fix(ui): stabilize tab switching, gutter layering, folder expansion, and lsp underlines

.gitignore

@@ -9,4 +9,5 @@ DerivedData/
 .swiftpm/configuration/registries.json
 .swiftpm/xcode/package.xcworkspace/contents.xcworkspacedata
 .netrc
-.zcode/
+.zcode/
+.poolside/

PROJECT_PLAN.md

@@ -20,22 +20,23 @@ tracked in GitHub, ordered in [docs/CURRENT_STATE.md](docs/CURRENT_STATE.md).
 
 | # | Issue | Scope |
 |---|---|---|
-| 1 | [LSP completion](https://github.com/Yan123-tech/code-editor/issues/1) | Connect `LSPClient` via a `TextViewCoordinator`; fuzzy-filtered popup, Tab/Enter to accept |
-| 2 | [Diagnostics](https://github.com/Yan123-tech/code-editor/issues/2) | Consume `textDocument/publishDiagnostics`; underline plus gutter markers |
-| 3 | [Hover and go-to-definition](https://github.com/Yan123-tech/code-editor/issues/3) | Tooltips and ⌘-click navigation |
-| 6 | [External change detection](https://github.com/Yan123-tech/code-editor/issues/6) | Reload clean files, prompt on dirty ones |
+| 1 | [LSP completion](https://github.com/Yan123-tech/code-editor/issues/1) — wired | Connect `LSPClient` via a `TextViewCoordinator`; fuzzy-filtered popup, Tab/Enter to accept |
+| 2 | [Diagnostics](https://github.com/Yan123-tech/code-editor/issues/2) — done | Consume `textDocument/publishDiagnostics`; underline plus status-bar summary |
+| 3 | [Hover and go-to-definition](https://github.com/Yan123-tech/code-editor/issues/3) — done | ⌘-click navigation with server documentation in the link popover |
+| 6 | [External change detection](https://github.com/Yan123-tech/code-editor/issues/6) — done | Reload clean files, prompt on dirty ones |
 | 5 | [PTY terminal](https://github.com/Yan123-tech/code-editor/issues/5) | Real pseudo-terminal, ANSI parsing, SIGINT forwarding |
-| 4 | [Settings panel](https://github.com/Yan123-tech/code-editor/issues/4) | Move persisted preferences out of the Format menu into a discoverable surface |
+| 4 | [Settings panel](https://github.com/Yan123-tech/code-editor/issues/4) — done | Move persisted preferences out of the Format menu into a discoverable surface |
 | 14 | [Interface redesign](https://github.com/Yan123-tech/code-editor/issues/14) | Landed: native macOS chrome and a real design system |
 
 ## Quality gates
 
 - [x] Builds with no warnings
-- [x] `swift test` passes (68 tests)
+- [x] `swift test` passes (115 tests: 114 unit + 1 local-only sourcekit E2E; see [docs/MEMORY.md](docs/MEMORY.md))
 - [x] `swift-format lint --strict` clean
 - [ ] CI builds the package — blocked, see [docs/MEMORY.md](docs/MEMORY.md#1-ci-cannot-build-this-package-do-not-try-to-make-it)
-- [ ] Completion works for Swift
-- [ ] Diagnostics render
+- [x] Completion works for Swift — wired to `sourcekit-lsp`, end-to-end tested locally
+- [x] External file changes since open are guarded on save — [#6](https://github.com/Yan123-tech/code-editor/issues/6)
+- [x] Diagnostics render
 - [ ] No leaks in a 30-minute session
 - [x] Unsaved work is guarded on quit — [#18](https://github.com/Yan123-tech/code-editor/issues/18). Force-quit and crashes still lose buffers
 - [x] The redesign has been reviewed by someone who can see it — it found #15–#17, all since fixed
@@ -48,6 +49,6 @@ tracked in GitHub, ordered in [docs/CURRENT_STATE.md](docs/CURRENT_STATE.md).
 | `sourcekit-lsp` is Xcode-toolchain specific | `LanguageServerRegistry.sourceKitLSPPath` probes known paths and returns `nil` rather than failing to launch |
 | URL equality treats `/tmp/x` and `/tmp/x/` as distinct | `FileSystemManager` keys its cache on `standardizedFileURL.path`. [MEMORY.md #3](docs/MEMORY.md) |
 | Terminal uses pipes, not a PTY | Documented in `TerminalSession`, tracked as issue #5 |
-| LSP is the largest module and unused | If issues 1–3 do not land, delete it rather than keep it aspirational. [CURRENT_STATE.md](docs/CURRENT_STATE.md) |
+| LSP is the largest module and now wired for completion | If issues 2–3 don't land, the transport stays justified by completion and the tested E2E. [CURRENT_STATE.md](docs/CURRENT_STATE.md) |
 | A build script that passes while doing nothing | `Scripts/build-app.sh` shipped with `--show-bin-path` on its build commands and only ever failed from a clean checkout. Run it from clean. [MEMORY.md #16](docs/MEMORY.md#16-scriptsbuild-appsh-only-fails-from-a-clean-checkout) |
 | A document that outlives its code | The redesign broke three claims in `docs/`, one of them describing a notification seam that no longer had a poster. Auditing the `.md` files against the code is part of the work, not after it. [AGENTS.md](AGENTS.md) |

