From d8797c2a1fbaab307bba5f083fa3daf58162f904 Mon Sep 17 00:00:00 2001
From: Simon Cropp <simon.cropp@gmail.com>
Date: Fri, 9 Oct 2026 17:36:36 +1100
Subject: [PATCH 1/2] Stop treating WSL as a build server

---
 src/DiffEngine/BuildServerDetector.cs | 1 -
 src/Directory.Build.props             | 2 +-
 2 files changed, 1 insertion(+), 2 deletions(-)

diff --git a/src/DiffEngine/BuildServerDetector.cs b/src/DiffEngine/BuildServerDetector.cs
index d0e92fd24..485c70da0 100644
--- a/src/DiffEngine/BuildServerDetector.cs
+++ b/src/DiffEngine/BuildServerDetector.cs
@@ -65,7 +65,6 @@ static BuildServerDetector()
                    IsMyGet ||
                    IsGoDc ||
                    IsDocker ||
-                   IsWsl ||
                    IsAppVeyor ||
                    IsBitbucketPipelines;
     }
diff --git a/src/Directory.Build.props b/src/Directory.Build.props
index 0d39a80b3..69ab8b7d9 100644
--- a/src/Directory.Build.props
+++ b/src/Directory.Build.props
@@ -1,7 +1,7 @@
 <?xml version="1.0" encoding="utf-8"?>
 <Project>
   <PropertyGroup>
-    <Version>20.7.2</Version>
+    <Version>20.8.0</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>

From 7b841dc854e2212f8c7342314e35caca11644983 Mon Sep 17 00:00:00 2001
From: Simon Cropp <simon.cropp@gmail.com>
Date: Fri, 9 Oct 2026 17:41:53 +1100
Subject: [PATCH 2/2] Document detecting a build that runs under WSL

---
 readme.md        | 28 ++++++++++++++++++++++++++++
 readme.source.md | 27 +++++++++++++++++++++++++++
 2 files changed, 55 insertions(+)

diff --git a/readme.md b/readme.md
index e355c757f..1d62ff03b 100644
--- a/readme.md
+++ b/readme.md
@@ -44,6 +44,7 @@ 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)
+    * [WSL](#wsl)
     * [Override in tests](#override-in-tests)
   * [Automatic AI detection](#automatic-ai-detection)
     * [Programmatic usage](#programmatic-usage)
@@ -193,6 +194,33 @@ var isBitbucketPipelines = BuildServerDetector.IsBitbucketPipelines;
 <!-- endSnippet -->
 
 
+### WSL
+
+Running under [WSL](https://learn.microsoft.com/en-us/windows/wsl/about) is not treated as a build server, since a WSL session is usually a developer machine. `BuildServerDetector.IsWsl` reports it, and `BuildServerDetector.Detected` ignores it.
+
+A build that runs its tests inside WSL from a Windows build agent is the case to watch. The variables the build server sets exist on the Windows side, and WSL only passes across the ones named in [WSLENV](https://learn.microsoft.com/en-us/windows/wsl/filesystems#share-environment-variables-between-windows-and-wsl-with-wslenv). So inside WSL nothing is detected, and diff tools are launched on the build agent.
+
+To have such a build detected, either name the build server's variable in `WSLENV` on the Windows side, for example on Azure DevOps:
+
+```
+set WSLENV=TF_BUILD:%WSLENV%
+```
+
+or set one of the detected variables on the command that starts the tests:
+
+```
+wsl -- env TF_BUILD=True dotnet test
+```
+
+To treat every WSL run as a build server, in a test:
+
+```cs
+BuildServerDetector.Detected = BuildServerDetector.Detected || BuildServerDetector.IsWsl;
+```
+
+That value is scoped to the current async context, as described below.
+
+
 ### Override in tests
 
 `BuildServerDetector.Detected` can be set at test time. The value is stored in an `AsyncLocal`, so it is scoped to the current async context and does not leak to other threads or tests running in parallel.
diff --git a/readme.source.md b/readme.source.md
index 23206ecf6..9ac3d547b 100644
--- a/readme.source.md
+++ b/readme.source.md
@@ -89,6 +89,33 @@ There are also individual properties to check for each specific build system
 snippet: BuildServerDetectorProps
 
 
+### WSL
+
+Running under [WSL](https://learn.microsoft.com/en-us/windows/wsl/about) is not treated as a build server, since a WSL session is usually a developer machine. `BuildServerDetector.IsWsl` reports it, and `BuildServerDetector.Detected` ignores it.
+
+A build that runs its tests inside WSL from a Windows build agent is the case to watch. The variables the build server sets exist on the Windows side, and WSL only passes across the ones named in [WSLENV](https://learn.microsoft.com/en-us/windows/wsl/filesystems#share-environment-variables-between-windows-and-wsl-with-wslenv). So inside WSL nothing is detected, and diff tools are launched on the build agent.
+
+To have such a build detected, either name the build server's variable in `WSLENV` on the Windows side, for example on Azure DevOps:
+
+```
+set WSLENV=TF_BUILD:%WSLENV%
+```
+
+or set one of the detected variables on the command that starts the tests:
+
+```
+wsl -- env TF_BUILD=True dotnet test
+```
+
+To treat every WSL run as a build server, in a test:
+
+```cs
+BuildServerDetector.Detected = BuildServerDetector.Detected || BuildServerDetector.IsWsl;
+```
+
+That value is scoped to the current async context, as described below.
+
+
 ### Override in tests
 
 `BuildServerDetector.Detected` can be set at test time. The value is stored in an `AsyncLocal`, so it is scoped to the current async context and does not leak to other threads or tests running in parallel.