no-unused-modules.js

/**
 * @fileOverview Ensures that modules contain exports and/or all
 * modules are consumed within other modules.
 * @author René Fermann
 */

import Exports, { recursivePatternCapture } from '../ExportMap';
import { getFileExtensions } from 'eslint-module-utils/ignore';
import resolve from 'eslint-module-utils/resolve';
import visit from 'eslint-module-utils/visit';
import docsUrl from '../docsUrl';
import { dirname, join } from 'path';
import readPkgUp from 'read-pkg-up';
import values from 'object.values';
import includes from 'array-includes';

let FileEnumerator;
let listFilesToProcess;

try {
  ({ FileEnumerator } = require('eslint/use-at-your-own-risk'));
} catch (e) {
  try {
    // has been moved to eslint/lib/cli-engine/file-enumerator in version 6
    ({ FileEnumerator } = require('eslint/lib/cli-engine/file-enumerator'));
  } catch (e) {
    try {
      // eslint/lib/util/glob-util has been moved to eslint/lib/util/glob-utils with version 5.3
      const { listFilesToProcess: originalListFilesToProcess } = require('eslint/lib/util/glob-utils');

      // Prevent passing invalid options (extensions array) to old versions of the function.
      // https://github.com/eslint/eslint/blob/v5.16.0/lib/util/glob-utils.js#L178-L280
      // https://github.com/eslint/eslint/blob/v5.2.0/lib/util/glob-util.js#L174-L269
      listFilesToProcess = function (src, extensions) {
        return originalListFilesToProcess(src, {
          extensions,
        });
      };
    } catch (e) {
      const { listFilesToProcess: originalListFilesToProcess } = require('eslint/lib/util/glob-util');
      
      listFilesToProcess = function (src, extensions) {
        const patterns = src.reduce((carry, pattern) => {
          return carry.concat(extensions.map((extension) => {
            return /\*\*|\*\./.test(pattern) ? pattern : `${pattern}/**/*${extension}`;
          }));
        }, src.slice());
    
        return originalListFilesToProcess(patterns);
      };
    }
  }
}

if (FileEnumerator) {
  listFilesToProcess = function (src, extensions) {
    const e = new FileEnumerator({
      extensions,
    });

    return Array.from(e.iterateFiles(src), ({ filePath, ignored }) => ({
      ignored,
      filename: filePath,
    }));
  };
}

const EXPORT_DEFAULT_DECLARATION = 'ExportDefaultDeclaration';
const EXPORT_NAMED_DECLARATION = 'ExportNamedDeclaration';
const EXPORT_ALL_DECLARATION = 'ExportAllDeclaration';
const IMPORT_DECLARATION = 'ImportDeclaration';
const IMPORT_NAMESPACE_SPECIFIER = 'ImportNamespaceSpecifier';
const IMPORT_DEFAULT_SPECIFIER = 'ImportDefaultSpecifier';
const VARIABLE_DECLARATION = 'VariableDeclaration';
const FUNCTION_DECLARATION = 'FunctionDeclaration';
const CLASS_DECLARATION = 'ClassDeclaration';
const IDENTIFIER = 'Identifier';
const OBJECT_PATTERN = 'ObjectPattern';
const TS_INTERFACE_DECLARATION = 'TSInterfaceDeclaration';
const TS_TYPE_ALIAS_DECLARATION = 'TSTypeAliasDeclaration';
const TS_ENUM_DECLARATION = 'TSEnumDeclaration';
const DEFAULT = 'default';

function forEachDeclarationIdentifier(declaration, cb) {
  if (declaration) {
    if (
      declaration.type === FUNCTION_DECLARATION ||
      declaration.type === CLASS_DECLARATION ||
      declaration.type === TS_INTERFACE_DECLARATION ||
      declaration.type === TS_TYPE_ALIAS_DECLARATION ||
      declaration.type === TS_ENUM_DECLARATION
    ) {
      cb(declaration.id.name);
    } else if (declaration.type === VARIABLE_DECLARATION) {
      declaration.declarations.forEach(({ id }) => {
        if (id.type === OBJECT_PATTERN) {
          recursivePatternCapture(id, (pattern) => {
            if (pattern.type === IDENTIFIER) {
              cb(pattern.name);
            }
          });
        } else {
          cb(id.name);
        }
      });
    }
  }
}

