Support converting React Components with null state

Author: tylerkrupicka-stripe

src/convert/declarations.test.ts

@@ -509,6 +509,16 @@ describe("transform declarations", () => {
     expect(await transform(src)).toBe(expected);
   });
 
+  it("Converts makes sure React.Component is valid JSX, with no null for state", async () => {
+    const src = dedent`class Foo extends React.Component<Props, null>  {
+      test(): string {return 'string'};
+    };`;
+    const expected = dedent`class Foo extends React.Component<Props> {
+      test(): string {return 'string'};
+    };`;
+    expect(await transform(src)).toBe(expected);
+  });
+
   it("Converts React.Node to React.ReactElement in render", async () => {
     const src = dedent`class Foo extends React.Component {
       render(): React.Node {return <div />};

src/convert/declarations.ts

@@ -453,6 +453,27 @@ export function transformDeclarations({
     ClassDeclaration(path) {
       const { node } = path;
       if (node.superClass && node.superTypeParameters) {
+        // If it extends React.Component, we may need to modify the type to make sure it's still valid
+        // in TS. Some parameters like null make it an invalid component.
+        const isReactComponent =
+          node.superClass.type === "MemberExpression" &&
+          t.isIdentifier(node.superClass.object) &&
+          t.isIdentifier(node.superClass.property) &&
+          node.superClass.object.name === "React" &&
+          node.superClass.property.name === "Component";
+
+        const nullSecondParam =
+          node.superTypeParameters.params.length === 2 &&
+          node.superTypeParameters.params[1].type ===
+            "NullLiteralTypeAnnotation";
+
+        // React.Component<Props, null> -> React.Component<Props> (null makes it invalid JSX)
+        if (isReactComponent && nullSecondParam) {
+          node.superTypeParameters.params =
+            node.superTypeParameters.params.slice(0, 1);
+        }
+
+        // Process the type parameters
         node.superTypeParameters = migrateTypeParameterInstantiation(
           reporter,
           state,