Merge pull request #9547 from dotty-staging/fix-#9266

Fix #9266: Offer rewrites for parentheses in implicit closures

Author: odersky

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

@@ -2169,11 +2169,11 @@ object Parsers {
                 // Don't error in non-strict mode, as the alternative syntax "implicit (x: T) => ... "
                 // is not supported by Scala2.x
               report.errorOrMigrationWarning(
-                s"This syntax is no longer supported; parameter needs to be enclosed in (...)",
-                in.sourcePos())
+                s"This syntax is no longer supported; parameter needs to be enclosed in (...)${rewriteNotice()}",
+                source.atSpan(Span(start, in.lastOffset)))
             in.nextToken()
             val t = infixType()
-            if (false && migrateTo3) {
+            if (sourceVersion == `3.1-migration`) {
               patch(source, Span(start), "(")
               patch(source, Span(in.lastOffset), ")")
             }

tests/neg-custom-args/fatal-warnings/i9266.check

@@ -0,0 +1,5 @@
+-- Error: tests/neg-custom-args/fatal-warnings/i9266.scala:3:22 --------------------------------------------------------
+3 |def test = { implicit x: Int => x + x } // error
+  |                      ^
+  |                      This syntax is no longer supported; parameter needs to be enclosed in (...)
+  |                      This construct can be rewritten automatically under -rewrite.

tests/neg-custom-args/fatal-warnings/i9266.scala

@@ -0,0 +1,3 @@
+import language.`3.1-migration`
+
+def test = { implicit x: Int => x + x } // error

tests/pos/i9266.scala

@@ -0,0 +1,3 @@
+import language.`3.1-migration`
+
+def test = { implicit x: Int => x + x }