Permit indent at width after colon arrow eol

Author: som-snytt

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

@@ -1090,6 +1090,7 @@ object Parsers {
       def isArrowIndent() =
         lookahead.isArrow
         && {
+          lookahead.observeArrowEOL()
           lookahead.nextToken()
           lookahead.token == INDENT || lookahead.token == EOF
         }
@@ -2654,10 +2655,14 @@ object Parsers {
 
     def closureRest(start: Int, location: Location, params: List[Tree]): Tree =
       atSpan(start, in.offset) {
+        if location == Location.InColonArg then
+          in.observeArrowEOL()
         if in.token == CTXARROW then
           if params.isEmpty then
             syntaxError(em"context function literals require at least one formal parameter", Span(start, in.lastOffset))
           in.nextToken()
+        else if in.token == ARROWeol then
+          in.nextToken()
         else
           accept(ARROW)
         val body =

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

@@ -92,7 +92,7 @@ object Scanners {
       || token == IDENTIFIER && isOperatorPart(name(name.length - 1))
 
     def isArrow =
-      token == ARROW || token == CTXARROW
+      token == ARROW || token == CTXARROW || token == ARROWeol
   }
 
   abstract class ScannerCommon(source: SourceFile)(using Context) extends CharArrayReader with TokenData {
@@ -612,7 +612,11 @@ object Scanners {
         insert(if (pastBlankLine) NEWLINES else NEWLINE, lineOffset)
       else if indentIsSignificant then
         if nextWidth < lastWidth
-           || nextWidth == lastWidth && (indentPrefix == MATCH || indentPrefix == CATCH) && token != CASE then
+        || nextWidth == lastWidth
+          && indentPrefix.match
+             case MATCH | CATCH => token != CASE
+             case _ => false
+        then
           if currentRegion.isOutermost then
             if nextWidth < lastWidth then currentRegion = topLevelRegion(nextWidth)
           else if !isLeadingInfixOperator(nextWidth) && !statCtdTokens.contains(lastToken) && lastToken != INDENT then
@@ -638,9 +642,13 @@ object Scanners {
                     insert(OUTDENT, offset)
                 else if r.isInstanceOf[InBraces] && !closingRegionTokens.contains(token) then
                   report.warning("Line is indented too far to the left, or a `}` is missing", sourcePos())
-
         else if lastWidth < nextWidth
-             || lastWidth == nextWidth && (lastToken == MATCH || lastToken == CATCH) && token == CASE then
+             || lastWidth == nextWidth
+               && lastToken.match
+                  case MATCH | CATCH => token == CASE
+                  case ARROWeol => true
+                  case _ => false
+        then
           if canStartIndentTokens.contains(lastToken) then
             currentRegion = Indented(nextWidth, lastToken, currentRegion)
             insert(INDENT, offset)
@@ -658,7 +666,7 @@ object Scanners {
     def spaceTabMismatchMsg(lastWidth: IndentWidth, nextWidth: IndentWidth): Message =
       em"""Incompatible combinations of tabs and spaces in indentation prefixes.
           |Previous indent : $lastWidth
-         |Latest indent   : $nextWidth"""
+          |Latest indent   : $nextWidth"""
 
     def observeColonEOL(inTemplate: Boolean): Unit =
       val enabled =
@@ -672,6 +680,13 @@ object Scanners {
         reset()
         if atEOL then token = COLONeol
 
+    def observeArrowEOL(): Unit =
+      if indentSyntax && token == ARROW then
+        peekAhead()
+        val atEOL = isAfterLineEnd || token == EOF
+        reset()
+        if atEOL then token = ARROWeol
+
     def observeIndented(): Unit =
       if indentSyntax && isNewLine then
         val nextWidth = indentWidth(next.offset)
@@ -680,7 +695,6 @@ object Scanners {
           currentRegion = Indented(nextWidth, COLONeol, currentRegion)
           offset = next.offset
           token = INDENT
-    end observeIndented
 
     /** Insert an <outdent> token if next token closes an indentation region.
      *  Exception: continue if indentation region belongs to a `match` and next token is `case`.
@@ -1100,7 +1114,7 @@ object Scanners {
         reset()
       next
 
-    class LookaheadScanner(val allowIndent: Boolean = false) extends Scanner(source, offset, allowIndent = allowIndent) {
+    class LookaheadScanner(allowIndent: Boolean = false) extends Scanner(source, offset, allowIndent = allowIndent) {
       override protected def initialCharBufferSize = 8
       override def languageImportContext = Scanner.this.languageImportContext
     }
@@ -1652,7 +1666,7 @@ object Scanners {
   case class InCase(outer: Region) extends Region(OUTDENT)
 
   /** A class describing an indentation region.
-   *  @param width   The principal indendation width
+   *  @param width   The principal indentation width
    *  @param prefix  The token before the initial <indent> of the region
    */
   case class Indented(width: IndentWidth, prefix: Token, outer: Region | Null) extends Region(OUTDENT):

