eslint-plugin-ft-flow/dist/rules/requireTypesAtTop.js.flow

Flowtype linting rules for ESLint by flow-typed

import _ from 'lodash';

const schema = [
  {
    enum: ['always', 'never'],
    type: 'string',
  },
];

const create = (context) => {
  const always = (context.options[0] || 'always') === 'always';

  if (always) {
    const sourceCode = context.getSourceCode();

    // nodes representing type and import declarations
    const ignoredNodes = [
      // import ...
      (node) => node.type === 'ImportDeclaration',

      // export type Foo = ...
      // export opaque type Foo = ...
      // export type Foo from ...
      // export opaque type Foo from ...
      (node) => node.type === 'ExportNamedDeclaration' && node.exportKind === 'type',

      // type Foo = ...
      (node) => node.type === 'TypeAlias',

      // opaque type Foo = ...
      (node) => node.type === 'OpaqueType',
    ];

    const isIgnoredNode = (node) => {
      for (const predicate of ignoredNodes) {
        if (predicate(node)) {
          return true;
        }
      }

      return false;
    };

    let regularCodeStartRange;

    for (const node of sourceCode.ast.body) {
      if (!isIgnoredNode(node)) {
        regularCodeStartRange = node.range;
        break;
      }
    }

    if (!_.isArray(regularCodeStartRange)) {
      // a source with only ignored nodes
      return {};
    }

    return {
      'TypeAlias, OpaqueType': (node) => {
        if (node.range[0] > regularCodeStartRange[0]) {
          context.report({
            message: 'All type declaration must be at the top of the file, after any import declarations.',
            node,
          });
        }
      },
    };
  }

  return {};
};

export default {
  create,
  meta: {
    schema,
  },
};