From 8f7a178997a7eda086bd16b03b3963a224bedc87 Mon Sep 17 00:00:00 2001
From: Simon Cropp <simon.cropp@gmail.com>
Date: Sat, 22 Aug 2026 13:07:31 +1000
Subject: [PATCH] Expand the viewer's search directory on Linux and macOS

WildcardFileFinder expands with Environment.ExpandEnvironmentVariables, which
only understands %NAME%. The Linux and macOS entries were written shell style as
$HOME/.dotnet/tools/, so that string was passed through untouched and named a
literal directory called "$HOME" - which nothing has.

A globally installed DiffEngineViewer was therefore invisible on those
platforms. It only mattered when the bundled copy was absent, which is exactly
the case the dotnet tool install exists to cover.

The test asserts no definition anywhere uses the shell syntax, rather than this
one entry, since the mistake is easy to repeat and the two syntaxes look equally
plausible in a path.

Generated docs regenerated to match.
---
 docs/diff-tool.md                             |  4 +-
 .../SearchDirectoryExpansionTests.cs          | 41 +++++++++++++++++++
 src/DiffEngine.Tests/diffTools.include.md     |  4 +-
 .../Implementation/DiffEngineViewer.cs        |  4 +-
 4 files changed, 47 insertions(+), 6 deletions(-)
 create mode 100644 src/DiffEngine.Tests/SearchDirectoryExpansionTests.cs

diff --git a/docs/diff-tool.md b/docs/diff-tool.md
index e251516f..e803b25c 100644
--- a/docs/diff-tool.md
+++ b/docs/diff-tool.md
@@ -316,7 +316,7 @@ DiffTools.UseOrder(DiffTool.DiffEngineViewer);
    "tempFile.txt" "targetFile.txt"
    ```
   * Scanned paths:
-    * `$HOME/.dotnet/tools/DiffEngineViewer`
+    * `%HOME%/.dotnet/tools/DiffEngineViewer`
     * `%PATH%DiffEngineViewer`
 
 #### Linux settings:
@@ -330,7 +330,7 @@ DiffTools.UseOrder(DiffTool.DiffEngineViewer);
    "tempFile.txt" "targetFile.txt"
    ```
   * Scanned paths:
-    * `$HOME/.dotnet/tools/DiffEngineViewer`
+    * `%HOME%/.dotnet/tools/DiffEngineViewer`
     * `%PATH%DiffEngineViewer`
 
 ### [Diffinity](https://truehumandesign.se/s_diffinity.php)
diff --git a/src/DiffEngine.Tests/SearchDirectoryExpansionTests.cs b/src/DiffEngine.Tests/SearchDirectoryExpansionTests.cs
new file mode 100644
index 00000000..2c2bdf10
--- /dev/null
+++ b/src/DiffEngine.Tests/SearchDirectoryExpansionTests.cs
@@ -0,0 +1,41 @@
+/// <summary>
+/// Search directories are written in the one syntax that gets expanded.
+/// <para>
+/// WildcardFileFinder expands with Environment.ExpandEnvironmentVariables, which only understands
+/// %NAME%. A directory written shell style with $HOME was passed through untouched, so it named a
+/// literal directory called "$HOME" and never matched - which is why a globally installed
+/// DiffEngineViewer was invisible on Linux and macOS whenever the bundled copy was absent.
+/// </para>
+/// </summary>
+public class SearchDirectoryExpansionTests
+{
+    [Test]
+    public async Task NoDefinitionUsesShellStyleExpansion()
+    {
+        var shellStyle = Definitions.Tools
+            .SelectMany(
+                definition => Directories(definition)
+                    .Where(_ => _.Contains('$'))
+                    .Select(_ => $"{definition.Tool}: {_}"))
+            .ToList();
+
+        await Assert.That(shellStyle).IsEmpty();
+    }
+
+    static IEnumerable<string> Directories(Definition definition)
+    {
+        var support = definition.OsSupport;
+        foreach (var settings in new[] { support.Windows, support.Linux, support.Osx })
+        {
+            if (settings == null)
+            {
+                continue;
+            }
+
+            foreach (var directory in settings.SearchDirectories)
+            {
+                yield return directory;
+            }
+        }
+    }
+}
diff --git a/src/DiffEngine.Tests/diffTools.include.md b/src/DiffEngine.Tests/diffTools.include.md
index f6243f7b..1a99761c 100644
--- a/src/DiffEngine.Tests/diffTools.include.md
+++ b/src/DiffEngine.Tests/diffTools.include.md
@@ -181,7 +181,7 @@ DiffTools.UseOrder(DiffTool.DiffEngineViewer);
    "tempFile.txt" "targetFile.txt"
    ```
   * Scanned paths:
-    * `$HOME/.dotnet/tools/DiffEngineViewer`
+    * `%HOME%/.dotnet/tools/DiffEngineViewer`
     * `%PATH%DiffEngineViewer`
 
 #### Linux settings:
@@ -195,7 +195,7 @@ DiffTools.UseOrder(DiffTool.DiffEngineViewer);
    "tempFile.txt" "targetFile.txt"
    ```
   * Scanned paths:
-    * `$HOME/.dotnet/tools/DiffEngineViewer`
+    * `%HOME%/.dotnet/tools/DiffEngineViewer`
     * `%PATH%DiffEngineViewer`
 
 ### [Diffinity](https://truehumandesign.se/s_diffinity.php)
diff --git a/src/DiffEngine/Implementation/DiffEngineViewer.cs b/src/DiffEngine/Implementation/DiffEngineViewer.cs
index ac344921..88627735 100644
--- a/src/DiffEngine/Implementation/DiffEngineViewer.cs
+++ b/src/DiffEngine/Implementation/DiffEngineViewer.cs
@@ -23,11 +23,11 @@ public static Definition DiffEngineViewer()
                 Linux: new(
                     "DiffEngineViewer",
                     launchArguments,
-                    SearchDirectories("$HOME/.dotnet/tools/")),
+                    SearchDirectories("%HOME%/.dotnet/tools/")),
                 Osx: new(
                     "DiffEngineViewer",
                     launchArguments,
-                    SearchDirectories("$HOME/.dotnet/tools/"))),
+                    SearchDirectories("%HOME%/.dotnet/tools/"))),
             UseShellExecute: false,
             // Console subsystem, so without this a window flashes on every launch.
             CreateNoWindow: true,