Add Dotnet Implementation #219

clrudolphi · 2025-11-01T22:13:51Z

🤔 What's changed?

Add a .NET implementation.
This uses a hand-written parser/evaluator.
Passes tests equivalent to those in the Java implementation using the same testdata.

⚡️ What's your motivation?

Eventual incorporation into Reqnroll.

🏷️ What kind of change is this?

⚡ New feature (non-breaking change which adds new behaviour)

♻️ Anything particular you want feedback on?

Open to any feedback.

📋 Checklist:

I agree to respect and uphold the Cucumber Community Code of Conduct
I've changed the behaviour of the code
- I have added/updated tests to cover my changes.
My change requires a change to the documentation.
- I have updated the documentation accordingly.
Users should know about my change
- I have added an entry to the "Unreleased" section of the CHANGELOG, linking to this pull request.

This text was originally generated from a template, then edited by hand. You can modify the template here.

Added README.md

Fixed a problem when the input tag text is null.

gasparnagy

Super. Looks good, I have made a few smaller comments.

gasparnagy · 2025-11-03T09:16:22Z

dotnet/TagExpressions/TagExpressionParser.cs

+    /// <exception cref="Exception">Always thrown to indicate a syntax error.</exception>
+    private void ThrowSyntaxError(string message)
+    {
+        throw new Exception($"Tag expression \"{_text}\" could not be parsed because of syntax error: {message}.");


Could we make a specific exception type for tag expression errors?

Good catch. I had meant to and forgotten.

gasparnagy · 2025-11-03T09:18:55Z

dotnet/TagExpressions/TagExpressions.csproj

+  </ItemGroup>
+
+  <PropertyGroup Label="Package Properties">
+    <Product>TagExpressions</Product>


I would consider calling this package and the namespaces to "Cucumber.TagExpressions" instead. The "TagExpressions" term is too generic (like we call the cucumber expressions package "Cucumber.CucumberExpressions", although there we have missed the opportunity to have a matching namespace).

gasparnagy · 2025-11-03T09:21:59Z

dotnet/TagExpressions/TagToken.cs

+
+internal class TagToken
+{
+    public TagTokenType Type { get; }


From other similar project experience, I have found it very useful to store the position of the token value as well withing the original expression. (I.e. the character index where this particular token has been found). This can be used to provide a better error message in case the error is related to a token. Like:

Invalid operation "and": "@foo and and @bar" ^

I will enhance the token to include the position, and include the Token object as a property of the custom exception type.
However, regarding including positioning information in the exception message: doing so would break the expectations set in the poly conformance tests as there is a specific content and format expected for each type of parsing error. (See cucumber/tag-expressions/testdata/errors.yml).

Would you rather that we:

retain exact compatibility with the existing testsuite

enhance the test suite to include positional information in error messages (and expect the other language implementations to match)

diverge (and exclude the existing errors.yml tests from the dotnet implementation)

I think for now we can just retain the compatibility, but just have the information in the exception as you suggested, so if someone wants to have a better visualization for the error, they can do it.

gasparnagy · 2025-11-03T09:24:05Z

dotnet/TagExpressionsTest/TagExpressionsTest.csproj

+      -->
+    <TestingPlatformShowTestsFailure>true</TestingPlatformShowTestsFailure>
+    <SignAssembly>True</SignAssembly>
+    <AssemblyOriginatorKeyFile>TagExpressionsTest.snk</AssemblyOriginatorKeyFile>


We can use the TagExpressions.snk from the folder above (../TagExpressions.snk)

gasparnagy · 2025-11-03T09:25:41Z

dotnet/TagExpressionsTest/TagLexerTests.cs

+using System;
+using TagExpressions;
+
+namespace TagExpressionsTest


Change to file-scoped namespace declaration.