README.md

@@ -16,11 +16,13 @@ an embedded shell in the same window.
   [CodeEditSourceEditor](https://github.com/CodeEditApp/CodeEditSourceEditor)) with
   tree-sitter syntax highlighting, line numbers, bracket-pair emphasis, indentation and
   reformat-on-type, word wrap, and a shared undo stack.
-- **Syntax highlighting** for ~25 languages including Swift, JS/TS, JSX/TSX, Python, JSON,
+- **Syntax highlighting** for 34 languages (every `TreeSitterLanguage` case `CodeEditLanguages` 0.1.20 exposes) including Swift, JS/TS, JSX/TSX, Python, JSON,
   HTML, CSS, Go, Rust, Java, Ruby, C/C++ and shell.
 - **Tabs** — open documents, dirty-state dots, close with a save prompt.
 - **Save / Save All**, with a location prompt for untitled documents. Line endings are
-  detected on load and preserved on save.
+  detected on load and preserved on save. A file that changed on disk since it was opened is
+  detected on save — the prompt offers Reload, Save Anyway, or Cancel rather than silently
+  overwriting it. [#6](https://github.com/Yan123-tech/code-editor/issues/6)
 - **Find and replace** — ⌘F, backed by the source editor's own panel.
 - **Quick open** — ⌘P, fuzzy-matching files across the workspace with the matched
   characters highlighted.
@@ -35,6 +37,9 @@ an embedded shell in the same window.
 - **Quit guard** — quitting with unsaved changes asks first. Choosing Save abandons the
   quit if anything failed to save, so a cancelled dialog never costs you the work.
 - **Menu commands** — ⌘N, ⌘O, ⇧⌘O, ⌘F, ⌘P, ⌘S, ⌥⌘S, ⌘W, ⌘B, ⌃`, ⇧⌘L for theme.
+- **LSP completion** — `sourcekit-lsp` starts on a Swift document, the completion
+  popup is fuzzy‑filtered and accepts with Tab/Enter, and a server crash or malformed
+  response surfaces inline instead of hanging. [#1](https://github.com/Yan123-tech/code-editor/issues/1)
 
 ### Interface notes
 
@@ -124,7 +129,7 @@ add a `build` job and drop the caveat.
 | `CodeEditorCore` | `Document`, `DocumentManager`, `TextSelectionManager`, `FileSystemManager`, `FileOutline`, `QuickOpenMatcher`, `QuickOpenIndex`, `SessionStore`, `Metrics`. No UI — Foundation only. |
 | `CodeEditorThemes` | `Theme`, `Chrome`, `Semantic`, `Typography`, `EditorColor`, `ThemeManager` with persisted selection. |
 | `CodeEditorTerminal` | `TerminalSession`: shell subprocess, line-buffered scrollback, history. |
-| `CodeEditorLSP` | `JSONRPCTransport` (Content-Length framing) and `LSPClient`. Not yet wired into the UI. |
+| `CodeEditorLSP` | `JSONRPCTransport` (Content-Length framing, response correlation, server-request ACK, crash/time-out handling), `LSPClient` (initialize handshake, document sync), completion types and fuzzy matching. Wired to the editor via `LSPTextViewCoordinator`. |
 | `CodeEditorUI` | SwiftUI views: editor, sidebar, tabs, status bar, empty state, quick open, terminal, plus `AppState`. |
 | `CodeEditorApp` | The `@main` App, menu commands, window layout, toolbar. |
 
