Expand the viewer's search directory on Linux and macOS

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)

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;
+            }
+        }
+    }
+}

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)

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,