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Perf: Optimize ignoreModule calls in no-cycle #2612

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Perf: Optimize ignoreModule calls in no-cycle #2612

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Perf: Optimize ignoreModule calls in no-cycle
DHedgecock Dec 12, 2022
f1feb78
Update src/rules/no-cycle.js
DHedgecock Dec 12, 2022
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45 changes: 40 additions & 5 deletions src/rules/no-cycle.js
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Original file line number Diff line number Diff line change
Expand Up @@ -10,6 +10,16 @@ import moduleVisitor, { makeOptionsSchema } from 'eslint-module-utils/moduleVisi
import docsUrl from '../docsUrl';

const traversed = new Set();
/**
* Cache of resolved paths for faster subsequent lookups
* @type {{ [importPath: string]: string }}
*/
const resolvedPaths = {};
/**
* Cache of external module evaluations for faster subsequent lookups
* @type {{ [resolvedPath: string]: boolean }}
*/
const externalModules = {};

Comment on lines +13 to 23
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these caches need to be cleared in the same place traversed is

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The Program:exit hook is called at the exit of each file, so clearing the caches there cut the number of cache hits in our repo by about 50% (although it only added ~45s to our repo test case)

The high level attempt at this update was to quick filter down to "maybe external" modules like 'react', '@reduxjs/toolkit' or '@/some/alias/path' - where those resolved paths can be safely cached across files 馃

Is that possible to accomplish with any of the existing data structures?

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oh, hmm - you're right, it's less about clearing it after the file and more about clearing it after the "run" - since in editors, eslint can be long-running.

I think that in every file, there could be a different resolver, so the cache would have to be on the resolver and the resolver config and the fully normalized file path, i think?

module.exports = {
meta: {
Expand Down Expand Up @@ -52,11 +62,36 @@ module.exports = {

const options = context.options[0] || {};
const maxDepth = typeof options.maxDepth === 'number' ? options.maxDepth : Infinity;
const ignoreModule = (name) => options.ignoreExternal && isExternalModule(
name,
resolve(name, context),
context,
);

const ignoreModule = (name) => {
// Note: This fn is optimized to eliminate call time because it may be
// called hundreds of thousands of times during a full repository lint run
// and can add minutes to the total time in large codebases

// Low cost evaluation; do not ignore if not opted in or module starts
// with a relative path
// NOTE: skipping further resolve codepath also ensures that only unique
// import paths are set in resolvedPaths, eg "./index.js", or "../file.js"
// should not be stored because there could be duplicates that resolve to
// different paths
if (!options.ignoreExternal || name[0] === '.') return false;
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couldn't a resolver choose to configure a relative path as external?

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馃 I suppose so, there's probably some monorepo setup out there like that...

I think removing this assumption means that we can't confidently cache the resolved module path we looked up because then there could be duplicate import paths that resolve to different files (eg import paths of './index.js').

Trying to approach this from a different angle: The current time to determine if a module is "external" is the performance bottleneck and this PR is attempting to short circuit that whenever possible.

Do you have suggestions on an approach?

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What if the no-cycle rule option ignoreExternal could be a boolean or a regex, and if it's a regex it's used for this short circuit?

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I'm not sure what the best configuration fields are, but doing a quick test with a regex short circuit has about the same performance improvement as the cache implementation.

Alternative approach tested:

    const ignoreModule = (name) => {
      if (!options.ignoreExternal) return false;

      if (options.ignoreExternalRegex) {
        return options.ignoreExternalRegex.test(name);
      }

      const path = resolve(name, context);

      let isExternal = externalModules[path];
      if (isExternal === undefined) {
        isExternal = isExternalModule(name, path, context);
        externalModules[path] = isExternal;
      }
      
      return isExternal;
    };

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Maybe the better question is, why is isExternalModule slow?

Perhaps the node and webpack resolvers can add a cache there, rather than inside the main plugin?


// High cost evaluation; cache evaluations of resolve() and
// isExternalModule() calls for faster subsequent lookups
let path = resolvedPaths[name];
if (path === undefined) {
path = resolve(name, context);
resolvedPaths[name] = path;
}

let isExternal = externalModules[path];
if (isExternal === undefined) {
isExternal = isExternalModule(name, path, context);
externalModules[path] = isExternal;
}

return isExternal;
};

function checkSourceValue(sourceNode, importer) {
if (ignoreModule(sourceNode.value)) {
Expand Down