From 43714dd62f7353091aa9be078d58f84035119647 Mon Sep 17 00:00:00 2001
From: Nicolas Stucki <nicolas.stucki@gmail.com>
Date: Tue, 7 Nov 2023 09:49:23 +0100
Subject: [PATCH] Deprecation warnings for old syntax (`xs: _*` varargs)

---
 compiler/src/dotty/tools/dotc/parsing/Parsers.scala | 9 +++++----
 tests/neg/i18862-3.4.check                          | 5 +++++
 tests/neg/i18862-3.4.scala                          | 6 ++++++
 tests/neg/i18862-future-migration.scala             | 6 ++++++
 tests/neg/i18862-future.scala                       | 4 ++++
 5 files changed, 26 insertions(+), 4 deletions(-)
 create mode 100644 tests/neg/i18862-3.4.check
 create mode 100644 tests/neg/i18862-3.4.scala
 create mode 100644 tests/neg/i18862-future-migration.scala
 create mode 100644 tests/neg/i18862-future.scala

diff --git a/compiler/src/dotty/tools/dotc/parsing/Parsers.scala b/compiler/src/dotty/tools/dotc/parsing/Parsers.scala
index 805c25ad40e4..717ec9197e7a 100644
--- a/compiler/src/dotty/tools/dotc/parsing/Parsers.scala
+++ b/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(
diff --git a/tests/neg/i18862-3.4.check b/tests/neg/i18862-3.4.check
new file mode 100644
index 000000000000..b56454feeeaa
--- /dev/null
+++ b/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.
diff --git a/tests/neg/i18862-3.4.scala b/tests/neg/i18862-3.4.scala
new file mode 100644
index 000000000000..a30c8c8f1a59
--- /dev/null
+++ b/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
diff --git a/tests/neg/i18862-future-migration.scala b/tests/neg/i18862-future-migration.scala
new file mode 100644
index 000000000000..ff8ba1c377c3
--- /dev/null
+++ b/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
diff --git a/tests/neg/i18862-future.scala b/tests/neg/i18862-future.scala
new file mode 100644
index 000000000000..07fc72aef34a
--- /dev/null
+++ b/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