Add read-only SysML v2 source text viewer with syntax highlighting

.cspell.yaml

@@ -75,6 +75,12 @@ words:
   - SysML2
   - SysML2Tools
   - SysML2Workbench
+  - Antlr
+  - Xshd
+  - XSHD
+  - xshd
+  - avaloniaedit
+  - avares
 ignorePaths:
   - '**/.git/**'
   - '**/node_modules/**'

.reviewmark.yaml

@@ -305,7 +305,11 @@ reviews:
       - docs/design/sysml2-workbench/app-shell-subsystem/main-window-shell.md
       - docs/verification/sysml2-workbench/app-shell-subsystem/main-window-shell.md
       - src/**/AppShellSubsystem/MainWindowShell.cs
+      - src/**/AppShellSubsystem/SourceTextDocumentViewModel.cs
+      - src/**/AppShellSubsystem/SourceTextDocumentView.axaml
+      - src/**/AppShellSubsystem/SourceTextDocumentView.axaml.cs
       - test/**/AppShellSubsystem/MainWindowShellTests.cs
+      - test/**/AppShellSubsystem/SourceTextDocumentViewModelTests.cs
   - id: SysML2Workbench-AppShellSubsystem-WorkspacePanel
     title: Review that SysML2Workbench AppShellSubsystem WorkspacePanel Implementation
       is Correct
@@ -390,3 +394,10 @@ reviews:
       - docs/reqstream/ots/communitytoolkit-mvvm.yaml
       - docs/design/ots/communitytoolkit-mvvm.md
       - docs/verification/ots/communitytoolkit-mvvm.md
+  - id: OTS-AvaloniaEdit
+    title: Review that AvaloniaEdit Provides Required Functionality
+    paths:
+      - docs/reqstream/ots/avaloniaedit.yaml
+      - docs/design/ots/avaloniaedit.md
+      - docs/verification/ots/avaloniaedit.md
+      - test/OtsSoftwareTests/AvaloniaEditTests.cs

README.md

@@ -10,7 +10,9 @@ interactive pan/zoom viewer, and lets you build ad-hoc custom views through a
 GUI - picking a view kind, multi-selecting target elements, and optionally
 filtering - without hand-writing SysML `view` syntax. Custom views can be
 exported as copy-pasteable SysML `view ... expose ...` text to promote them
-into a permanent model file. A live-updating diagnostics panel surfaces parser
+into a permanent model file, and any workspace `.sysml` file's raw source
+text can be opened read-only, with syntax highlighting, by double-clicking
+it in the workspace tree. A live-updating diagnostics panel surfaces parser
 and reference-resolution problems across the whole workspace, and a local
 rolling log file is written for bug-report attachments.
 

docs/design/introduction.md

@@ -31,6 +31,7 @@ OTS items:
   semantic model, layout engine).
 - **DemaConsulting.Rendering**: integration and usage design (SVG rendering).
 - **Avalonia**: integration and usage design (UI framework).
+- **AvaloniaEdit**: integration and usage design (read-only syntax-highlighted text editor control).
 - **xUnit**: integration and usage design (test framework).
 
 Out of scope: no Shared Packages exist in this repository. Design documents

docs/design/ots.md

@@ -35,11 +35,13 @@ OTS items are consumed through narrow integration seams. SysML2Tools and
 DemaConsulting.Rendering are wrapped behind local units that translate
 workspace or view state into library calls. Avalonia is used as the application
 shell and control layer, with Dock providing the resizable, floatable,
-closable panel-docking layout for that shell and CommunityToolkit.Mvvm
-supplying observable-property generation for the Dock panel view models, but
-subsystem responsibilities remain in local units rather than in code-behind
-spread across the UI. xUnit is confined to verification projects and does not
-participate in runtime behavior. Across all items, the local code treats OTS
+closable panel-docking layout for that shell, CommunityToolkit.Mvvm
+supplying observable-property generation for the Dock panel view models, and
+AvaloniaEdit providing the read-only, syntax-highlighted text editor control
+used by the source-text viewer document tabs, but subsystem responsibilities
+remain in local units rather than in code-behind spread across the UI. xUnit
+is confined to verification projects and does not participate in runtime
+behavior. Across all items, the local code treats OTS
 failures as diagnosable events: exceptions are surfaced to the shell, and
 notable integration faults are logged through the local rolling logger.
 

