import-js/eslint-plugin-import

`import/namespace` is very slow

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#2340 opened on Dec 29, 2021

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 (26 comments) (31 reactions) (0 assignees)JavaScript (4,946 stars) (1,540 forks)batch import
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Description

In our medium-sized mixed JS/TS codebase, specifically disabling import/namespace significantly reduced our lint times. I haven't found this mentioned by anyone else, so I wanted to share the finding, because it was very surprising.

Our prior configuration ran like this:

Rule                              | Time (ms) | Relative
:---------------------------------|----------:|--------:
import/namespace                  |  5762.140 |    64.7%
import/no-relative-packages       |   673.212 |     7.6%
import/named                      |   471.116 |     5.3%
import/no-extraneous-dependencies |   317.690 |     3.6%
import/extensions                 |   254.717 |     2.9%
Done in 14.53s.

I always assumed this was just the "first rule tax" while the export map is created, but adding "import/namespace": "off" did this for us:

Rule                              | Time (ms) | Relative
:---------------------------------|----------:|--------:
import/named                      |  1459.028 |    33.6%
import/no-relative-packages       |   577.911 |    13.3%
import/no-duplicates              |   408.152 |     9.4%
import/extensions                 |   401.591 |     9.2%
import/no-extraneous-dependencies |   276.880 |     6.4%
Done in 9.44s.

Given we already use "import/no-namespace": "error", this rule wasn't doing anything for us anyway. With one line we've managed to significantly improve IDE responsiveness.

Contributor guide

Tech stack
javascripttypescriptnodejs
Domain
developer experienceperformancetooling
Issue type
performance
DifficultyEstimated implementation difficulty for a new contributor, from 1 for very small changes to 5 for expert-level work.
3
Estimated timeA rough time range for an experienced contributor to investigate, implement, test, and prepare a pull request.
over 1 week
Activity statusHow available the issue appears right now: fresh, active, stale, blocked, or waiting on maintainer input.
active
ClarityHow clearly the issue explains the expected change, acceptance criteria, and next step.
mostly clear
Prerequisites
ESLint plugin developmentNode.js profiling basics
Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.
30
Research direction
Investigate the implementation of the import/namespace rule in lib/rules/namespace.ts. Profile the rule using ESLint's timing feature to identify bottlenecks. Check if there is redundant resolution of namespace exports. Consider caching the export map or optimizing the deep traversal of namespace objects. Also review the existing discussion in the issue for potential leads. The user reports that disabling the rule greatly improves lint times, suggesting the rule's cost is high.