Warn if int setting is multiply set

Author: som-snytt

compiler/src/dotty/tools/dotc/config/Settings.scala

@@ -110,7 +110,10 @@ object Settings:
           choices match
             case Some(r: Range) if x < r.head || r.last < x => fail(s"$argValue is out of legal range ${r.head}..${r.last} for $name", args)
             case Some(xs) if !xs.contains(x)                => fail(s"$argValue is not a valid choice for $name", args)
-            case _                                          => update(x, args)
+            case _                                          =>
+              val dubious = changed && x != valueIn(sstate).asInstanceOf[Int]
+              val updated = update(x, args)
+              if dubious then updated.warn(s"Option $name was updated") else updated
         catch case _: NumberFormatException => fail(s"$argValue is not an integer argument for $name", args)
 
       def doSet(argRest: String): ArgsSummary = (summon[ClassTag[T]]: @unchecked) match {

compiler/test/dotty/tools/dotc/SettingsTests.scala

@@ -216,6 +216,15 @@ class SettingsTests {
     assertFalse("Multiple conflicting options is a warning", summary.warnings.isEmpty)
     assertTrue(summary.warnings.forall(_.contains("updated")))
 
+  @Test def `int option also warns`: Unit =
+    object Settings extends SettingGroup:
+      val option = IntSetting("-option", "Some option", 42)
+    val args = List("-option:17", "-option:27")
+    val summary = Settings.processArguments(args, processAll = true)
+    assertTrue("Multiple options is not an error", summary.errors.isEmpty)
+    assertFalse("Multiple conflicting options is a warning", summary.warnings.isEmpty)
+    assertTrue(summary.warnings.forall(_.contains("updated")))
+
   // use the supplied summary for evaluating settings
   private def withProcessedArgs(summary: ArgsSummary)(f: SettingsState ?=> Unit) = f(using summary.sstate)