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perf: capture parse Position without boxing the offset Int #876

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perf: capture parse Position without boxing the offset Int #876

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11 changes: 10 additions & 1 deletion sjsonnet/src/sjsonnet/Parser.scala
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Original file line number Diff line number Diff line change
Expand Up @@ -96,7 +96,16 @@ class Parser(
throw new ParseError(msg, offset = offset)
}

def Pos[$: P]: P[Position] = Index.map(offset => new Position(fileScope, offset))
// Capture the current parse offset as a Position directly, rather than `Index.map(...)`.
// `Index` stores the offset as an `Int` in fastparse's `successValue: Any`, boxing it, and the
// `.map` then unboxes it and allocates a closure — both per AST node (Pos is called for nearly
// every node). Writing the Position straight into successValue (a reference) skips the box/unbox
// and the lambda. boxToInteger via SharedPackageDefs.Index was a top self-frame in the parse
// flamegraph on kube-prometheus.
def Pos[$: P]: P[Position] = {
val ctx = implicitly[P[$]]
ctx.freshSuccess(new Position(fileScope, ctx.index))
}

def id[$: P]: P[String] = P(
CharIn("_a-zA-Z") ~~
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