Revert to Scala 2 rules for handling opening brace on next line

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

@@ -1353,15 +1353,7 @@ object Parsers {
 
     def argumentStart(): Unit =
       colonAtEOLOpt()
-      if migrateTo3 && in.token == NEWLINE && in.next.token == LBRACE then
-        in.nextToken()
-        if in.indentWidth(in.offset) == in.currentRegion.indentWidth then
-          report.errorOrMigrationWarning(
-            em"""This opening brace will start a new statement in Scala 3.
-                |It needs to be indented to the right to keep being treated as
-                |an argument to the previous expression.${rewriteNotice()}""",
-            in.sourcePos(), from = `3.0`)
-          patch(source, Span(in.offset), "  ")
+      newLineOptWhenFollowedBy(LBRACE)
 
     def possibleTemplateStart(isNew: Boolean = false): Unit =
       in.observeColonEOL(inTemplate = true)

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

@@ -569,9 +569,9 @@ object Scanners {
        *   - In Scala 2: Only `{` is treated as continuing, irrespective of indentation.
        *     But this is in fact handled by Parser.argumentStart which skips a NEWLINE,
        *     so we always assume false here.
-       *   - In Scala 3: Only indented statements are treated as continuing, as long as
+       *   - In Scala 3: Indented statements are treated as continuing, as long as
        *     they start with `(`, `[` or `{`, or the last statement ends in a `return`.
-       *   The Scala 2 rules apply under source `3.0-migration` or under `-no-indent`.
+       *  The Scala 2 rules apply under source `3.0-migration` or under `-no-indent`.
        */
       inline def isContinuing =
         lastWidth < nextWidth

compiler/src/dotty/tools/dotc/reporting/trace.scala

@@ -55,7 +55,7 @@ trait TraceSyntax:
     apply(question, printer, {
       val showOp: T => String = inline if show == true then
         val showT = summonInline[Show[T]]
-        {
+        locally {
           given Show[T] = showT
           t => i"$t"
         }

compiler/src/dotty/tools/dotc/typer/Typer.scala

@@ -3555,7 +3555,7 @@ class Typer(@constructorOnly nestingLevel: Int = 0) extends Namer
         else
           errorTree(tree, em"Missing arguments for $methodStr")
       case _ => tryInsertApplyOrImplicit(tree, pt, locked) {
-        errorTree(tree, MethodDoesNotTakeParameters(tree))
+        errorTree(tree, MethodDoesNotTakeParameters(tree), tree.srcPos.endPos)
       }
     }
 

compiler/test/dotty/tools/dotc/CompilationTests.scala

@@ -149,7 +149,6 @@ class CompilationTests {
       compileFile("tests/neg-custom-args/i3246.scala", scala2CompatMode),
       compileFile("tests/neg-custom-args/overrideClass.scala", scala2CompatMode),
       compileFile("tests/neg-custom-args/ovlazy.scala", scala2CompatMode.and("-Xfatal-warnings")),
-      compileFile("tests/neg-custom-args/newline-braces.scala", scala2CompatMode.and("-Xfatal-warnings")),
       compileFile("tests/neg-custom-args/autoTuplingTest.scala", defaultOptions.andLanguageFeature("noAutoTupling")),
       compileFile("tests/neg-custom-args/i1650.scala", allowDeepSubtypes),
       compileFile("tests/neg-custom-args/i3882.scala", allowDeepSubtypes),

tests/neg/bad-unapplies.check

@@ -19,10 +19,10 @@
    |         D cannot be used as an extractor in a pattern because it lacks an unapply or unapplySeq method
    |
    | longer explanation available when compiling with `-explain`
--- [E050] Type Error: tests/neg/bad-unapplies.scala:25:9 ---------------------------------------------------------------
+-- [E050] Type Error: tests/neg/bad-unapplies.scala:25:10 --------------------------------------------------------------
 25 |    case E("2") => // error (value unapply in object E does not take parameters)
-   |         ^
-   |         value unapply in object E does not take parameters
+   |          ^
+   |          value unapply in object E does not take parameters
    |
    | longer explanation available when compiling with `-explain`
 -- [E107] Syntax Error: tests/neg/bad-unapplies.scala:26:10 ------------------------------------------------------------

