[2.x] feat: Add English aliases cross and switch for + / ++ (#9051)

Fixes #3137. Adds discoverable English-name alternatives for the symbolic
cross-build commands using the | parser combinator, making them more
beginner-friendly without adding separate commands.

main/src/main/scala/sbt/Cross.scala

@@ -41,7 +41,7 @@ object Cross {
 
   private def switchParser(state: State): Parser[Switch] = {
     import DefaultParsers.*
-    def versionAndCommand(spacePresent: Boolean) = {
+    def versionAndCommand(commandName: String)(spacePresent: Boolean) = {
       val x = Project.extract(state)
       import x.*
       val knownVersions = crossVersions(x, currentRef)
@@ -56,7 +56,7 @@ object Cross {
             ScalaHomeVersion(new File(home), Some(v).filterNot(_.isEmpty), force)
         }
       }
-      val spacedVersion = if (spacePresent) version else version & spacedFirst(SwitchCommand)
+      val spacedVersion = if (spacePresent) version else version & spacedFirst(commandName)
       val verboseOpt = Parser.opt(token(Space ~> "-v"))
       // Accept valid commands, or project/command patterns that may reference projects
       // not yet available after version switch (fixes #7574)
@@ -74,19 +74,24 @@ object Cross {
       switch1 | switch2
     }
 
-    token(SwitchCommand ~> OptSpace) flatMap { sp =>
+    def parse(commandName: String) =
-      versionAndCommand(sp.nonEmpty)
+      token(commandName ~> OptSpace) flatMap { sp =>
-    }
+        versionAndCommand(commandName)(sp.nonEmpty)
+      }
+    parse(SwitchCommand) | parse(SwitchAlias)
   }
 
   private case class CrossArgs(command: String, verbose: Boolean)
 
-  private def crossParser(state: State): Parser[CrossArgs] =
+  private def crossParser(state: State): Parser[CrossArgs] = {
-    token(CrossCommand <~ OptSpace) flatMap { _ =>
+    def parse(commandName: String) =
-      (token(Parser.opt("-v" <~ Space)) ~ token(matched(state.combinedParser))).map {
+      token(commandName <~ OptSpace) flatMap { _ =>
-        (verbose, command) => CrossArgs(command, verbose.isDefined)
+        (token(Parser.opt("-v" <~ Space)) ~ token(matched(state.combinedParser))).map {
+          (verbose, command) => CrossArgs(command, verbose.isDefined)
+        }
       }
-    }
+    parse(CrossCommand) | parse(CrossAlias)
+  }
 
   private def crossRestoreSessionParser: Parser[String] = token(CrossRestoreSessionCommand)
 

main/src/main/scala/sbt/internal/CommandStrings.scala

@@ -331,15 +331,19 @@ defaults
       Nil
 
   val CrossCommand = "+"
+  val CrossAlias = "cross"
   val CrossRestoreSessionCommand = "+-"
   val SwitchCommand = "++"
+  val SwitchAlias = "switch"
 
-  def crossHelp: Help = Help.more(CrossCommand, CrossDetailed)
+  def crossHelp: Help =
+    Help.more(CrossCommand, CrossDetailed) ++ Help.more(CrossAlias, CrossDetailed)
   def crossRestoreSessionHelp = Help.more(CrossRestoreSessionCommand, CrossRestoreSessionDetailed)
-  def switchHelp: Help = Help.more(SwitchCommand, SwitchDetailed)
+  def switchHelp: Help =
+    Help.more(SwitchCommand, SwitchDetailed) ++ Help.more(SwitchAlias, SwitchDetailed)
 
   def CrossDetailed =
-    s"""$CrossCommand [-v] <command>
+    s"""$CrossCommand (or $CrossAlias) [-v] <command>
 	Runs <command> for each Scala version specified for cross-building.
 
 	For each string in `crossScalaVersions` in each project project, this command sets
@@ -359,7 +363,7 @@ defaults
 """
 
   def SwitchDetailed =
-    s"""$SwitchCommand <scala-version>[!] [-v] [<command>]
+    s"""$SwitchCommand (or $SwitchAlias) <scala-version>[!] [-v] [<command>]
 	Changes the Scala version and runs a command.
 
 	<scala-version> may be an actual Scala version such as 3.1.3, or a Semantic Version selector

sbt-app/src/sbt-test/actions/cross-alias/build.sbt

@@ -0,0 +1,9 @@
+lazy val scala212 = "2.12.21"
+lazy val scala213 = "2.13.12"
+
+ThisBuild / scalaVersion := scala212
+
+lazy val root = (project in file("."))
+  .settings(
+    crossScalaVersions := Seq(scala212, scala213),
+  )

sbt-app/src/sbt-test/actions/cross-alias/test

@@ -0,0 +1,11 @@
+# Test that "cross" works as an alias for "+"
+> cross clean
+
+# Test that "cross" works with verbose flag
+> cross -v compile
+
+# Test that "switch" works as an alias for "++"
+> switch 2.13.12!
+
+# Test that "switch" works with a command
+> switch 2.12.21! compile