Fix FormatString false positive for switch expression arguments#5967
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Fix FormatString false positive for switch expression arguments#5967arimu1 wants to merge 2 commits into
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When a switch expression is passed directly to printf, javac types the expression as Object. Infer the result type from case bodies so format validation uses the real primitive or reference type. Fixes google#5831
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Use getExpressionType for arrow-case bodies and the body fallback so nested switch expressions are typed correctly. Handle colon/yield cases via CaseTree.getStatements when getBody() is null. Add lean regression tests for nested switch, block/colon yield, string cases, and mixed types.
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Summary
FormatStringreported a spuriousillegal format conversionwhen anint-typed switch expression was passed directly toprintf("%d", ...)because javac types the whole expression asObject, so validation fell back to a generic placeholder instance.vartemporary form and the inlined switch expression.Fixes #5831
Test plan
mvn -pl core clean test -Dtest=FormatStringTest(50/50 pass, JDK 25 toolchain)mvn -pl core test -Dtest=LenientFormatStringValidationTest,FormatStringTestFormatStringValidation.javamakesswitchExpressionArgumentfail with the originalFormatStringValidation$…/%ddiagnosticHuman-reviewed AI assistance (Cursor implementator).
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