/**
 * List of imports per file.
 *
 * Represented by a two-level Map to a Set of identifiers. The upper-level Map
 * keys are the paths to the modules containing the imports, while the
 * lower-level Map keys are the paths to the files which are being imported
 * from. Lastly, the Set of identifiers contains either names being imported
 * or a special AST node name listed above (e.g ImportDefaultSpecifier).
 *
 * For example, if we have a file named foo.js containing:
 *
 *   import { o2 } from './bar.js';
 *
 * Then we will have a structure that looks like:
 *
 *   Map { 'foo.js' => Map { 'bar.js' => Set { 'o2' } } }
 *
 * @type {Map<string, Map<string, Set<string>>>}
 */
const importList = new Map();

/**
 * List of exports per file.
 *
 * Represented by a two-level Map to an object of metadata. The upper-level Map
 * keys are the paths to the modules containing the exports, while the
 * lower-level Map keys are the specific identifiers or special AST node names
 * being exported. The leaf-level metadata object at the moment only contains a
 * `whereUsed` property, which contains a Set of paths to modules that import
 * the name.
 *
 * For example, if we have a file named bar.js containing the following exports:
 *
 *   const o2 = 'bar';
 *   export { o2 };
 *
 * And a file named foo.js containing the following import:
 *
 *   import { o2 } from './bar.js';
 *
 * Then we will have a structure that looks like:
 *
 *   Map { 'bar.js' => Map { 'o2' => { whereUsed: Set { 'foo.js' } } } }
 *
 * @type {Map<string, Map<string, object>>}
 */
const exportList = new Map();

const visitorKeyMap = new Map();

const ignoredFiles = new Set();
const filesOutsideSrc = new Set();

const isNodeModule = path => {
  return /\/(node_modules)\//.test(path);
};

/**
 * read all files matching the patterns in src and ignoreExports
 *
 * return all files matching src pattern, which are not matching the ignoreExports pattern
 */
const resolveFiles = (src, ignoreExports, context) => {
  const extensions = Array.from(getFileExtensions(context.settings));

  const srcFiles = new Set();
  const srcFileList = listFilesToProcess(src, extensions);

  // prepare list of ignored files
  const ignoredFilesList =  listFilesToProcess(ignoreExports, extensions);
  ignoredFilesList.forEach(({ filename }) => ignoredFiles.add(filename));

  // prepare list of source files, don't consider files from node_modules
  srcFileList.filter(({ filename }) => !isNodeModule(filename)).forEach(({ filename }) => {
    srcFiles.add(filename);
  });
  return srcFiles;
};

/**
 * parse all source files and build up 2 maps containing the existing imports and exports
 */
const prepareImportsAndExports = (srcFiles, context) => {
  const exportAll = new Map();
  srcFiles.forEach(file => {
    const exports = new Map();
    const imports = new Map();
    const currentExports = Exports.get(file, context);
    if (currentExports) {
      const {
        dependencies,
        reexports,
        imports: localImportList,
        namespace,
        visitorKeys,
      } = currentExports;

      visitorKeyMap.set(file, visitorKeys);
      // dependencies === export * from
      const currentExportAll = new Set();
      dependencies.forEach(getDependency => {
        const dependency = getDependency();
        if (dependency === null) {
          return;
        }

        currentExportAll.add(dependency.path);
      });
      exportAll.set(file, currentExportAll);

      reexports.forEach((value, key) => {
        if (key === DEFAULT) {
          exports.set(IMPORT_DEFAULT_SPECIFIER, { whereUsed: new Set() });
        } else {
          exports.set(key, { whereUsed: new Set() });
        }
        const reexport =  value.getImport();
        if (!reexport) {
          return;
        }
        let localImport = imports.get(reexport.path);
        let currentValue;
        if (value.local === DEFAULT) {
          currentValue = IMPORT_DEFAULT_SPECIFIER;
        } else {
          currentValue = value.local;
        }
        if (typeof localImport !== 'undefined') {
          localImport = new Set([...localImport, currentValue]);
        } else {
          localImport = new Set([currentValue]);
        }
        imports.set(reexport.path, localImport);
      });

