Allow : instead of with in front of templates

Author: odersky

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

@@ -913,7 +913,10 @@ object Parsers {
           lookahead.nextToken()
         if lookahead.token == IDENTIFIER then
           lookahead.nextToken()
-          lookahead.token == COLON
+          if lookahead.token == COLON then
+            lookahead.nextToken()
+            !lookahead.isAfterLineEnd
+          else false
         else false
       else false
 
@@ -943,7 +946,10 @@ object Parsers {
         lookahead.nextToken()
       while lookahead.token == LPAREN || lookahead.token == LBRACKET do
         lookahead.skipParens()
-      lookahead.token == COLON || lookahead.token == SUBTYPE
+      if lookahead.token == COLON then
+        lookahead.nextToken()
+        !lookahead.isAfterLineEnd
+      else lookahead.token == SUBTYPE
 
     def followingIsExtension() =
       val lookahead = in.LookaheadScanner()
@@ -1304,7 +1310,12 @@ object Parsers {
     }
 
     def possibleTemplateStart(isNew: Boolean = false): Unit =
-      if in.token == WITH then
+      in.observeColonEOL()
+      if in.token == COLONEOL then
+        in.nextToken()
+        if in.token != INDENT then
+          syntaxError(i"indented definitions expected")
+      else if in.token == WITH then
         in.nextToken()
         if in.token != LBRACE && in.token != INDENT then
           syntaxError(i"indented definitions or `{` expected")
@@ -3415,7 +3426,7 @@ object Parsers {
     }
 
     /** GivenDef       ::=  [GivenSig (‘:’ | <:)] {FunArgTypes ‘=>’} AnnotType ‘=’ Expr
-     *                   |  [GivenSig ‘:’] {FunArgTypes ‘=>’} ConstrApps [[‘with’] TemplateBody]
+     *                   |  [GivenSig ‘:’] {FunArgTypes ‘=>’} ConstrApps [‘:’ nl | ‘with’] TemplateBody]
      *                   |  [id ‘:’] ExtParamClause {GivenParamClause} ‘extended’ ‘with’ ExtMethods
      *  GivenSig       ::=  [id] [DefTypeParamClause] {GivenParamClause}
      *  ExtParamClause ::=  [DefTypeParamClause] DefParamClause

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

@@ -550,6 +550,13 @@ object Scanners {
          |Previous indent : $lastWidth
          |Latest indent   : $nextWidth"""
 
+    def observeColonEOL(): Unit =
+      if token == COLON then
+        lookahead()
+        val atEOL = isAfterLineEnd
+        reset()
+        if atEOL then token = COLONEOL
+
     def observeIndented(): Unit =
       if indentSyntax && isNewLine then
         val nextWidth = indentWidth(next.offset)
@@ -575,19 +582,21 @@ object Scanners {
         insert(OUTDENT, offset)
       case _ =>
 
+    def lookahead() = {
+      prev.copyFrom(this)
+      lastOffset = lastCharOffset
+      fetchToken()
+    }
+
+    def reset() = {
+      next.copyFrom(this)
+      this.copyFrom(prev)
+    }
+
     /** - Join CASE + CLASS => CASECLASS, CASE + OBJECT => CASEOBJECT, SEMI + ELSE => ELSE, COLON + <EOL> => COLONEOL
      *  - Insert missing OUTDENTs at EOF
      */
     def postProcessToken(): Unit = {
-      def lookahead() = {
-        prev.copyFrom(this)
-        lastOffset = lastCharOffset
-        fetchToken()
-      }
-      def reset() = {
-        next.copyFrom(this)
-        this.copyFrom(prev)
-      }
       def fuse(tok: Int) = {
         token = tok
         offset = prev.offset
@@ -611,10 +620,7 @@ object Scanners {
             /* skip the trailing comma */
           } else reset()
         case COLON =>
-          lookahead()
-          val atEOL = isAfterLineEnd
-          reset()
-          if (colonSyntax && atEOL) token = COLONEOL
+          if colonSyntax then observeColonEOL()
         case EOF | RBRACE =>
           currentRegion match {
             case r: Indented if !r.isOutermost =>

