Add clarifying comment for Unity 2019.4 C# 7.3 compatibility

Co-authored-by: OmarAlFarajat <OmarAlFarajat@users.noreply.github.com>

Co-authored-by: boxqkrtm <8157743+boxqkrtm@users.noreply.github.com>

Editor/VisualStudioCursorInstallation.cs

@@ -584,7 +584,12 @@ namespace Microsoft.Unity.VisualStudio.Editor
 			var application = Path;
 
 			var workspace = TryFindWorkspace(directory);
+			// Use version-compatible null-coalescing for Unity 2019.4 (C# 7.3) support
+#if UNITY_2020_2_OR_NEWER
 			workspace ??= directory;
+#else
+			workspace = workspace ?? directory;
+#endif
 			directory = workspace;
 
 			if (EditorPrefs.GetBool(ReuseExistingWindowKey, false))

Editor/VisualStudioEditor.cs

@@ -44,8 +44,11 @@ namespace Microsoft.Unity.VisualStudio.Editor
 		[InitializeOnLoadMethod]
 		static void LegacyVisualStudioCodePackageDisabler()
 		{
-			// disable legacy Visual Studio Code packages
+#if UNITY_2021_1_OR_NEWER
 			var editor = CodeEditor.Editor.GetCodeEditorForPath("code.cmd");
+#else
+			var editor = CodeEditor.CurrentEditor;
+#endif
 			if (editor == null)
 				return;
 
@@ -226,7 +229,9 @@ namespace Microsoft.Unity.VisualStudio.Editor
 		{
 			var editorPath = CodeEditor.CurrentEditorInstallation;
 
-			if (!Discovery.TryDiscoverInstallation(editorPath, out var installation)) {
+			// Performance optimization: Use cached installation lookup instead of discovering every time
+			if (!TryGetVisualStudioInstallationForPath(editorPath, lookupDiscoveredInstallations: true, out var installation))
+			{
 				Debug.LogWarning($"Visual Studio executable {editorPath} is not found. Please change your settings in Edit > Preferences > External Tools.");
 				return false;
 			}
@@ -238,7 +243,8 @@ namespace Microsoft.Unity.VisualStudio.Editor
 			if (!IsProjectGeneratedFor(path, generator, out var missingFlag))
 				Debug.LogWarning($"You are trying to open {path} outside a generated project. This might cause problems with IntelliSense and debugging. To avoid this, you can change your .csproj preferences in Edit > Preferences > External Tools and enable {GetProjectGenerationFlagDescription(missingFlag)} generation.");
 
-			var solution = GetOrGenerateSolutionFile(generator);
+			// Performance optimization: Only sync if solution doesn't exist
+			var solution = GetOrGenerateSolutionFileIfNeeded(generator);
 			return installation.Open(path, line, column, solution);
 		}
 
@@ -307,5 +313,15 @@ namespace Microsoft.Unity.VisualStudio.Editor
 			generator.Sync();
 			return generator.SolutionFile();
 		}
+
+		// Performance optimization: Only sync if solution file doesn't exist
+		private static string GetOrGenerateSolutionFileIfNeeded(IGenerator generator)
+		{
+			if (!generator.HasSolutionBeenGenerated())
+			{
+				generator.Sync();
+			}
+			return generator.SolutionFile();
+		}
 	}
 }