babel-plugin-react-require/lib/index.js

module.exports = function babelPluginReactRequire({ types: t }) {
  const plugin = {
    visitor: {
      Program: {
        enter(path, { file }) {
          // Do nothing if React is already declared
          if (path.scope.hasBinding("React")) {
            return;
          }

          const ourNode = t.importDeclaration(
            [t.importDefaultSpecifier(t.identifier("React"))],
            t.stringLiteral("react")
          );

          // Add an import early, so that other plugins get to see it
          const [newPath] = path.unshiftContainer("body", ourNode);
          newPath.get("specifiers").forEach((specifier) => {
            path.scope.registerBinding("module", specifier);
          });
          file.set("ourPath", newPath);
        },

        exit(_, { file }) {
          // If our import is still intact and we haven't encountered any JSX in
          // the program, then we just remove it. There's an edge case, where
          // some other plugin could add JSX in its `Program.exit`, so our
          // `JSXOpeningElement` will trigger only after this method, but it's
          // likely that said plugin will also add a React import too.
          const ourPath = file.get("ourPath");
          if (ourPath && !file.get("hasJSX")) {
            if (!ourPath.removed) {
              ourPath.remove();
            }
            file.set("ourPath", undefined);
          }
        },
      },

      ImportDeclaration(path, { file }) {
        // Return early if this has nothing to do with React
        if (path.node.specifiers.every((x) => x.local.name !== "React")) {
          return;
        }

        // If our import is still intact and we encounter some other import
        // which also imports `React`, then we remove ours.
        const ourPath = file.get("ourPath");
        if (ourPath && path !== ourPath) {
          if (!ourPath.removed) {
            ourPath.remove();
          }
          file.set("ourPath", undefined);
        }
      },

      JSXOpeningElement(_, { file }) {
        file.set("hasJSX", true);
      },

      JSXOpeningFragment(_, { file }) {
        file.set("hasJSX", true);
      },
    },
  };

  return plugin;
};