Remove module pattern function component support (flag only)

> This is a redo of facebook#27742, but only including the flag removal, excluding further simplifications.

The module pattern

```
function MyComponent() {
  return {
    render() {
      return this.state.foo
    }
  }
}
```

has been deprecated for approximately 5 years now. This PR removes
support for this pattern.

Author: kassens

packages/react-dom/src/__tests__/ReactComponentLifeCycle-test.js

@@ -14,7 +14,6 @@ let act;
 let React;
 let ReactDOM;
 let ReactDOMClient;
-let PropTypes;
 let findDOMNode;
 
 const clone = function (o) {
@@ -99,7 +98,6 @@ describe('ReactComponentLifeCycle', () => {
     findDOMNode =
       ReactDOM.__SECRET_INTERNALS_DO_NOT_USE_OR_YOU_WILL_BE_FIRED.findDOMNode;
     ReactDOMClient = require('react-dom/client');
-    PropTypes = require('prop-types');
   });
 
   it('should not reuse an instance when it has been unmounted', async () => {
@@ -1114,72 +1112,6 @@ describe('ReactComponentLifeCycle', () => {
     });
   });
 
-  if (!require('shared/ReactFeatureFlags').disableModulePatternComponents) {
-    // @gate !disableLegacyContext
-    it('calls effects on module-pattern component', async () => {
-      const log = [];
-
-      function Parent() {
-        return {
-          render() {
-            expect(typeof this.props).toBe('object');
-            log.push('render');
-            return <Child />;
-          },
-          UNSAFE_componentWillMount() {
-            log.push('will mount');
-          },
-          componentDidMount() {
-            log.push('did mount');
-          },
-          componentDidUpdate() {
-            log.push('did update');
-          },
-          getChildContext() {
-            return {x: 2};
-          },
-        };
-      }
-      Parent.childContextTypes = {
-        x: PropTypes.number,
-      };
-      function Child(props, context) {
-        expect(context.x).toBe(2);
-        return <div />;
-      }
-      Child.contextTypes = {
-        x: PropTypes.number,
-      };
-
-      const root = ReactDOMClient.createRoot(document.createElement('div'));
-      await expect(async () => {
-        await act(() => {
-          root.render(<Parent ref={c => c && log.push('ref')} />);
-        });
-      }).toErrorDev(
-        'Warning: The <Parent /> component appears to be a function component that returns a class instance. ' +
-          'Change Parent to a class that extends React.Component instead. ' +
-          "If you can't use a class try assigning the prototype on the function as a workaround. " +
-          '`Parent.prototype = React.Component.prototype`. ' +
-          "Don't use an arrow function since it cannot be called with `new` by React.",
-      );
-      await act(() => {
-        root.render(<Parent ref={c => c && log.push('ref')} />);
-      });
-
-      expect(log).toEqual([
-        'will mount',
-        'render',
-        'did mount',
-        'ref',
-
-        'render',
-        'did update',
-        'ref',
-      ]);
-    });
-  }
-
   it('should warn if getDerivedStateFromProps returns undefined', async () => {
     class MyComponent extends React.Component {
       state = {};

packages/react-dom/src/__tests__/ReactCompositeComponent-test.js

@@ -211,64 +211,35 @@ describe('ReactCompositeComponent', () => {
     });
   });
 
-  if (require('shared/ReactFeatureFlags').disableModulePatternComponents) {
-    it('should not support module pattern components', async () => {
-      function Child({test}) {
-        return {
-          render() {
-            return <div>{test}</div>;
-          },
-        };
-      }
+  it('should not support module pattern components', async () => {
+    function Child({test}) {
+      return {
+        render() {
+          return <div>{test}</div>;
+        },
+      };
+    }
 
