Cleanup observeIndented logic

Author: odersky

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

@@ -1230,6 +1230,10 @@ object Parsers {
       // note: next is defined here because current == NEWLINE
       if (in.token == NEWLINE && in.next.token == token) in.nextToken()
 
+    def newLinesOptWhenFollowedBy(name: Name): Unit =
+      if in.isNewLine && in.next.token == IDENTIFIER && in.next.name == name then
+        in.nextToken()
+
     def newLineOptWhenFollowing(p: Int => Boolean): Unit =
       // note: next is defined here because current == NEWLINE
       if (in.token == NEWLINE && p(in.next.token)) newLineOpt()
@@ -1245,7 +1249,7 @@ object Parsers {
     }
 
     def possibleTemplateStart(): Unit = {
-      in.observeIndented(unless = noIndentTemplateTokens, unlessSoftKW = nme.derives)
+      in.observeIndented()
       newLineOptWhenFollowedBy(LBRACE)
     }
 
@@ -2373,7 +2377,7 @@ object Parsers {
                 dropParensOrBraces(start, if (in.token == YIELD || in.token == DO) "" else "do")
               }
             }
-            in.observeIndented(unless = noIndentAfterEnumeratorTokens)
+            in.observeIndented()
             res
           }
           else {
@@ -3505,6 +3509,7 @@ object Parsers {
     /** Template          ::=  InheritClauses [TemplateBody]
      */
     def template(constr: DefDef, isEnum: Boolean = false): Template = {
+      newLinesOptWhenFollowedBy(nme.derives)
       val (parents, derived) = inheritClauses()
       possibleTemplateStart()
       if (isEnum) {
@@ -3517,10 +3522,11 @@ object Parsers {
     /** TemplateOpt = [Template]
      */
     def templateOpt(constr: DefDef): Template =
-      possibleTemplateStart()
+      newLinesOptWhenFollowedBy(nme.derives)
       if in.token == EXTENDS || isIdent(nme.derives) then
         template(constr)
       else
+        possibleTemplateStart()
         if in.isNestedStart then
           template(constr)
         else

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

@@ -385,7 +385,7 @@ object Scanners {
         lookahead.allowLeadingInfixOperators = false
           // force a NEWLINE a after current token if it is on its own line
         lookahead.nextToken()
-        canStartExpressionTokens.contains(lookahead.token)
+        canStartExprTokens.contains(lookahead.token)
       }
       && {
         if isScala2Mode || oldSyntax && !rewrite then
@@ -541,29 +541,19 @@ object Scanners {
          |Previous indent : $lastWidth
          |Latest indent   : $nextWidth"""
 
-    def observeIndented(
-      unless: BitSet = BitSet.empty,
-      unlessSoftKW: TermName = EmptyTermName): Unit
-    =
-      if (indentSyntax && isAfterLineEnd && token != INDENT) {
-        val nextOffset = if (isNewLine) next.offset else offset
-        val nextToken = if (isNewLine) next.token else token
-        val nextWidth = indentWidth(nextOffset)
-        val lastWidth = currentRegion match {
+    def observeIndented(): Unit =
+      if indentSyntax && isNewLine then
+        val nextWidth = indentWidth(next.offset)
+        val lastWidth = currentRegion match
           case r: Indented => r.width
           case r: InBraces => r.width
           case _ => nextWidth
-        }
 
-        if (lastWidth < nextWidth
-           && !unless.contains(nextToken)
-           && (unlessSoftKW.isEmpty || token != IDENTIFIER || name != unlessSoftKW)) {
+        if lastWidth < nextWidth then
           currentRegion = Indented(nextWidth, Set(), COLONEOL, currentRegion)
-          if (!isNewLine) next.copyFrom(this)
-          offset = nextOffset
+          offset = next.offset
           token = INDENT
-        }
-      }
+    end observeIndented
 
     /** - Join CASE + CLASS => CASECLASS, CASE + OBJECT => CASEOBJECT, SEMI + ELSE => ELSE, COLON + <EOL> => COLONEOL
      *  - Insert missing OUTDENTs at EOF