Add extra logic to handle tag refs in GithubActions

Author: david-driscoll

src/GitVersion.BuildAgents.Tests/Agents/GitHubActionsTests.cs

@@ -18,6 +18,7 @@ public void SetUp()
         this.environment = sp.GetRequiredService<IEnvironment>();
         this.buildServer = sp.GetRequiredService<GitHubActions>();
         this.environment.SetEnvironmentVariable(GitHubActions.EnvironmentVariableName, "true");
+        this.environment.SetEnvironmentVariable("GITHUB_REF_TYPE", "branch");
 
         this.githubSetEnvironmentTempFilePath = Path.GetTempFileName();
         this.environment.SetEnvironmentVariable(GitHubActions.GitHubSetEnvTempFileEnvironmentVariableName, this.githubSetEnvironmentTempFilePath);
@@ -75,26 +76,30 @@ public void GetCurrentBranchShouldHandleBranches()
     public void GetCurrentBranchShouldHandleTags()
     {
         // Arrange
+        this.environment.SetEnvironmentVariable("GITHUB_REF_TYPE", "tag");
         this.environment.SetEnvironmentVariable("GITHUB_REF", "refs/tags/1.0.0");
 
         // Act
         var result = this.buildServer.GetCurrentBranch(false);
 
         // Assert
-        result.ShouldBe("refs/tags/1.0.0");
+        result.ShouldBeNull();
     }
 
     [Test]
     public void GetCurrentBranchShouldHandlePullRequests()
     {
         // Arrange
+        this.environment.SetEnvironmentVariable("GITHUB_EVENT_NAME", "pull_request");
+        this.environment.SetEnvironmentVariable("GITHUB_HEAD_REF", "some-branch");
+        this.environment.SetEnvironmentVariable("GITHUB_BASE_REF", MainBranch);
         this.environment.SetEnvironmentVariable("GITHUB_REF", "refs/pull/1/merge");
 
         // Act
         var result = this.buildServer.GetCurrentBranch(false);
 
         // Assert
-        result.ShouldBe("refs/pull/1/merge");
+        result.ShouldBe("some-branch");
     }
 
     [Test]

src/GitVersion.BuildAgents/Agents/GitHubActions.cs

@@ -50,7 +50,28 @@ public override void WriteIntegration(Action<string?> writer, GitVersionVariable
         }
     }
 
-    public override string? GetCurrentBranch(bool usingDynamicRepos) => Environment.GetEnvironmentVariable("GITHUB_REF");
+
+    public override string? GetCurrentBranch(bool usingDynamicRepos)
+    {
+        var refType = Environment.GetEnvironmentVariable("GITHUB_REF_TYPE") ?? "";
+        var eventName = Environment.GetEnvironmentVariable("GITHUB_EVENT_NAME") ?? "";
+        // https://docs.github.com/en/actions/learn-github-actions/environment-variables#default-environment-variables
+        // GITHUB_REF must be used only for "real" branches, not for tags.
+        // Bug fix for https://github.com/GitTools/GitVersion/issues/2838
+        
+        // pull_request or pull_request_target
+        if (eventName.StartsWith("pull_request", StringComparison.OrdinalIgnoreCase))
+        {
+            return Environment.GetEnvironmentVariable("GITHUB_HEAD_REF");
+        }
+
+        if (refType.Equals("tag", StringComparison.OrdinalIgnoreCase))
+        {
+            return null;
+        }
+        
+        return Environment.GetEnvironmentVariable("GITHUB_REF");
+    }
 
     public override bool PreventFetch() => true;
 }