gasparnagy · 2025-11-03T09:26:53Z

dotnet/TagExpressionsTest/TestFolderHelper.cs

+using System.Text;
+using System.Threading.Tasks;
+
+namespace QueryTest


Wrong namespace, use file-scoped namespace declaration.

gasparnagy · 2025-11-03T09:28:24Z

dotnet/Directory.Build.props

+  <PropertyGroup>
+    <LangVersion>13</LangVersion>
+    <ImplicitUsings>enable</ImplicitUsings>
+    <TreatWarningsAsErrors>true</TreatWarningsAsErrors>


I would also add <Nullable>enable</Nullable> here and handle nullable details.

gasparnagy · 2025-11-03T09:28:55Z

dotnet/README.md

@@ -0,0 +1,5 @@
+[![Maven Central](https://img.shields.io/maven-central/v/io.cucumber/tag-expressions.svg?label=Maven%20Central)](https://search.maven.org/search?q=g:%22io.cucumber%22%20AND%20a:%22tag-expressions%22)


Should be replaced to a NuGet badge

luke-hill

Got to 15/27 items. Mainly non-poly stuff. Will get to others alter

luke-hill · 2025-11-03T09:26:50Z

dotnet/TagExpressions/InternalsVisibleTo.TagExpressionsTest.cs

@@ -0,0 +1,3 @@
+using System.Runtime.CompilerServices;
+
+[assembly: InternalsVisibleTo("TagExpressionsTest, PublicKey=0024000004800000940000000602000000240000525341310004000001000100bd9b4db256712217f4906b5eb0113e633e319ef574450f83cb837097cac352cfac3a3d3e652c74e2f19e4af0464877e171602bb254fba62c9023894123393ca270ac5c1c01e99e233d0ccdb75f1ebf9b18b66f1618c1d9904658bc7e0a836c5488fb6e54845d9daabbf37594f54bc58f9136fd66cdad9b2761e8710956b2f1ce")]


This seems a weird test? Not quite sure what it's doing. Just a comment to check if this is correct

This statement enables that the "TagExpressionsTest" project should have visibility on those stuff that are declared as "internal". This is a common practice in .NET.

Changed Namespaces. Added custom exception type. Include position information in Token. Corrected namespaces in Test project. Nullable by default. Readme.md now includes a nuget badge.

Copilot

Pull Request Overview

This PR adds a .NET implementation of tag expressions for Cucumber, enabling parsing and evaluation of logical tag expressions in .NET projects. The implementation follows the existing tag-expressions specification and includes comprehensive test coverage using YAML-based test data.

Implements a complete tag expression parser with lexer, parser, and AST nodes
Adds NuGet package configuration for distribution
Includes extensive test suite with unit tests and YAML-based acceptance tests

Reviewed Changes

Copilot reviewed 25 out of 27 changed files in this pull request and generated 7 comments.

Show a summary per file

File	Description
dotnet/TagExpressions/TagExpressionParser.cs	Core parser implementing recursive descent parsing for tag expressions
dotnet/TagExpressions/TagLexer.cs	Lexer for tokenizing tag expression strings
dotnet/TagExpressions/TagExpression.cs	AST node classes representing parsed expressions
dotnet/TagExpressions/TagToken.cs	Token types and token class for lexical analysis
dotnet/TagExpressions/ITagExpression.cs	Interface defining the tag expression contract
dotnet/TagExpressionsTest/ParsingTest.cs	YAML-based tests for parsing behavior
dotnet/TagExpressionsTest/EvaluationsTest.cs	YAML-based tests for expression evaluation
dotnet/TagExpressionsTest/ErrorsTest.cs	YAML-based tests for error handling
dotnet/TagExpressionsTest/TagLexerTests.cs	Unit tests for the lexer
dotnet/TagExpressionsTest/TestFolderHelper.cs	Helper utility to locate test data files
dotnet/TagExpressions/Cucumber.TagExpressions.csproj	NuGet package configuration
.github/workflows/test-dotnet.yml	CI workflow for .NET testing
.github/workflows/release-nuget.yaml	Release workflow for NuGet publishing