docs/design/ots/avaloniaedit.md

@@ -0,0 +1,39 @@
+## AvaloniaEdit
+
+### Purpose
+
+AvaloniaEdit was chosen to provide read-only, syntax-highlighted text
+viewing of a `.sysml` file's raw source without the workbench hand-rolling
+its own text control, line-numbered gutter, or highlighting engine. It backs
+the source-text viewer's document tabs, giving a user a faithful, readable
+view of a file's exact on-disk text alongside its rendered diagrams.
+
+### Features Used
+
+- **`AvaloniaEdit.TextEditor`** — the hosted text control, configured
+  `IsReadOnly = true` so the source-text viewer can never mutate the
+  underlying file.
+- **`AvaloniaEdit.Highlighting.Xshd.HighlightingLoader`** — loads a
+  self-authored XSHD v2 highlighting definition from an embedded
+  `AvaloniaResource` at runtime.
+- **`AvaloniaEdit.Highlighting.HighlightingManager`** — registers the
+  loaded definition once, lazily, and resolves any XSHD-internal
+  references during load.
+
+### Integration Pattern
+
+`SourceTextDocumentView`'s code-behind loads and registers the embedded
+`avares://DemaConsulting.SysML2Workbench/Assets/SysML.xshd` highlighting
+definition once, via a static, lazily-initialized `IHighlightingDefinition`
+shared across every open source-text tab, and assigns it to the hosted
+`TextEditor.SyntaxHighlighting` property. The XSHD file itself is generic
+(comment, string, and number rules only); the keyword-highlighting rule is
+built at load time by reflecting
+`DemaConsulting.SysML2Tools.Parser.Antlr.SysMLv2Lexer`'s literal-token table
+rather than hand-copying a keyword list that could drift from the real
+grammar, with a hard-coded fallback keyword list used if the reflection
+call ever fails. `TextEditor.Text` is a plain CLR property rather than an
+Avalonia styled property, so the view model's `Text` is assigned to it
+imperatively in code-behind rather than through an XAML binding; this is
+safe because the source-text viewer never changes `Text` after
+construction. There is no write-back path in this phase.

docs/design/sysml2-workbench/app-shell-subsystem.md

@@ -65,9 +65,13 @@ environment.
    discarded on close rather than living in the persistent Dock layout. The
    diagram area hosts zero or more independently closable diagram
    Documents - one per open `WorkbenchTab`, each bound to its own
-   `SvgCanvasHost` - and the Dock `DocumentDock` container itself remains
-   visibly present even when no diagram tab is open, so an empty diagram
-   area is a normal, supported state rather than a dead end. MainWindowShell
+   `SvgCanvasHost` - and the same `DocumentDock` container also hosts
+   independently closable read-only source-text Documents, one per
+   `WorkbenchTab` opened via double-click from the workspace tree, sharing
+   the diagram tabs' tabbed presentation area - and the Dock `DocumentDock`
+   container itself remains visibly present even when no diagram tab is
+   open, so an empty diagram area is a normal, supported state rather than
+   a dead end. MainWindowShell
    itself has no dependency on Avalonia or Dock and is unaware of how its
    panels are arranged on screen.
 7. A workspace with zero sources open is a first-class, non-error state, not

docs/design/sysml2-workbench/app-shell-subsystem/main-window-shell.md

@@ -23,8 +23,9 @@ user is in predefined-view mode.
 the user is composing a preview.
 
 **OpenTabs**: `IReadOnlyList<WorkbenchTab>` — tabs representing rendered
-diagrams, builder surfaces, or related shell content. Each `WorkbenchTab`
-owns its own `SvgCanvasHost`, so multiple open diagram tabs have fully
+diagrams, builder surfaces, read-only source-text views, or related shell
+content. Each `WorkbenchTab` owns its own `SvgCanvasHost` (unused/never
+loaded for a source-text tab), so multiple open diagram tabs have fully
 independent zoom/pan/content state.
 
