Indentation for generic parameter lists

[dabrahams]

The automatic indentation for cases like this is somewhat suboptimal:

struct NonuniformTrainingBatches<
  BaseSamples: Collection, 
  BaseIndices: MutableCollection, BatchSample: Equatable
> {
  func foo() {}
}

I get:

struct NonuniformTrainingBatches<
BaseSamples: Collection, 
BaseIndices: MutableCollection, BatchSample: Equatable
                                  > {
  func foo() {}
}

The original indentation is what I'd have wanted. Generic parameter lists should probably be treated as "parenthesized expressions".

[taku0]

Short answer: it could be improved. I will try it.

Discussion:

< and > are used as either binary operators or angle brackets. Treating them as a bracket unconditionally would break indentation of expressions. So we must distinguish them.

There are two cases where < ... > is used other than binary operator:

• generic-parameter-clause

  • typealias-declaration
  • function-declaration
  • union-style-enum
  • raw-value-style-enum
  • struct-declaration
  • class-declaration
  • protocol-method-declaration
  • protocol-initializer-declaration
  • initializer-declaration
  • subscript-head

• generic-argument-clause

  • type-identifier
  • primary-expression
  • explicit-member-expression

generic-argument-clause is ambiguous: foo(A < B, C > (d)) could be parsed as foo((A < B), (C > (d))) or foo(A<B, C>(d)) (invocation of A with two type arguments B, C and one value d). On the other hand, generic-parameter-clause seems to be much simpler; looking back one or two tokens is sufficient to recognize the open bracket.

Summary of grammers of generic-parameter-clause:

• typealias-declaration:

  • "typealias" identifier "<"

• function-declaration:

  • "func" identifier "<"
  • "func" operator "<"

• union-style-enum:

  • "enum" identifier "<"

• raw-value-style-enum

  • "enum" identifier "<"

• struct-declaration

  • "struct" identifier "<"

• class-declaration

  • "class" identifier "<"

• protocol-method-declaration:

  • "func" identifier "<"
  • "func" operator "<"

• protocol-initializer-declaration

  • "init" "<"
  • "init" "?" "<"
  • "init" "!" "<"

• initializer-declaration:

  • "init" "<"
  • "init" "?" "<"
  • "init" "!" "<"

• subscript-head:

  • "subscript" "<"

[taku0]

Fixed by https://github.com/swift-emacs/swift-mode/commit/29759f529032fff9b88a77318a10b2a1ec8ef5c7. Thank you for reporting.

[dabrahams]

Thank you!

On Fri, Apr 17, 2020 at 11:19 PM taku0 notifications@github.com wrote:

Fixed by 29759f5 https://github.com/swift-emacs/swift-mode/commit/29759f529032fff9b88a77318a10b2a1ec8ef5c7 .

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-- Dave