gracefully ignore projects with unsupported binary version

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

@@ -98,6 +98,8 @@ object ScalafixPlugin extends AutoPlugin {
     def scalafixConfigSettings(config: Configuration): Seq[Def.Setting[?]] =
       inConfig(config)(
         relaxScalacOptionsConfigSettings ++ Seq(
+          config / scalafix / skip := (config / scalafix / skip).value ||
+            Seq("2.10", "2.11").contains(scalaBinaryVersion.value),
           scalafix := {
             // force evaluation of keys looked up in the same scope (config) within
             // dynamic tasks to workaround https://github.com/sbt/sbt/issues/5647
@@ -502,7 +504,14 @@ object ScalafixPlugin extends AutoPlugin {
         }
       }
     }
-    task.tag(Scalafix)
+    Def.taskDyn {
+      if (!(config / scalafix / skip).value)
+        task.tag(Scalafix)
+      else
+        Def.task {
+          (config / scalafix / streams).value.log.info("Skipping scalafix")
+        }
+    }
   }
 
   private def scalafixSyntactic(

src/sbt-test/sbt-scalafix/skip/.scalafix.conf

@@ -0,0 +1,2 @@
+rules = [DisableSyntax]
+DisableSyntax.noNulls = true

src/sbt-test/sbt-scalafix/skip/project/plugins.sbt

@@ -0,0 +1,2 @@
+resolvers += Resolver.sonatypeRepo("public")
+addSbtPlugin("ch.epfl.scala" % "sbt-scalafix" % sys.props("plugin.version"))

src/sbt-test/sbt-scalafix/skip/src/main/scala/Null1.scala

@@ -0,0 +1,3 @@
+object Null1 {
+  println(null)
+}

src/sbt-test/sbt-scalafix/skip/src/test/scala/Null2.scala

@@ -0,0 +1,3 @@
+object Null2 {
+  println(null)
+}

src/sbt-test/sbt-scalafix/skip/test

@@ -0,0 +1,41 @@
+-> scalafix
+-> Test / scalafix
+-> scalafixAll
+
+##############################
+# Project level
+##############################
+> set skip := true
+
+> scalafix
+> Test / scalafix
+> scalafixAll
+
+> set skip := false
+
+##############################
+# Task level
+##############################
+> set scalafix / skip := true
+
+> scalafix
+> Test / scalafix
+> scalafixAll
+
+> set scalafix / skip := false
+
+##############################
+# Config / Task level
+##############################
+> set Test / scalafix / skip := true
+
+-> scalafix
+> Test / scalafix
+-> scalafixAll
+
+> set Compile / skip := true
+
+> scalafix
+> Test / scalafix
+> scalafixAll
+

src/sbt-test/skip-sbt1.4/scalafixEnable/test

@@ -13,4 +13,7 @@
 # check that we can run a semantic rule against a Scala 3 dialect source file
 -> scala3 / scalafix --check SemanticRule
 > scala3 / scalafix SemanticRule
-> scala3 / scalafix --check SemanticRule
+> scala3 / scalafix --check SemanticRule
+
+# check that a global, aggregating scalafix is safe as unsupported projects are ignored
+> scalafix