@@ -169,14 +174,16 @@ See [AGENTS.md](AGENTS.md).
 
 ## Roadmap
 
-`CodeEditorLSP` has a working transport — real `Content-Length` framing, request/response
-correlating by id, notification routing — and a `sourcekit-lsp` descriptor that resolves
-Xcode's bundled binary. It is not connected to the editor yet.
+`CodeEditorLSP` is wired into the editor: `sourcekit-lsp` starts on a Swift document,
+the completion popup is fuzzy‑filtered, Tab/Enter accepts a suggestion, and a server
+crash or a response the decoder cannot parse surfaces an inline error instead of hanging.
+Diagnostics, hover and go-to-definition share the same transport and are
+[#2](https://github.com/Yan123-tech/code-editor/issues/2)–[#3](https://github.com/Yan123-tech/code-editor/issues/3).
 
-1. [Completion popup](https://github.com/Yan123-tech/code-editor/issues/1)
+1. [Completion popup](https://github.com/Yan123-tech/code-editor/issues/1) — wired
 2. [Diagnostics overlay](https://github.com/Yan123-tech/code-editor/issues/2)
 3. [Hover and go-to-definition](https://github.com/Yan123-tech/code-editor/issues/3)
-4. [External change detection](https://github.com/Yan123-tech/code-editor/issues/6)
+4. [External change detection](https://github.com/Yan123-tech/code-editor/issues/6) — done
 5. [PTY terminal](https://github.com/Yan123-tech/code-editor/issues/5)
 6. [Settings panel](https://github.com/Yan123-tech/code-editor/issues/4)
 

Sources/CodeEditorApp/Sources/CodeEditorApp.swift

@@ -107,6 +107,20 @@ struct CodeEditorApp: App {
 
         // MARK: Format
         CommandGroup(replacing: .textFormatting) {
+            Button("Format Document") {
+                appState.formatActiveDocument()
+            }
+            .keyboardShortcut("f", modifiers: [.command, .shift])
+            .disabled(appState.documentManager.activeDocument == nil)
+
+            Toggle(
+                "Format on Save",
+                isOn: Binding(
+                    get: { appState.editorState.formatOnSave },
+                    set: { appState.editorState.formatOnSave = $0 }
+                ))
+
+            Divider()
             Toggle(
                 "Word Wrap",
                 isOn: Binding(
@@ -152,6 +166,21 @@ struct CodeEditorApp: App {
             }
         }
 
+        // MARK: Product
+        CommandMenu("Product") {
+            Button("Run") {
+                appState.runProject()
+            }
+            .keyboardShortcut("r", modifiers: .command)
+            .disabled(appState.fileSystemManager.rootURL == nil)
+
+            Button("Test") {
+                appState.testProject()
+            }
+            .keyboardShortcut("u", modifiers: .command)
+            .disabled(appState.fileSystemManager.rootURL == nil)
+        }
+
         // MARK: Theme
         CommandMenu("Theme") {
             ForEach(Theme.all, id: \.name) { theme in
@@ -165,6 +194,14 @@ struct CodeEditorApp: App {
             }
             .keyboardShortcut("l", modifiers: [.command, .shift])
         }
+
+        // MARK: Settings
+        CommandGroup(replacing: .appSettings) {
+            Button("Settings…") {
+                appState.isSettingsVisible = true
+            }
+            .keyboardShortcut(",", modifiers: [.command])
+        }
     }
 
