Relax and restrict only colon regions

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

@@ -735,8 +735,8 @@ object Scanners {
             case _ => false
           currentRegion match
             case r: Indented if isEnclosedInParens(r.outer) =>
-              // For some region prefixes (COLONeol, EQUALS) only OUTDENT if COMMA at EOL
-              if canStartIndentTokens.contains(r.prefix) && !statCtdTokens.contains(r.prefix) then
+              // For region prefix COLONeol, only OUTDENT if COMMA at EOL
+              if r.prefix == COLONeol then
                 val lookahead = LookaheadScanner()
                 lookahead.nextToken()
                 if lookahead.isAfterLineEnd then

tests/neg/i22527.scala

@@ -6,12 +6,6 @@ def test: Unit =
       true, "ok" // error end of statement expected but ',' found
   )
 
-def toss: Unit =
-  assert(
-    throw
-      null, "ok" // error same
-  )
-
 def callme[A](x: => A, msg: String) = try x.toString catch case t: RuntimeException => msg
 
 // not all indented regions require COMMA at EOL for OUTDENT
@@ -22,3 +16,10 @@ def orElse(x: Int): Unit =
       true // error ',' or ')' expected, but 'true' found
     else
       false, "fail")
+
+def g: Unit =
+  identity(
+    x =
+      class X extends AnyRef, Serializable // error
+      27 // error
+  )

tests/pos/i22527.scala

@@ -6,13 +6,6 @@ def f: Unit =
       42
   )
 
-def g: Unit =
-  identity(
-    x =
-      class X extends AnyRef, Serializable
-      27
-  )
-
 def test: Unit =
   assert(
     identity:
@@ -26,6 +19,11 @@ def toss: Unit =
       null,
     "ok"
   )
+def raise: Unit =
+  assert(
+    throw
+      null, "ok" // ok now
+  )
 
 def callme[A](x: => A, msg: String) = try x.toString catch case t: RuntimeException => msg