Avoid removing uninitialized class fields with flow (#10120)

* flow avoid removing class fields

* fix test case

* Update test

Co-authored-by: Nicolò Ribaudo <nicolo.ribaudo@gmail.com>

packages/babel-plugin-transform-flow-strip-types/src/index.js

@@ -101,8 +101,6 @@ export default declare((api, opts) => {
 
             if (node.declare) {
               child.remove();
-            } else if (!allowDeclareFields && !node.value && !node.decorators) {
-              child.remove();
             } else {
               node.variance = null;
               node.typeAnnotation = null;

packages/babel-plugin-transform-flow-strip-types/test/fixtures/regression/class-prop-values/input.js → packages/babel-plugin-transform-flow-strip-types/test/fixtures/regression/class-fields-initialized/input.js

@@ -1,5 +1,4 @@
 class X {
   foo = 2
   bar: number = 3
-  baz: ?string
 }

packages/babel-plugin-transform-flow-strip-types/test/fixtures/regression/class-prop-types/options.json → packages/babel-plugin-transform-flow-strip-types/test/fixtures/regression/class-fields-uninitialized/options.json

@@ -1,7 +1,7 @@
 {
   "plugins": [
     "transform-flow-strip-types",
-    "transform-classes",
+    "proposal-class-properties",
     "external-helpers"
   ]
 }

packages/babel-plugin-transform-flow-strip-types/test/fixtures/regression/class-fields-uninitialized/output.js

@@ -0,0 +1,6 @@
+class Test {
+  constructor() {
+    babelHelpers.defineProperty(this, "prop", void 0);
+  }
+
+}

packages/babel-plugin-transform-flow-strip-types/test/fixtures/strip-types/def-site-variance/output.js

@@ -2,6 +2,10 @@ class C1 {}
 
 function f() {}
 
-class C2 {}
+class C2 {
+  p;
+}
 
-class C3 {}
+class C3 {
+  p;
+}

packages/babel-plugin-transform-flow-strip-types/test/fixtures/strip-types/strip-type-annotations/output.mjs

@@ -119,9 +119,15 @@ class Foo8 {
 
 function foo19(requiredParam, optParam) {}
 
-class Foo9 {}
+class Foo9 {
+  prop1;
+  prop2;
+}
 
-class Foo10 {}
+class Foo10 {
+  static prop1;
+  prop2;
+}
 
 class Foo11 {
   #prop1;