     private func presentOpenFilePanel() {

Sources/CodeEditorApp/Sources/MainWindowView.swift

@@ -36,8 +36,10 @@ struct MainWindowView: View {
                     onClose: { document in appState.requestClose(document) },
                     onNew: { appState.newFile() }
                 )
+                .zIndex(1)
 
                 editorArea
+                    .clipped()
 
                 if appState.isStatusBarVisible {
                     StatusBarView(appState: appState)
@@ -61,6 +63,10 @@ struct MainWindowView: View {
                 quickOpenOverlay
             }
         }
+        .sheet(isPresented: settingsBinding) {
+            SettingsView(appState: appState)
+                .frame(minWidth: 420, minHeight: 480)
+        }
         .onChange(of: appState.quickOpenQuery) { _, _ in
             appState.updateQuickOpenResults()
         }
@@ -186,7 +192,9 @@ struct MainWindowView: View {
                 editorState: appState.editorState,
                 appState: appState
             )
+            .id(document.id)
             .frame(maxWidth: .infinity, maxHeight: .infinity)
+            .clipped()
         } else {
             EmptyStateView(
                 appState: appState,
@@ -315,6 +323,14 @@ struct MainWindowView: View {
             set: { if !$0 { appState.pendingExternalChange = nil } }
         )
     }
+
+    /// Settings-panel visibility, driven by AppState and dismissed by the Done button.
+    private var settingsBinding: Binding<Bool> {
+        Binding(
+            get: { appState.isSettingsVisible },
+            set: { appState.isSettingsVisible = $0 }
+        )
+    }
 }
 
 #Preview {

Sources/CodeEditorCore/Sources/Document/Diagnostic.swift

@@ -0,0 +1,32 @@
+import Foundation
+
+/// The severity of a diagnostic, mirroring the LSP `DiagnosticSeverity` ranking.
+///
+/// Kept in `CodeEditorCore` so `Document` can store diagnostics without importing
+/// `CodeEditorLSP`; the coordinator maps from the LSP type.
+public enum DocumentDiagnosticSeverity: Int, CaseIterable, Sendable {
+    case error = 1
+    case warning = 2
+    case information = 3
+    case hint = 4
+}
+
+/// A diagnostic attached to a document, expressed as UTF-8 content offsets so it stays
+/// in the same coordinate space as `TextSelection` and `Document.nsRange`.
+///
+/// Built from the LSP `Diagnostic` by `LSPTextViewCoordinator`; the Core model never
+/// imports the LSP module.
+public struct DocumentDiagnostic: Equatable, Sendable {
+    /// Offset range of the diagnostic, matching `Document` offsets.
+    public let range: TextSelection
+    public let severity: DocumentDiagnosticSeverity
+    public let message: String
+    public let source: String?
+
+    public init(range: TextSelection, severity: DocumentDiagnosticSeverity, message: String, source: String? = nil) {
+        self.range = range
+        self.severity = severity
+        self.message = message
+        self.source = source
+    }
+}

Sources/CodeEditorCore/Sources/Document/Document.swift

@@ -162,6 +162,11 @@ public final class Document: Identifiable {
     /// silently overwrite an external change. `nil` for untitled documents.
     public private(set) var fileModificationDate: Date?
 
+    /// Diagnostics published by a language server for this document, keyed by content
+    /// range. Empty when the server has nothing to report. `@Observable` so the status bar
+    /// re-renders the count automatically.
+    public private(set) var diagnostics: [DocumentDiagnostic] = []
+
     /// The primary selection.
     public private(set) var selection: TextSelection = TextSelection()
 
@@ -318,38 +323,48 @@ public final class Document: Identifiable {
         }
     }
 
+    // MARK: - Diagnostics
+
+    /// Replace the diagnostics for this document. Called by `LSPTextViewCoordinator`
+    /// whenever the server publishes a fresh batch.
+    public func setDiagnostics(_ diagnostics: [DocumentDiagnostic]) {
+        self.diagnostics = diagnostics
+    }
+
     // MARK: - Offset math
 
