Fix #3309: Crash in REPL Auto-completion

When auto-completing in the REPL, we sometime tried to manipulate a
tree with no position. Not anymore

Author: allanrenucci

compiler/src/dotty/tools/repl/ParseResult.scala

@@ -4,6 +4,7 @@ package repl
 import dotc.reporting.diagnostic.MessageContainer
 import dotc.core.Contexts.Context
 import dotc.parsing.Parsers.Parser
+import dotc.parsing.Tokens
 import dotc.util.SourceFile
 import dotc.ast.untpd
 import dotc.reporting._
@@ -97,6 +98,12 @@ object ParseResult {
 
   @sharable private[this] val CommandExtract = """(:[\S]+)\s*(.*)""".r
 
+  private def parseStats(parser: Parser): List[untpd.Tree] = {
+    val stats = parser.blockStatSeq()
+    parser.accept(Tokens.EOF)
+    stats
+  }
+
   /** Extract a `ParseResult` from the string `sourceCode` */
   def apply(sourceCode: String)(implicit ctx: Context): ParseResult =
     sourceCode match {
@@ -114,7 +121,7 @@ object ParseResult {
         val source = new SourceFile("<console>", sourceCode.toCharArray)
         val parser = new Parser(source)
 
-        val (_, stats) = parser.templateStatSeq()
+        val stats = parseStats(parser)
 
         if (ctx.reporter.hasErrors) {
           SyntaxErrors(sourceCode,
@@ -140,7 +147,7 @@ object ParseResult {
         reporter.withIncompleteHandler(_ => _ => needsMore = true) {
           val source = new SourceFile("<console>", sourceCode.toCharArray)
           val parser = new Parser(source)(ctx.fresh.setReporter(reporter))
-          parser.templateStatSeq()
+          parseStats(parser)
           !reporter.hasErrors && needsMore
         }
       }

compiler/src/dotty/tools/repl/ReplCompiler.scala

@@ -238,7 +238,7 @@ class ReplCompiler(val directory: AbstractFile) extends Compiler {
         PackageDef(Ident(nme.EMPTY_PACKAGE),
           TypeDef("EvaluateExpr".toTypeName, tmpl)
             .withMods(new Modifiers(Final))
-            .withPos(Position(trees.head.pos.start, trees.last.pos.end)) :: Nil
+            .withPos(Position(0, expr.length)) :: Nil
         )
       }
 

compiler/test/dotty/tools/repl/TabcompleteTests.scala

@@ -52,4 +52,10 @@ class TabcompleteTests extends ReplTest {
       assert(tabComplete(src2).suggestions.nonEmpty)
     }
   }
+
+  @Test def i3309: Unit =
+    fromInitialState { implicit s =>
+      List("\"", "#", ")", "=", "'", "¨", "£", ".", ":", ",", ";", "@", "}", "[", "]")
+        .foreach(src => assertTrue(tabComplete(src).suggestions.isEmpty))
+    }
 }