Fix #7655: [ can start an expression

Author: odersky

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

@@ -220,7 +220,7 @@ object Tokens extends TokensCommon {
     USCORE, NULL, THIS, SUPER, TRUE, FALSE, RETURN, QUOTEID, XMLSTART)
 
   final val canStartExprTokens3: TokenSet = atomicExprTokens | BitSet(
-    LBRACE, LPAREN, INDENT, QUOTE, IF, WHILE, FOR, NEW, TRY, THROW)
+    LBRACE, LPAREN, LBRACKET, INDENT, QUOTE, IF, WHILE, FOR, NEW, TRY, THROW)
 
   final val canStartExprTokens2: TokenSet = canStartExprTokens3 | BitSet(DO)
 

tests/pos/i7655.scala

@@ -0,0 +1,6 @@
+object bug2 {
+  val id: [U] => U => U = [U] => (none: U) => none
+  val id1: [U] => U => U = { [U] => (none: U) => none }
+  val id2: [U] => U => U =
+    [U] => (none: U) => none
+}