buildExpression overload for ListBuilder proposal

[RoBo-Inc]

There is an overload in ListBuilder:

@_disfavoredOverload
static func buildExpression(_ expression: FinalResult) -> Component {
  expression.map { $0 }
}

This overload isn't a "standard" function for a resultBuilder to have. It's a convenience overload for the "swift-syntax" library. If it happens that our expression is already of type FinalResult, we can still use the same syntax without needing to handle this scenario separately. I stumbled upon this overload accidentally while working on my pet project when was surprised to find that my code still compiles. So, yes, it's quite convenient.

In this PR, I propose adding one more buildExpression overload for convenience:

static func buildExpression(_ expression: Component) -> Component {
  expression
}

Its purpose is similar to the function:

static func buildArray(_ components: [Component]) -> Component {
  components.flatMap { $0 }
}

It allows to build arrays. While the above function facilitates array building using the for ... in ... syntax, the overload I propose enables array building using result of .map { } expression.
It has always felt strange to me that "standard" resultBuilders work with for ... in ... but not with .map { }. It seems counterintuitive. Personally, I prefer the .map { } syntax over for ... in .... I believe it would be beneficial to allow developers to use both syntaxes when working with resultBuilders.

This proposal is additive and has no impact on existing source code.

[ahoppen]

Looks nice. Thank you!

Could you also add a short test case that uses this?

[RoBo-Inc]

Updated ✅

[RoBo-Inc]

By the way, for some reason ./swift-syntax-dev-utils local-pr-precheck started to fail on my machine. On the main branch, so it's not related to my changes 🙂

error: couldn't build /Users/roman/Projects/swift-syntax/SwiftParserCLI/.build/x86_64-apple-macosx/debug/_AtomicBool.build/src/AtomicBool.c.o because of missing inputs: /Users/roman/Projects/swift-syntax/Sources/_AtomicBool/src/AtomicBool.c

[Matejkob]

By the way, for some reason ./swift-syntax-dev-utils local-pr-precheck started to fail on my machine. On the main branch, so it's not related to my changes 🙂

error: couldn't build /Users/roman/Projects/swift-syntax/SwiftParserCLI/.build/x86_64-apple-macosx/debug/_AtomicBool.build/src/AtomicBool.c.o because of missing inputs: /Users/roman/Projects/swift-syntax/Sources/_AtomicBool/src/AtomicBool.c

Hmm, that's odd. It works for me. Have you tried after @keith's changes: #2484

[RoBo-Inc]

By the way, for some reason ./swift-syntax-dev-utils local-pr-precheck started to fail on my machine. On the main branch, so it's not related to my changes 🙂

error: couldn't build /Users/roman/Projects/swift-syntax/SwiftParserCLI/.build/x86_64-apple-macosx/debug/_AtomicBool.build/src/AtomicBool.c.o because of missing inputs: /Users/roman/Projects/swift-syntax/Sources/_AtomicBool/src/AtomicBool.c

Hmm, that's odd. It works for me. Have you tried after @keith's changes: #2484

Funny, looks like it depends on Terminal application (I'm using "Warp"). 🤯 But in "iTerm2" it seems everything works fine. ✅

[keith]

(note my changes are unrelated unless you're using bazel)

looks like you just needed a clean build

[ahoppen]

Thanks!

[ahoppen]

@swift-ci Please test

[RoBo-Inc]

So can the PR be merged now? 😃

[ahoppen]

@swift-ci Please test Windows

[ahoppen]

Oh, sorry. Forgot about it. Thanks for the reminder.