Fix wrong diagnostic for generics

[kimdv]

Fixes #1483

Opened to see if I was on the right path

[kimdv]

@swift-ci please test

[ahoppen]

I think we should not diagnose this in the parser. A generic parameter list can be represented perfectly well in the SwiftSyntax tree and should thus be diagnosed by later stages of the compilation pipeline.

I should have added that comment to the GitHub issue, sorry. We should fix the crash though.

[kimdv]

@ahoppen I'm not sure I understand.
When debugging this, I looked into the old parser and try to make the same as the old parser.

I think the reason is, because here the current token is <> (a binary operator).
https://github.com/apple/swift-syntax/blob/ac4f8f3ee2d3866152bcd555a62cb8317ea3cb11/Sources/SwiftParser/Declarations.swift#L467

The line after we then consume the token and remap it to <.
Then it crash here because text is not empty, it is <>.
https://github.com/apple/swift-syntax/blob/ac4f8f3ee2d3866152bcd555a62cb8317ea3cb11/Sources/SwiftSyntax/generated/TokenKind.swift#L982-L983

So what I try to do, is only consume the < and then move the lexer to >.

[ahoppen]

Forget what I said. I was stupid and didn’t read your PR properly, I’m sorry.

I thought you had added code in ParseDiagnosticGenerator that detected empty generic argument lists but that’s just not what you did. Looking at your PR again, it looks good, I’m just wondering why you can’t use consumePrefix.

[kimdv]

@swift-ci please test

[kimdv]

@swift-ci please test windows