[Python] Fix nonlocal declarations inside match/case blocks (SyntaxError regression)#4379
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[Python] Fix nonlocal declarations inside match/case blocks (SyntaxError regression)#4379
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…ror regression) Python requires `nonlocal`/`global` declarations to appear before any use of the variable in the enclosing function. Because `match/case` does not create a new scope, nonlocal statements generated inside case bodies caused `SyntaxError: name 'x' is used prior to nonlocal declaration` at runtime. Fix: lift NonLocal/Global statements out of all match case bodies before building the `Statement.match'` node. The lifted declarations are prepended to the result list, where `transformBody`'s existing `getNonLocals` pass then hoists them to the top of the enclosing function. Add `getNonLocals` and `getNonLocalsFromMatchCases` helpers to `Fable2Python.Util` and apply them at all 6 match statement creation sites in `Fable2Python.Transforms`. Also add regression tests covering the `take` operator pattern and nested union match with mutable closure captures. Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
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Summary
nonlocal/globaldeclarations were being generated insidecasebodies inmatch/casestatements, causingSyntaxError: name 'x' is used prior to nonlocal declarationat runtime (regression reported infsharp_control_async_rx/filter.py)Statement.match'node; prepend them before the match sotransformBodycan hoist them to the top of the enclosing functiongetNonLocalsandgetNonLocalsFromMatchCaseshelpers toFable2Python.Util(single source of truth) and apply them at all 6 match statement creation sites inFable2Python.TransformstakeFn(take operator with mutable closure) andnestedUnionMatch(nested union match with mutable capture)Test plan
./build.sh test python --skip-fable-librarypasses all tests including the two new regression testsfsharp_control_async_rx/filter.py(timeflies example) no longer throwsSyntaxErrornonlocal/globaldeclarations appear before any use of the variable in generated Python output🤖 Generated with Claude Code