Make indentation significant after ?=> and throw

Author: odersky

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

@@ -276,8 +276,7 @@ object Tokens extends TokensCommon {
   final val closingRegionTokens = BitSet(RBRACE, RPAREN, RBRACKET, CASE) | statCtdTokens
 
   final val canStartIndentTokens: BitSet =
-    statCtdTokens | BitSet(COLONEOL, WITH, EQUALS, ARROW, LARROW, WHILE, TRY, FOR, IF)
-    // TODO: add THROW, CTXARROW
+    statCtdTokens | BitSet(COLONEOL, WITH, EQUALS, ARROW, CTXARROW, LARROW, WHILE, TRY, FOR, IF, THROW)
 
   /** Faced with the choice between a type and a formal parameter, the following
    *  tokens determine it's a formal parameter.

docs/docs/reference/other-new-features/indentation.md

@@ -64,8 +64,8 @@ There are two rules:
      - after one of the following tokens:
 
        ```
-       =  =>  <-  catch  do  else  finally  for
-       if  match  return  then  try  while  yield
+       =  =>  ?=>  <-  catch  do  else  finally  for
+       if  match  return  then  throw  try  while  yield
        ```
 
     If an `<indent>` is inserted, the indentation width of the token on the next line

tests/pos/indent.scala

@@ -51,6 +51,10 @@ object Test:
       y * y
   }
 
+  val gg = (x: Int) ?=>
+    val y = x + 1
+    y
+
   xs.map {
     x =>
     val y = x * x
@@ -80,11 +84,15 @@ object Test:
 
 class Test2:
   self =>
-  def foo = 1
+  def foo(x: Int) =
+    if x < 0 then throw
+      val ex = new AssertionError()
+      ex
+    x
 
   val x =
     new Test2 {
-      override def foo = 2
+      override def foo(x: Int) = 2
     }
   end x
 end Test2