fix(utils): export map cache is tainted by unreliable parse results

This change addresses and issue observed with the v9 upgrade, where the ExportMap Cache is being tainted with a bad export map, if the parse doesn't yield a `visitorKeys` (which can happen if an incompatible parser is used (e.g. og babel eslint)) for one run of the no-cycle rule.  If a subsequent test is run with a compatible parser, then the bad export map will be found in the cache and used instead of attempting to proceed with the parse.

I also updated the `getExports` test to use a valid parserPath, rather than a mocked one, so that the tests are acting on a valid parserPath.  Otherwise the export map won't be cached following this change.

src/exportMap/builder.js

@@ -92,7 +92,11 @@ export default class ExportMapBuilder {
 
     exportMap.mtime = stats.mtime;
 
-    exportCache.set(cacheKey, exportMap);
+    // If the visitor keys were not populated, then we shouldn't save anything to the cache,
+    // since the parse results may not be reliable.
+    if (exportMap.visitorKeys) {
+      exportCache.set(cacheKey, exportMap);
+    }
     return exportMap;
   }
 

tests/src/core/getExports.js

@@ -21,7 +21,7 @@ describe('ExportMap', function () {
     },
     {
       settings: {},
-      parserPath: 'babel-eslint',
+      parserPath: require.resolve('babel-eslint'),
     },
   );
 
@@ -41,6 +41,15 @@ describe('ExportMap', function () {
       .to.exist.and.equal(ExportMapBuilder.get('./named-exports', fakeContext));
   });
 
+  it('does not return a cached copy if the parse does not yield a visitor keys', function () {
+    const mockContext = {
+      ...fakeContext,
+      parserPath: 'not-real',
+    }
+    expect(ExportMapBuilder.get('./named-exports', mockContext))
+      .to.exist.and.not.equal(ExportMapBuilder.get('./named-exports', mockContext));
+  });
+
   it('does not return a cached copy after modification', (done) => {
     const firstAccess = ExportMapBuilder.get('./mutator', fakeContext);
     expect(firstAccess).to.exist;