tests/neg/i10857.check

@@ -0,0 +1,31 @@
+-- [E008] Not Found Error: tests/neg/i10857.scala:33:17 ----------------------------------------------------------------
+33 |  println(Module.valueOf("Red")) // error: value valueOf is not a member
+   |          ^^^^^^^^^^^^^^
+   |          value valueOf is not a member of object Module
+-- [E008] Not Found Error: tests/neg/i10857.scala:36:21 ----------------------------------------------------------------
+36 |  println(new Module.GivenBar()) // error: type GivenBar is not a member
+   |              ^^^^^^^^^^^^^^^
+   |              type GivenBar is not a member of object Module - did you mean Module.Givens.type?
+-- [E050] Type Error: tests/neg/i10857.scala:37:25 ---------------------------------------------------------------------
+37 |  println(Module.GivenBar(23)) // error: method GivenBar does not take parameters
+   |                         ^
+   |                         given instance GivenBar in object Module does not take parameters
+   |
+   | longer explanation available when compiling with `-explain`
+-- [E007] Type Mismatch Error: tests/neg/i10857.scala:41:24 ------------------------------------------------------------
+41 |  println(Module.Member("?")(23)) // error: Found: ("?" : String) Required: Int // error: method Member in object Module does not take more parameters
+   |                        ^^^
+   |                        Found:    ("?" : String)
+   |                        Required: Int
+   |
+   | longer explanation available when compiling with `-explain`
+-- [E050] Type Error: tests/neg/i10857.scala:41:28 ---------------------------------------------------------------------
+41 |  println(Module.Member("?")(23)) // error: Found: ("?" : String) Required: Int // error: method Member in object Module does not take more parameters
+   |                            ^
+   |                            method Member in object Module does not take more parameters
+   |
+   | longer explanation available when compiling with `-explain`
+-- [E172] Type Error: tests/neg/i10857.scala:42:28 ---------------------------------------------------------------------
+42 |  println(summon[Module.Baz]) // error: no implicit argument of type Module.Baz was found
+   |                            ^
+   |                No given instance of type Module.Baz was found for parameter x of method summon in object Predef

tests/neg/i10857.scala

@@ -38,7 +38,7 @@ object Module:
 
   println(new Module.Member())
   println(Module.Member(23))
-  println(Module.Member("?")(23)) // error: Found: ("?" : String) Required: Int
+  println(Module.Member("?")(23)) // error: Found: ("?" : String) Required: Int // error: method Member in object Module does not take more parameters
   println(summon[Module.Baz]) // error: no implicit argument of type Module.Baz was found
 
   println(summon[Module.Qux])

tests/neg/i12554a.scala

@@ -17,7 +17,7 @@ object Test {
 
   def i: Unit = {
     f("Foo")
-    {}    // ok, error in Scala 2
+    {}    // error, error in Scala 2
   }
 
   def j: Int = {

tests/neg/i14818.check

@@ -3,10 +3,10 @@
   |               ^^^^^^
   |               no eligible member B at M
   |               M.B cannot be exported because it clashes with another export in the same export clause
--- [E050] Type Error: tests/neg/i14818.scala:16:10 ---------------------------------------------------------------------
+-- [E050] Type Error: tests/neg/i14818.scala:16:11 ---------------------------------------------------------------------
 16 |  val x = b(1)  // error
-   |          ^
-   |          method b in object T3 does not take parameters
+   |           ^
+   |           method b in object T3 does not take parameters
    |
    | longer explanation available when compiling with `-explain`
 -- Error: tests/neg/i14818.scala:19:22 ---------------------------------------------------------------------------------

tests/neg/i1707.scala

@@ -17,6 +17,7 @@ object DepBug {
     import d.*
     a m (b)
   }
+
   {
     import dep.*
     a m (b) // error: not found: a

tests/neg/i9437.check

@@ -1,6 +1,6 @@
--- [E050] Type Error: tests/neg/i9437.scala:7:10 -----------------------------------------------------------------------
+-- [E050] Type Error: tests/neg/i9437.scala:7:14 -----------------------------------------------------------------------
 7 |  println(x.f1())  // error
-  |          ^^^^
-  |          method selectDynamic in trait Selectable does not take parameters
+  |              ^
+  |              method selectDynamic in trait Selectable does not take parameters
   |
   | longer explanation available when compiling with `-explain`

tests/new/i16760.scala

@@ -0,0 +1,13 @@
+object Test {
+  def main(args: Array[String]): Unit = {
+    def process(arg: Int)(block: => Unit): Int = arg
+    val x = process(1)
+    {
+    }
+    println(x)
+    val y = process(2)
+      ( ()
+      )
+    println(y)
+  }
+}

tests/pos-with-compiler-cc/dotc/reporting/trace.scala

@@ -55,7 +55,7 @@ trait TraceSyntax:
     apply(question, printer, {
       val showOp: T => String = inline if show == true then
         val showT = summonInline[Show[T]]
-        {
+        locally {
           given Show[T] = showT
           t => i"$t"
         }

tests/pos/indented-parens.scala

@@ -7,5 +7,6 @@ def f(x: Int)
     (2)
     + f(1)
        {2}
+
   { println(x) }