Bugfix/issue #507

.gitignore

@@ -42,3 +42,10 @@ coverage.json
 ruleset1.ruleset
 opencov.bat
 BenchmarkDotNet.Artifacts
+
+*.nupkg
+*.snupkg
+*.swp
+AotTester/*
+*.dtp
+*.dtp.state

src/samples/ParserExample/Program.cs

@@ -134,6 +134,13 @@ public static object Rec(List<object> args)
         }
 
 
+        private static void TestIssue507()
+        {
+            var tests = new EBNFTests();
+            //tests.TestIssue507TransitiveEmptyStarter();
+            tests.TestIssue507MoreTransitiveEmptyStarter();
+        }
+
         private static void BenchSimpleExpression()
         {
             GenericSimpleExpressionParser p = new GenericSimpleExpressionParser();
@@ -1353,7 +1360,8 @@ print a
         }
         private static void Main(string[] args)
         {
-            TestFStrings();
+            TestIssue507();
+            //TestFStrings();
             //TestIssue495();
             //testGenericLexerJson();
             // TestIssue487();

src/sly/parser/generator/EBNFParserBuilder.cs

@@ -59,6 +59,7 @@ public override BuildResult<Parser<IN, OUT>> BuildParser(object parserInstance,
                 configuration.AutoCloseIndentations = autoCloseIndentations;
                 LeftRecursionChecker<IN, OUT> recursionChecker = new LeftRecursionChecker<IN, OUT>();
 
+                SetEmptyNonTerminals(configuration);
                 // check left recursion.
                 var (foundRecursion, recursions) = LeftRecursionChecker<IN, OUT>.CheckLeftRecursion(configuration);
                 if (foundRecursion)
@@ -118,6 +119,31 @@ protected override ISyntaxParser<IN, OUT> BuildSyntaxParser(ParserConfiguration<
             return parser;
         }
 
+        private void SetEmptyNonTerminals(ParserConfiguration<IN, OUT> conf)
+        {
+            bool stillSetting = true;
+            while (stillSetting)
+            {
+                stillSetting = false;
+                foreach (var nt in conf.NonTerminals)
+                {
+                    foreach (var rule in nt.Value.Rules)
+                    {
+                        foreach (var clause in rule.Clauses)
+                        {
+                            if (clause is NonTerminalClause<IN> nonTerminalClause)
+                            {
+                                var rules = conf.GetRulesForNonTerminal(nonTerminalClause.NonTerminalName);
+                                stillSetting |= nonTerminalClause.SetMayBeEmpty(rules.Exists(x => x.MayBeEmpty));
+                            }
+                        }
+                    }
+                }
+            }
+        }
+
+
+
 
         #region configuration
 

src/sly/parser/generator/ParserConfiguration.cs

@@ -61,6 +61,15 @@ public List<TerminalClause<IN>> GetAllExplicitTokenClauses()
             return clauses;
         }
 
+        public List<Rule<IN>> GetRulesForNonTerminal(string nonTerminal)
+        {
+            if (NonTerminals.TryGetValue(nonTerminal, out NonTerminal<IN> nonTerminalConfig))
+            {
+                return nonTerminalConfig.Rules.ToList();
+            }
+            return new List<Rule<IN>>();
+        }
+
         [ExcludeFromCodeCoverage]
         public string Dump()
         {

src/sly/parser/syntax/grammar/NonTerminalClause.cs

@@ -1,4 +1,3 @@
-using System;
 using System.Diagnostics.CodeAnalysis;
 
 namespace sly.parser.syntax.grammar
@@ -14,9 +13,18 @@ public NonTerminalClause(string name)
 
         public bool IsGroup { get; set; } = false;
 
+        private bool _mayBeEmpty = false;
+
         public bool MayBeEmpty()
         {
-            return false;
+            return _mayBeEmpty;
+        }
+
+        public bool SetMayBeEmpty(bool mayBeEmpty)
+        {
+            bool setted = mayBeEmpty && !_mayBeEmpty;
+            _mayBeEmpty = mayBeEmpty;
+            return setted;
         }
 