      localImportList.forEach((value, key) => {
        if (isNodeModule(key)) {
          return;
        }
        const localImport = imports.get(key) || new Set();
        value.declarations.forEach(({ importedSpecifiers }) =>
          importedSpecifiers.forEach(specifier => localImport.add(specifier))
        );
        imports.set(key, localImport);
      });
      importList.set(file, imports);

      // build up export list only, if file is not ignored
      if (ignoredFiles.has(file)) {
        return;
      }
      namespace.forEach((value, key) => {
        if (key === DEFAULT) {
          exports.set(IMPORT_DEFAULT_SPECIFIER, { whereUsed: new Set() });
        } else {
          exports.set(key, { whereUsed: new Set() });
        }
      });
    }
    exports.set(EXPORT_ALL_DECLARATION, { whereUsed: new Set() });
    exports.set(IMPORT_NAMESPACE_SPECIFIER, { whereUsed: new Set() });
    exportList.set(file, exports);
  });
  exportAll.forEach((value, key) => {
    value.forEach(val => {
      const currentExports = exportList.get(val);
      const currentExport = currentExports.get(EXPORT_ALL_DECLARATION);
      currentExport.whereUsed.add(key);
    });
  });
};

/**
 * traverse through all imports and add the respective path to the whereUsed-list
 * of the corresponding export
 */
const determineUsage = () => {
  importList.forEach((listValue, listKey) => {
    listValue.forEach((value, key) => {
      const exports = exportList.get(key);
      if (typeof exports !== 'undefined') {
        value.forEach(currentImport => {
          let specifier;
          if (currentImport === IMPORT_NAMESPACE_SPECIFIER) {
            specifier = IMPORT_NAMESPACE_SPECIFIER;
          } else if (currentImport === IMPORT_DEFAULT_SPECIFIER) {
            specifier = IMPORT_DEFAULT_SPECIFIER;
          } else {
            specifier = currentImport;
          }
          if (typeof specifier !== 'undefined') {
            const exportStatement = exports.get(specifier);
            if (typeof exportStatement !== 'undefined') {
              const { whereUsed } = exportStatement;
              whereUsed.add(listKey);
              exports.set(specifier, { whereUsed });
            }
          }
        });
      }
    });
  });
};

const getSrc = src => {
  if (src) {
    return src;
  }
  return [process.cwd()];
};

/**
 * prepare the lists of existing imports and exports - should only be executed once at
 * the start of a new eslint run
 */
let srcFiles;
let lastPrepareKey;
const doPreparation = (src, ignoreExports, context) => {
  const prepareKey = JSON.stringify({
    src: (src || []).sort(),
    ignoreExports: (ignoreExports || []).sort(),
    extensions: Array.from(getFileExtensions(context.settings)).sort(),
  });
  if (prepareKey === lastPrepareKey) {
    return;
  }

  importList.clear();
  exportList.clear();
  ignoredFiles.clear();
  filesOutsideSrc.clear();

  srcFiles = resolveFiles(getSrc(src), ignoreExports, context);
  prepareImportsAndExports(srcFiles, context);
  determineUsage();
  lastPrepareKey = prepareKey;
};

const newNamespaceImportExists = specifiers =>
  specifiers.some(({ type }) => type === IMPORT_NAMESPACE_SPECIFIER);

const newDefaultImportExists = specifiers =>
  specifiers.some(({ type }) => type === IMPORT_DEFAULT_SPECIFIER);

const fileIsInPkg = file => {
  const { path, pkg } = readPkgUp.sync({ cwd: file, normalize: false });
  const basePath = dirname(path);

  const checkPkgFieldString = pkgField => {
    if (join(basePath, pkgField) === file) {
      return true;
    }
  };

