swift-ci please test platform macOS

swift-ci · 2020-07-03T18:36:15Z

Linux Toolchain (Ubuntu 16.04)
Download Toolchain
Git Sha - f0b8eb1

Install command
tar zxf swift-PR-32644-371-ubuntu16.04.tar.gz
More info

swift-ci · 2020-07-03T19:05:03Z

macOS Toolchain
Download Toolchain
Git Sha - f0b8eb1

Install command
tar -zxf swift-PR-32644-540-osx.tar.gz --directory ~/

DougGregor · 2020-07-04T04:10:08Z

@swift-ci please smoke test platform macOS

DougGregor · 2020-07-16T22:30:05Z

Closing out this dead-end approach. See #32891 for the proposed way forward

DougGregor added 2 commits July 2, 2020 13:40

DougGregor force-pushed the forward-trailing-closure-matching branch from b689423 to 32ae69f Compare July 2, 2020 20:59

DougGregor force-pushed the forward-trailing-closure-matching branch from 32ae69f to f0b8eb1 Compare July 3, 2020 17:35

DougGregor closed this Jul 16, 2020

[WIP] Forward matching of trailing closure arguments. #32644

[WIP] Forward matching of trailing closure arguments. #32644

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