 **ActiveTabId**: `string?` — identifier of the diagram tab currently
@@ -41,7 +42,17 @@ Each `WorkbenchTab` also carries a `SourceDefinition: ViewDefinitionModel?` —
 the definition that produced the tab's currently rendered diagram, or `null`
 when none could be derived (an unscoped predefined view with zero expose
 members, or a brand-new custom-preview tab that has not rendered anything
-yet). This backs the tab's "Copy as SysML" context-menu action.
+yet, or a source-text tab, which has no rendered diagram at all). This backs
+the tab's "Copy as SysML" context-menu action.
+
+`WorkbenchTab` also carries a `FilePath: string?` — the absolute path of the
+file a source-text tab displays; `null` for predefined-view and
+custom-view-preview tabs. `WorkbenchTabKind` has a corresponding
+`SourceText` member alongside `PredefinedView` and `CustomViewPreview`.
+`WorkbenchTab.Id` for a source-text tab is the file's own absolute path,
+which both gives it a stable dedupe key (opening the same file twice
+re-focuses the existing tab rather than duplicating it) and lets
+`GetTabFilePath` resolve it without exposing `OpenTabs` internals further.
 
 #### Key Methods
 
@@ -151,6 +162,35 @@ UI focus.
   when Dock reports a focus change onto a diagram document - never by
   `MainWindowShell` itself, which stays Dock-agnostic.
 
+**OpenSourceTextTab**: Opens a read-only source-text tab for a given file
+path.
+
+- *Parameters*: `string filePath` — absolute path of the `.sysml` file to
+  display.
+- *Returns*: `WorkbenchTab` — the newly opened tab, or the already-open tab
+  for the same path if one exists.
+- *Postconditions*: If a source-text tab for `filePath` is already open, it
+  is reused (its `FilePath` is left unchanged) and refocused rather than
+  duplicated; otherwise a new `WorkbenchTabKind.SourceText` tab is appended,
+  titled with the file's own name (`Path.GetFileName`) and identified by the
+  file's absolute path. Either way the tab becomes `ActiveTabId` and
+  `TabsChanged` is raised. Backs `WorkspacePanelToolView`'s double-click
+  handler; the view built for a source-text tab
+  (`SourceTextDocumentView`/`SourceTextDocumentViewModel`, see "Supporting
+  Types" below) reads the file's contents directly rather than through
+  `MainWindowShell`, which never loads file text itself.
+
+**GetTabFilePath**: Resolves the file path of an open source-text tab.
+
+- *Parameters*: `string tabId` — identifier of an open tab.
+- *Returns*: `string?` — the tab's `FilePath`, or `null` when `tabId` does
+  not refer to a currently open tab, or refers to a tab of a different kind
+  (whose `FilePath` is always `null`). Mirrors the existing `GetTabCanvas`
+  lookup pattern.
+- *Postconditions*: None (read-only). Lets `SourceTextDocumentViewModel`
+  resolve which file it displays without `MainWindowShell` needing to
+  expose `OpenTabs` internals further.
+
 **CanExportTabAsSysml**: Reports whether an open diagram tab has a derivable
 source definition and can export its diagram as a SysML snippet.
 
@@ -171,6 +211,20 @@ the diagram currently rendered in an open tab.
   successful export is also logged at `Info` level, mirroring
   `ExportCustomViewSnippet`'s existing style.
 
+#### Supporting Types
+
+**SourceTextDocumentViewModel**/**SourceTextDocumentView**: the Dock
+`Document`/view pair backing a source-text tab, following the same
+convention already used for `DiagramDocumentViewModel`/`DiagramDocumentView`
+(neither pair is a separately documented unit). `SourceTextDocumentViewModel`
+resolves its file path via `GetTabFilePath`, sets its `Title` to
+`Path.GetFileName(FilePath)`, and eagerly loads `Text` via `File.ReadAllText`
+once at construction, substituting a friendly in-editor error message for a
+deleted or locked file instead of throwing (no caching, no file-watch, no
+write-back). `SourceTextDocumentView` hosts a read-only AvaloniaEdit
+`TextEditor` with SysML v2 syntax highlighting (see
+`docs/design/ots/avaloniaedit.md`).
+
 #### Error Handling
 
 MainWindowShell handles user-cancelled operations, empty workspace selections,
@@ -218,6 +272,9 @@ the time subscribers observe the notification.
   notifications onto the thread required by UI-facing subscribers; defaults
   to an immediate, synchronous dispatcher when none is supplied.
 - **Avalonia** — provides the window, tab, and application-lifetime framework.
+- **AvaloniaEdit** — provides the read-only, syntax-highlighted `TextEditor`
+  control hosted by `SourceTextDocumentView` (see
+  `docs/design/ots/avaloniaedit.md`).
 