  const checkPkgFieldObject = pkgField => {
    const pkgFieldFiles = values(pkgField).map(value => join(basePath, value));
    if (includes(pkgFieldFiles, file)) {
      return true;
    }
  };

  const checkPkgField = pkgField => {
    if (typeof pkgField === 'string') {
      return checkPkgFieldString(pkgField);
    }

    if (typeof pkgField === 'object') {
      return checkPkgFieldObject(pkgField);
    }
  };

  if (pkg.private === true) {
    return false;
  }

  if (pkg.bin) {
    if (checkPkgField(pkg.bin)) {
      return true;
    }
  }

  if (pkg.browser) {
    if (checkPkgField(pkg.browser)) {
      return true;
    }
  }

  if (pkg.main) {
    if (checkPkgFieldString(pkg.main)) {
      return true;
    }
  }

  return false;
};

module.exports = {
  meta: {
    type: 'suggestion',
    docs: { url: docsUrl('no-unused-modules') },
    schema: [{
      properties: {
        src: {
          description: 'files/paths to be analyzed (only for unused exports)',
          type: 'array',
          minItems: 1,
          items: {
            type: 'string',
            minLength: 1,
          },
        },
        ignoreExports: {
          description:
            'files/paths for which unused exports will not be reported (e.g module entry points)',
          type: 'array',
          minItems: 1,
          items: {
            type: 'string',
            minLength: 1,
          },
        },
        missingExports: {
          description: 'report modules without any exports',
          type: 'boolean',
        },
        unusedExports: {
          description: 'report exports without any usage',
          type: 'boolean',
        },
      },
      not: {
        properties: {
          unusedExports: { enum: [false] },
          missingExports: { enum: [false] },
        },
      },
      anyOf:[{
        not: {
          properties: {
            unusedExports: { enum: [true] },
          },
        },
        required: ['missingExports'],
      }, {
        not: {
          properties: {
            missingExports: { enum: [true] },
          },
        },
        required: ['unusedExports'],
      }, {
        properties: {
          unusedExports: { enum: [true] },
        },
        required: ['unusedExports'],
      }, {
        properties: {
          missingExports: { enum: [true] },
        },
        required: ['missingExports'],
      }],
    }],
  },

  create: context => {
    const {
      src,
      ignoreExports = [],
      missingExports,
      unusedExports,
    } = context.options[0] || {};

    if (unusedExports) {
      doPreparation(src, ignoreExports, context);
    }

    const file = context.getPhysicalFilename ? context.getPhysicalFilename() : context.getFilename();

    const checkExportPresence = node => {
      if (!missingExports) {
        return;
      }

      if (ignoredFiles.has(file)) {
        return;
      }

      const exportCount = exportList.get(file);
      const exportAll = exportCount.get(EXPORT_ALL_DECLARATION);
      const namespaceImports = exportCount.get(IMPORT_NAMESPACE_SPECIFIER);

      exportCount.delete(EXPORT_ALL_DECLARATION);
      exportCount.delete(IMPORT_NAMESPACE_SPECIFIER);
      if (exportCount.size < 1) {
        // node.body[0] === 'undefined' only happens, if everything is commented out in the file
        // being linted
        context.report(node.body[0] ? node.body[0] : node, 'No exports found');
      }
      exportCount.set(EXPORT_ALL_DECLARATION, exportAll);
      exportCount.set(IMPORT_NAMESPACE_SPECIFIER, namespaceImports);
    };

    const checkUsage = (node, exportedValue) => {
      if (!unusedExports) {
        return;
      }

      if (ignoredFiles.has(file)) {
        return;
      }

      if (fileIsInPkg(file)) {
        return;
      }

      if (filesOutsideSrc.has(file)) {
        return;
      }

      // make sure file to be linted is included in source files
      if (!srcFiles.has(file)) {
        srcFiles = resolveFiles(getSrc(src), ignoreExports, context);
        if (!srcFiles.has(file)) {
          filesOutsideSrc.add(file);
          return;
        }
      }

      exports = exportList.get(file);