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

@@ -202,9 +202,10 @@ object Tokens extends TokensCommon {
   inline val COLONeol = 89;         enter(COLONeol, ":", ": at eol")
     // A `:` recognized as starting an indentation block
   inline val SELFARROW = 90;        enter(SELFARROW, "=>") // reclassified ARROW following self-type
+  inline val ARROWeol = 99;         enter(ARROWeol, "=>", "=> at eol") // lambda ARROW at eol followed by indent
 
   /** XML mode */
-  inline val XMLSTART = 99;         enter(XMLSTART, "$XMLSTART$<") // TODO: deprecate
+  inline val XMLSTART = 100;        enter(XMLSTART, "$XMLSTART$<") // TODO: deprecate
 
   final val alphaKeywords: TokenSet = tokenRange(IF, END)
   final val symbolicKeywords: TokenSet = tokenRange(USCORE, CTXARROW)
@@ -282,7 +283,7 @@ object Tokens extends TokensCommon {
   final val closingRegionTokens = BitSet(RBRACE, RPAREN, RBRACKET, CASE) | statCtdTokens
 
   final val canStartIndentTokens: BitSet =
-    statCtdTokens | BitSet(COLONeol, WITH, EQUALS, ARROW, CTXARROW, LARROW, WHILE, TRY, FOR, IF, THROW, RETURN)
+    statCtdTokens | BitSet(COLONeol, WITH, EQUALS, ARROWeol, ARROW, CTXARROW, LARROW, WHILE, TRY, FOR, IF, THROW, RETURN)
 
   /** Faced with the choice between a type and a formal parameter, the following
    *  tokens determine it's a formal parameter.

tests/neg/i22193.scala

@@ -0,0 +1,44 @@
+
+def fn2(arg: String, arg2: String)(f: String => Unit): Unit = f(arg)
+
+def fn3(arg: String, arg2: String)(f: => Unit): Unit = f
+
+def test1() =
+
+  fn2(arg = "blue sleeps faster than tuesday", arg2 = "the quick brown fox jumped over the lazy dog"): env =>
+    val x = env
+    println(x)
+
+  fn2( // error not a legal formal parameter for a function literal
+      arg = "blue sleeps faster than tuesday",
+      arg2 = "the quick brown fox jumped over the lazy dog"): env =>
+  val x = env // error
+  println(x)
+
+  fn2( // error
+      arg = "blue sleeps faster than tuesday",
+      arg2 = "the quick brown fox jumped over the lazy dog"): env =>
+    val x = env // error
+    println(x)
+
+  fn2(
+      arg = "blue sleeps faster than tuesday",
+      arg2 = "the quick brown fox jumped over the lazy dog"):
+  env => // error indented definitions expected, identifier env found
+      val x = env
+      println(x)
+
+def test2() =
+
+  fn2(
+      arg = "blue sleeps faster than tuesday",
+      arg2 = "the quick brown fox jumped over the lazy dog"
+  ): env =>
+    val x = env
+    println(x)
+
+  fn3( // error missing argument list for value of type (=> Unit) => Unit
+    arg = "blue sleeps faster than tuesday",
+    arg2 = "the quick brown fox jumped over the lazy dog"):
+  val x = "Hello" // error
+  println(x) // error

tests/pos/i22193.scala

@@ -0,0 +1,57 @@
+
+def fn2(arg: String, arg2: String)(f: String => Unit): Unit = f(arg)
+
+def fn3(arg: String, arg2: String)(f: => Unit): Unit = f
+
+def test() =
+
+  fn2(arg = "blue sleeps faster than tuesday", arg2 = "the quick brown fox jumped over the lazy dog"): env =>
+    val x = env
+    println(x)
+
+  // doesn't compile
+  fn2(
+      arg = "blue sleeps faster than tuesday",
+      arg2 = "the quick brown fox jumped over the lazy dog"): env =>
+      val x = env
+      println(x)
+
+  fn2(
+      arg = "blue sleeps faster than tuesday",
+      arg2 = "the quick brown fox jumped over the lazy dog"): env =>
+       val x = env
+       println(x)
+
+  // does compile
+  fn2(
+      arg = "blue sleeps faster than tuesday",
+      arg2 = "the quick brown fox jumped over the lazy dog"):
+    env =>
+      val x = env
+      println(x)
+
+  // does compile
+  fn2(
+      arg = "blue sleeps faster than tuesday",
+      arg2 = "the quick brown fox jumped over the lazy dog"
+  ): env =>
+      val x = env
+      println(x)
+
+  fn3(
+    arg = "blue sleeps faster than tuesday",
+    arg2 = "the quick brown fox jumped over the lazy dog"):
+    val x = "Hello"
+    println(x)
+
+  fn3(
+      arg = "blue sleeps faster than tuesday",
+      arg2 = "the quick brown fox jumped over the lazy dog"):
+      val x = "Hello"
+      println(x)
+
+// don't turn innocent empty cases into functions
+def regress(x: Int) =
+  x match
+  case 42 =>
+  case _ =>