 #### Callers
 

docs/design/sysml2-workbench/app-shell-subsystem/workspace-panel.md

@@ -40,9 +40,11 @@ already covers everything beneath it).
 **WorkspaceFileNode**: `WorkspaceTreeNode` with `required string FilePath`,
 `required string SourceId`, and a computed `Name` (`Path.GetFileName(FilePath)`,
 shown in the tree since ancestor nodes already convey the file's directory) —
-a leaf node for one file. `FilePath` is a stable identity intended for a
-future, out-of-scope, double-click read-only file viewer; it is preserved
-even though nothing else currently reads it beyond display.
+a leaf node for one file. `FilePath` is a stable identity used by
+`WorkspacePanelToolView`'s double-click handler to open a `.sysml` file's
+read-only source-text tab via `MainWindowShell.OpenSourceTextTab`; it is
+preserved even though nothing else currently reads it beyond display and
+that handler.
 
 **SelectedNode**: `WorkspaceTreeNode?` — the tree node currently selected by
 the user, used to resolve which source `RemoveSelected` acts on.
@@ -94,6 +96,15 @@ into `MainWindowShell.AddFileSourceAsync` / `AddFolderSourceAsync`.
   and surfaced via `StatusMessage` rather than propagated, since a failed
   remove should not crash the shell.
 
+`WorkspacePanelToolView`'s code-behind also wires a `DoubleTapped` handler on
+its `TreeView` directly to `MainWindowShell.OpenSourceTextTab`: when the
+selected item is a `WorkspaceFileNode` whose `FilePath` ends in `.sysml`
+(case-insensitive), double-clicking it opens the file's read-only
+source-text tab. No view-model method backs this - it follows the same
+"view calls `Shell` directly" pattern already used by the Add File/Add
+Folder picker flows, and is thin enough that it is not unit tested (see
+`docs/verification/sysml2-workbench/app-shell-subsystem/workspace-panel.md`).
+
 #### Error Handling
 
 WorkspacePanel treats a failed `RemoveSelectedAsync` as a locally recoverable

docs/reqstream/ots/avaloniaedit.yaml

@@ -0,0 +1,20 @@
+---
+sections:
+  - title: 'OTS Software Requirements'
+    sections:
+      - title: 'AvaloniaEdit Requirements'
+        requirements:
+          - id: 'AvaloniaEdit-RenderReadOnlySyntaxHighlightedText'
+            title: 'The SysML2Workbench shall render read-only, syntax-highlighted .sysml source text using AvaloniaEdit''s TextEditor control.'
+            justification: |
+              AvaloniaEdit provides the text-editing control, read-only enforcement, and highlighting engine required for the source-text viewer without the workbench hand-rolling its own text control.
+            tests:
+              - 'Text_OpenedFile_MatchesFileContents'
+              - 'TextEditor_IsReadOnly_PreventsEdits'
+
+          - id: 'AvaloniaEdit-LoadEmbeddedSysmlHighlighting'
+            title: 'The SysML2Workbench shall load a self-authored SysML v2 highlighting definition from an embedded resource via AvaloniaEdit''s HighlightingLoader, with keywords derived from the real SysML v2 lexer rather than a hand-copied list.'
+            justification: |
+              Highlighting fidelity depends on the keyword set staying in sync with the actual grammar; loading the definition through AvaloniaEdit's own XSHD loader and populating keywords by reflecting the lexer avoids a hand-copied list silently drifting out of date.
+            tests:
+              - 'EmbeddedXshd_Loads_AndKeywordRuleMatchesSysmlKeyword'

docs/reqstream/sysml2-workbench/app-shell-subsystem/main-window-shell.yaml

@@ -69,3 +69,12 @@ sections:
                 tests:
                   - 'RenderCustomViewPreview_DoesNotMutateOpenTabsOrActiveTab'
                   - 'RenderCustomViewPreview_NoWorkspaceOpened_ThrowsInvalidOperationException'
+
+              - id: 'SysML2Workbench-AppShellSubsystem-MainWindowShell-OpenSourceTextTab'
+                title: 'The MainWindowShell shall open a read-only source-text tab for a given file path, reusing an already-open tab for the same path instead of duplicating it, and shall resolve an open source-text tab''s file path on request.'
+                justification: |
+                  Double-clicking a .sysml file in the workspace tree must open its raw text in its own tab without duplicating tabs on repeated double-clicks, and the resulting view model needs a way to resolve which file it displays without MainWindowShell exposing OpenTabs internals further.
+                tests:
+                  - 'OpenSourceTextTab_NewFile_CreatesOneNewActiveTab'
+                  - 'OpenSourceTextTab_SamePathTwice_RefocusesExistingTabWithoutDuplicating'
+                  - 'GetTabFilePath_ReturnsPathForSourceTextTab_AndNullOtherwise'