Comments suppressed due to low confidence (1)

dotnet/TagExpressionsTest/TagLexerTests.cs:94

Generic catch clause.

        catch (Exception ex)
        {
            StringAssert.Contains(ex.Message, "Illegal escape");
        }

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dotnet/TagExpressions/TagExpression.cs

dotnet/TagExpressionsTest/TagLexerTests.cs

dotnet/TagExpressions/TagLexer.cs

dotnet/TagExpressionsTest/ErrorsTest.cs

dotnet/TagExpressionsTest/EvaluationsTest.cs

dotnet/TagExpressionsTest/ParsingTest.cs

dotnet/TagExpressionsTest/TestFolderHelper.cs

mpkorstanje · 2025-11-07T18:43:39Z

@clrudolphi please do take these into account: #222, #221.

…ken ToString() should be empty string rather than "true").

…ful test names

clrudolphi · 2025-11-09T22:21:11Z

@clrudolphi please do take these into account: #222, #221.

@mpkorstanje This PR now matches the changes made in #221 and #222.

mpkorstanje

At a glance it looks like you've made some implementation parts public. To make it easier to evolve the implementation - not that I expect much of it- it is generally nicer if the internal are kept internal. But I'm not a .Net expert so not 100% sure if that is actually the case.

Nitpicks aside, LGTM.

Feel free to merge. When you're happy.

mpkorstanje · 2025-11-10T14:51:19Z

dotnet/TagExpressions/ITagExpressionParser.cs

+/// <summary>
+/// Defines a parser for tag expressions.
+/// </summary>
+public interface ITagExpressionParser


Out of curiosity. Why an interface for the parser? There is only one concrete type and I don't imagine we'll ever have a second.

For the benefit of Reqnroll. It will have a Tag Expression parser implementation that wraps this one. See below for explanation.

Ah I see. But that means ITagExpressionParser can live with RnR right? You'd have a Cucumber implementation and a RnR implementation.

mpkorstanje · 2025-11-10T14:51:52Z

dotnet/TagExpressions/TagExpression.cs

+/// <summary>
+/// Provides an abstract base for tag expressions that can be evaluated against a set of input tags.
+/// </summary>
+public abstract class TagExpression : ITagExpression


Should this and other classes in this file be public?

I need them to be public for Reqnroll.

The tag-expression library itself is not opiniated on whether literals in expressions must or must not always have the @ prefix.

Reqnroll is liberal in that respect. If a tag expression is given without, then Reqnroll rewrites the expression such that the tag literals in the expression are given the @ prefix.

In order to rewrite the expression, Reqnroll needs to be able to instantiate new instances of each of the TagExpression types.

public class ReqnrollTagExpressionParser(ITagExpressionParser tagExpressionParser) : ITagExpressionParser { public ITagExpression Parse(string tagExpression) { return Rewrite(tagExpressionParser.Parse(tagExpression)); } private ITagExpression Rewrite(ITagExpression expression) { return expression switch { NullExpression nullExpression => nullExpression, NotNode notNode => new NotNode(Rewrite(notNode.Operand)), BinaryOpNode binaryOpNode => new BinaryOpNode(binaryOpNode.Op, Rewrite(binaryOpNode.Left), Rewrite(binaryOpNode.Right)), LiteralNode literalNode => new LiteralNode(PrefixLiteral(literalNode.Name)), _ => throw new NotSupportedException($"Unsupported tag expression type: {expression.GetType().FullName}"), }; } private string PrefixLiteral(string name) { if (name.IsNullOrEmpty() ) return name; if (name.StartsWith("@")) return name; return "@" + name; } }

I'm okay with these classes being public, but then please do ensure they're not extensible, ect.