 

src/sly/sly.csproj

@@ -1,6 +1,6 @@
 <Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
-    <TargetFrameworks>netstandard2.0;netstandard2.1;net6.0;net7.0</TargetFrameworks>
+    <TargetFrameworks>net7.0;netstandard2.0;netstandard2.1;net6.0</TargetFrameworks>
     <PublishRepositoryUrl>true</PublishRepositoryUrl>
     <EmbedUntrackedSources>true</EmbedUntrackedSources>
     <AllowedOutputExtensionsInPackageBuildOutputFolder>$(AllowedOutputExtensionsInPackageBuildOutputFolder);.pdb</AllowedOutputExtensionsInPackageBuildOutputFolder>

tests/ParserTests/EBNFTests.cs

@@ -2,7 +2,6 @@
 using System.Collections.Generic;
 using System.Linq;
 using System.Text;
-using expressionparser;
 using indented;
 using jsonparser;
 using jsonparser.JsonModel;
@@ -580,6 +579,64 @@ public string A(Token<OptionTestToken> t)
 
     }
 
+    public class Issue507TransitiveEmptyStarterParser
+    {
+        [Production("x : y")]
+        public string X(string y)
+        {
+            return y;
+        }
+
+        [Production("y : z*")]
+        public string Y(List<string> zs)
+        {
+            if (zs.Any())
+            {
+                return string.Join(",", zs);
+            }
+
+            return "empty";
+        }
+
+        [Production("z : a")]
+        public string Z(Token<OptionTestToken> a)
+        {
+            return a.Value;
+        }
+    }
+
+    public class Issue507MoreTransitiveEmptyStarterParser
+    {
+        [Production("x : w")]
+        public string X(string w)
+        {
+            return w;
+        }
+
+        [Production("w : y")]
+        public string W(string y)
+        {
+            return y;
+        }
+
+        [Production("y : z*")]
+        public string Y(List<string> zs)
+        {
+            if (zs.Any())
+            {
+                return string.Join(",", zs);
+            }
+
+            return "empty";
+        }
+
+        [Production("z : a")]
+        public string Z(Token<OptionTestToken> a)
+        {
+            return a.Value;
+        }
+    }
+
     public class Bugfix104Test
     {
         [Production("testNonTerm : sub (COMMA[d] unreachable)? ")]
@@ -1324,6 +1381,42 @@ public void TestAlternateChoiceInGroupLeftRecursion()
         }
 
 
+        [Fact]
+        public void TestIssue507TransitiveEmptyStarter()
+        {
+            var startingRule = $"x";
+            var parserInstance = new Issue507TransitiveEmptyStarterParser();
+            var builder = new ParserBuilder<OptionTestToken, string>();
+            var builtParser = builder.BuildParser(parserInstance, ParserType.EBNF_LL_RECURSIVE_DESCENT, startingRule);
+            Check.That(builtParser).IsOk();
+            var parser = builtParser.Result;
+            var parserResultNotEmpty = parser.Parse("a a a");
+            Check.That(parserResultNotEmpty).IsOkParsing();
+            Check.That(parserResultNotEmpty.Result).IsEqualTo("a,a,a");
+
+            var parserResultEmpty = parser.Parse("");
+            Check.That(parserResultEmpty).IsOkParsing();
+            Check.That(parserResultEmpty.Result).IsEqualTo("empty");
+        }
+
+        [Fact]
+        public void TestIssue507MoreTransitiveEmptyStarter()
+        {
+            var startingRule = $"x";
+            var parserInstance = new Issue507MoreTransitiveEmptyStarterParser();
+            var builder = new ParserBuilder<OptionTestToken, string>();
+            var builtParser = builder.BuildParser(parserInstance, ParserType.EBNF_LL_RECURSIVE_DESCENT, startingRule);
+            Check.That(builtParser).IsOk();
+            var parser = builtParser.Result;
+            var parserResultNotEmpty = parser.Parse("a a a");
+            Check.That(parserResultNotEmpty).IsOkParsing();
+            Check.That(parserResultNotEmpty.Result).IsEqualTo("a,a,a");
+
+            var parserResultEmpty = parser.Parse("");
+            Check.That(parserResultEmpty).IsOkParsing();
+            Check.That(parserResultEmpty.Result).IsEqualTo("empty");
+        }
+
         [Fact]
         public void TestIssue190()
         {

tests/ParserTests/ParserTests.csproj

@@ -33,6 +33,7 @@
     <ProjectReference Include="..\..\src\samples\SlowEOS\SlowEOS.csproj" />
     <ProjectReference Include="..\..\src\samples\while\while.csproj" />
     <ProjectReference Include="..\..\src\samples\XML\XML.csproj" />
+    <ProjectReference Include="..\..\src\sly\sly.csproj" />
   </ItemGroup>
   <ItemGroup>
     <Service Include="{82a7f48d-3b50-4b1e-b82e-3ada8210c358}" />