downlevel readonly array & readonly tuple

sandersn · Mar 11, 2020 · 60355a5 · 60355a5
1 parent b811012
commit 60355a5
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Showing 3 changed files with 18 additions and 1 deletion.
diff --git a/baselines/ts3.4/src/test.d.ts b/baselines/ts3.4/src/test.d.ts
@@ -17,3 +17,5 @@ export interface E {
     b: number;
 }
 export type F = Omit<E, 'a'>;
+export declare let readonlyArr: ReadonlyArray<string>;
+export declare let readonlyTuple: Readonly<[string, number]>;
diff --git a/index.js b/index.js
@@ -141,6 +141,18 @@ function doTransform(checker, k) {
           ])
         ]);
       }
+    } else if (ts.isTypeOperatorNode(n) && n.operator === ts.SyntaxKind.ReadonlyKeyword) {
+      if (ts.isArrayTypeNode(n.type)) {
+        // let arr: readonly number[];
+        // =>
+        // let arr: ReadonlyArray<number>;
+        return ts.createTypeReferenceNode('ReadonlyArray', [transform(n.type.elementType)]);
+      } else if (ts.isTupleTypeNode(n.type)) {
+        // let tup: readonly [string, number];
+        // =>
+        // let tup: Readonly<[string, number]>;
+        return ts.createTypeReferenceNode('Readonly', [transform(n.type)]);
+      }
     }
     return ts.visitEachChild(n, transform, k);
   };

diff --git a/test/src/test.d.ts b/test/src/test.d.ts
@@ -22,4 +22,7 @@ export interface E {
   b: number;
 }
 
-export type F = Omit<E, 'a'>;
+export type F = Omit<E, 'a'>;
+
+export declare let readonlyArr: readonly string[];
+export declare let readonlyTuple: readonly [string, number];