CHANGELOG.md

Co-authored-by: M.P. Korstanje <[email protected]>

clrudolphi · 2025-11-10T17:12:33Z

Nitpicks aside, LGTM.

Feel free to merge. When you're happy.

Thanks for looking it over.
I'll ping Gaspar to take another look (likely next week) and then we'll merge. Let me know if that timing works for you.

mpkorstanje · 2025-11-10T17:22:43Z

Let me know if that timing works for you.

On short time frames anything works.

Ideally I'd get you onboarded with https://github.com/cucumber/polyglot-release then you can release it yourself.

clrudolphi added 5 commits November 1, 2025 11:22

First commit

61ccca5

Add github workflows and nuget package creation.

f32ad14

Code refactoring, comments, and unit tests for the Lexer.

5191a32

Improve documentation, tests, and assembly signing

6d5ffb0

Added README.md

Update CHANGELOG.md

f6544ef

clrudolphi self-assigned this Nov 1, 2025

clrudolphi requested review from gasparnagy, luke-hill and mpkorstanje November 1, 2025 22:15

Improve Lexer Handling of Null Input

1941994

Fixed a problem when the input tag text is null.

gasparnagy requested changes Nov 3, 2025

View reviewed changes

luke-hill reviewed Nov 3, 2025

View reviewed changes

Updates per review comments.

08614a9

Changed Namespaces. Added custom exception type. Include position information in Token. Corrected namespaces in Test project. Nullable by default. Readme.md now includes a nuget badge.

mpkorstanje mentioned this pull request Nov 3, 2025

Add Dotnet Implementation cucumber/query#81

Open

7 tasks

complete the renaming process to Cucumber.TagExpressions

0a67e22

clrudolphi requested a review from Copilot November 4, 2025 20:45

Copilot AI reviewed Nov 4, 2025

View reviewed changes

clrudolphi added 2 commits November 4, 2025 17:07

Refactor from Github Copilot review.

c8df619

CodeMaid cleanups.

4a7282f

clrudolphi added 3 commits November 9, 2025 16:02

Merge branch 'main' into dotnet

d00b994

Update .NET to match changes made in PRs #221 and #222 (empty/NULL to…

4dbb567

…ken ToString() should be empty string rather than "true").

Housekeeping: modify tests so that VS2022 Test Explorer shows meaning…

9b974e9

…ful test names

mpkorstanje approved these changes Nov 10, 2025

View reviewed changes

Update CHANGELOG.md

c43a411

Co-authored-by: M.P. Korstanje <[email protected]>

clrudolphi requested a review from gasparnagy November 10, 2025 23:29

		@@ -0,0 +1,5 @@
		[![Maven Central](https://img.shields.io/maven-central/v/io.cucumber/tag-expressions.svg?label=Maven%20Central)](https://search.maven.org/search?q=g:%22io.cucumber%22%20AND%20a:%22tag-expressions%22)

		@@ -0,0 +1,3 @@
		using System.Runtime.CompilerServices;

		[assembly: InternalsVisibleTo("TagExpressionsTest, PublicKey=0024000004800000940000000602000000240000525341310004000001000100bd9b4db256712217f4906b5eb0113e633e319ef574450f83cb837097cac352cfac3a3d3e652c74e2f19e4af0464877e171602bb254fba62c9023894123393ca270ac5c1c01e99e233d0ccdb75f1ebf9b18b66f1618c1d9904658bc7e0a836c5488fb6e54845d9daabbf37594f54bc58f9136fd66cdad9b2761e8710956b2f1ce")]

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Add Dotnet Implementation #219

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Add Dotnet Implementation #219

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clrudolphi commented Nov 1, 2025

🤔 What's changed?

⚡️ What's your motivation?

🏷️ What kind of change is this?

♻️ Anything particular you want feedback on?

📋 Checklist:

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Pull Request Overview

Reviewed Changes

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mpkorstanje commented Nov 7, 2025

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clrudolphi commented Nov 9, 2025

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