Offer rewriting to new import syntax

Author: odersky

compiler/src/dotty/tools/dotc/parsing/Parsers.scala

@@ -3111,6 +3111,11 @@ object Parsers {
 
       /** ‘*' | ‘_' */
       def wildcardSelector() =
+        if in.token == USCORE && sourceVersion.isAtLeast(`3.1`) then
+          report.errorOrMigrationWarning(
+            em"`_` is no longer supported for a wildcard import; use `*` instead${rewriteNotice("3.1")}",
+            in.sourcePos())
+          patch(source, Span(in.offset, in.offset + 1), "*")
         ImportSelector(atSpan(in.skipToken()) { Ident(nme.WILDCARD) })
 
       /** 'given [InfixType]' */
@@ -3124,6 +3129,13 @@ object Parsers {
       /** id [‘as’ (id | ‘_’) */
       def namedSelector(from: Ident) =
         if in.token == ARROW || isIdent(nme.as) then
+          if in.token == ARROW && sourceVersion.isAtLeast(`3.1`) then
+            report.errorOrMigrationWarning(
+              em"The import renaming `a => b` is no longer supported ; use `a as b` instead${rewriteNotice("3.1")}",
+              in.sourcePos())
+            patch(source, Span(in.offset, in.offset + 2),
+                if testChar(in.offset - 1, ' ') && testChar(in.offset + 2, ' ') then "as"
+                else " as ")
           atSpan(startOffset(from), in.skipToken()) {
             val to = if in.token == USCORE then wildcardIdent() else termIdent()
             ImportSelector(from, if to.name == nme.ERROR then EmptyTree else to)

tests/rewrites/rewrites3x.scala

@@ -1,6 +1,9 @@
+import scala.{collection => coll, runtime=>_, _}
+import coll._
+
 def f(xs: Int*) = xs.sum
 def test =
-  f(List(1, 2, 3) *)
+  f(List(1, 2, 3): _*)
 
 def g = { implicit x: Int =>
   x + 1