Align treatment of colon in template bodies and arguments

Author: odersky

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

@@ -648,8 +648,10 @@ object Scanners {
 
     def observeColonEOL(inTemplate: Boolean): Unit =
       val enabled =
-        if inTemplate then token == COLONop || token == COLONfollow
-        else token == COLONfollow && fewerBracesEnabled
+        if token == COLONop && inTemplate then
+          report.deprecationWarning(em"`:` after symbolic operator is deprecated; use backticks around operator instead", sourcePos(offset))
+          true
+        else token == COLONfollow && (inTemplate || fewerBracesEnabled)
       if enabled then
         lookAhead()
         val atEOL = isAfterLineEnd || token == EOF

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

@@ -283,7 +283,7 @@ object Tokens extends TokensCommon {
 
   final val endMarkerTokens = identifierTokens | BitSet(IF, WHILE, FOR, MATCH, TRY, NEW, THROW, GIVEN, VAL, THIS)
 
-  final val colonEOLPredecessors = BitSet(RPAREN, RBRACKET, BACKQUOTED_IDENT, THIS, SUPER)
+  final val colonEOLPredecessors = BitSet(RPAREN, RBRACKET, BACKQUOTED_IDENT, THIS, SUPER, NEW)
 
   final val closingParens = BitSet(RPAREN, RBRACKET, RBRACE)
 

docs/_docs/internals/syntax.md

@@ -99,7 +99,7 @@ notation `:<<< ts >>>` indicates a token sequence `ts` that is either enclosed i
 a `colon` token.
 
 A `colon` token reads as the standard colon "`:`" but is generated instead of it where `colon` is legal according to the context free syntax, but only if the previous token
-is an alphanumeric identifier, a backticked identifier, or one of the tokens `this`, `super`, "`)`", and "`]`".
+is an alphanumeric identifier, a backticked identifier, or one of the tokens `this`, `super`, `new`, "`)`", and "`]`".
 
 ```
 colon         ::=  ':'    -- with side conditions explained above

tests/run/LazyLists.scala

@@ -46,7 +46,7 @@ package xcollections:
     val empty: LazyList[Nothing] = new:
       protected def force(): LazyList[Nothing] = this
 
-    object #:: :
+    object `#::`:
       def unapply[T](xs: LazyList[T]): Option[(T, LazyList[T])] =
         if xs.isEmpty then None
         else Some((xs.head, xs.tail))