tests/neg-custom-args/explicit-nulls/byname-nullables.scala

@@ -1,4 +1,4 @@
-object Test1 with
+object Test1:
 
   def f(x: String) =
     x ++ x
@@ -9,7 +9,7 @@ object Test1 with
     else x
 
 
-object Test2 with
+object Test2:
 
   def f(x: => String) =
     x ++ x
@@ -19,7 +19,7 @@ object Test2 with
     if x != null then f(x)   // error: f is call-by-name
     else x
 
-object Test3 with
+object Test3:
 
   def f(x: String, y: String) = x
 
@@ -31,7 +31,7 @@ object Test3 with
     if x != null then f(x, 1)   // OK: not-null check successfully dropped
     else x
 
-object Test4 with
+object Test4:
 
   def f(x: String, y: String) = x
 
@@ -43,7 +43,7 @@ object Test4 with
     if x != null then f(identity(x), 1)   // error: dropping not null check fails typing
     else x
 
-object Test5 with
+object Test5:
   import compiletime.byName
 
   def f(x: String, y: String) = x
@@ -56,7 +56,7 @@ object Test5 with
     if x != null then f(byName(identity(x)), 1)   // OK, byName avoids the flow typing
     else x
 
-object Test6 with
+object Test6:
 
   def f(x: String, y: String) = x
 
@@ -68,7 +68,7 @@ object Test6 with
     if x != null then f(x, 1)   // error: dropping not null check typechecks OK, but gives incompatible result type
     else x
 
-object Test7 with
+object Test7:
   import compiletime.byName
 
   def f(x: String, y: String) = x

tests/neg-custom-args/explicit-nulls/byname-nullables1.scala

@@ -1,7 +1,7 @@
 def f(op: => Boolean): Unit = ()
 def f(op: Int): Unit = ()
 
-class C with
+class C:
   var fld: String | Null = null
 
 def test() =

tests/neg/case-semi.scala

@@ -1,4 +1,4 @@
-object Test with
+object Test:
   type X = Int
   val x: X = 1
 

tests/neg/endmarkers1.scala

@@ -4,7 +4,7 @@ def f7[T](x: Option[T]) = x match
   case None =>
 end if  // error: misaligned end marker
 
-object Test4 with
+object Test4:
   def f[T](x: Option[T]) = x match
     case Some(y) =>
     case None =>

tests/neg/i6900.scala

@@ -1,7 +1,7 @@
 object Test2 {
 
   // Works with extension method
-  extension on [A](a: A) with
+  extension on [A](a: A):
     def foo[C]: C => A = _ => a   // error: extension method cannot have type parameters
 
   1.foo.foo

tests/neg/i7526.scala

@@ -1,9 +1,9 @@
 type Tr[-I, +O, +A] = I => (O, A)
 
-trait NetApi with
+trait NetApi:
   type Comp
 
-trait NetDB extends NetApi with
+trait NetDB extends NetApi:
   class Comp
 
 trait NetHelper extends NetApi

tests/neg/i7529.scala

@@ -1,4 +1,4 @@
-extension fooOps on [A](a: A) with
+extension fooOps on [A](a: A):
 
   @nonsense    // error: not found: nonsense
   def foo = ???

tests/neg/missing-implicit1.scala

@@ -1,4 +1,4 @@
-object testObjectInstance with
+object testObjectInstance:
   trait Zip[F[_]]
   trait Traverse[F[_]] {
     def [A, B, G[_] : Zip](fa: F[A]) traverse(f: A => G[B]): G[F[B]]
@@ -7,7 +7,7 @@ object testObjectInstance with
   object instances {
     given zipOption: Zip[Option] = ???
     given traverseList: Traverse[List] = ???
-    extension listExtension on [T](xs: List[T]) with
+    extension listExtension on [T](xs: List[T]):
       def second: T = xs.tail.head
     def [T](xs: List[T]) first: T = xs.head
   }