decouple sbt-scalafix from scalafix lifecycle #482

bjaglin · 2025-04-13T18:31:38Z

Levarages

Instead of supporting a scalafix version in .scalafix.conf (which was the option most discussed in the corresponding issue long time ago), this takes the simpler but effective approach to force the user to explicitly define a scalafix version (via scalafix-interfaces) alongside the sbt-scalafix version in the meta-build, letting sbt handle resolution, evictions and compatibility checks.

When no scalafix-interfaces is explicitly provided, scalafix invocations will fail unless scalafixAllowDynamicFallback := true. Steward and other "one-shot" users are not impacted by this breaking change though, as scalafixEnable sets scalafixAllowDynamicFallback := true, which results in loading the latest stable version of scalafix at invocation time. Since that scalafix version & the corresponding recommended scalameta version are not known by the meta-build, scalafixEnable downloads the latest semanticdb-scalac for Scala 2 projects.

Other build tools integrations should be able to replicate that approach. As for CLI usage (which does not use scalafix-interfaces), coursier makes things easy enough to run a specific cli version, so I am not sure it's worth investing time in supporting a scalafix version in .scalafix.conf just for that use-case.

TODO

smooth update
- scalafix rule to make scalafix-interfaces explicit
- reference in steward
interfaces is early-semver, is that what we want? - add scripted to exercise that with old scalafix-interfaces versions?
update sbt-specific docs on scalafix repo, picking the sbt-scalafix version from the one injected in the build (updated via steward without delay)
- installation
- tutorial
- local rules
update g8
update all example repos under scalacenter org

bjaglin · 2025-04-13T23:15:19Z

project/Dependencies.scala


  val all = List(
+    "ch.epfl.scala" % "scalafix-interfaces" % scalafixVersion
+      exclude ("ch.epfl.scala", "scalafix-properties"),


This is the key change in this PR, leveraging scalacenter/scalafix#2226.

exclude is honored in the POM, and thus will allow a sbt-scalafix-only install to load ScalafixPlugin without linking errors (since classes from interfaces are present) but fail at invocation time (because properties file cannot be found).

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project/Dependencies.scala: Language not supported
project/plugins.sbt: Language not supported
src/main/scala/scalafix/internal/sbt/ScalafixInterface.scala: Language not supported
src/main/scala/scalafix/sbt/BuildInfo.scala: Language not supported
src/main/scala/scalafix/sbt/ScalafixPlugin.scala: Language not supported
src/sbt-test/sbt-scalafix/basic/project/plugins.sbt: Language not supported
src/sbt-test/sbt-scalafix/build-lint/project/plugins.sbt: Language not supported
src/sbt-test/sbt-scalafix/concurrency/project/plugins.sbt: Language not supported
src/sbt-test/sbt-scalafix/cross-build/project/plugins.sbt: Language not supported
src/sbt-test/sbt-scalafix/custom-config/project/plugins.sbt: Language not supported
src/sbt-test/sbt-scalafix/custom-src-directory/project/plugins.sbt: Language not supported
src/sbt-test/sbt-scalafix/dependency/project/plugins.sbt: Language not supported
src/sbt-test/sbt-scalafix/explicit-files/project/plugins.sbt: Language not supported
src/sbt-test/sbt-scalafix/inconfig/project/plugins.sbt: Language not supported
src/sbt-test/sbt-scalafix/interfaces-missing/build.sbt: Language not supported
src/sbt-test/sbt-scalafix/interfaces-missing/project/plugins.sbt: Language not supported
src/sbt-test/sbt-scalafix/interfaces-missing/test: Language not supported
src/sbt-test/sbt-scalafix/resolvers/project/plugins.sbt: Language not supported
src/sbt-test/sbt-scalafix/root-validation/project/plugins.sbt: Language not supported

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project/Dependencies.scala: Language not supported
project/plugins.sbt: Language not supported
src/main/scala/scalafix/sbt/BuildInfo.scala: Language not supported
src/main/scala/scalafix/sbt/ScalafixEnable.scala: Language not supported
src/main/scala/scalafix/sbt/ScalafixPlugin.scala: Language not supported
src/sbt-test/sbt-scalafix/basic/project/plugins.sbt: Language not supported
src/sbt-test/sbt-scalafix/build-lint/project/plugins.sbt: Language not supported
src/sbt-test/sbt-scalafix/concurrency/project/plugins.sbt: Language not supported
src/sbt-test/sbt-scalafix/cross-build/project/plugins.sbt: Language not supported
src/sbt-test/sbt-scalafix/custom-config/project/plugins.sbt: Language not supported
src/sbt-test/sbt-scalafix/custom-src-directory/project/plugins.sbt: Language not supported
src/sbt-test/sbt-scalafix/dependency/project/plugins.sbt: Language not supported
src/sbt-test/sbt-scalafix/explicit-files/project/plugins.sbt: Language not supported
src/sbt-test/sbt-scalafix/inconfig/project/plugins.sbt: Language not supported
src/sbt-test/sbt-scalafix/interfaces-missing/build.sbt: Language not supported
src/sbt-test/sbt-scalafix/interfaces-missing/project/plugins.sbt: Language not supported
src/sbt-test/sbt-scalafix/interfaces-missing/src/main/scala/A.scala: Language not supported
src/sbt-test/sbt-scalafix/interfaces-missing/test: Language not supported
src/sbt-test/sbt-scalafix/resolvers/project/plugins.sbt: Language not supported

Comments suppressed due to low confidence (1)

readme.md:22

Consider adding an explanatory comment to clarify why the Sonatype snapshots resolver is required for these snapshot dependencies to aid user understanding.

