[2.x] fix: Reject java.io.File as cached task output type#8766
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eed3si9n merged 5 commits intosbt:developfrom Feb 21, 2026
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[2.x] fix: Reject java.io.File as cached task output type#8766eed3si9n merged 5 commits intosbt:developfrom
eed3si9n merged 5 commits intosbt:developfrom
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Change the behavior when a cached task's output type contains java.io.File: instead of silently skipping the cache, throw a compile-time error with a message recommending xsbti.VirtualFileRef, xsbti.HashedVirtualFileRef, or xsbti.VirtualFile, and linking to the caching documentation. Internal sbt tasks that return File types are wrapped with Def.uncached to opt out of caching. Fixes sbt#8762 Generated-by: GitHub Copilot (Claude)
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| ((ThisBuild / baseDirectory).value / "target" / "sona-bundle" / "bundle.zip").toPath() | ||
| ) | ||
| .toFile(), | ||
| sonaBundle := Def.uncached( |
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As a general strategy, I think we should put @trainsient on Keys.scala instead of putting Def.uncached(...) in Defaults.scala since this would force the build users to also put Def.uncached(...) when they rewire the task.
Use @transient on File-returning keys in Keys.scala instead of wrapping tasks with Def.uncached in Defaults.scala. This ensures build users who rewire these tasks also get caching skipped automatically. - Add @transient to 19 File-returning taskKey definitions in Keys.scala - Revert Def.uncached wrappers from Defaults.scala - Error at compile time when File is used as cached task output type - Update error message to recommend @transient and link to docs - Update scripted tests to use @transient approach Fixes sbt#8762 Generated-by: GitHub Copilot (Claude Opus 4.6)
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Problem
Fixes #8762
When a task returns
java.io.File(e.g.assembly / assemblyOutputPath), the result gets cached byActionCache. SinceFileserializes as an absolute path string, the cached value becomes stale whenscalaVersionchanges via++ 2.13.18!— the path still contains the old Scala version directory.Reproduction (from #8762)
Solution
In
Cont.scala'scallActionCachemethod, detect when the task's return typeAcontainsjava.io.Fileat compile time usingcontainsFileType[A]. When it does, skip wrapping the task body withActionCache.cache(...), while still processing anyDef.declareOutput(...)calls vialetOutput. This way:taskKey[File]tasks are never cached (sinceFileisn't content-addressable)Def.declareOutput(...)continues to work correctly for File tasksTests
cache/skip-file-cachescripted test: Defines ataskKey[File]that depends onscalaVersion, switches versions, and asserts the returned path updates.actions/task-map(usesDef.declareOutputwithtaskKey[File]) continues to pass.actions/* cache/* tests/* compiler-project/*etc. — all pass.