Add migration rewrite for non-named arguments in Java annotations (#2…

…1397)

Followup to #21329
It might be beneficial for Scala 3.6 migration to allow for an automatic
rewrite of unnamed Java annotation parameters to ease the migration.
We can assume that already compiling code is already using correct
positions for annotation arguments.
Based on that, we can use the order of the annotation decls and their
indexes to assume the names of annotation arguments

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
@@ -3293,6 +3294,7 @@ class NonNamedArgumentInJavaAnnotation(using Context) extends SyntaxMsg(NonNamed
 
   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 = 
     i"""Starting from Scala 3.6.0, named arguments are required for Java defined annotations.

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.startPos, s"$paramName = ")
         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/neg/i20554-a.check

@@ -2,6 +2,7 @@
 3 |@Annotation(3, 4) // error // error : Java defined annotation should be called with named arguments
   |            ^
   |            Named arguments are required for Java defined annotations
+  |            This can be rewritten automatically under -rewrite -source 3.6-migration.
   |---------------------------------------------------------------------------------------------------------------------
   | Explanation (enabled by `-explain`)
   |- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
@@ -23,6 +24,7 @@
 3 |@Annotation(3, 4) // error // error : Java defined annotation should be called with named arguments
   |               ^
   |               Named arguments are required for Java defined annotations
+  |               This can be rewritten automatically under -rewrite -source 3.6-migration.
   |---------------------------------------------------------------------------------------------------------------------
   | Explanation (enabled by `-explain`)
   |- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -

tests/neg/i20554-b.check

@@ -2,6 +2,7 @@
 3 |@SimpleAnnotation(1) // error: the parameters is not named 'value'
   |                  ^
   |                  Named arguments are required for Java defined annotations
+  |                  This can be rewritten automatically under -rewrite -source 3.6-migration.
   |---------------------------------------------------------------------------------------------------------------------
   | Explanation (enabled by `-explain`)
   |- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -

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