[Fix] extensions: avoid crashing on partially typed import/export statements

Fixes #2118.

Author: ljharb

Diff for: CHANGELOG.md

@@ -8,6 +8,7 @@ This change log adheres to standards from [Keep a CHANGELOG](http://keepachangel
 
 ### Fixed
 - [`no-duplicates`]: ensure autofix avoids excessive newlines ([#2028], thanks [@ertrzyiks])
+- [`extensions`]: avoid crashing on partially typed import/export statements ([#2118], thanks [@ljharb])
 
 ## [2.23.4] - 2021-05-29
 
@@ -1043,6 +1044,7 @@ for info on changes for earlier releases.
 [#211]: https://github.com/benmosher/eslint-plugin-import/pull/211
 [#164]: https://github.com/benmosher/eslint-plugin-import/pull/164
 [#157]: https://github.com/benmosher/eslint-plugin-import/pull/157
+[#2118]: https://github.com/benmosher/eslint-plugin-import/issues/2118
 [#2067]: https://github.com/benmosher/eslint-plugin-import/issues/2067
 [#2056]: https://github.com/benmosher/eslint-plugin-import/issues/2056
 [#2063]: https://github.com/benmosher/eslint-plugin-import/issues/2063

Diff for: src/rules/extensions.js

@@ -136,8 +136,8 @@ module.exports = {
     }
 
     function checkFileExtension(source) {
-      // bail if the declaration doesn't have a source, e.g. "export { foo };"
-      if (!source) return;
+      // bail if the declaration doesn't have a source, e.g. "export { foo };", or if it's only partially typed like in an editor
+      if (!source || !source.value) return;
 
       const importPathWithQueryString = source.value;