Find exports for underscore.js

Because of how their exported module is constructed, finding named
exports turned out to be a little bit of a challenge. But through a
combination of remembering the defined objects, plus using a regexp to
find the actual `module.exports`, I was able to get it working.

Because this ended up being a little brittle, I added a regression test
for a bug that I was close to introducing.

lib/__tests__/findExports-test.js

@@ -225,3 +225,46 @@ module.exports = React;
     hasDefault: true,
   });
 });
+
+it('finds underscore exports', () => {
+  expect(findExports(`
+    (function() {
+      var _ = function() {};
+
+      if (typeof exports !== 'undefined') {
+        if (typeof module !== 'undefined' && module.exports) {
+          exports = module.exports = _;
+        }
+        exports._ = _;
+      } else {
+        root._ = _;
+      }
+
+      _.debounce = function() {};
+      _.pluck = function() {};
+    })();
+  `)).toEqual({
+    named: [
+      'debounce',
+      'pluck',
+    ],
+    hasDefault: true,
+  });
+});
+
+it('does not fail for inner exports that are not objects', () => {
+  expect(findExports(`
+    (function() {
+      var snowden = '';
+
+      if (typeof exports !== 'undefined') {
+        if (typeof module !== 'undefined' && module.exports) {
+          exports = module.exports = snowden;
+        }
+      }
+    })();
+  `)).toEqual({
+    named: [],
+    hasDefault: true,
+  });
+});

lib/findExports.js

@@ -101,20 +101,20 @@ function findDefinedNames(node, definedNames) {
     return;
   }
   node.declarations.forEach(({ id, init }) => {
-    if (!init || init.type !== 'ObjectExpression') {
+    if (!init) {
       return;
     }
-    definedNames[id.name] = // eslint-disable-line no-param-reassign
-      init.properties.map(({ key }) => key.name).filter(Boolean);
+    if (init.type === 'ObjectExpression') {
+      definedNames[id.name] = // eslint-disable-line no-param-reassign
+        init.properties.map(({ key }) => key.name).filter(Boolean);
+    } else if (init.type === 'FunctionExpression') {
+      definedNames[id.name] = []; // eslint-disable-line no-param-reassign
+    }
   });
 }
 
-function findNamedExports(nodes, absPathToFile) {
+function findNamedExports(nodes, absPathToFile, definedNames) {
   const result = [];
-  const definedNames = {};
-  nodes.forEach((node) => {
-    findDefinedNames(node, definedNames);
-  });
   nodes.forEach((node) => {
     result.push(...findESNamedExports(node));
     result.push(...findCommonJSExports(node, definedNames,
@@ -148,9 +148,13 @@ function hasDefaultExport(nodes) {
   });
 }
 
-const DEFAULT_EXPORT_MATCH = /\smodule\.exports\s*=/;
-function hasRawModuleExportsMatch(data) {
-  return DEFAULT_EXPORT_MATCH.test(data);
+const DEFAULT_EXPORT_PATTERN = /\smodule\.exports\s*=\s*(\w+)/;
+function findRawModuleExportIdentifier(data) {
+  const match = data.match(DEFAULT_EXPORT_PATTERN);
+  if (match) {
+    return match[1];
+  }
+  return undefined;
 }
 
 function findRootNodes(ast) {
@@ -179,9 +183,21 @@ function findRootNodes(ast) {
 export default function findExports(data, absPathToFile) {
   const ast = parse(data);
   const rootNodes = findRootNodes(ast);
+  const definedNames = {};
+  rootNodes.forEach((node) => {
+    findDefinedNames(node, definedNames);
+  });
+  const named = findNamedExports(rootNodes, absPathToFile, definedNames);
+  let hasDefault = hasDefaultExport(rootNodes);
+  if (!hasDefault) {
+    const rawExportedId = findRawModuleExportIdentifier(data);
+    hasDefault = !!rawExportedId;
+    if (!named.length) {
+      named.push(...(definedNames[rawExportedId] || []));
+    }
+  }
   return {
-    named: findNamedExports(rootNodes, absPathToFile),
-    hasDefault: hasDefaultExport(rootNodes) ||
-      hasRawModuleExportsMatch(data),
+    named,
+    hasDefault,
   };
 }