Benchmark fails to compile with Xcode 16

[BjornRuud]

The benchmark will not compile with Xcode 16, it fails in JSON.swift (latest on main):

swift-parsing/Sources/swift-parsing-benchmark/JSON.swift

Line 71 in 82f10fc

var body: some ParserPrinter<Substring.UTF8View, [String: JSONValue.Output]> {

Failed to produce diagnostic for expression; please submit a bug report (https://swift.org/contributing/#reporting-bugs)

[DivineDominion]

I got a similar error in a production app where Xcode 15.1/Swift 5.9.2 can infer the type just fine, while Xcode 15.4/Swift 5.10 can't.

I wonder if there's a way to flatten the parser builder expressions?

The inferred type is this in our case:

Many<Substring.UTF8View, ParserBuilder<Substring.UTF8View>.SkipSecond<ParserBuilder<Substring.UTF8View>.Take2<ParserBuilder<Substring.UTF8View>.SkipSecond<ParserBuilder<Substring.UTF8View>.SkipSecond<ParserBuilder<Substring.UTF8View>.SkipSecond<ParserBuilder<Substring.UTF8View>.SkipFirst<Parsers.OverridePrinting<Whitespace<PartialRangeFrom<Int>, Conversions.Identity<Substring.UTF8View>>, EmptyParserPrinter>, Parsers.OverridePrinting<JSONStringParser, JSONStringParser>>, Parsers.OverridePrinting<Whitespace<PartialRangeFrom<Int>, Conversions.Identity<Substring.UTF8View>>, EmptyParserPrinter>>, Parsers.OverridePrinting<String.UTF8View, String.UTF8View>>, Parsers.OverridePrinting<Whitespace<PartialRangeFrom<Int>, Conversions.Identity<Substring.UTF8View>>, EmptyParserPrinter>>, JSONScalarParser>, Parsers.OverridePrinting<Whitespace<PartialRangeFrom<Int>, Conversions.Identity<Substring.UTF8View>>, EmptyParserPrinter>>, JSONFlatObject, String.UTF8View, Parse<Substring.UTF8View, ParserBuilder<Substring.UTF8View>.SkipSecond<ParserBuilder<Substring.UTF8View>.SkipSecond<Parsers.OverridePrinting<OneOf<Substring.UTF8View, (), OneOfBuilder<Substring.UTF8View, ()>.OneOf2<String.UTF8View, Whitespace<PartialRangeFrom<Int>, Conversions.Identity<Substring.UTF8View>>>>, EmptyParserPrinter>, Parsers.OverridePrinting<Whitespace<PartialRangeFrom<Int>, Conversions.Identity<Substring.UTF8View>>, EmptyParserPrinter>>, Parsers.OverridePrinting<String.UTF8View, String.UTF8View>>>, ()>

From this expression:

        Many(0..., into: JSONFlatObject()) { object, pair in
            let (name, value) = pair
            object[name] = value
        } decumulator: { object in
            object.keys
                .map { key -> (String, JSONScalar) in
                    return ("\(key)", object[key]!)
                }
                .reversed()
                .makeIterator()
        } element: {
            Whitespace(0...).noPrinting()
            JSONStringParser()
                .prettyPrinter(printOptions) {
                    JSONStringParser(printOptions: printOptions.indented())
                }
            Whitespace(0...).noPrinting()
            ":".utf8
                .prettyPrinter(printOptions) { ": ".utf8 }
            Whitespace(0...).noPrinting()
            JSONScalarParser()
            Whitespace(0...).noPrinting()
        } separator: {
            ",".utf8
        } terminator: {
            Parse {
                OneOf {
                    ",".utf8
                    Whitespace(0...)
                }
                .noPrinting()

                Whitespace(0...).noPrinting()

                "}".utf8
                    .prettyPrinter(printOptions) {
                        ("\n" + printOptions.indentation + "}").utf8
                    }
            }
        }

[mbrandonw]

Hi @DivineDominion and @BjornRuud, as far as I can tell this was fixed in #355. We just needed to add a type annotation to get it compiling again, and it now compiles just fine for me in 16.0 and 16.1.

Do you have an example of a parser that does not compile in Xcode 16?

I wonder if there's a way to flatten the parser builder expressions?

Just as with SwiftUI, you can break these parsers into smaller ones. For example, the element and terminator parsers are quite complex, so you can extract them into a dedicated Parser conformance.

I am going to convert this to a discussion since I am not sure it is an issue anymore. Let's continue the conversation over there.

[BjornRuud]

Yes benchmark on main compiles for me in Xcode 16.1. 👍

[DivineDominion]

Helping the compiler with type annotations fixed it in the library (and also in my app's parser example) 👍

I only noticed this very late after reinstalling Xcode 15.1 to get the inferred type (which also works when added as an as type hint).

I'd like to suggest a recommendation in the docstring to annotate the types in the accumulator block, or in the Many type docs, then it's visible from browsing the documentation page.