Fix #935 + implement #770: context-function-scoped path selectors - #948
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MateuszKubuszok merged 3 commits intoSep 1, 2026
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When deriving Foo → Option[Bar], TransformToOptionRule wraps Foo into Option[Foo] and delegates to OptionToOption, which recurses into Foo → Bar. Source-side subtype overrides (from withEnumCaseHandled) are dropped during that recursion because their paths don't match the Option wrapper path, and their return type (Option[Bar]) doesn't match the inner target (Bar). Fix: when source-side subtype overrides exist and From is a sealed hierarchy, generate the pattern match directly at the From → Option[To] level — consuming overrides there and deriving non-overridden subtypes by name-matching against the inner target's subtypes.
Path extension methods (matching, everyItem, everyMapKey, everyMapValue, matchingSome, matchingLeft, matchingRight) were available on every value once dsl.* or syntax.* was imported. Now they require a ChimneySelector given, which is only provided inside DSL selector lambdas via context functions (ChimneySelector ?=> From => T). - Add sealed trait ChimneySelector phantom type in internal.runtime - Add `using ChimneySelector` to path extension blocks in syntax.scala - Change selector params in all Scala 3 DSL classes to context functions - Update DslDefinitions parser to unwrap Block/nested-lambda wrapping - Widen macro adapter selector params to Expr[Any] Not a breaking change: selector functions are inline macro parameters, so the context function wrapper is invisible to existing user code.
Remove dead `OptionFromType` implicit val from `wrapInOptionAndTransform` (moved to `wrapAndDelegateToOptionToOption` during #935 refactor) — Scala 2.13 -Werror rejects unused locals. Fix Scaladoc line wrap in ChimneySelector.scala for scalafmt.
MateuszKubuszok
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September 1, 2026 21:32
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Summary
withEnumCaseHandledoverride silently dropped when target type isOption[B]— the override is now consumed at the correct derivation level before Option wrappingmatching,everyItem,everyMapKey, etc.) are now scoped to selector lambdas via context functions, no longer polluting the global scopeFix #935: withEnumCaseHandled with Option target
Root cause:
TransformToOptionRulewrapsFromintoOption[From]and delegates toOptionToOption, which recurses intoFrom → InnerTo. During recursion, source-side subtype overrides are dropped because:matching[Some[From]].value(the recursion prefix)Option[To]) doesn't match the inner target (InnerTo)Fix: When source-side subtype overrides exist and
Fromis a sealed hierarchy,TransformToOptionRulenow generates the pattern match directly at theFrom → Option[To]level — consuming overrides there (where the return type matches) and deriving non-overridden subtypes by name-matching againstInnerTo's subtypes.Implement #770: context-function-scoped path extensions
Path extension methods were available on every value once
dsl.*orsyntax.*was imported. Now they requireusing ChimneySelector, which is only provided inside DSL selector lambdas via context functions (ChimneySelector ?=> From => T).Changes:
ChimneySelectorsealed trait phantom type ininternal.runtimeusing ChimneySelectorconstraint on path extension blocks insyntax.scalaDslDefinitionsparser updated to unwrap Block/nested-lambda wrapping from context function resolutionExpr[Any]Not a breaking change: selector functions are
inlinemacro parameters, so the context function wrapper is invisible to existing user code.Test plan
withEnumCaseHandledtoOptiontarget)