      // special case: export * from
      const exportAll = exports.get(EXPORT_ALL_DECLARATION);
      if (typeof exportAll !== 'undefined' && exportedValue !== IMPORT_DEFAULT_SPECIFIER) {
        if (exportAll.whereUsed.size > 0) {
          return;
        }
      }

      // special case: namespace import
      const namespaceImports = exports.get(IMPORT_NAMESPACE_SPECIFIER);
      if (typeof namespaceImports !== 'undefined') {
        if (namespaceImports.whereUsed.size > 0) {
          return;
        }
      }

      // exportsList will always map any imported value of 'default' to 'ImportDefaultSpecifier'
      const exportsKey = exportedValue === DEFAULT ? IMPORT_DEFAULT_SPECIFIER : exportedValue;

      const exportStatement = exports.get(exportsKey);

      const value = exportsKey === IMPORT_DEFAULT_SPECIFIER ? DEFAULT : exportsKey;

      if (typeof exportStatement !== 'undefined') {
        if (exportStatement.whereUsed.size < 1) {
          context.report(
            node,
            `exported declaration '${value}' not used within other modules`
          );
        }
      } else {
        context.report(
          node,
          `exported declaration '${value}' not used within other modules`
        );
      }
    };

    /**
     * only useful for tools like vscode-eslint
     *
     * update lists of existing exports during runtime
     */
    const updateExportUsage = node => {
      if (ignoredFiles.has(file)) {
        return;
      }

      let exports = exportList.get(file);

      // new module has been created during runtime
      // include it in further processing
      if (typeof exports === 'undefined') {
        exports = new Map();
      }

      const newExports = new Map();
      const newExportIdentifiers = new Set();

      node.body.forEach(({ type, declaration, specifiers }) => {
        if (type === EXPORT_DEFAULT_DECLARATION) {
          newExportIdentifiers.add(IMPORT_DEFAULT_SPECIFIER);
        }
        if (type === EXPORT_NAMED_DECLARATION) {
          if (specifiers.length > 0) {
            specifiers.forEach(specifier => {
              if (specifier.exported) {
                newExportIdentifiers.add(specifier.exported.name);
              }
            });
          }
          forEachDeclarationIdentifier(declaration, (name) => {
            newExportIdentifiers.add(name);
          });
        }
      });

      // old exports exist within list of new exports identifiers: add to map of new exports
      exports.forEach((value, key) => {
        if (newExportIdentifiers.has(key)) {
          newExports.set(key, value);
        }
      });

      // new export identifiers added: add to map of new exports
      newExportIdentifiers.forEach(key => {
        if (!exports.has(key)) {
          newExports.set(key, { whereUsed: new Set() });
        }
      });

      // preserve information about namespace imports
      const exportAll = exports.get(EXPORT_ALL_DECLARATION);
      let namespaceImports = exports.get(IMPORT_NAMESPACE_SPECIFIER);

      if (typeof namespaceImports === 'undefined') {
        namespaceImports = { whereUsed: new Set() };
      }

      newExports.set(EXPORT_ALL_DECLARATION, exportAll);
      newExports.set(IMPORT_NAMESPACE_SPECIFIER, namespaceImports);
      exportList.set(file, newExports);
    };

    /**
     * only useful for tools like vscode-eslint
     *
     * update lists of existing imports during runtime
     */
    const updateImportUsage = node => {
      if (!unusedExports) {
        return;
      }

      let oldImportPaths = importList.get(file);
      if (typeof oldImportPaths === 'undefined') {
        oldImportPaths = new Map();
      }

      const oldNamespaceImports = new Set();
      const newNamespaceImports = new Set();

      const oldExportAll = new Set();
      const newExportAll = new Set();

      const oldDefaultImports = new Set();
      const newDefaultImports = new Set();

      const oldImports = new Map();
      const newImports = new Map();
      oldImportPaths.forEach((value, key) => {
        if (value.has(EXPORT_ALL_DECLARATION)) {
          oldExportAll.add(key);
        }
        if (value.has(IMPORT_NAMESPACE_SPECIFIER)) {
          oldNamespaceImports.add(key);
        }
        if (value.has(IMPORT_DEFAULT_SPECIFIER)) {
          oldDefaultImports.add(key);
        }
        value.forEach(val => {
          if (val !== IMPORT_NAMESPACE_SPECIFIER &&
              val !== IMPORT_DEFAULT_SPECIFIER) {
            oldImports.set(val, key);
          }
        });
      });

