Offer TALA layout when bundled with d2, and fix edge fill in preview

package.json

@@ -192,7 +192,7 @@
           "enumDescriptions": [
             "The directed graph layout library Dagre",
             "Eclipse Layout Kernel (ELK) with the Layered algorithm",
-            "Terrastruct's AutoLayout Approach - available if installed"
+            "Terrastruct's AutoLayout Approach"
           ],
           "description": "Layout used for preview."
         },

pages/previewPage.html

@@ -66,7 +66,7 @@
         height: 100%;
       }
 
-      path {
+      #toolbar path {
         fill: var(--vscode-button-foreground);
       }
 

src/layoutPicker.ts

@@ -33,8 +33,9 @@ const talaPluginName: string =
  */
 export class layoutPicker {
   constructor() {
-    // If the plugin file exists, add the option if it hasn't been added before
-    if (util.isFileOnPath(talaPluginName)) {
+    // If d2 reports TALA (bundled or as a plugin), or the plugin file exists,
+    // add the option if it hasn't been added before
+    if (util.isLayoutAvailable("tala") || util.isFileOnPath(talaPluginName)) {
       if (layouts.indexOf(layoutTala) === -1) {
         layouts.push(layoutTala);
       }

src/utility.ts

@@ -122,6 +122,21 @@ class Utility {
       util.showErrorToolsNotFound("");
     }
   }
+
+  /**
+   * isLayoutAvailable - returns true if `d2 layout` reports the given
+   *   layout engine, whether it is bundled with d2 or installed as a
+   *   plugin on the path.
+   */
+  isLayoutAvailable(layout: string): boolean {
+    const d2Path: string = ws.get("execPath", "d2");
+    const result = spawnSync(d2Path, ["layout"], { encoding: "utf-8" });
+    if (result.error || result.status !== 0) {
+      return false;
+    }
+
+    return new RegExp(`^${layout}\\b`, "m").test(result.stdout);
+  }
 }
 
 export class VT {