fix: tryEagerEval does not force unevaluated lazy thunks#949
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stephenamar-db merged 2 commits intoJun 18, 2026
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Motivation: The resolveAsDouble optimization called binding.value on scope bindings, which forced lazy thunk evaluation even when the result would be discarded (e.g., dead branches). This violated Jsonnet's lazy evaluation semantics — side effects like std.trace or error in unused bindings would execute when they should not. Modification: In resolveAsDouble, pattern match on the binding directly instead of calling binding.value. Only Val.Num (already evaluated numbers) are used; unevaluated lazy thunks return NaN (skip), preserving lazy semantics. Result: `local a = error "x"; local b = a + 1; if false then b else 0` now returns 0 without evaluating 'a', matching go-jsonnet and jrsonnet behavior.
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Motivation
The
tryEagerEvaloptimization forced evaluation of lazy thunks by callingbinding.valueon scope bindings, violating Jsonnet's lazy evaluation semantics. Unused bindings with side effects (e.g.,error,std.trace) were evaluated even when their results were never needed.Modification
resolveAsDoubleto pattern-match on the binding directly instead of forcing.valueVal.Numbindings are used for eager evaluationDouble.NaN(skip optimization), preserving lazy semanticsResult
local a = error "should not be evaluated"; local b = a + 1; if false then b else 0now correctly returns0without evaluatinga, matching go-jsonnet and jrsonnet lazy evaluation semantics.References
local f(x) = x; local y = f(error "boom"); if true then 42 else y424242✅local a = error "x"; if false then a + 1 else 0000✅0✅