Refactor statement loops

Author: odersky

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

@@ -254,6 +254,7 @@ object Parsers {
         || skipStopTokens.contains(in.token) && (in.currentRegion eq lastRegion)
       while !atStop do
         in.nextToken()
+      lastErrorOffset = in.offset
 
     def warning(msg: Message, sourcePos: SourcePosition): Unit =
       report.warning(msg, sourcePos)
@@ -273,11 +274,9 @@ object Parsers {
      */
     def syntaxErrorOrIncomplete(msg: Message, offset: Int = in.offset): Unit =
       if (in.token == EOF) incompleteInputError(msg)
-      else {
+      else
         syntaxError(msg, offset)
         skip()
-        lastErrorOffset = in.offset
-      }
 
     /** Consume one token of the specified type, or
       * signal an error if it is not there.
@@ -312,6 +311,35 @@ object Parsers {
     def acceptStatSep(): Unit =
       if in.isNewLine then in.nextToken() else accept(SEMI)
 
+    def exitStats[T <: Tree](stats: ListBuffer[T], altEnd: Token = EOF, noPrevStat: Boolean): Boolean =
+      def recur(sepSeen: Boolean, endSeen: Boolean): Boolean =
+        if isStatSep then
+          in.nextToken()
+          recur(true, endSeen)
+        else if in.token == END then
+          if endSeen then syntaxError("duplicate end marker")
+          checkEndMarker(stats)
+          recur(sepSeen, true)
+        else if isStatSeqEnd || in.token == altEnd then
+          true
+        else if sepSeen || endSeen then
+          false
+        else
+          val found = in.token
+          syntaxError(
+            if noPrevStat then IllegalStartOfStatement(isModifier)
+            else i"end of statement expected but ${showToken(found)} found")
+          if mustStartStatTokens.contains(found) then
+            true // it's a statement that might be legal in an outer context
+          else
+            in.nextToken() // needed to ensure progress; otherwise we might cycle forever
+            skip()
+            false
+
+      in.observeOutdented()
+      recur(false, false)
+    end exitStats
+
     def acceptStatSepUnlessAtEnd[T <: Tree](stats: ListBuffer[T], altEnd: Token = EOF): Unit =
       def skipEmptyStats(): Unit =
         while (in.token == SEMI || in.token == NEWLINE || in.token == NEWLINES) do in.nextToken()
@@ -3891,8 +3919,8 @@ object Parsers {
      */
     def blockStatSeq(): List[Tree] = checkNoEscapingPlaceholders {
       val stats = new ListBuffer[Tree]
-      var exitOnError = false
-      while (!isStatSeqEnd && in.token != CASE && !exitOnError) {
+      while
+        var empty = false
         if (in.token == IMPORT)
           stats ++= importClause(IMPORT, mkImport())
         else if (isExprIntro)
@@ -3903,12 +3931,10 @@ object Parsers {
           stats += extension()
         else if isDefIntro(localModifierTokens, excludedSoftModifiers = Set(nme.`opaque`)) then
           stats +++= localDef(in.offset)
-        else if (!isStatSep && (in.token != CASE)) {
-          exitOnError = mustStartStat
-          syntaxErrorOrIncomplete(IllegalStartOfStatement(isModifier))
-        }
-        acceptStatSepUnlessAtEnd(stats, CASE)
-      }
+        else
+          empty = true
+        !exitStats(stats, CASE, empty)
+      do ()
       stats.toList
     }
 

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

@@ -1826,7 +1826,7 @@ import transform.SymUtils._
 
   class IllegalStartOfStatement(isModifier: Boolean)(using Context) extends SyntaxMsg(IllegalStartOfStatementID) {
     def msg = {
-      val addendum = if (isModifier) ": no modifiers allowed here" else ""
+      val addendum = if (isModifier) ": this modifier is not allowed here" else ""
       "Illegal start of statement" + addendum
     }
     def explain = "A statement is either an import, a definition or an expression."

tests/neg-macros/i7603.scala

@@ -2,6 +2,6 @@ import scala.quoted.*
 class Foo {
   def f[T2: Type](e: Expr[T2])(using Quotes) = e match {
     case '{ $x: ${'[List[$t]]} } => // error
-    case '{ $x: ${y @ '[List[$t]]} } => // error // error
+    case '{ $x: ${y @ '[List[$t]]} } => // error
   }
 }

tests/neg/indent.scala

@@ -2,7 +2,7 @@ object Test {
 
   extension (x: Int) def gt(y: Int) = x > y
   val y3 =
-    if (1) max 10 gt 0  // error: end of statement expected but integer literal found // error // error // error
+    if (1) max 10 gt 0  // error: end of statement expected but integer literal found // error // error
       1
     else
       2

tests/neg/multiLineOps.scala

@@ -6,7 +6,7 @@ val b1 = {
   22
   * 22  // ok
   */*one more*/22 // error: end of statement expected // error: not found: *
-}                 // error: ';' expected, but '}' found
+}
 
 val b2: Boolean = {
   println(x)