From 4ccce6f58ed2595c89a1e872c5788c69489ab85d Mon Sep 17 00:00:00 2001
From: Nikita Stenin <stenin.nikita@gmail.com>
Date: Wed, 24 Aug 2022 14:14:41 +0300
Subject: [PATCH] [Fix] `ExportMap`: add caching after parsing for an ambiguous
 module

---
 src/ExportMap.js                         |  6 +++++-
 tests/files/typescript-declare-module.ts |  3 +++
 tests/src/core/getExports.js             | 21 +++++++++++++++++++++
 3 files changed, 29 insertions(+), 1 deletion(-)
 create mode 100644 tests/files/typescript-declare-module.ts

diff --git a/src/ExportMap.js b/src/ExportMap.js
index e18797a4d7..885801fbbb 100644
--- a/src/ExportMap.js
+++ b/src/ExportMap.js
@@ -346,7 +346,11 @@ ExportMap.for = function (context) {
   exportMap = ExportMap.parse(path, content, context);
 
   // ambiguous modules return null
-  if (exportMap == null) return null;
+  if (exportMap == null) {
+    log('ignored path due to ambiguous parse:', path);
+    exportCache.set(cacheKey, null);
+    return null;
+  }
 
   exportMap.mtime = stats.mtime;
 
diff --git a/tests/files/typescript-declare-module.ts b/tests/files/typescript-declare-module.ts
new file mode 100644
index 0000000000..8a9e304e91
--- /dev/null
+++ b/tests/files/typescript-declare-module.ts
@@ -0,0 +1,3 @@
+declare module "typescript-declare-module-foo" {
+  export const foo: string;
+}
diff --git a/tests/src/core/getExports.js b/tests/src/core/getExports.js
index 867644bc19..9b1100adfd 100644
--- a/tests/src/core/getExports.js
+++ b/tests/src/core/getExports.js
@@ -104,6 +104,27 @@ describe('ExportMap', function () {
     expect(imports.has('Bar')).to.be.true;
   });
 
+  it('should cache after parsing for an ambiguous module', function () {
+    const context = Object.assign({}, fakeContext, {
+      settings: {
+        'import/extensions': ['.js'],
+        'import/parsers': {
+          '@typescript-eslint/parser': ['.ts', '.tsx'],
+        },
+      },
+    });
+    const source = './typescript-declare-module.ts';
+    const parseSpy = sinon.spy(ExportMap, 'parse');
+
+    expect(ExportMap.get(source, context)).to.be.null;
+
+    ExportMap.get(source, context);
+
+    expect(parseSpy.callCount).to.equal(1);
+
+    parseSpy.restore();
+  });
+
   context('deprecation metadata', function () {
 
     function jsdocTests(parseContext, lineEnding) {