fix transform-typescript logic to remove definite fields (#12149)

packages/babel-plugin-transform-typescript/src/index.js

@@ -69,17 +69,26 @@ export default declare(
               `@babel/plugin-transform-typescript or @babel/preset-typescript is enabled.`,
           );
         }
-        if (node.definite || node.declare) {
+        if (node.declare) {
           if (node.value) {
             throw path.buildCodeFrameError(
-              `Definitely assigned fields and fields with the 'declare' modifier cannot` +
-                ` be initialized here, but only in the constructor`,
+              `Fields with the 'declare' modifier cannot be initialized here, but only in the constructor`,
             );
           }
-
           if (!node.decorators) {
             path.remove();
           }
+        } else if (node.definite) {
+          if (node.value) {
+            throw path.buildCodeFrameError(
+              `Definitely assigned fields cannot be initialized here, but only in the constructor`,
+            );
+          }
+          // keep the definitely assigned fields only when `allowDeclareFields` (equivalent of
+          // Typescript's `useDefineForClassFields`) is true
+          if (!allowDeclareFields && !node.decorators) {
+            path.remove();
+          }
         } else if (
           !allowDeclareFields &&
           !node.value &&

packages/babel-plugin-transform-typescript/test/fixtures/class/uninitialized-definite-with-declare-disabled/input.ts

@@ -0,0 +1,3 @@
+class A {
+  x!;
+}

packages/babel-plugin-transform-typescript/test/fixtures/class/uninitialized-definite-with-declare-disabled/options.json

@@ -0,0 +1,3 @@
+{
+  "plugins": [["transform-typescript", { "allowDeclareFields": false }]]
+}

packages/babel-plugin-transform-typescript/test/fixtures/class/uninitialized-definite-with-declare-disabled/output.js

@@ -0,0 +1 @@
+class A {}

packages/babel-plugin-transform-typescript/test/fixtures/class/uninitialized-definite-with-declare-enabled/output.js

@@ -1 +1,3 @@
-class A {}
+class A {
+  x;
+}