Deprecation warnings for old syntax (xs: _* varargs)

Author: nicolasstucki

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

@@ -2344,11 +2344,12 @@ object Parsers {
           val isVarargSplice = location.inArgs && followingIsVararg()
           in.nextToken()
           if isVarargSplice then
-            report.errorOrMigrationWarning(
-              em"The syntax `x: _*` is no longer supported for vararg splices; use `x*` instead${rewriteNotice(`future-migration`)}",
+            report.gradualErrorOrMigrationWarning(
+              em"The syntax `x: _*` is no longer supported for vararg splices; use `x*` instead${rewriteNotice(`3.4-migration`)}",
               in.sourcePos(uscoreStart),
-              future)
-            if sourceVersion == `future-migration` then
+              warnFrom = `3.4`,
+              errorFrom = future)
+            if sourceVersion.isMigrating && sourceVersion.isAtLeast(`3.4-migration`) then
               patch(source, Span(t.span.end, in.lastOffset), "*")
           else if opStack.nonEmpty then
             report.errorOrMigrationWarning(