Move trailing comma handling to Parser

Author: adampauls

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

@@ -567,9 +567,17 @@ object Parsers {
       in.currentRegion.withCommasExpected {
         val ts = new ListBuffer[T]
         if (readFirst) ts += part()
-        while in.token == COMMA do
+        var done = false
+        while in.token == COMMA && !done do
           in.nextToken()
-          ts += part()
+          if in.token == RPAREN || in.token == RBRACKET || in.token == RBRACE || in.token == OUTDENT then
+            if in.isAfterLineEnd then
+              // skip the trailing comma
+              done = true
+            else
+              syntaxError("trailing comma must be followed by newline")
+          else
+            ts += part()
         ts.toList
       }
 
@@ -3271,7 +3279,7 @@ object Parsers {
      */
     def patDefOrDcl(start: Offset, mods: Modifiers): Tree = atSpan(start, nameStart) {
       val first = pattern2()
-      var lhs = first match {
+      val lhs = first match {
         case id: Ident if in.token == COMMA =>
           in.nextToken()
           id :: commaSeparated(() => termIdent())

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

@@ -698,13 +698,6 @@ object Scanners {
             case r: Indented if isEnclosedInParens(r.outer) =>
               insert(OUTDENT, offset)
             case _ =>
-              lookAhead()
-              if isAfterLineEnd
-                 && (token == RPAREN || token == RBRACKET || token == RBRACE || token == OUTDENT)
-              then
-                () /* skip the trailing comma */
-              else
-                reset()
         case END =>
           if !isEndMarker then token = IDENTIFIER
         case COLON =>

tests/neg/syntax-error-recovery.check

@@ -36,12 +36,10 @@
    |              expression expected but ',' found
    |
    | longer explanation available when compiling with `-explain`
--- [E018] Syntax Error: tests/neg/syntax-error-recovery.scala:59:15 ----------------------------------------------------
+-- Error: tests/neg/syntax-error-recovery.scala:59:15 ------------------------------------------------------------------
 59 |    foo2(foo2(,) // error // error
    |               ^
-   |               expression expected but ')' found
-   |
-   | longer explanation available when compiling with `-explain`
+   |               trailing comma must be followed by newline
 -- [E040] Syntax Error: tests/neg/syntax-error-recovery.scala:62:8 -----------------------------------------------------
 62 |// error
    |        ^

tests/neg/t11900.check

@@ -0,0 +1,18 @@
+-- Error: tests/neg/t11900.scala:44:16 ---------------------------------------------------------------------------------
+44 |      a => a + 1,   // error: weird comma
+   |                ^
+   |                end of statement expected but ',' found
+-- Error: tests/neg/t11900.scala:48:16 ---------------------------------------------------------------------------------
+48 |    println("a"),   // error: weird comma
+   |                ^
+   |                end of statement expected but ',' found
+-- Error: tests/neg/t11900.scala:52:16 ---------------------------------------------------------------------------------
+52 |    println("b"),   // error: weird comma
+   |                ^
+   |                end of statement expected but ',' found
+-- [E032] Syntax Error: tests/neg/t11900.scala:64:8 --------------------------------------------------------------------
+64 |      _*, // error
+   |        ^
+   |        pattern expected
+   |
+   | longer explanation available when compiling with `-explain`

tests/neg/t11900.scala

@@ -0,0 +1,79 @@
+
+trait t11900 {
+  // cf pos/trailing-commas
+  //
+  import scala.collection.{
+    immutable,
+    mutable,
+  }
+
+  def h[A,
+  ]: List[A] = Nil
+
+  def u(
+      x: Int,
+      y: Int,
+  )(using List[Int],
+      Set[Int],
+  )(using l: List[Int],
+    s : Set[Int],
+  ): Int = 1
+
+  def g = List(
+    1,
+    2,
+    3,
+  )
+
+  def star =
+    List(1, 2, 3, 4, 5) match {
+      case List(
+      1,
+      2,
+      3,
+      ) => false
+      case List(
+      1,
+      2,
+      _*,
+      ) => true
+    }
+
+  def f =
+    List(1, 2, 3).map {
+      a => a + 1,   // error: weird comma
+    }
+
+  class A() {
+    println("a"),   // error: weird comma
+  }
+
+  def b() = {
+    println("b"),   // error: weird comma
+  }
+
+  def starcrossed =
+    List(1, 2, 3, 4, 5) match {
+      case List(
+      1,
+      2,
+      3,
+      ) => false
+      case List(
+      1,
+      _*, // error
+      2,
+      ) => true
+    }
+
+  def p(p: (Int,
+      String,
+      )
+  ): Unit
+
+  def q: (Int,
+      String,
+      )
+
+  val z = 42
+}

