Add migration rewrite for non-named arguments in Java annotations

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

@@ -43,6 +43,8 @@ object MigrationVersion:
   val WithOperator = MigrationVersion(`3.4`, future)
   val FunctionUnderscore = MigrationVersion(`3.4`, future)
 
+  val NonNamedArgumentInJavaAnnotation = MigrationVersion(`3.6`, `3.6`)
+
   val ImportWildcard = MigrationVersion(future, future)
   val ImportRename = MigrationVersion(future, future)
   val ParameterEnclosedByParenthesis = MigrationVersion(future, future)

compiler/src/dotty/tools/dotc/reporting/messages.scala

@@ -35,6 +35,7 @@ import dotty.tools.dotc.util.Spans.Span
 import dotty.tools.dotc.util.SourcePosition
 import scala.jdk.CollectionConverters.*
 import dotty.tools.dotc.util.SourceFile
+import dotty.tools.dotc.config.SourceVersion
 import DidYouMean.*
 
 /**  Messages
@@ -3291,13 +3292,14 @@ object UnusedSymbol {
 
 class NonNamedArgumentInJavaAnnotation(using Context) extends SyntaxMsg(NonNamedArgumentInJavaAnnotationID):
 
-  override protected def msg(using Context): String = 
+  override protected def msg(using Context): String =
     "Named arguments are required for Java defined annotations"
+    + Message.rewriteNotice("This", version = SourceVersion.`3.6-migration`)
 
-  override protected def explain(using Context): String = 
+  override protected def explain(using Context): String =
     i"""Starting from Scala 3.6.0, named arguments are required for Java defined annotations.
-        |Java defined annotations don't have an exact constructor representation 
-        |and we previously relied on the order of the fields to create one. 
+        |Java defined annotations don't have an exact constructor representation
+        |and we previously relied on the order of the fields to create one.
         |One possible issue with this representation is the reordering of the fields.
         |Lets take the following example:
         |

compiler/src/dotty/tools/dotc/typer/Checking.scala

@@ -891,14 +891,26 @@ object Checking {
     def annotationHasValueField: Boolean =
       sym.info.decls.exists(_.name == nme.value)
 
+    lazy val annotationFieldNamesByIdx: Map[Int, TermName] =
+      sym.info.decls.filter: decl =>
+        decl.is(Method) && decl.name != nme.CONSTRUCTOR
+      .map(_.name.toTermName)
+      .zipWithIndex
+      .map(_.swap)
+      .toMap
+
     annot match
       case untpd.Apply(fun, List(param)) if !param.isInstanceOf[untpd.NamedArg] && annotationHasValueField =>
         untpd.cpy.Apply(annot)(fun, List(untpd.cpy.NamedArg(param)(nme.value, param)))
       case untpd.Apply(_, params) =>
         for
-          param <- params
+          (param, paramIdx) <- params.zipWithIndex
           if !param.isInstanceOf[untpd.NamedArg]
-        do report.error(NonNamedArgumentInJavaAnnotation(), param)
+        do
+          report.errorOrMigrationWarning(NonNamedArgumentInJavaAnnotation(), param, MigrationVersion.NonNamedArgumentInJavaAnnotation)
+          if MigrationVersion.NonNamedArgumentInJavaAnnotation.needsPatch then
+            annotationFieldNamesByIdx.get(paramIdx).foreach: paramName =>
+              patch(param.span, untpd.cpy.NamedArg(param)(paramName, param).show)
         annot
       case _ => annot
   end checkNamedArgumentForJavaAnnotation

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

@@ -76,6 +76,7 @@ class CompilationTests {
       compileFile("tests/rewrites/i17187.scala", unindentOptions.and("-rewrite")),
       compileFile("tests/rewrites/i17399.scala", unindentOptions.and("-rewrite")),
       compileFile("tests/rewrites/i20002.scala", defaultOptions.and("-indent", "-rewrite")),
+      compileDir("tests/rewrites/annotation-named-pararamters", defaultOptions.and("-rewrite", "-source:3.6-migration")),
     ).checkRewrites()
   }
 

tests/rewrites/annotation-named-pararamters/MyAnnotation.java

@@ -0,0 +1,8 @@
+import java.util.concurrent.TimeUnit;
+
+public @interface MyAnnotation {
+  public TimeUnit D() default TimeUnit.DAYS;
+  TimeUnit C() default TimeUnit.DAYS;
+  String A() default "";
+  public String B() default "";
+}

tests/rewrites/annotation-named-pararamters/test.check

@@ -0,0 +1,6 @@
+import java.util.concurrent.TimeUnit
+@MyAnnotation() class Test1
+@MyAnnotation(D = TimeUnit.DAYS) class Test2
+@MyAnnotation(D = TimeUnit.DAYS, C = TimeUnit.DAYS) class Test3
+@MyAnnotation(D = TimeUnit.DAYS, C = TimeUnit.DAYS, A = "foo") class Test4
+@MyAnnotation(D = TimeUnit.DAYS, C = TimeUnit.DAYS, A = "foo", B = "bar") class Test5

tests/rewrites/annotation-named-pararamters/test.scala

@@ -0,0 +1,6 @@
+import java.util.concurrent.TimeUnit
+@MyAnnotation() class Test1
+@MyAnnotation(TimeUnit.DAYS) class Test2
+@MyAnnotation(TimeUnit.DAYS, TimeUnit.DAYS) class Test3
+@MyAnnotation(TimeUnit.DAYS, TimeUnit.DAYS, "foo") class Test4
+@MyAnnotation(TimeUnit.DAYS, TimeUnit.DAYS, "foo", "bar") class Test5