Refine automatic rewriting of trailing closures #1788

woolsweater · 2024-10-27T19:55:26Z

Description

Context

Following from the rationale given in #1787, whether to expand a trailing closure is not a syntactical decision; it depends on the function's semantics. As discussed, predicate-based functions (map, filter) are one case where an expansion is often inappropriate. Since the introduction of async functions we can also see callback-passing style become less common/prominent altogether, meaning that the relative proportion of predicate-like calls is increasing.

In the case of multiple closures, it is again a stylistic choice whether to expand all of them, or only some. Sometimes only the last should be expanded; e.g., this is a perfectly common style in SwiftUI code:

Button(action: { self.viewModel.makeItDo() }) {
  Text("Tap me!")
    .other(.modifiers)
    .etc(.etc)
}

Proposed Change

Since the expansion logic has limited or no knowledge of a function's semantics, I believe that it should be made much less aggressive. By default, it should always produce a closure on the same line as the call, with a single placeholder inside the closure: i.e. completion for a call to func foo(bar: Bar, baz: @escaping () -> Void) should expand to:

foo(baz: <#Baz#>) { <##> }

This is a much better experience for the user in the case where they did not want a multi-line expansion, while preserving most of the benefits of the current behavior from #1072. A "full expansion" configuration setting could opt the user in to current behavior.

A further refinement might be to use an allowlist for known "callback-like" methods, and produce the multi-line expansion only for them. But since users can always define their own methods with trailing closures, and the LSP server has no way to distinguish the semantics of those cases, the default should remain the single-line form.

The text was updated successfully, but these errors were encountered:

ahoppen · 2024-10-27T20:02:42Z

Synced to Apple’s issue tracker as rdar://138732066

This resolves <swiftlang#1788>, following the discussion of alternatives on <https://github.com/swiftlang/sourcekit-lsp/pulls/1789>. The bulk of the change updates the translation from SourceKit placeholders to LSP placeholders to handle nesting.

This addresses <swiftlang/sourcekit-lsp#1788>. Per <swiftlang/sourcekit-lsp#1789>, these placeholders no longer expand to multi-line trailing closures. Instead they become inline closures, with nested placeholders for the signature and body. This introduces a new formatter, `ClosureLiteralFormat`, so that other uses of `BasicFormat` are not impacted. `ClosureLiteralFormat` does not insert newlines into a closure when there is only a single statement in the body.

This resolves <swiftlang#1788>, following the discussion of alternatives on <https://github.com/swiftlang/sourcekit-lsp/pulls/1789>. The bulk of the change updates the translation from SourceKit placeholders to LSP placeholders to handle nesting.

This addresses <swiftlang/sourcekit-lsp#1788>, refining code completion for closure placeholders. By default function-typed placeholders will continue to expand to multi-line trailing form. A caller, such as sourcekit-lsp, may now customize the behavior by passing its own formatter. It may additionally request that the closure itself be marked as a placeholder, with the argument and return type placeholders nested inside.

This resolves <swiftlang#1788>, following the discussion of alternatives on <https://github.com/swiftlang/sourcekit-lsp/pulls/1789>. The bulk of the change updates the translation from SourceKit placeholders to LSP placeholders to handle nesting. The `CodeCompletionSession` also passes a new custom formatter to the swift-syntax expansion routine, which disables the transformation to trailing closures.

woolsweater added the enhancement New feature or request label Oct 27, 2024

This was referenced Oct 27, 2024

Configuration option for auto-rewrite of trailing closures #1787

Open

Add config option for trailing closure rewriting #1789

Closed

This was referenced Nov 17, 2024

Allow customization of expansion for function-typed placeholders swiftlang/swift-syntax#2897

Open

Handle new swift-syntax closure expansion behavior #1831

Open

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Refine automatic rewriting of trailing closures #1788

Refine automatic rewriting of trailing closures #1788

woolsweater commented Oct 27, 2024 •

edited

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ahoppen commented Oct 27, 2024

Refine automatic rewriting of trailing closures #1788

Refine automatic rewriting of trailing closures #1788

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woolsweater commented Oct 27, 2024 • edited Loading

Description

Context

Proposed Change

ahoppen commented Oct 27, 2024

woolsweater commented Oct 27, 2024 •

edited

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