Merge pull request #10861 from dotty-staging/with-templates

Parsing indentation cleanup

Author: odersky

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

@@ -1283,7 +1283,7 @@ object Parsers {
 
     def possibleTemplateStart(isNew: Boolean = false): Unit =
       in.observeColonEOL()
-      if in.token == COLONEOL || in.token == WITHEOL then
+      if in.token == COLONEOL || in.token == WITH then
         if in.lookahead.isIdent(nme.end) then in.token = NEWLINE
         else
           in.nextToken()
@@ -3545,7 +3545,7 @@ object Parsers {
             ValDef(name, parents.head, subExpr())
           else
             DefDef(name, tparams, vparamss, parents.head, subExpr())
-        else if in.token != WITH && in.token != WITHEOL && parentsIsType then
+        else if in.token != WITH && parentsIsType then
           if name.isEmpty then
             syntaxError(em"anonymous given cannot be abstract")
           DefDef(name, tparams, vparamss, parents.head, EmptyTree)
@@ -3633,12 +3633,12 @@ object Parsers {
     /** `{`with` ConstrApp} but no EOL allowed after `with`.
      */
     def withConstrApps(): List[Tree] =
-      if in.token == WITH then
-        in.observeWithEOL() // converts token to WITHEOL if at end of line
-        if in.token == WITH && in.lookahead.token != LBRACE then
-          in.nextToken()
-          constrApp() :: withConstrApps()
-        else Nil
+      def isTemplateStart =
+        val la = in.lookahead
+        la.isAfterLineEnd || la.token == LBRACE
+      if in.token == WITH && !isTemplateStart then
+        in.nextToken()
+        constrApp() :: withConstrApps()
       else Nil
 
     /** Template          ::=  InheritClauses [TemplateBody]
@@ -3708,8 +3708,8 @@ object Parsers {
 
     /** with Template, with EOL <indent> interpreted */
     def withTemplate(constr: DefDef, parents: List[Tree]): Template =
-      if in.token != WITHEOL then accept(WITH)
-      possibleTemplateStart() // consumes a WITHEOL token
+      if in.token != WITH then syntaxError(em"`with` expected")
+      possibleTemplateStart() // consumes a WITH token
       val (self, stats) = templateBody()
       Template(constr, parents, Nil, self, stats)
         .withSpan(Span(constr.span.orElse(parents.head.span).start, in.lastOffset))

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

@@ -74,6 +74,9 @@ object Scanners {
 
     def isNestedStart = token == LBRACE || token == INDENT
     def isNestedEnd = token == RBRACE || token == OUTDENT
+
+    /** Is current token first one after a newline? */
+    def isAfterLineEnd: Boolean = lineOffset >= 0
   }
 
   abstract class ScannerCommon(source: SourceFile)(using Context) extends CharArrayReader with TokenData {
@@ -512,15 +515,12 @@ object Scanners {
          |Previous indent : $lastWidth
          |Latest indent   : $nextWidth"""
 
-    private def switchAtEOL(testToken: Token, eolToken: Token): Unit =
-      if token == testToken then
+    def observeColonEOL(): Unit =
+      if token == COLON then
         lookAhead()
         val atEOL = isAfterLineEnd || token == EOF
         reset()
-        if atEOL then token = eolToken
-
-    def observeColonEOL(): Unit = switchAtEOL(COLON, COLONEOL)
-    def observeWithEOL(): Unit = switchAtEOL(WITH, WITHEOL)
+        if atEOL then token = COLONEOL
 
     def observeIndented(): Unit =
       if indentSyntax && isNewLine then
@@ -610,9 +610,6 @@ object Scanners {
       }
     }
 
-    /** Is current token first one after a newline? */
-    def isAfterLineEnd: Boolean = lineOffset >= 0
-
     /** Is there a blank line between the current token and the last one?
      *  A blank line consists only of characters <= ' '.
      *  @pre  afterLineEnd().

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

@@ -204,8 +204,7 @@ object Tokens extends TokensCommon {
   final val QUOTE = 87;            enter(QUOTE, "'")
 
   final val COLONEOL = 88;         enter(COLONEOL, ":", ": at eol")
-  final val WITHEOL = 89;          enter(WITHEOL, "with", "with at eol")
-  final val SELFARROW = 90;        enter(SELFARROW, "=>") // reclassified ARROW following self-type
+  final val SELFARROW = 89;        enter(SELFARROW, "=>") // reclassified ARROW following self-type
 