      function processDynamicImport(source) {
        if (source.type !== 'Literal') {
          return null;
        }
        const p = resolve(source.value, context);
        if (p == null) {
          return null;
        }
        newNamespaceImports.add(p);
      }

      visit(node, visitorKeyMap.get(file), {
        ImportExpression(child) {
          processDynamicImport(child.source);
        },
        CallExpression(child) {
          if (child.callee.type === 'Import') {
            processDynamicImport(child.arguments[0]);
          }
        },
      });

      node.body.forEach(astNode => {
        let resolvedPath;

        // support for export { value } from 'module'
        if (astNode.type === EXPORT_NAMED_DECLARATION) {
          if (astNode.source) {
            resolvedPath = resolve(astNode.source.raw.replace(/('|")/g, ''), context);
            astNode.specifiers.forEach(specifier => {
              const name = specifier.local.name;
              if (specifier.local.name === DEFAULT) {
                newDefaultImports.add(resolvedPath);
              } else {
                newImports.set(name, resolvedPath);
              }
            });
          }
        }

        if (astNode.type === EXPORT_ALL_DECLARATION) {
          resolvedPath = resolve(astNode.source.raw.replace(/('|")/g, ''), context);
          newExportAll.add(resolvedPath);
        }

        if (astNode.type === IMPORT_DECLARATION) {
          resolvedPath = resolve(astNode.source.raw.replace(/('|")/g, ''), context);
          if (!resolvedPath) {
            return;
          }

          if (isNodeModule(resolvedPath)) {
            return;
          }

          if (newNamespaceImportExists(astNode.specifiers)) {
            newNamespaceImports.add(resolvedPath);
          }

          if (newDefaultImportExists(astNode.specifiers)) {
            newDefaultImports.add(resolvedPath);
          }

          astNode.specifiers.forEach(specifier => {
            if (specifier.type === IMPORT_DEFAULT_SPECIFIER ||
                specifier.type === IMPORT_NAMESPACE_SPECIFIER) {
              return;
            }
            newImports.set(specifier.imported.name, resolvedPath);
          });
        }
      });

      newExportAll.forEach(value => {
        if (!oldExportAll.has(value)) {
          let imports = oldImportPaths.get(value);
          if (typeof imports === 'undefined') {
            imports = new Set();
          }
          imports.add(EXPORT_ALL_DECLARATION);
          oldImportPaths.set(value, imports);

          let exports = exportList.get(value);
          let currentExport;
          if (typeof exports !== 'undefined') {
            currentExport = exports.get(EXPORT_ALL_DECLARATION);
          } else {
            exports = new Map();
            exportList.set(value, exports);
          }

          if (typeof currentExport !== 'undefined') {
            currentExport.whereUsed.add(file);
          } else {
            const whereUsed = new Set();
            whereUsed.add(file);
            exports.set(EXPORT_ALL_DECLARATION, { whereUsed });
          }
        }
      });

      oldExportAll.forEach(value => {
        if (!newExportAll.has(value)) {
          const imports = oldImportPaths.get(value);
          imports.delete(EXPORT_ALL_DECLARATION);

          const exports = exportList.get(value);
          if (typeof exports !== 'undefined') {
            const currentExport = exports.get(EXPORT_ALL_DECLARATION);
            if (typeof currentExport !== 'undefined') {
              currentExport.whereUsed.delete(file);
            }
          }
        }
      });

      newDefaultImports.forEach(value => {
        if (!oldDefaultImports.has(value)) {
          let imports = oldImportPaths.get(value);
          if (typeof imports === 'undefined') {
            imports = new Set();
          }
          imports.add(IMPORT_DEFAULT_SPECIFIER);
          oldImportPaths.set(value, imports);

