Reject modifier conditionals in if/unless predicates#4120
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kddnewton merged 2 commits intoJun 1, 2026
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Prism accepted a modifier conditional as the predicate of an `if`/`unless`
(and `elsif`), while parse.y rejects it:
if a if b then end # parse.y: SyntaxError, prism: accepted
unless a unless b then end
The `if`/`unless`/`elsif` predicate was parsed with a floor of
`PM_BINDING_POWER_MODIFIER`, which is inclusive of the modifier
conditionals (`if`/`unless`/`while`/`until`, left binding power
`PM_BINDING_POWER_MODIFIER`), so they were absorbed into the predicate.
`while`/`until` predicates already use `PM_BINDING_POWER_COMPOSITION` and
reject these correctly.
Raise the floor to `PM_BINDING_POWER_MODIFIER + 1` so the predicate still
absorbs `and`/`or` (and tighter operators) but excludes the modifier
conditionals, matching parse.y and aligning `if`/`unless` with
`while`/`until`.
Collaborator
|
Yeah this is great, I'm good with almost all the changes here. I think we should go with |
Contributor
Author
|
The two failing |
The `+ 1` form is meant to express associativity, not a binding-power floor; use the named constant instead, matching while/until conditions.
Contributor
Author
@kddnewton Thanks for the advice, switched to |
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Fixes Bug #22089.
Prism accepted a statement modifier (
if/unless/while/until) in anif/unless/elsifcondition, while parse.y rejects it.Those conditions were parsed with a binding-power floor of
PM_BINDING_POWER_MODIFIER. That floor is inclusive: statement modifiers have left binding powerPM_BINDING_POWER_MODIFIER, so they were consumed as part of the condition.while/untilconditions already usePM_BINDING_POWER_COMPOSITIONand reject this syntax.This raises the floor to
PM_BINDING_POWER_MODIFIER + 1, which keepsand/orand tighter operators in the condition but excludes statement modifiers, matching parse.y.while/untilusePM_BINDING_POWER_COMPOSITIONfor the same effect because there is currently no precedence betweenMODIFIERandCOMPOSITION. I usedPM_BINDING_POWER_MODIFIER + 1to match the existing+ 1floor idiom (PM_BINDING_POWER_DEFINED + 1,PM_BINDING_POWER_MATCH + 1) and state the boundary directly. I can switch this toPM_BINDING_POWER_COMPOSITIONif keeping the paths aligned is preferred.Added an error fixture under
test/prism/errors/.