Add detection for AI CLI environment variables (#669)

* Add AiCliDetector for AI CLI environment detection

Introduces AiCliDetector to detect if running in an AI-powered CLI environment (GitHub Copilot CLI, Aider, Claude Code) via environment variables. Updates documentation and DisabledChecker to include AiCliDetector. Adds related tests and documentation snippets.

* Update Directory.Build.props

Author: SimonCropp

readme.md

@@ -46,6 +46,7 @@ DiffEngine manages launching and cleanup of diff tools. It is designed to be use
   * [Closing a tool](#closing-a-tool)
   * [File type detection](#file-type-detection)
   * [BuildServerDetector](#buildserverdetector)
+  * [AiCliDetector](#aiclidetector)
   * [Disable for a machine/process](#disable-for-a-machineprocess)
   * [Disable in code](#disable-in-code)
   * [Icons](#icons)<!-- endToc -->
@@ -161,6 +162,29 @@ var isAppVeyor = BuildServerDetector.IsAppVeyor;
 <!-- endSnippet -->
 
 
+## AiCliDetector
+
+`AiCliDetector.Detected` returns true if the current code is running in an AI-powered CLI environment.
+
+Supports:
+
+ * [GitHub Copilot CLI](https://docs.github.com/en/copilot/using-github-copilot/using-github-copilot-in-the-command-line)
+ * [Aider](https://aider.chat/docs/config/dotenv.html)
+ * [Claude Code](https://docs.anthropic.com/en/docs/build-with-claude/claude-cli)
+
+There are also individual properties to check for each specific AI CLI
+
+<!-- snippet: AiCliDetectorProps -->
+<a id='snippet-AiCliDetectorProps'></a>
+```cs
+var isCopilotCli = AiCliDetector.IsCopilotCli;
+var isAider = AiCliDetector.IsAider;
+var isClaudeCode = AiCliDetector.IsClaudeCode;
+```
+<sup><a href='/src/DiffEngine.Tests/AiCliDetectorTest.cs#L9-L15' title='Snippet source file'>snippet source</a> | <a href='#snippet-AiCliDetectorProps' title='Start of snippet'>anchor</a></sup>
+<!-- endSnippet -->
+
+
 ## Disable for a machine/process
 
 Set an environment variable `DiffEngine_Disabled` with the value `true`.

readme.source.md

@@ -84,6 +84,21 @@ There are also individual properties to check for each specific build system
 snippet: BuildServerDetectorProps
 
 
+## AiCliDetector
+
+`AiCliDetector.Detected` returns true if the current code is running in an AI-powered CLI environment.
+
+Supports:
+
+ * [GitHub Copilot CLI](https://docs.github.com/en/copilot/using-github-copilot/using-github-copilot-in-the-command-line)
+ * [Aider](https://aider.chat/docs/config/dotenv.html)
+ * [Claude Code](https://docs.anthropic.com/en/docs/build-with-claude/claude-cli)
+
+There are also individual properties to check for each specific AI CLI
+
+snippet: AiCliDetectorProps
+
+
 ## Disable for a machine/process
 
 Set an environment variable `DiffEngine_Disabled` with the value `true`.

src/DiffEngine.Tests/AiCliDetectorTest.cs

@@ -0,0 +1,19 @@
+public class AiCliDetectorTest(ITestOutputHelper output) :
+    XunitContextBase(output)
+{
+    [Fact]
+    public void Props()
+    {
+        // ReSharper disable UnusedVariable
+
+        #region AiCliDetectorProps
+
+        var isCopilotCli = AiCliDetector.IsCopilotCli;
+        var isAider = AiCliDetector.IsAider;
+        var isClaudeCode = AiCliDetector.IsClaudeCode;
+
+        #endregion
+
+        // ReSharper restore UnusedVariable
+    }
+}

src/DiffEngine/AiCliDetector.cs

@@ -0,0 +1,33 @@
+namespace DiffEngine;
+
+public static class AiCliDetector
+{
+    static AiCliDetector()
+    {
+        var variables = Environment.GetEnvironmentVariables();
+        
+        // GitHub Copilot CLI
+        // https://docs.github.com/en/copilot/using-github-copilot/using-github-copilot-in-the-command-line
+        IsCopilotCli = variables.Contains("GITHUB_COPILOT_CLI");
+
+        // Aider
+        // https://aider.chat/docs/config/dotenv.html
+        IsAider = variables.Contains("AIDER_GIT_DNAME") || variables.Contains("AIDER");
+
+        // Claude Code
+        // https://docs.anthropic.com/en/docs/build-with-claude/claude-cli
+        IsClaudeCode = variables.Contains("CLAUDE_CODE") || variables.Contains("ANTHROPIC_CLI");
+
+        Detected = IsCopilotCli ||
+                   IsAider ||
+                   IsClaudeCode;
+    }
+
+    public static bool IsCopilotCli { get; }
+
+    public static bool IsAider { get; }
+
+    public static bool IsClaudeCode { get; }
+
+    public static bool Detected { get; set; }
+}

src/DiffEngine/DisabledChecker.cs

@@ -5,6 +5,7 @@ public static bool IsDisable()
         var variable = Environment.GetEnvironmentVariable("DiffEngine_Disabled");
         return string.Equals(variable, "true", StringComparison.OrdinalIgnoreCase) ||
                BuildServerDetector.Detected ||
-               ContinuousTestingDetector.Detected;
+               ContinuousTestingDetector.Detected ||
+               AiCliDetector.Detected;
     }
 }

src/Directory.Build.props

@@ -2,7 +2,7 @@
 <Project>
   <PropertyGroup>
     <NoWarn>CS1591;CS0649;NU1608;NU1109</NoWarn>
-    <Version>18.0.1</Version>
+    <Version>18.1.0</Version>
     <AssemblyVersion>1.0.0</AssemblyVersion>
     <PackageTags>Testing, Snapshot, Diff, Compare</PackageTags>
     <Description>Launches diff tools based on file extensions. Designed to be consumed by snapshot testing libraries.</Description>