fixUnusedIdentifier: Delete trailing comma in array binding pattern (microsoft#24800)

Andy · web-flow · commit 855c3a6d4fb2 · 2018-06-08T10:39:01.000-07:00
diff --git a/src/services/codefixes/fixUnusedIdentifier.ts b/src/services/codefixes/fixUnusedIdentifier.ts
@@ -228,15 +228,12 @@ namespace ts.codefix {
 
             case SyntaxKind.BindingElement: {
                 const pattern = (parent as BindingElement).parent;
-                switch (pattern.kind) {
-                    case SyntaxKind.ArrayBindingPattern:
-                        changes.deleteNode(sourceFile, parent); // Don't delete ','
-                        break;
-                    case SyntaxKind.ObjectBindingPattern:
-                        changes.deleteNodeInList(sourceFile, parent);
-                        break;
-                    default:
-                        return Debug.assertNever(pattern);
+                const preserveComma = pattern.kind === SyntaxKind.ArrayBindingPattern && parent !== last(pattern.elements);
+                if (preserveComma) {
+                    changes.deleteNode(sourceFile, parent);
+                }
+                else {
+                    changes.deleteNodeInList(sourceFile, parent);
                 }
                 break;
             }
diff --git a/tests/cases/fourslash/codeFixUnusedIdentifier_destructure_partlyUnused.ts b/tests/cases/fourslash/codeFixUnusedIdentifier_destructure_partlyUnused.ts
@@ -57,15 +57,15 @@ verify.codeFixAll({
     x; z;
 }
 {
-    const [x,] = o;
+    const [x] = o;
     x;
 }
 {
     const [, y] = o;
     y;
 }
 {
-    const [, y,] = o;
+    const [, y] = o;
     y;
 }
 {

Original file line number	Diff line number	Diff line change
`@@ -57,15 +57,15 @@ verify.codeFixAll({`
`57`	`57`	`x; z;`
`58`	`58`	`}`
`59`	`59`	`{`
`60`		`- const [x,] = o;`
	`60`	`+ const [x] = o;`
`61`	`61`	`x;`
`62`	`62`	`}`
`63`	`63`	`{`
`64`	`64`	`const [, y] = o;`
`65`	`65`	`y;`
`66`	`66`	`}`
`67`	`67`	`{`
`68`		`- const [, y,] = o;`
	`68`	`+ const [, y] = o;`
`69`	`69`	`y;`
`70`	`70`	`}`
`71`	`71`	`{`