-      const el = document.createElement('div');
-      const root = ReactDOMClient.createRoot(el);
+    const el = document.createElement('div');
+    const root = ReactDOMClient.createRoot(el);
+    await expect(async () => {
       await expect(async () => {
-        await expect(async () => {
-          await act(() => {
-            root.render(<Child test="test" />);
-          });
-        }).rejects.toThrow(
-          'Objects are not valid as a React child (found: object with keys {render}).',
-        );
-      }).toErrorDev(
-        'Warning: The <Child /> component appears to be a function component that returns a class instance. ' +
-          'Change Child to a class that extends React.Component instead. ' +
-          "If you can't use a class try assigning the prototype on the function as a workaround. " +
-          '`Child.prototype = React.Component.prototype`. ' +
-          "Don't use an arrow function since it cannot be called with `new` by React.",
-      );
-
-      expect(el.textContent).toBe('');
-    });
-  } else {
-    it('should support module pattern components', () => {
-      function Child({test}) {
-        return {
-          render() {
-            return <div>{test}</div>;
-          },
-        };
-      }
-
-      const el = document.createElement('div');
-      const root = ReactDOMClient.createRoot(el);
-      expect(() => {
-        ReactDOM.flushSync(() => {
+        await act(() => {
           root.render(<Child test="test" />);
         });
-      }).toErrorDev(
-        'Warning: The <Child /> component appears to be a function component that returns a class instance. ' +
-          'Change Child to a class that extends React.Component instead. ' +
-          "If you can't use a class try assigning the prototype on the function as a workaround. " +
-          '`Child.prototype = React.Component.prototype`. ' +
-          "Don't use an arrow function since it cannot be called with `new` by React.",
+      }).rejects.toThrow(
+        'Objects are not valid as a React child (found: object with keys {render}).',
       );
+    }).toErrorDev(
+      'Warning: The <Child /> component appears to be a function component that returns a class instance. ' +
+        'Change Child to a class that extends React.Component instead. ' +
+        "If you can't use a class try assigning the prototype on the function as a workaround. " +
+        '`Child.prototype = React.Component.prototype`. ' +
+        "Don't use an arrow function since it cannot be called with `new` by React.",
+    );
 
-      expect(el.textContent).toBe('test');
-    });
-  }
-
+    expect(el.textContent).toBe('');
+  });
   it('should use default values for undefined props', async () => {
     class Component extends React.Component {
       static defaultProps = {prop: 'testKey'};

packages/react-dom/src/__tests__/ReactCompositeComponentState-test.js

@@ -527,72 +527,6 @@ describe('ReactCompositeComponent-state', () => {
     ]);
   });
 
-  if (!require('shared/ReactFeatureFlags').disableModulePatternComponents) {
-    it('should support stateful module pattern components', async () => {
-      function Child() {
-        return {
-          state: {
-            count: 123,
-          },
-          render() {
-            return <div>{`count:${this.state.count}`}</div>;
-          },
-        };
-      }
-
-      const el = document.createElement('div');
-      const root = ReactDOMClient.createRoot(el);
-      expect(() => {
-        ReactDOM.flushSync(() => {
-          root.render(<Child />);
-        });
-      }).toErrorDev(
-        'Warning: The <Child /> component appears to be a function component that returns a class instance. ' +
-          'Change Child to a class that extends React.Component instead. ' +
-          "If you can't use a class try assigning the prototype on the function as a workaround. " +
-          '`Child.prototype = React.Component.prototype`. ' +
-          "Don't use an arrow function since it cannot be called with `new` by React.",
-      );
-
-      expect(el.textContent).toBe('count:123');
-    });
-
-    it('should support getDerivedStateFromProps for module pattern components', async () => {
-      function Child() {
-        return {
-          state: {
-            count: 1,
-          },
-          render() {
-            return <div>{`count:${this.state.count}`}</div>;
-          },
-        };
-      }
-      Child.getDerivedStateFromProps = (props, prevState) => {
-        return {
-          count: prevState.count + props.incrementBy,
-        };
-      };
-
-      const el = document.createElement('div');
-      const root = ReactDOMClient.createRoot(el);
-      await act(() => {
-        root.render(<Child incrementBy={0} />);
-      });
-
-      expect(el.textContent).toBe('count:1');
-      await act(() => {
-        root.render(<Child incrementBy={2} />);
-      });
-      expect(el.textContent).toBe('count:3');
-
-      await act(() => {
-        root.render(<Child incrementBy={1} />);
-      });
-      expect(el.textContent).toBe('count:4');
-    });
-  }
-
   it('should not support setState in componentWillUnmount', async () => {
     let subscription;
     class A extends React.Component {