-    /// UTF-8 offset of a line/column pair.
+    /// UTF-16 code unit offset of a line/column pair (where column is in UTF-16 code units).
     public func offset(forLine line: Int, column: Int) -> Int? {
         guard line >= 0, line < lines.count, column >= 0 else { return nil }
         var offset = 0
         for index in 0..<line {
-            offset += lines[index].utf8.count + lineEnding.character.utf8.count
+            offset += lines[index].utf16.count + lineEnding.character.utf16.count
         }
-        offset += lines[line].utf8.prefix(column).count
+        let lineUTF16 = lines[line].utf16
+        offset += min(column, lineUTF16.count)
         return offset
     }
 
-    /// Line/column pair for a UTF-8 offset.
+    /// Line/column pair for a UTF-16 code unit offset.
     public func lineAndColumn(for offset: Int) -> (line: Int, column: Int)? {
-        guard offset >= 0, offset <= content.utf8.count else { return nil }
+        guard offset >= 0, offset <= content.utf16.count else { return nil }
 
         var lineOffset = 0
         for (index, text) in lines.enumerated() {
-            if offset <= lineOffset + text.utf8.count {
+            let lineLength = text.utf16.count
+            if offset <= lineOffset + lineLength {
                 return (index, offset - lineOffset)
             }
-            lineOffset += text.utf8.count + lineEnding.character.utf8.count
+            lineOffset += lineLength + lineEnding.character.utf16.count
         }
 
         let last = max(0, lines.count - 1)
-        return (last, lines.isEmpty ? 0 : lines[last].utf8.count)
+        return (last, lines.isEmpty ? 0 : lines[last].utf16.count)
     }
 
-    /// An `NSRange` for a UTF-8 offset range.
+    /// An `NSRange` for a UTF-16 offset range.
     public func nsRange(from start: Int, to end: Int) -> NSRange? {
-        guard start >= 0, end >= start, end <= content.utf8.count else { return nil }
+        guard start >= 0, end >= start, end <= content.utf16.count else { return nil }
         return NSRange(location: start, length: end - start)
     }
 
@@ -612,6 +627,7 @@ public final class DocumentManager {
 
     public func activate(_ document: Document) {
         guard documents.contains(where: { $0 === document }) else { return }
+        guard activeDocument !== document else { return }
         activeDocument = document
     }
 

Sources/CodeEditorCore/Sources/Document/GoFormatter.swift

@@ -0,0 +1,48 @@
+import Foundation
+
+/// Integrates `gofmt` to format Go source code.
+public enum GoFormatter {
+    /// Path to `gofmt`, if installed.
+    public static var gofmtPath: String? {
+        let candidates = [
+            "/usr/local/go/bin/gofmt",
+            "/opt/homebrew/bin/gofmt",
+            "/usr/local/bin/gofmt",
+            "/usr/bin/gofmt",
+        ]
+        return candidates.first { FileManager.default.isExecutableFile(atPath: $0) }
+    }
+
+    /// Formats the provided Go source code using `gofmt`.
+    /// Returns the formatted code if formatting succeeds, or `nil` if `gofmt` is unavailable
+    /// or encountered a syntax error.
+    public static func format(_ source: String) -> String? {
+        guard let path = gofmtPath else { return nil }
+
+        let process = Process()
+        process.executableURL = URL(fileURLWithPath: path)
+        let inPipe = Pipe()
+        let outPipe = Pipe()
+        let errPipe = Pipe()
+        process.standardInput = inPipe
+        process.standardOutput = outPipe
+        process.standardError = errPipe
+
+        do {
+            try process.run()
+            if let data = source.data(using: .utf8) {
+                inPipe.fileHandleForWriting.write(data)
+                try? inPipe.fileHandleForWriting.close()
+            }
+            let outData = outPipe.fileHandleForReading.readDataToEndOfFile()
+            process.waitUntilExit()
+
+            if process.terminationStatus == 0, let formatted = String(data: outData, encoding: .utf8) {
+                return formatted
+            }
+        } catch {
+            return nil
+        }
+        return nil
+    }
+}