fix: reject duplicate function parameters with correct error in all contexts#1011
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…ontexts Motivation: go-jsonnet issue databricks#873 reports that (function(x, x, x) x)(null, 3, 2) silently returns 2 instead of rejecting duplicate parameter names. sjsonnet already rejected duplicates in function expressions, but the error message was misleading in local bindings and object methods. Modification: The params parser correctly detects duplicates via flatMapX + Fail. However, in bind (local f(x,x)=...) and field ({f(x,x):...}), the optional group .? around params swallowed the "no duplicate parameter" error and backtracked, producing misleading errors like "Expected )". Replaced .? with ./ (committed-or): "(" ~/ params ~ ")" ./ | Pass(null). The cut ~/ after "(" commits to the params path, and ./ prevents the | alternative from trying the fallback when the committed path fails. Result: All duplicate parameter contexts now produce the correct error: "Expected no duplicate parameter: x" with accurate position info. - (function(x, x, x) x) -> ParseError (already worked) - local f(x, x) = x -> ParseError (was "Expected )") - { f(x, x): x } -> ParseError (was "Expected :") - { local f(x, x) = x } -> ParseError (was "Expected )") Tests pass on Scala 3.3.7, 2.13.18, 2.12.21. References: - google/go-jsonnet#873
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Motivation
go-jsonnet issue #873 reports that
(function(x, x, x) x)(null, 3, 2)silently returns
2instead of rejecting duplicate parameter names.sjsonnet already rejected duplicates in function expressions, but the
error message was misleading in local bindings and object methods
(e.g. "Expected ")"" or "Expected ":"").
Modification
The
paramsparser correctly detects duplicates viaflatMapX+Fail. However, inbind(local f(x,x)=...) andfield(
{f(x,x):...}), the optional group.?aroundparamsswallowedthe "no duplicate parameter" error and backtracked, producing
misleading errors.
Two changes fix this:
field(): added~/(cut) after"("to commit to the paramspath once
"("is matched:"(" ~/ params(...) ~ ")".params(): setctx.cut = trueprogrammatically when aduplicate is detected, preventing outer
.?operators fromswallowing the error. Also captures
Posfor each parameter toposition the error at the duplicate parameter name (not at the
closing paren).
Result
All duplicate parameter contexts now produce the correct error
"Expected no duplicate parameter: x"with accurate position info:(function(x, x, x) x)-> ParseError (already worked)local f(x, x) = x-> ParseError (was"Expected )"){ f(x, x): x }-> ParseError (was"Expected :"){ local f(x, x) = x }-> ParseError (was"Expected )")Tests pass on Scala 3.3.7, 2.13.18, 2.12.21.
References