Mono: Add editor integration for external assembly scripts

GodotSharpEditor.OpenInExternalEditor resolves csharp:// paths to real
source files via ResolveScriptFilePath() before passing to external
editors (VS, Rider, VsCode, MonoDevelop, custom). When source is
unavailable (NuGet packages), a warning is shown instead of an error.

InspectorPlugin skips timestamp checks for csharp:// scripts. For
generic types over assembly-backed base scripts, File.Exists()
determines whether to check timestamps.

GodotSharpDirs adds dotnet/project/project_directory setting to support
layouts where the .csproj is in a subdirectory of the project root.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: matelq

doc/classes/ProjectSettings.xml

@@ -1115,6 +1115,9 @@
 		<member name="dotnet/project/assembly_reload_attempts" type="int" setter="" getter="" default="3">
 			Number of times to attempt assembly reloading after rebuilding .NET assemblies. Effectively also the timeout in seconds to wait for unloading of script assemblies to finish.
 		</member>
+		<member name="dotnet/project/project_directory" type="String" setter="" getter="" default="&quot;&quot;">
+			Directory containing the [code].csproj[/code] file, relative to [code]res://[/code]. By default, the [code].csproj[/code] is expected in the project root alongside [code]project.godot[/code]. Set this when using a multi-project layout where the main C# project is in a subdirectory (e.g. [code]MainProject[/code]).
+		</member>
 		<member name="dotnet/project/solution_directory" type="String" setter="" getter="" default="&quot;&quot;">
 			Directory that contains the [code].sln[/code] file. By default, the [code].sln[/code] files is in the root of the project directory, next to the [code]project.godot[/code] and [code].csproj[/code] files.
 			Changing this value allows setting up a multi-project scenario where there are multiple [code].csproj[/code]. Keep in mind that the Godot project is considered one of the C# projects in the workspace and it's root directory should contain the [code]project.godot[/code] and [code].csproj[/code] next to each other.

modules/mono/editor/GodotTools/GodotTools/GodotSharpEditor.cs

@@ -180,9 +180,29 @@ public void ShowConfirmCreateSlnDialog()
             "code", "code-oss", "vscode", "vscode-oss", "visual-studio-code", "visual-studio-code-oss", "codium"
         };
 
-        [UsedImplicitly]
+        private static string? ResolveScriptFilePath(Script script)
+        {
+            string resourcePath = script.ResourcePath;
+            if (resourcePath.StartsWith("csharp://", StringComparison.Ordinal))
+            {
+                string? sourceFile = Godot.Bridge.ScriptManagerBridge.GetSourceFilePath(resourcePath);
+                if (sourceFile != null && File.Exists(sourceFile))
+                    return sourceFile;
+                return null;
+            }
+            return ProjectSettings.GlobalizePath(resourcePath);
+        }
+
         public Error OpenInExternalEditor(Script script, int line, int col)
         {
+            string? resolvedFilePath = ResolveScriptFilePath(script);
+            if (resolvedFilePath == null)
+            {
+                GD.PushWarning($"Cannot open script: source file not available for '{script.ResourcePath}'. " +
+                               "This script is from a compiled assembly (e.g. NuGet package) with no source on disk.");
+                return Error.Ok;
+            }
+
             var editorId = _editorSettings.GetSetting(Settings.ExternalEditor).As<ExternalEditorId>();
 
             switch (editorId)
@@ -192,7 +212,7 @@ public Error OpenInExternalEditor(Script script, int line, int col)
                     return Error.Unavailable;
                 case ExternalEditorId.CustomEditor:
                 {
-                    string file = ProjectSettings.GlobalizePath(script.ResourcePath);
+                    string file = resolvedFilePath;
                     string project = ProjectSettings.GlobalizePath("res://");
                     // Since ProjectSettings.GlobalizePath replaces only "res:/", leaving a trailing slash, it is removed here.
                     project = project[..^1];
@@ -256,7 +276,7 @@ public Error OpenInExternalEditor(Script script, int line, int col)
                 }
                 case ExternalEditorId.VisualStudio:
                 {
-                    string scriptPath = ProjectSettings.GlobalizePath(script.ResourcePath);
+                    string scriptPath = resolvedFilePath;
 
