Error while loading rule 'import/no-unused-modules': Cannot read properties of undefined (reading 'get')

[magic-m-johnson]

was closed here, but is still randomly occurring today:

#2388

[ljharb]

Can you provide more info? The code being linted, or a repro repo?

[iz-podpolja]

This occurs for us only when run through LSP, I cannot provide a full repro, but the following patch fixes it locally:

diff --git a/lib/rules/no-unused-modules.js b/lib/rules/no-unused-modules.js
index 098f72a5340a706e0652a272e96d473b6abc6051..d248367f5c4ab68d69806a762b8a90cdeb11e43b 100644
--- a/lib/rules/no-unused-modules.js
+++ b/lib/rules/no-unused-modules.js
@@ -525,7 +525,7 @@ module.exports = {
           exports = exportList.get(file);
 
           // special case: export * from
-          var exportAll = exports.get(EXPORT_ALL_DECLARATION);
+          var exportAll = exports && exports.get(EXPORT_ALL_DECLARATION);
           if (typeof exportAll !== 'undefined' && exportedValue !== IMPORT_DEFAULT_SPECIFIER) {
             if (exportAll.whereUsed.size > 0) {
               return;
@@ -533,7 +533,7 @@ module.exports = {
           }
 
           // special case: namespace import
-          var namespaceImports = exports.get(IMPORT_NAMESPACE_SPECIFIER);
+          var namespaceImports = exports && exports.get(IMPORT_NAMESPACE_SPECIFIER);
           if (typeof namespaceImports !== 'undefined') {
             if (namespaceImports.whereUsed.size > 0) {
               return;
@@ -543,7 +543,7 @@ module.exports = {
           // exportsList will always map any imported value of 'default' to 'ImportDefaultSpecifier'
           var exportsKey = exportedValue === DEFAULT ? IMPORT_DEFAULT_SPECIFIER : exportedValue;
 
-          var exportStatement = exports.get(exportsKey);
+          var exportStatement = exports && exports.get(exportsKey);
 
           var value = exportsKey === IMPORT_DEFAULT_SPECIFIER ? DEFAULT : exportsKey;

[ljharb]

What's LSP?

Thanks, that helps; I'll take a look (altho I'm still confused why exports there would be falsy)

[ljharb]

In order to fix this, I need a regression test. Are you sure you can't provide some code that triggers this?

[iz-podpolja]

What's LSP?

Thanks, that helps; I'll take a look (altho I'm still confused why exports there would be falsey)

LSP -> Language Server Protocol, in my particular case, eslint was run by a VSCode extension.

In order to fix this, I need a regression test. Are you sure you can't provide some code that triggers this?

Yeah unfortunately it's a big private monorepo, and my attempts to distill the issue were in vain

[ljharb]

Is this an issue with code in the middle of typing? or is it with code that parses correctly?

[iz-podpolja]

At least in my case, it's enough to open the file to cause eslint service in the IDE to crash in these specific places

[ljharb]

Gotcha - and there's no way to share even the code in just that file? You're welcome to send it to me privately, or let me see it over screen share, if you prefer not to post it publicly.

[iz-podpolja]

@ljharb It's not one file though - it's actually any file triggering eslint in the whole monorepo. As for the sharing session - I'd need to ask - however I'm pretty sure I could send you at the very least some screencasts of the issue and relevant config files. Perhaps Thursday~ish?

[ljharb]

Sounds good. If it’s really any file - and assuming there’s not something consistent across every file (like, every file uses jsx, or every file is native ESM, or something) then that suggests it’s part of the eslint config, which may include a custom parser.

Could you provide your eslint config?

[olsonpm]

I'm finally digging into this now. In my case it's a vscode error that prompts upon copy/pasting a file. Reloading the window resolves it but hopefully I can get a PR or at least a failing test today.

[olsonpm]

Okay I've distilled the issue at least from how I encounter it

$ git clone git@github.com:olsonpm/repro.git
$ cd repro
$ git checkout eslint-plugin-import-issue-2866
$ npm ci
$ code .
# then when in vscode, select the file `dep.mjs` and copy/paste it to create `dep copy.mjs`
# at this point you'll trigger the error

Error in vscode

[Error - 10:55:46 AM] An unexpected error occurred:
[Error - 10:55:46 AM] TypeError: Cannot read properties of undefined (reading 'get')
Occurred while linting /path/to/repro/dep copy.mjs:1
Rule: "import/no-unused-modules"
    at checkUsage (/path/to/repro/node_modules/eslint-plugin-import/lib/rules/no-unused-modules.js:533:35)
    at ExportDefaultDeclaration (/path/to/repro/node_modules/eslint-plugin-import/lib/rules/no-unused-modules.js:933:13)
    at ruleErrorHandler (/path/to/repro/node_modules/eslint/lib/linter/linter.js:1076:28)
    at /path/to/repro/node_modules/eslint/lib/linter/safe-emitter.js:45:58
    at Array.forEach (<anonymous>)
    at Object.emit (/path/to/repro/node_modules/eslint/lib/linter/safe-emitter.js:45:38)
    at NodeEventGenerator.applySelector (/path/to/repro/node_modules/eslint/lib/linter/node-event-generator.js:297:26)
    at NodeEventGenerator.applySelectors (/path/to/repro/node_modules/eslint/lib/linter/node-event-generator.js:326:22)
    at NodeEventGenerator.enterNode (/path/to/repro/node_modules/eslint/lib/linter/node-event-generator.js:340:14)
    at CodePathAnalyzer.enterNode (/path/to/repro/node_modules/eslint/lib/linter/code-path-analysis/code-path-analyzer.js:803:23)

---

I looked into creating a failing test but it's simply the file not existing exportList at the point it's traversed - i.e. Program:exit hasn't been called yet.

LJharb - if you have a suggestion on how you'd want a fix implemented then I'm willing to create a PR.

[ljharb]

hmm, that's not reproducing the error for me. what version of vscode do you have? I have 1.85.1.

[olsonpm]

yeah 1.85.1 on my end too. Tomorrow I'll get this in a clean ubuntu vm to rule out settings/plugins.

[olsonpm]

Okay I was able to reproduce in a fresh ubuntu instance. Not sure if you feel like messing with an image but here's a link with everything ready. After importing the image into virtualbox, I reproduced the error via

# close initial "Online Accounts" window and open terminal
$ cd git-repos/personal/repro/
$ rm dep\ copy.mjs
$ code .
# default keyring nonsense pops up.  pass = "testing"
# close the "dep\ copy.mjs" tab
# ctrl+shift+p -> reload window
# in left file panel, select 'dep.mjs' then ctrl+c -> ctrl+v
# error will show up in output