docs/sysml2/model/ots.sysml

@@ -42,5 +42,12 @@ package SysML2WorkbenchArchitecture {
             comment verificationRef /* Verification: docs/verification/ots/communitytoolkit-mvvm.md */
             comment reqRef /* Requirements: docs/reqstream/ots/communitytoolkit-mvvm.yaml */
         }
+        part def AvaloniaEdit {
+            doc /* Avalonia.AvaloniaEdit NuGet dependency for the read-only, syntax-highlighted text editor control backing the source-text viewer document tabs. */
+
+            comment designRef /* Design: docs/design/ots/avaloniaedit.md */
+            comment verificationRef /* Verification: docs/verification/ots/avaloniaedit.md */
+            comment reqRef /* Requirements: docs/reqstream/ots/avaloniaedit.yaml */
+        }
     }
 }

docs/user_guide/getting_started.md

@@ -84,6 +84,15 @@ no concrete view definition can be derived for the tab, for example an
 unscoped predefined view or a custom-view preview tab that has not yet been
 rendered.
 
+## Viewing a File's Raw Source
+
+Double-click any `.sysml` file in the **Workspace** panel's tree to open its
+raw source text, read-only, with SysML v2 syntax highlighting, in its own
+tab in the same tabbed area as diagram tabs. Double-clicking the same file
+again switches focus to its already-open tab instead of opening a
+duplicate. This is a view-only capability - editing and saving `.sysml`
+files is a future phase (see "Out of Scope" below).
+
 ## Building a Custom View
 
 Choose **View > Custom View Builder...** to open the View Builder dialog. The

docs/verification/ots/avaloniaedit.md

@@ -0,0 +1,28 @@
+## AvaloniaEdit
+
+### Verification Approach
+
+OTS integration tests in `test/OtsSoftwareTests/AvaloniaEditTests.cs` verify AvaloniaEdit's read-only enforcement
+and highlighting-load behavior directly: `[AvaloniaFact]` tests host a real, headless `AvaloniaEdit.TextEditor` to
+confirm its `IsReadOnly` mode installs a section provider that genuinely rejects insertion, and that the embedded
+`Assets/SysML.xshd` highlighting definition loads via `HighlightingLoader.Load` without throwing and defines a
+keyword-highlighting rule (built the same way `SourceTextDocumentView` builds it at runtime, by reflecting the real
+SysML v2 lexer's literal-token table) that matches a genuine SysML v2 keyword. Unit tests in
+`test/DemaConsulting.SysML2Workbench.Tests/AppShellSubsystem/SourceTextDocumentViewModelTests.cs` additionally
+verify that a file's text is faithfully surfaced, unmodified, to the editor's view model.
+
+### Test Scenarios
+
+**TextEditor_IsReadOnly_PreventsEdits**: A real, headless-hosted `TextEditor` with `IsReadOnly = true` installs a
+`TextArea.ReadOnlySectionProvider` whose `CanInsert` rejects insertion anywhere in the document, while a normal
+(non-read-only) editor's provider allows it - proving the read-only "View Source" tab genuinely cannot be edited
+through the editor's own input pipeline.
+
+**EmbeddedXshd_Loads_AndKeywordRuleMatchesSysmlKeyword**: The embedded `Assets/SysML.xshd` resource loads via
+`HighlightingLoader.Load` without throwing and defines the expected named colors (Keyword, Comment, String,
+Number); a keyword-highlighting rule built the same way `SourceTextDocumentView` builds it at runtime - by
+independently reflecting `SysMLv2Lexer._LiteralNames` - matches a real SysML v2 keyword (`part`).
+
+**Text_OpenedFile_MatchesFileContents**: `SourceTextDocumentViewModel.Text`, backing the hosted `TextEditor`'s
+displayed content, exactly matches the contents of the opened temp file. Verified by
+`SourceTextDocumentViewModelTests.Text_OpenedFile_MatchesFileContents`.