Let GitHubActionsAttribute name the generated job with JobName

src/Fallout.Common/CI/GitHubActions/GitHubActionsAttribute.cs

@@ -161,6 +161,16 @@ public GitHubActionsAttribute(
     /// </summary>
     public string[] RunsOnLabels { get; set; } = new string[0];
 
+    /// <summary>
+    /// Overrides the generated job's id and <c>name:</c>, which otherwise default to the runner image
+    /// (e.g. <c>windows-latest</c>). Useful with <see cref="RunsOnLabels"/>, where the image is only a
+    /// placeholder, since the job name is what shows in the PR checks list and what branch protection matches.
+    /// <para/>
+    /// Must be a valid job id (letters, digits, <c>-</c> and <c>_</c>, starting with a letter or <c>_</c>)
+    /// and requires exactly one image, as a matrix would produce duplicate ids. Unset keeps the default.
+    /// </summary>
+    public string JobName { get; set; }
+
     public GitHubActionsSubmodules Submodules
     {
         set => submodules = value;
@@ -307,6 +317,10 @@ public override ConfigurationEntity GetConfiguration(IReadOnlyCollection<Executa
 
         Assert.True(RunsOnLabels.All(x => !x.IsNullOrWhiteSpace()),
             $"'{nameof(RunsOnLabels)}' entries must not be null, empty, or whitespace");
+        Assert.True(JobName == null || images.Length == 1,
+            $"Cannot use '{nameof(JobName)}' with multiple images; each job in the matrix would get the same id");
+        Assert.True(JobName == null || System.Text.RegularExpressions.Regex.IsMatch(JobName, "^[A-Za-z_][A-Za-z0-9_-]*$"),
+            $"'{nameof(JobName)}' must be a valid job id: letters, digits, '-' and '_', starting with a letter or '_'");
 
         return configuration;
     }
@@ -315,7 +329,7 @@ protected virtual GitHubActionsJob GetJobs(GitHubActionsImage image, IReadOnlyCo
     {
         return new GitHubActionsJob
         {
-            Name = image.GetValue().Replace(".", "_"),
+            Name = JobName ?? image.GetValue().Replace(".", "_"),
             RunsOnLabels = RunsOnLabels,
             EnvironmentName = EnvironmentName,
             EnvironmentUrl = EnvironmentUrl,

tests/Fallout.Common.Specs/CI/GitHubActionsJobNameSpecs.cs

@@ -0,0 +1,93 @@
+using System;
+using System.Linq;
+using Fallout.Common.CI;
+using Fallout.Common.CI.GitHubActions;
+using Fallout.Common.CI.GitHubActions.Configuration;
+using Fallout.Common.Execution;
+using Fallout.Common.Utilities;
+using FluentAssertions;
+using Xunit;
+
+namespace Fallout.Common.Specs.CI;
+
+public class GitHubActionsJobNameSpecs
+{
+    [Fact]
+    public void Unset_job_name_uses_image_value()
+    {
+        var job = GetJobs(new[] { GitHubActionsImage.WindowsLatest }, jobName: null).Single();
+
+        job.Name.Should().Be("windows-latest");
+    }
+
+    [Fact]
+    public void Unset_job_name_keeps_dots_replaced_in_matrix()
+    {
+        var jobs = GetJobs(new[] { GitHubActionsImage.UbuntuLatest, GitHubActionsImage.Ubuntu2204 }, jobName: null);
+
+        jobs.Select(x => x.Name).Should().Equal("ubuntu-latest", "ubuntu-22_04");
+    }
+
+    [Fact]
+    public void Job_name_is_used_as_job_id_and_name()
+    {
+        var job = GetJobs(new[] { GitHubActionsImage.WindowsLatest }, "build-windows").Single();
+
+        job.Name.Should().Be("build-windows");
+        using var stream = new System.IO.MemoryStream();
+        using (var streamWriter = new System.IO.StreamWriter(stream, leaveOpen: true))
+        {
+            job.Write(new CustomFileWriter(streamWriter, 2, "#"));
+        }
+
+        var output = System.Text.Encoding.UTF8.GetString(stream.ToArray());
+        output.Should().StartWith("build-windows:").And.Contain("name: build-windows");
+    }
+
+    [Fact]
+    public void Job_name_with_multiple_images_throws()
+    {
+        var act = () => GetJobs(new[] { GitHubActionsImage.UbuntuLatest, GitHubActionsImage.WindowsLatest }, "build");
+
+        act.Should().Throw<Exception>().WithMessage("*JobName*");
+    }
+
+    [Theory]
+    [InlineData("build")]
+    [InlineData("_build")]
+    [InlineData("Build-1_x")]
+    public void Valid_job_name_does_not_throw(string jobName)
+    {
+        var act = () => GetJobs(new[] { GitHubActionsImage.UbuntuLatest }, jobName);
+
+        act.Should().NotThrow();
+    }
+
+    [Theory]
+    [InlineData("")]
+    [InlineData("   ")]
+    [InlineData("1build")]
+    [InlineData("-build")]
+    [InlineData("build job")]
+    [InlineData("build.job")]
+    public void Invalid_job_name_throws(string jobName)
+    {
+        var act = () => GetJobs(new[] { GitHubActionsImage.UbuntuLatest }, jobName);
+
+        act.Should().Throw<Exception>().WithMessage("*JobName*");
+    }
+
+    private static GitHubActionsJob[] GetJobs(GitHubActionsImage[] images, string jobName)
+    {
+        var build = new ConfigurationGenerationSpecs.TestBuild();
+        var relevantTargets = ExecutableTargetFactory.CreateAll(build, x => x.Compile);
+        var attribute = new TestGitHubActionsAttribute(images[0], images[1..])
+                        {
+                            On = new[] { GitHubActionsTrigger.Push },
+                            InvokedTargets = new[] { nameof(ConfigurationGenerationSpecs.TestBuild.Test) },
+                            JobName = jobName
+                        };
+        ((ConfigurationAttributeBase)attribute).Build = build;
+        return ((GitHubActionsConfiguration)attribute.GetConfiguration(relevantTargets)).Jobs;
+    }
+}