                     var args = new List<string>
                     {
@@ -288,13 +308,13 @@ public Error OpenInExternalEditor(Script script, int line, int col)
                 case ExternalEditorId.Rider:
                 case ExternalEditorId.Fleet:
                 {
-                    string scriptPath = ProjectSettings.GlobalizePath(script.ResourcePath);
+                    string scriptPath = resolvedFilePath;
                     RiderPathManager.OpenFile(editorId, GodotSharpDirs.ProjectSlnPath, scriptPath, line + 1, col);
                     return Error.Ok;
                 }
                 case ExternalEditorId.MonoDevelop:
                 {
-                    string scriptPath = ProjectSettings.GlobalizePath(script.ResourcePath);
+                    string scriptPath = resolvedFilePath;
 
                     GodotIdeManager.LaunchIdeAsync().ContinueWith(launchTask =>
                     {
@@ -366,7 +386,7 @@ public Error OpenInExternalEditor(Script script, int line, int col)
 
                     args.Add(Path.GetDirectoryName(GodotSharpDirs.ProjectSlnPath)!);
 
-                    string scriptPath = ProjectSettings.GlobalizePath(script.ResourcePath);
+                    string scriptPath = resolvedFilePath;
 
                     if (line >= 0)
                     {

modules/mono/editor/GodotTools/GodotTools/Inspector/InspectorPlugin.cs

@@ -42,12 +42,22 @@ public override void _ParseBegin(GodotObject godotObject)
                     break;
                 }
 
-                if (scriptPath.StartsWith("csharp://"))
+                if (scriptPath.StartsWith("csharp://", StringComparison.Ordinal))
                 {
-                    // This is a virtual path used by generic types, extract the real path.
                     var scriptPathSpan = scriptPath.AsSpan("csharp://".Length);
-                    scriptPathSpan = scriptPathSpan[..scriptPathSpan.IndexOf(':')];
-                    scriptPath = $"res://{scriptPathSpan}";
+                    int colonIdx = scriptPathSpan.IndexOf(':');
+                    if (colonIdx >= 0)
+                    {
+                        string basePath = $"res://{scriptPathSpan[..colonIdx]}";
+                        string globalBasePath = ProjectSettings.GlobalizePath(basePath);
+                        if (!File.Exists(globalBasePath))
+                            continue;
+                        scriptPath = basePath;
+                    }
+                    else
+                    {
+                        continue;
+                    }
                 }
 
                 if (File.GetLastWriteTime(scriptPath) > BuildManager.LastValidBuildDateTime)

modules/mono/editor/GodotTools/GodotTools/Internals/GodotSharpDirs.cs

@@ -79,8 +79,11 @@ public static void DetermineProjectLocation()
             else if (!slnParentDir.StartsWith("res://", StringComparison.Ordinal))
                 slnParentDir = "res://" + slnParentDir;
 
-            // The csproj should be in the same folder as project.godot.
-            string csprojParentDir = "res://";
+            string? csprojParentDir = (string?)ProjectSettings.GetSetting("dotnet/project/project_directory");
+            if (string.IsNullOrEmpty(csprojParentDir))
+                csprojParentDir = "res://";
+            else if (!csprojParentDir.StartsWith("res://", StringComparison.Ordinal))
+                csprojParentDir = "res://" + csprojParentDir;
 
             // Set csproj path first and use it to find the sln/slnx file with the assembly
             _projectCsProjPath = Path.Combine(ProjectSettings.GlobalizePath(csprojParentDir),
@@ -182,7 +185,7 @@ public static string ProjectBaseOutputPath
             {
                 if (_projectCsProjPath == null)
                     DetermineProjectLocation();
-                return Path.Combine(Path.GetDirectoryName(_projectCsProjPath)!, ".godot", "mono", "temp", "bin");
+                return Path.Combine(ProjectSettings.GlobalizePath("res://"), ".godot", "mono", "temp", "bin");
             }
         }