          let exports = exportList.get(value);
          let currentExport;
          if (typeof exports !== 'undefined') {
            currentExport = exports.get(IMPORT_DEFAULT_SPECIFIER);
          } else {
            exports = new Map();
            exportList.set(value, exports);
          }

          if (typeof currentExport !== 'undefined') {
            currentExport.whereUsed.add(file);
          } else {
            const whereUsed = new Set();
            whereUsed.add(file);
            exports.set(IMPORT_DEFAULT_SPECIFIER, { whereUsed });
          }
        }
      });

      oldDefaultImports.forEach(value => {
        if (!newDefaultImports.has(value)) {
          const imports = oldImportPaths.get(value);
          imports.delete(IMPORT_DEFAULT_SPECIFIER);

          const exports = exportList.get(value);
          if (typeof exports !== 'undefined') {
            const currentExport = exports.get(IMPORT_DEFAULT_SPECIFIER);
            if (typeof currentExport !== 'undefined') {
              currentExport.whereUsed.delete(file);
            }
          }
        }
      });

      newNamespaceImports.forEach(value => {
        if (!oldNamespaceImports.has(value)) {
          let imports = oldImportPaths.get(value);
          if (typeof imports === 'undefined') {
            imports = new Set();
          }
          imports.add(IMPORT_NAMESPACE_SPECIFIER);
          oldImportPaths.set(value, imports);

          let exports = exportList.get(value);
          let currentExport;
          if (typeof exports !== 'undefined') {
            currentExport = exports.get(IMPORT_NAMESPACE_SPECIFIER);
          } else {
            exports = new Map();
            exportList.set(value, exports);
          }

          if (typeof currentExport !== 'undefined') {
            currentExport.whereUsed.add(file);
          } else {
            const whereUsed = new Set();
            whereUsed.add(file);
            exports.set(IMPORT_NAMESPACE_SPECIFIER, { whereUsed });
          }
        }
      });

      oldNamespaceImports.forEach(value => {
        if (!newNamespaceImports.has(value)) {
          const imports = oldImportPaths.get(value);
          imports.delete(IMPORT_NAMESPACE_SPECIFIER);

          const exports = exportList.get(value);
          if (typeof exports !== 'undefined') {
            const currentExport = exports.get(IMPORT_NAMESPACE_SPECIFIER);
            if (typeof currentExport !== 'undefined') {
              currentExport.whereUsed.delete(file);
            }
          }
        }
      });

      newImports.forEach((value, key) => {
        if (!oldImports.has(key)) {
          let imports = oldImportPaths.get(value);
          if (typeof imports === 'undefined') {
            imports = new Set();
          }
          imports.add(key);
          oldImportPaths.set(value, imports);

          let exports = exportList.get(value);
          let currentExport;
          if (typeof exports !== 'undefined') {
            currentExport = exports.get(key);
          } else {
            exports = new Map();
            exportList.set(value, exports);
          }

          if (typeof currentExport !== 'undefined') {
            currentExport.whereUsed.add(file);
          } else {
            const whereUsed = new Set();
            whereUsed.add(file);
            exports.set(key, { whereUsed });
          }
        }
      });

      oldImports.forEach((value, key) => {
        if (!newImports.has(key)) {
          const imports = oldImportPaths.get(value);
          imports.delete(key);

          const exports = exportList.get(value);
          if (typeof exports !== 'undefined') {
            const currentExport = exports.get(key);
            if (typeof currentExport !== 'undefined') {
              currentExport.whereUsed.delete(file);
            }
          }
        }
      });
    };

    return {
      'Program:exit': node => {
        updateExportUsage(node);
        updateImportUsage(node);
        checkExportPresence(node);
      },
      'ExportDefaultDeclaration': node => {
        checkUsage(node, IMPORT_DEFAULT_SPECIFIER);
      },
      'ExportNamedDeclaration': node => {
        node.specifiers.forEach(specifier => {
          checkUsage(node, specifier.exported.name);
        });
        forEachDeclarationIdentifier(node.declaration, (name) => {
          checkUsage(node, name);
        });
      },
    };
  },
};