tests/neg/t5702-neg-bad-and-wild.check

@@ -1,15 +1,11 @@
--- [E032] Syntax Error: tests/neg/t5702-neg-bad-and-wild.scala:10:22 ---------------------------------------------------
+-- Error: tests/neg/t5702-neg-bad-and-wild.scala:10:22 -----------------------------------------------------------------
 10 |      case List(1, _*,) => // error: pattern expected
    |                      ^
-   |                      pattern expected
-   |
-   | longer explanation available when compiling with `-explain`
--- [E032] Syntax Error: tests/neg/t5702-neg-bad-and-wild.scala:12:23 ---------------------------------------------------
+   |                      trailing comma must be followed by newline
+-- Error: tests/neg/t5702-neg-bad-and-wild.scala:12:23 -----------------------------------------------------------------
 12 |      case List(1, _*3,) => // error: pattern expected // error
    |                       ^
-   |                       pattern expected
-   |
-   | longer explanation available when compiling with `-explain`
+   |                       trailing comma must be followed by newline
 -- [E040] Syntax Error: tests/neg/t5702-neg-bad-and-wild.scala:13:23 ---------------------------------------------------
 13 |      case List(1, _*3:) =>  // error // error
    |                       ^

tests/neg/trailing-comma-pattern2.check

@@ -1,9 +1,7 @@
--- [E032] Syntax Error: tests/neg/trailing-comma-pattern2.scala:2:21 ---------------------------------------------------
+-- Error: tests/neg/trailing-comma-pattern2.scala:2:21 -----------------------------------------------------------------
 2 |  val List(x, y, _*, ) // error
   |                     ^
-  |                     pattern expected
-  |
-  | longer explanation available when compiling with `-explain`
+  |                     trailing comma must be followed by newline
 -- [E040] Syntax Error: tests/neg/trailing-comma-pattern2.scala:3:8 ----------------------------------------------------
 3 |// error
   |        ^

tests/neg/trailingCommas.scala

@@ -56,3 +56,27 @@ object `package` {
   case class Foo(foo: Any)
   case class Bar(foo: Any)
 }
+
+// Unparenthesized lists
+trait Deriv1[T]
+object Deriv1 {
+  def derived[T]: Deriv1[T] = new Deriv1[T] {}
+}
+
+trait Deriv2[T]
+object Deriv2 {
+  def derived[T]: Deriv2[T] = new Deriv2[T] {}
+}
+
+class Derives1 derives Deriv1, Deriv2,
+object End // error: an identifier expected, but 'object' found
+
+class Derives2 derives Deriv1,
+     Deriv2,
+object End2 // error: an identifier expected, but 'object' found
+
+val a,
+    b,
+    c,
+    = (1, 2, 3) // error
+val x, y, z, = (1, 2, 3) // error

tests/pos/comma-separated.scala

@@ -0,0 +1,19 @@
+trait Bar[T]
+object Bar {
+  def derived[T]: Bar[T] = new Bar[T] {}
+}
+
+trait Baz[T]
+object Baz {
+  def derived[T]: Baz[T] = new Baz[T] {}
+}
+
+class Foo derives Bar, Baz
+
+class Foo2 derives Bar,
+   Baz
+
+val x, y, z = (1, 2, 3)
+val a,
+    b,
+    c = (1, 2, 3)