fix parsing whitespaces

Author: RomanSoloweow

src/SimpleStateMachine.StructuralSearch/Parsers/PlaceholderParser.cs

@@ -20,7 +20,7 @@ public override Parser<char, string> BuildParser(Func<Parser<char, string>?> nex
             Func<Parser<char, string>?> nextNext)
         {
             var _next = next();
-            var _nextNext = nextNext() ?? Parser<char>.End.ThenReturn(string.Empty);
+            var _nextNext = nextNext() ?? Parser.OneOf(CommonParser.WhiteSpaces, Parser<char>.End.ThenReturn(string.Empty));
             var lookahead = Parsers.Lookahead(_next.Then(_nextNext, (s1, s2) =>
             {
                 OnLookahead = () => new List<LookaheadResult<char, string>>

src/SimpleStateMachine.StructuralSearch/Rules/Parameters/PlaceholderFileParameter.cs

@@ -25,8 +25,6 @@ public string GetValue()
                 FileProperty.Lenght => input.Lenght.ToString(),
                 _ => throw new ArgumentOutOfRangeException()
             };
-
-            return null;
         }
 
         public override string ToString()

src/SimpleStateMachine.StructuralSearch/SeriesParser.cs

@@ -27,7 +27,7 @@ public override bool TryParse(ref ParseState<char> state, ref PooledList<Expecte
                 var parser = Parsers.ElementAt(i);
                 if (!parser.TryParse(ref state, ref expecteds, out var _result))
                 {
-                    result = Enumerable.Empty<string>();
+                    result = results;
                     return false;
                 }
 

src/SimpleStateMachine.StructuralSearch/StructuralSearch/CommonParser.cs

@@ -25,7 +25,8 @@ internal static readonly Parser<char, string> LineEnds
             = EndOfLine.AtLeastOnceString();
 
         internal static readonly Parser<char, string> WhiteSpaces
-            = OneOf(Spaces, LineEnds);
+            = OneOf(Spaces, LineEnds, LineEnds)
+                .AtLeastOnceString();
 
         internal static readonly Parser<char, string> Identifier
             = Letter.Then(AnyString, (h, t) => h + t);

src/SimpleStateMachine.StructuralSearch/StructuralSearch/FindTemplateParser.cs

@@ -32,7 +32,7 @@ static FindTemplateParser()
                 .Try();
 
         internal static readonly Parser<char, Parser<char, string>> WhiteSpaces =
-            ParserToParser.ResultAsParser(CommonParser.WhiteSpaces)
+            ParserToParser.ParserAsParser(CommonParser.WhiteSpaces)
                 .Try();  
 
         internal static readonly Parser<char, Parser<char, string>> Placeholder = 

src/SimpleStateMachine.StructuralSearch/Templates/FindTemplate/ParserToParser.cs

@@ -27,6 +27,11 @@ public static Parser<char, Parser<char, string>> ResultAsParser(Parser<char, str
             return parser.Select(value => Parsers.String(value, ignoreCase));
         }
 
+        public static Parser<char, Parser<char, string>> ParserAsParser(Parser<char, string> parser)
+        {
+            return parser.Select(value => parser);
+        }
+        
         public static Parser<char, Parser<char, SourceMatch>> ResultAsMatch(Parser<char, string> parser, bool ignoreCase = false)
         {
             return parser.Select(x=> Parsers.String(x, ignoreCase).AsMatch());