   /** XML mode */
   final val XMLSTART = 99;         enter(XMLSTART, "$XMLSTART$<") // TODO: deprecate
@@ -277,8 +276,7 @@ object Tokens extends TokensCommon {
   final val closingRegionTokens = BitSet(RBRACE, RPAREN, RBRACKET, CASE) | statCtdTokens
 
   final val canStartIndentTokens: BitSet =
-    statCtdTokens | BitSet(COLONEOL, WITHEOL, EQUALS, ARROW, LARROW, WHILE, TRY, FOR, IF)
-      // `if` is excluded because it often comes after `else` which makes for awkward indentation rules  TODO: try to do without the exception
+    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.
@@ -287,7 +285,7 @@ object Tokens extends TokensCommon {
 
   final val scala3keywords = BitSet(ENUM, ERASED, GIVEN)
 
-  final val endMarkerTokens = identifierTokens | BitSet(IF, WHILE, FOR, MATCH, TRY, NEW, GIVEN, VAL, THIS)
+  final val endMarkerTokens = identifierTokens | BitSet(IF, WHILE, FOR, MATCH, TRY, NEW, THROW, GIVEN, VAL, THIS)
 
   final val softModifierNames = Set(nme.inline, nme.opaque, nme.open, nme.transparent, nme.infix)
 }

docs/docs/reference/changed-features/match-syntax.md

@@ -6,42 +6,41 @@ title: Match Expressions
 The syntactical precedence of match expressions has been changed.
 `match` is still a keyword, but it is used like an alphabetical operator. This has several consequences:
 
-1. `match` expressions can be chained:
-
-   ```scala
-   xs match {
-      case Nil => "empty"
-      case x :: xs1 => "nonempty"
-   } match {
-      case "empty" => 0
-      case "nonempty" => 1
-   }
-   ```
-
-   (or, dropping the optional braces)
-
-   ```scala
-   xs match
-      case Nil => "empty"
-      case x :: xs1 => "nonempty"
-   match
-      case "empty" => 0
-      case "nonempty" => 1
-   ```
-
-2. `match` may follow a period:
+ 1. `match` expressions can be chained:
 
     ```scala
-    if xs.match
-       case Nil => false
-       case _ => true
-    then "nonempty"
-    else "empty"
+    xs match {
+       case Nil => "empty"
+       case x :: xs1 => "nonempty"
+    } match {
+       case "empty" => 0
+       case "nonempty" => 1
+    }
     ```
 
-3. The scrutinee of a match expression must be an `InfixExpr`. Previously the scrutinee could be
-   followed by a type ascription `: T`, but this is no longer supported. So `x : T match { ... }`
-   now has to be written `(x: T) match { ... }`.
+    (or, dropping the optional braces)
+
+    ```scala
+    xs match
+       case Nil => "empty"
+       case x :: xs1 => "nonempty"
+    match
+       case "empty" => 0
+       case "nonempty" => 1
+    ```
+
+ 2. `match` may follow a period:
+
+     ```scala
+     if xs.match
+        case Nil => false
+        case _ => true
+     then "nonempty"
+     else "empty"
+     ```
+
+ 3. The scrutinee of a match expression must be an `InfixExpr`. Previously the scrutinee could be followed by a type ascription `: T`, but this is no longer supported. So `x : T match { ... }` now has to be
+ written `(x: T) match { ... }`.
 
 ## Syntax
 

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

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

@@ -94,3 +94,45 @@ class Object extends Any, Matchable
 
 `Matchable` is currently a marker trait without any methods. Over time
 we might migrate methods `getClass` and `isInstanceOf` to it, since these are closely related to pattern-matching.
+
+### `Matchable` and Universal Equality
+
+Methods that pattern-match on selectors of type `Any` will need a cast once the
+Matchable warning is turned on. The most common such method is the universal
+`equals` method. It will have to be written as in the following example:
+
+```scala
+class C(val x: String):
+
+   override def equals(that: Any): Boolean =
+      that.asInstanceOf[Matchable] match
+         case that: C => this.x == that.x
+         case _ => false
+```
+The cast of `that` to `Matchable` serves as an indication that universal equality
+is unsafe in the presence of abstract types and opaque types since it cannot properly distinguish the meaning of a type from its representation. The cast
+is guaranteed to succeed at run-time since `Any` and `Matchable` both erase to
+`Object`.
+
+For instance, consider the definitions
+```scala
+opaque type Meter = Double
+def Meter(x: Double) = x
+
+opaque type Second = Double
+def Second(x: Double) = x
+```
+Here, universal `equals` will return true for
+```scala
+   Meter(10).equals(Second(10))
+```
+even though this is clearly false mathematically. With [multiversal equality](../contextual/multiversal-equality.html) one can mitigate that problem somewhat by turning
+```scala
+   Meter(10) == Second(10)
+```
+into a type error.
+
+
+
+
+

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