Router: use spaces.afterColonInMatchPattern

docs/configuration.md

@@ -4691,6 +4691,50 @@ foo ===(baz)
 foo bar (baz)
 ```
 
+### `spaces.afterColonInMatchPattern`
+
+> Since v3.8.3.
+
+```scala mdoc:defaults
+spaces.afterColonInMatchPattern
+```
+
+This parameter controls whether to output a space between a colon and a type in
+typed match patterns. It takes the following values:
+
+- `Always`:
+
+```scala mdoc:scalafmt
+spaces.afterColonInMatchPattern = always
+---
+foo match {
+  case e: Etype | f: Ftype =>
+  case g: Gtype =>
+}
+```
+
+- `Never`:
+
+```scala mdoc:scalafmt
+spaces.afterColonInMatchPattern = never
+---
+foo match {
+  case e: Etype | f: Ftype =>
+  case g: Gtype =>
+}
+```
+
+- `NoAlternatives` (when there are no pipe-separated alternatives):
+
+```scala mdoc:scalafmt
+spaces.afterColonInMatchPattern = noAlternatives
+---
+foo match {
+  case e: Etype | f: Ftype =>
+  case g: Gtype =>
+}
+```
+
 ## Literals
 
 > Since v2.5.0.

scalafmt-core/shared/src/main/scala/org/scalafmt/config/Spaces.scala

@@ -61,9 +61,22 @@ case class Spaces(
     afterKeywordBeforeParen: Boolean = true,
     inByNameTypes: Boolean = true,
     afterSymbolicDefs: Boolean = false,
+    private val afterColonInMatchPattern: Spaces.AfterColonInMatchPattern =
+      Spaces.AfterColonInMatchPattern.Always,
 ) {
   def isSpaceAfterKeyword(tokenAfter: Token): Boolean =
     afterKeywordBeforeParen || !tokenAfter.is[Token.LeftParen]
+
+  def notAfterColon(owner: meta.Tree): Boolean = owner match {
+    case x: meta.Pat.Typed => afterColonInMatchPattern match {
+        case Spaces.AfterColonInMatchPattern.Never => true
+        case Spaces.AfterColonInMatchPattern.Always => false
+        case Spaces.AfterColonInMatchPattern.NoAlternatives => x.parent
+            .exists(_.is[meta.Pat.Alternative])
+      }
+    case _ => false
+  }
+
 }
 
 object Spaces {
@@ -84,6 +97,15 @@ object Spaces {
     case object IfMultipleBounds extends BeforeContextBound
   }
 
+  sealed abstract class AfterColonInMatchPattern
+  object AfterColonInMatchPattern {
+    implicit val codec: ConfCodecEx[AfterColonInMatchPattern] = ReaderUtil
+      .oneOf[AfterColonInMatchPattern](Always, Never, NoAlternatives)
+    case object Always extends AfterColonInMatchPattern
+    case object Never extends AfterColonInMatchPattern
+    case object NoAlternatives extends AfterColonInMatchPattern
+  }
+
   sealed abstract class BeforeArgInParens {
     def apply(name: => String): Boolean
   }

scalafmt-core/shared/src/main/scala/org/scalafmt/internal/Router.scala

@@ -2366,6 +2366,8 @@ class Router(formatOps: FormatOps) {
       case FormatToken(T.RightArrow(), _, _) if leftOwner.is[Type.ByName] =>
         val mod = Space(style.spaces.inByNameTypes)
         Seq(Split(mod, 0))
+      case FormatToken(_: T.Colon, _, _)
+          if style.spaces.notAfterColon(leftOwner) => Seq(Split(NoSplit, 0))
       case FormatToken(_: T.Symbolic, _, _) => Seq(Split(Space, 0))
       case tok =>
         logger.debug(s"MISSING CASE: $tok")

scalafmt-tests/src/test/resources/unit/Case.stat

@@ -108,3 +108,39 @@ object a {
     case e: Exception => bar; baz
   }
 }
+<<< pattern alternatives, afterColonInMatchPattern = always
+spaces.afterColonInMatchPattern = always
+===
+foo match {
+  case e: Etype | f: Ftype =>
+  case g: Gtype =>
+}
+>>>
+foo match {
+  case e: Etype | f: Ftype =>
+  case g: Gtype =>
+}
+<<< pattern alternatives, afterColonInMatchPattern = never
+spaces.afterColonInMatchPattern = never
+===
+foo match {
+  case e: Etype | f: Ftype =>
+  case g: Gtype =>
+}
+>>>
+foo match {
+  case e:Etype | f:Ftype =>
+  case g:Gtype =>
+}
+<<< pattern alternatives, afterColonInMatchPattern = noAlternatives
+spaces.afterColonInMatchPattern = noAlternatives
+===
+foo match {
+  case e: Etype | f: Ftype =>
+  case g: Gtype =>
+}
+>>>
+foo match {
+  case e:Etype | f:Ftype =>
+  case g: Gtype =>
+}