add support for drone

Author: Vadim Hatsura

src/GitVersionCore.Tests/BuildServers/DroneTests.cs

@@ -0,0 +1,39 @@
+namespace GitVersionCore.Tests.BuildServers
+{
+    using System;
+    using GitVersion;
+    using NUnit.Framework;
+    using Shouldly;
+
+    [TestFixture]
+    public class DroneTests : TestBase
+    {
+        [Test]
+        public void CanApplyToCurrentContext_ShouldBeTrue_WhenEnvironmentVariableIsSet()
+        {
+            // Arrange
+            Environment.SetEnvironmentVariable("DRONE", "true");
+            var buildServer = new Drone();
+
+            // Act
+            var result = buildServer.CanApplyToCurrentContext();
+
+            // Assert
+            result.ShouldBeTrue();
+        }
+
+        [Test]
+        public void CanApplyToCurrentContext_ShouldBeFalse_WhenEnvironmentVariableIsNotSet()
+        {
+            // Arrange
+            Environment.SetEnvironmentVariable("DRONE", "");
+            var buildServer = new Drone();
+
+            // Act
+            var result = buildServer.CanApplyToCurrentContext();
+
+            // Assert
+            result.ShouldBeFalse();
+        }
+    }
+}

src/GitVersionCore/BuildServers/BuildServerList.cs

@@ -1,4 +1,4 @@
-namespace GitVersion
+namespace GitVersion
 {
     using System;
     using System.Collections.Generic;
@@ -16,6 +16,7 @@ public static class BuildServerList
             new VsoAgent(),
             new TravisCI(),
             new EnvRun(),
+            new Drone()
         };
 
         public static IEnumerable<IBuildServer> GetApplicableBuildServers()

src/GitVersionCore/BuildServers/Drone.cs

@@ -0,0 +1,30 @@
+namespace GitVersion
+{
+    using System;
+
+    public class Drone : BuildServerBase
+    {
+        public override bool CanApplyToCurrentContext()
+        {
+            return Environment.GetEnvironmentVariable("DRONE")?.Equals("true", StringComparison.OrdinalIgnoreCase) ?? false;
+        }
+
+        public override string GenerateSetVersionMessage(VersionVariables variables)
+        {
+            return variables.FullSemVer;
+        }
+
+        public override string[] GenerateSetParameterMessage(string name, string value)
+        {
+            return new[]
+            {
+                $"GitVersion_{name}={value}"
+            };
+        }
+
+        public override string GetCurrentBranch(bool usingDynamicRepos)
+        {
+            return Environment.GetEnvironmentVariable("DRONE_BRANCH");
+        }
+    }
+}