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(

tests/neg/i18862-3.4.check

@@ -0,0 +1,5 @@
+-- Error: tests/neg/i18862-3.4.scala:6:38 ------------------------------------------------------------------------------
+6 |def test(xs: List[Int]): Unit = f(xs: _*) // error: migration warning
+  |                                      ^
+  |                               The syntax `x: _*` is no longer supported for vararg splices; use `x*` instead
+  |                               This construct can be rewritten automatically under -rewrite -source 3.4-migration.

tests/neg/i18862-3.4.scala

@@ -0,0 +1,6 @@
+//> using options -Werror
+
+import scala.language.`3.4`
+
+def f(x: Int*): Unit = ()
+def test(xs: List[Int]): Unit = f(xs: _*) // error: migration warning

tests/neg/i18862-future-migration.scala

@@ -0,0 +1,6 @@
+//> using options -Werror
+
+import scala.language.`future-migration`
+
+def f(x: Int*): Unit = ()
+def test(xs: List[Int]): Unit = f(xs: _*) // error: migration warning

tests/neg/i18862-future.scala

@@ -0,0 +1,4 @@
+import scala.language.future
+
+def f(x: Int*): Unit = ()
+def test(xs: List[Int]): Unit = f(xs: _*) // error: migration error