[2.x] feat: Add allowMismatchScala setting#8804
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eed3si9n merged 5 commits intosbt:developfrom Feb 25, 2026
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…date Scala versions
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Per review feedback, move the Scala version mismatch check from compileTask to projectDependenciesTask, where PR sbt#8681 already handles Scala version mixing logic. This provides earlier detection and keeps the validation co-located with cross-version resolution. Generated-by: Copilot
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sbt 2.x allows `dependsOn(...)` between subprojects with mismatched Scala versions without any warning or error. This can lead to confusing classpath issues at compile or runtime, especially now that Scala 3.8+ has dropped backward TASTy compatibility with 2.13. Per review feedback, move the Scala version mismatch check from compileTask to projectDependenciesTask, where PR sbt#8681 already handles Scala version mixing logic. This provides earlier detection and keeps the validation co-located with cross-version resolution. Generated-by: Copilot
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sbt 2.x allows `dependsOn(...)` between subprojects with mismatched Scala versions without any warning or error. This can lead to confusing classpath issues at compile or runtime, especially now that Scala 3.8+ has dropped backward TASTy compatibility with 2.13. Per review feedback, move the Scala version mismatch check from compileTask to projectDependenciesTask, where PR #8681 already handles Scala version mixing logic. This provides earlier detection and keeps the validation co-located with cross-version resolution. Generated-by: Copilot Co-authored-by: dev-miro26 <[email protected]>
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Fixes #8802
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Problem
sbt 2.x allows
dependsOn(...)between subprojects with mismatchedScala versions without any warning or error. This can lead to confusing
classpath issues at compile or runtime, especially now that Scala 3.8+
has dropped backward TASTy compatibility with 2.13.
Solution
allowMismatchScalasetting key (defaultfalseat global level).false, errors on Scala binary version mismatches betweendependsOnprojects, with an exception for the Scala 2.13 ↔ 3.0–3.7sandwich (traditional TASTy compatibility).
trueon a project, allows arbitrary Scala version dependencies.Testing
isAllowedScalaMismatchedge casesproject/allow-mismatch-scalacovering:allowMismatchScala := truemimaReportBinaryIssuespasses (no bincompat issues)AI Disclosure
This PR was created with AI assistance (Claude Opus 4.6). All changes
were compiled, tested, and verified.