packages/react-dom/src/__tests__/ReactDOMServerIntegrationElements-test.js

@@ -627,33 +627,20 @@ describe('ReactDOMServerIntegration', () => {
         checkFooDiv(await render(<ClassComponent />));
       });
 
-      if (require('shared/ReactFeatureFlags').disableModulePatternComponents) {
-        itThrowsWhenRendering(
-          'factory components',
-          async render => {
-            const FactoryComponent = () => {
-              return {
-                render: function () {
-                  return <div>foo</div>;
-                },
-              };
-            };
-            await render(<FactoryComponent />, 1);
-          },
-          'Objects are not valid as a React child (found: object with keys {render})',
-        );
-      } else {
-        itRenders('factory components', async render => {
+      itThrowsWhenRendering(
+        'factory components',
+        async render => {
           const FactoryComponent = () => {
             return {
               render: function () {
                 return <div>foo</div>;
               },
             };
           };
-          checkFooDiv(await render(<FactoryComponent />, 1));
-        });
-      }
+          await render(<FactoryComponent />, 1);
+        },
+        'Objects are not valid as a React child (found: object with keys {render})',
+      );
     });
 
     describe('component hierarchies', function () {

packages/react-dom/src/__tests__/ReactErrorBoundaries-test.internal.js

@@ -879,56 +879,6 @@ describe('ReactErrorBoundaries', () => {
     expect(container.firstChild.textContent).toBe('Caught an error: Hello.');
   });
 
-  // @gate !disableModulePatternComponents
-  it('renders an error state if module-style context provider throws in componentWillMount', async () => {
-    function BrokenComponentWillMountWithContext() {
-      return {
-        getChildContext() {
-          return {foo: 42};
-        },
-        render() {
-          return <div>{this.props.children}</div>;
-        },
-        UNSAFE_componentWillMount() {
-          throw new Error('Hello');
-        },
-      };
-    }
-    BrokenComponentWillMountWithContext.childContextTypes = {
-      foo: PropTypes.number,
-    };
-
-    const container = document.createElement('div');
-    const root = ReactDOMClient.createRoot(container);
-
-    await expect(async () => {
-      await act(() => {
-        root.render(
-          <ErrorBoundary>
-            <BrokenComponentWillMountWithContext />
-          </ErrorBoundary>,
-        );
-      });
-    }).toErrorDev([
-      'Warning: The <BrokenComponentWillMountWithContext /> component appears to be a function component that ' +
-        'returns a class instance. ' +
-        'Change BrokenComponentWillMountWithContext to a class that extends React.Component instead. ' +
-        "If you can't use a class try assigning the prototype on the function as a workaround. " +
-        '`BrokenComponentWillMountWithContext.prototype = React.Component.prototype`. ' +
-        "Don't use an arrow function since it cannot be called with `new` by React.",
-      ...gate(flags =>
-        flags.disableLegacyContext
-          ? [
-              'Warning: BrokenComponentWillMountWithContext uses the legacy childContextTypes API which was removed in React 19. Use React.createContext() instead.',
-              'Warning: BrokenComponentWillMountWithContext uses the legacy childContextTypes API which was removed in React 19. Use React.createContext() instead.',
-            ]
-          : [],
-      ),
-    ]);
-
-    expect(container.firstChild.textContent).toBe('Caught an error: Hello.');
-  });
-
   it('mounts the error message if mounting fails', async () => {
     function renderError(error) {
       return <ErrorMessage message={error.message} />;