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I found this issue interesting so I set up a little repo to work on it, to reproduce the problem outside of the somewhat ‘heavy’ environment of the full jenkins source code. I basically copied the smallest amount of code (including the grammar) to observe the issue. It’s available there.
Here’s what I can tell from the issue, complementing what’s already been found by Daniel.
In labelExpr.g, 7 ‘operators’ (or 'special tokens') are defined: AND, OR, NOT, IMPLIES, IFF, LPAREN, RPAREN. They’re made of a combination of the following characters: &|!->(). These characters are all excluded from what’s allowed in a “LabelAtom” token, except -, which is the issue.
When the lexer starts parsing a full label and starts a new token (for instance after a white space) with character ‘-‘, the token is either IMPLIES or ATOM. If the following character is >, the token is IMPLIES and should be complete (= a white space should follow). If it’s another character, the token must be an ATOM. Now if the lexer has already determined that it’s in an ATOM and finds a - followed by a >, it doesn’t understand that it should keep - and > together as an IMPLIES and backtrack before the - to close the ATOM it was reading. Instead it considers it’s an ATOM, and since > is not allowed in an ATOM the whole parsing fails.
Even though I (believe I) understand the issue I don’t see yet how to solve it by modifying the grammar.
One naive way to solve the problem is by forcefully looking for -> not preceded by space in the label, and add an extra space before feeding the parser/lexer. See function prepareLabelForParsing in TestGrammar.java.