Backport "Make sure that patches for 3.0 are also applied in later versions" to LTS (#20762)

Backports #19018 to the LTS branch.

PR submitted by the release tooling.
[skip ci]

Author: WojciechMazur

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

@@ -455,7 +455,7 @@ object Parsers {
           report.errorOrMigrationWarning(
             em"parentheses are required around the parameter of a lambda${rewriteNotice()}",
             in.sourcePos(), from = `3.0`)
-          if migrateTo3 then
+          if sourceVersion.isMigrating then
             patch(source, t.span.startPos, "(")
             patch(source, t.span.endPos, ")")
           convertToParam(t, mods) :: Nil
@@ -1305,7 +1305,7 @@ object Parsers {
                     |For now, you can also `import language.deprecated.symbolLiterals` to accept
                     |the idiom, but this possibility might no longer be available in the future.""",
                 in.sourcePos(), from = `3.0`)
-              if migrateTo3 then
+              if sourceVersion.isMigrating then
                 patch(source, Span(in.offset, in.offset + 1), "Symbol(\"")
                 patch(source, Span(in.charOffset - 1), "\")")
             atSpan(in.skipToken()) { SymbolLit(in.strVal) }
@@ -1403,7 +1403,8 @@ object Parsers {
                 |It needs to be indented to the right to keep being treated as
                 |an argument to the previous expression.${rewriteNotice()}""",
             in.sourcePos(), from = `3.0`)
-          patch(source, Span(in.offset), "  ")
+          if sourceVersion.isMigrating then
+            patch(source, Span(in.offset), "  ")
 
     def possibleTemplateStart(isNew: Boolean = false): Unit =
       in.observeColonEOL(inTemplate = true)
@@ -2222,7 +2223,7 @@ object Parsers {
           val whileStart = in.offset
           accept(WHILE)
           val cond = expr()
-          if migrateTo3 then
+          if sourceVersion.isMigrating then
             patch(source, Span(start, start + 2), "while ({")
             patch(source, Span(whileStart, whileStart + 5), ";")
             cond match {

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

@@ -18,10 +18,12 @@ import scala.collection.immutable.SortedMap
 import rewrites.Rewrites.patch
 import config.Feature
 import config.Feature.{migrateTo3, fewerBracesEnabled}
-import config.SourceVersion.`3.0`
+import config.SourceVersion.{`3.0`, `3.0-migration`}
 import reporting.{NoProfile, Profile, Message}
 
 import java.util.Objects
+import dotty.tools.dotc.reporting.Message.rewriteNotice
+import dotty.tools.dotc.config.Feature.sourceVersion
 
 object Scanners {
 
@@ -253,11 +255,12 @@ object Scanners {
         if scala3keywords.contains(keyword) && migrateTo3 then
           val what = tokenString(keyword)
           report.errorOrMigrationWarning(
-            em"$what is now a keyword, write `$what` instead of $what to keep it as an identifier",
+            em"$what is now a keyword, write `$what` instead of $what to keep it as an identifier${rewriteNotice("This", `3.0-migration`)}",
             sourcePos(),
             from = `3.0`)
-          patch(source, Span(offset), "`")
-          patch(source, Span(offset + identifier.length), "`")
+          if sourceVersion.isMigrating then
+            patch(source, Span(offset), "`")
+            patch(source, Span(offset + identifier.length), "`")
           IDENTIFIER
         else keyword
       val idx = identifier.start

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

@@ -441,7 +441,7 @@ class Typer(@constructorOnly nestingLevel: Int = 0) extends Namer
                   report.errorOrMigrationWarning(
                     AmbiguousReference(name, Definition, Inheritance, prevCtx)(using outer),
                     pos, from = `3.0`)
-                  if migrateTo3 then
+                  if sourceVersion.isMigrating then
                     patch(Span(pos.span.start),
                       if prevCtx.owner == refctx.owner.enclosingClass then "this."
                       else s"${prevCtx.owner.name}.this.")
@@ -2892,13 +2892,12 @@ class Typer(@constructorOnly nestingLevel: Int = 0) extends Namer
         val recovered = typed(qual)(using ctx.fresh.setExploreTyperState())
         val msg = OnlyFunctionsCanBeFollowedByUnderscore(recovered.tpe.widen, tree)
         report.errorOrMigrationWarning(msg, tree.srcPos, from = `3.0`)
-        if (migrateTo3) {
+        if sourceVersion.isMigrating then
           // Under -rewrite, patch `x _` to `(() => x)`
           msg.actions
             .headOption
             .foreach(Rewrites.applyAction)
           return typed(untpd.Function(Nil, qual), pt)
-        }
     }
     nestedCtx.typerState.commit()
     if sourceVersion.isAtLeast(future) then

tests/neg/i13440.check

@@ -2,11 +2,14 @@
 5 |def given = 42 // error
   |    ^
   |    given is now a keyword, write `given` instead of given to keep it as an identifier
+  |    This can be rewritten automatically under -rewrite -source 3.0-migration.
 -- Error: tests/neg/i13440.scala:7:13 ----------------------------------------------------------------------------------
 7 |case class C(enum: List[Int] = Nil) { // error
   |             ^
   |             enum is now a keyword, write `enum` instead of enum to keep it as an identifier
+  |             This can be rewritten automatically under -rewrite -source 3.0-migration.
 -- Error: tests/neg/i13440.scala:8:11 ----------------------------------------------------------------------------------
 8 |  val s = s"$enum" // error
   |           ^
   |           enum is now a keyword, write `enum` instead of enum to keep it as an identifier
+  |           This can be rewritten automatically under -rewrite -source 3.0-migration.