resolvers += Resolver.sonatypeRepo("snapshots")

bjaglin · 2025-04-16T08:17:17Z

project/Dependencies.scala

+
+  // keep this as low as possible, to allow bumping sbt-scalafix without scalafix-interfaces
+  def scalafixInterfacesVersion: String =
+    "0.14.2+48-9b6e03ac-SNAPSHOT" // scala-steward:off


🛑 this must be updated to the next stable version before merging, or at least tagging a release

- scalafixEnable & scalafixAllowDynamicFallback allow to load the latest cli versions if no explicit scalafix-interfaces was provided - scalafixEnable now simply targets the latest semanticdb-scalac version - pin build-time interfaces version to decouple as much as possible, but make sure to dogfood the latest scalafix version for scalafix invocation time, to detect potential regressions

bjaglin · 2025-04-16T08:35:09Z

@adpi2 @tgodzik @olafurpg can I get your opinion on this? I still have to write a salafix rule for a smooth steward migration in project/plugins.sbt and docs to update, but I am satisfied with the overall approach.

bjaglin · 2025-04-16T08:41:11Z

.scala-steward.conf

+dependencyOverrides = [
+  {
+    dependency = { groupId = "ch.epfl.scala", artifactId = "scalafix-interfaces" },
+    pullRequests = { frequency = "@asap" },


this makes sure the project/plugins.sbt version is up to date, for dogfooding

bjaglin · 2025-04-16T08:42:43Z

src/main/scala/scalafix/sbt/ScalafixPlugin.scala

+    val scalafixAllowDynamicFallback: SettingKey[Boolean] =
+      settingKey[Boolean](
+        "Control whether the latest version of scalafix may be downloaded instead of failing when " +
+          "scalafix-interfaces is not explicitly provided. Off by default because non-deterministic."
+      )


this was initially a private key used internally by scalafixEnable, but I thought we could make it public for power users, without necessarily advertizing it in the docs

tgodzik

Looks good from my side. For Metals and Scala CLI we already use interfaces, so we should not be impacted, right?

In scalafmt the approach was to include the version in config to make sure we always run the correct version irrelevant of the tool used. It might be less of an issue here, since the rules are much slower to evolve and also don't usually touch the whole code as scalafmt can.

What would be much more useful is having rule deps to be defined in in the config file as it's a bit of a hassle for the user to set up for metals, but we could potentially try exporting that information also

tgodzik · 2025-04-17T10:10:28Z

src/sbt-test/sbt-scalafix/custom-src-directory/project/plugins.sbt

@@ -1,2 +1,4 @@
 resolvers += Resolver.sonatypeRepo("public")
 addSbtPlugin("ch.epfl.scala" % "sbt-scalafix" % sys.props("plugin.version"))
+libraryDependencies += "ch.epfl.scala" % "scalafix-interfaces" %


So users will have to add the dependency now unless the additional flag is added? Doesn't look like a lot more work, seems sensible.

That's right, and I am planning to make that one-shot addition automatic for scala-steward users via a scalafix rule

bjaglin · 2025-04-17T18:31:06Z

For Metals and Scala CLI we already use interfaces, so we should not be impacted, right?

No impact indeed, scalafix-interfaces remains backward compatible for Metals, and there are no changes in scalafix-cli for scala-cli (we can't use scalafix-interfaces there because it wouldn't work on the native bundle).

include the version in config to make sure we always run the correct version irrelevant of the tool used

What would be much more useful is having rule deps to be defined in in the config file

We should have both at the same time indeed (the later is tracked under scalacenter/scalafix#1625 FWIW). And steward should know about these implicit and explicit maven coordinates in .scalafix.conf (just like it knows about the implicit one in .scalafmt.conf) to keep users up to date. Overall, it looked to me like a slightly bigger effort than keeping both as steward-friendly sbt dependencies like in this solution, but I agree this is the end goal which will benefit all scalafix-interfaces clients.

bjaglin · 2025-04-20T13:34:02Z

Overall, it looked to me like a slightly bigger effort than keeping both as steward-friendly sbt dependencies like in this solution, but I agree this is the end goal which will benefit all scalafix-interfaces clients.

Actually, since I’ve got a bit of free time coming up, I’ll give this a shot. If it turns out to be doable with limited efforts, I might just skip the intermediate step this PR was meant to be.

bjaglin force-pushed the decouple branch from 79bbd16 to 86966ca Compare April 13, 2025 18:43

bjaglin changed the title ~~decouple sbt-scalafix & scalafix versioning~~ decouple sbt-scalafix & scalafix lifecycle Apr 13, 2025

bjaglin changed the title ~~decouple sbt-scalafix & scalafix lifecycle~~ decouple sbt-scalafix & scalafix lifecycles Apr 13, 2025

bjaglin force-pushed the decouple branch from 86966ca to 2c0a386 Compare April 13, 2025 18:57

bjaglin mentioned this pull request Apr 13, 2025

spin off properties to a separate artifact scalacenter/scalafix#2226

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bjaglin changed the title ~~decouple sbt-scalafix & scalafix lifecycles~~ decouple sbt-scalafix from scalafix lifecycle Apr 13, 2025

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bjaglin force-pushed the decouple branch 3 times, most recently from 14bc74e to 256c56e Compare April 15, 2025 00:34

bjaglin mentioned this pull request Apr 15, 2025

allow usage of scalafix-interfaces without scalafix-properties scalacenter/scalafix#2231

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bjaglin-swile mentioned this pull request Apr 15, 2025

remove obsolete hack for non-semver scalameta (pending scalafix release) #484

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bjaglin mentioned this pull request Apr 27, 2025

add scalafix-loader supporting version & deps in .scalafix.conf scalacenter/scalafix#2236

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Revert scalafix-properties PRs scalacenter/scalafix#2240

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decouple sbt-scalafix from scalafix lifecycle #482

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decouple sbt-scalafix from scalafix lifecycle #482

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