Added error for missing values in lists

Author: Tobias-Kohn

tpParser/shared/src/main/scala/tigerpython/parser/errormessages/EnglishMessages.scala

@@ -97,6 +97,7 @@ object EnglishMessages extends ModifiableErrorMessages {
       case MISSING_COMMA => "There seems to be a comma missing."
       case MISSING_COMPARISON => "There is a comparison missing."
       case MISSING_DOT => "There seems to be a dot missing."
+      case MISSING_EXPRESSION => "There is an expression or value missing here."
       case MISSING_LEFT_BRACKET => "There is a missing left bracket or parenthesis: '%s'."
       case MISSING_LEFT_PARENTHESIS => "There is a missing left parenthesis '('."
       case MISSING_LINE_BREAK => "You need to put '%s' on a new (indented) line."

tpParser/shared/src/main/scala/tigerpython/parser/parsing/ExpressionParser.scala

@@ -760,7 +760,12 @@ class ExpressionParser(val parser: Parser, val parserState: ParserState) {
 
   protected def parseListMaker(tokens: TokenBuffer): Expression = {
     val startPos = tokens.head.pos
-    val test = parseTest(tokens)
+    val test =
+      if (tokens.headType == TokenType.COMMA) {
+        parserState.reportError(tokens, ErrorCode.MISSING_EXPRESSION)
+        null
+      } else
+        parseTest(tokens)
     if (tokens.hasType(TokenType.FOR)) {
       val c = parseComprehension(tokens)
       AstNode.ListComp(startPos, tokens.endPosOfList, test, c)
@@ -792,7 +797,7 @@ class ExpressionParser(val parser: Parser, val parserState: ParserState) {
         } else
         if (tokens.matchType(TokenType.SEMICOLON))
           parserState.reportError(tokens.prevPos, ErrorCode.TYPO, ";", ",")
-        if (!tokens.matchType(TokenType.COMMA))
+        else if (!tokens.matchType(TokenType.COMMA))
           parserState.reportError(tokens, ErrorCode.MISSING_OPERATOR_OR_COMMA)
         if (firstOfTest(tokens))
           result += parseTest(tokens)

tpParser/shared/src/test/programs/erroneous/lists_03.txt

@@ -0,0 +1,3 @@
+# 1
+# MISSING_EXPRESSION
+empty_list = [,,,]

tpParser/shared/src/test/scala/DebugTester.scala

@@ -14,10 +14,9 @@ class DebugTester extends FunSuite  {
   }
 
   private val PROGRAM: String =
-    """def foo(x);
-      |    pass
+    """my_list = [,,,]
       |
-      |foo(12)
+      |print(my_list)
       |""".stripMargin
 
   {