[zienag]

With known compilation conditions, an #else reached after false conditions was not treated as the active branch. An #else clause has no condition, and evaluating it gave nil, the same as an unknown condition, so the whole #if stayed unresolved. Reads inside it still worked, but an @Implicit declaration in the #else failed with "Cannot mutate implicit context inside '#if' block with unresolved condition", and the note pointed at a condition that was in fact known. A release build hit this with #if INTERNAL_BUILD ... #else @Implicit() var voiceDialog: VoiceDialog = io #endif when INTERNAL_BUILD was not defined.

Changes

• filterInactiveIfConfig recognizes an #else by its keyword and counts it as true once reached. An #else after an unknown condition still stays unresolved, as before.
• parsedCondition uses the same isElse check instead of inferring #else from a missing condition.
• if_config_code_block.swift covers declarations in an active #else after a false #if and #elseif.

Test plan

• The new case failed before the fix with the mutation error and notes at the known #if D and #elseif E lines.
• swift test (Xcode Swift 6.3.2): 121 tests pass.

[Copilot]

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Copilot review overview

3 open issues

• This makes #else clauses evaluate as active (true) unconditionally (because `condition ==… · New
• clause.condition.map(eval) produces a Bool?? (because condition is optional and eval… · New
• In this repo’s context excerpts, @Implicit() is used (with parentheses). These new tests use… · New

What changed in this PR

Fixes conditional-compilation branch resolution so a reachable #else becomes the active branch when all earlier conditions are known-false, preventing false “unresolved #if” mutation errors for @Implicit declarations.

Changes:

• Treats #else clauses as active (true) once reached in filterInactiveIfConfig.
• Adds test cases covering @Implicit declarations inside an active #else (after #if and after #elseif).

File	Description
Sources/​ImplicitsTool/​CompilationConditionsConfig.swift	Adjusts clause-activity evaluation so #else can resolve as active.
Sources/​TestResources/​test_data/​if_config_code_block.swift	Adds regression cases ensuring @Implicit declarations work in active #else branches.

_{Review effort: Lite}