swift should offer fixit for "#elif"

[ahoppen]

Description

Swift offers a fixit for #else if -> #elseif.

We should also offer a fixit for #elif, eg:

error: use of unknown directive '#elif'
                    #elif arch(arm64)
                    ^

---

error: unexpected 'if' keyword following '#else' conditional compilation directive; did you mean '#elseif'?
                    #else if arch(arm64)
                    ~~~~~~^~
                    #elseif

rdar://103506087

[TiagoMaiaL]

I've started investigating this issue. I've used the following code to check on the parser diagnostics:

let sourceFile = Parser.parse(source: """
    #if arch(arm64)
    debugPrint("arm64")
    #elif arch(x86_64)
    debugPrint("x86_64")
    #endif
""")

let diagnostics = ParseDiagnosticsGenerator.diagnostics(for: sourceFile)
print(diagnostics)
print(diagnostics.flatMap(\.fixIts).map(\.message.message))

The above code prints the following:

[3:6: consecutive statements on a line must be separated by ';']
["insert \';\'"]

Swift offers a fixit for #else if -> #elseif.

I've tried using ´#else if´ instead of ´#elseif´ in the code above, but here's the emitted diagnostic (which is different from the message in this issue):

[3:22: expected '{' in 'if' statement, 4:21: expected '}' to end 'if' statement]
["insert \'{\'", "insert \'}\'"]

@ahoppen Am I on the right track? Should I be looking for fixIts in ParseDiagnosticsGenerator?

Thanks in advance.

[bnbarham]

Thanks for having a look @TiagoMaiaL!

Swift offers a fixit for #else if -> #elseif.

Is referring to the C++ parser in the Swift compiler. It outputs a useful diagnostic on a #elseif. This bug is about adding a similar diagnostic to this parser + also handling elif as the current diagnostics for these cases aren't great (as you saw).

https://github.com/apple/swift-syntax/blob/main/Sources/SwiftParser/SwiftParser.docc/FixingBugs.md talks about this a little. In this case parsePoundIfDirective will need to be updated to produce an unexpected node for the #else + if and then a missing node for #elseif. Similar for the #elif case, ie. an unexpected for #elif and then missing #elseif. After that you'll want to add a custom diagnostic in the diagnostics generator.

[TiagoMaiaL]

@ahoppen I think this can be finally closed, right? Thank you for the help!

[ahoppen]

Yes, thanks for your patience and seeing this Fix-It through 🙏🏽