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fix(js): use Set for O(1) package.json root lookup #33757

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FrozenPandaz merged 1 commit into from
Dec 8, 2025
Merged

fix(js): use Set for O(1) package.json root lookup #33757

FrozenPandaz merged 1 commit into from
Dec 8, 2025

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@adwait1290
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@adwait1290 adwait1290 commented Dec 8, 2025 •
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Current Behavior

In buildExplicitPackageJsonDependencies, for every file in the project file map, we call isPackageJsonAtProjectRoot which uses Array.find():

function isPackageJsonAtProjectRoot(nodes, fileName) {
  return (
    fileName.endsWith('package.json') &&
    nodes.find((projectNode) =>  // O(n) lookup per file!
      joinPathFragments(projectNode.root, 'package.json') === fileName
    )
  );
}

This is O(files × projects) complexity.

Expected Behavior

Build a Set of valid package.json paths once, then use O(1) Set lookup:

const projectPackageJsonPaths = new Set(
  Object.values(ctx.projects).map((project) =>
    joinPathFragments(project.root, 'package.json')
  )
);

// Later: O(1) lookup
if (projectPackageJsonPaths.has(f.file)) { ... }

Performance Impact

Before (Array.find per file):       After (Set.has):
┌─────────────────────────┐         ┌─────────────────────────┐
│ For each file:          │         │ Build Set once:         │
│   nodes.find(...)       │         │   O(projects)           │
│   O(projects) per file  │         └───────────┬─────────────┘
└───────────┬─────────────┘                     │
            │                                   ▼
            ▼                         ┌─────────────────────────┐
┌─────────────────────────┐         │ For each file:          │
│ Total: O(files×projects)│         │   Set.has(f.file)       │
└─────────────────────────┘         │   O(1) per file         │
                                    └───────────┬─────────────┘
                                                │
                                                ▼
                                    ┌─────────────────────────┐
                                    │ Total: O(files+projects)│
                                    └─────────────────────────┘

Example: With 5,000 files and 200 projects:

  • Before: 5,000 × 200 = 1,000,000 comparisons (worst case)
  • After: 200 (build Set) + 5,000 (lookups) = 5,200 operations

Additional Changes

  • Replaced forEach with for...in/of loops
  • Removed unused isPackageJsonAtProjectRoot function
  • Removed unused ProjectConfiguration import
  • Net reduction of 7 lines

Why Accept This PR

  1. Significant complexity reduction: O(n²) → O(n)
  2. Hot path: Called during dependency graph construction for every file
  3. Cleaner code: Removed unused function, fewer lines

Related Issue(s)

Contributes to #32265

Merge Dependencies

This PR has no dependencies and can be merged independently.

@adwait1290
perf(js): use Set for O(1) package.json root lookup
8148d64 
Previously, isPackageJsonAtProjectRoot used Array.find() to check if
a file is a package.json at a project root, resulting in O(n) lookup
per file where n is number of projects.

Now builds a Set of valid package.json paths once at the start,
reducing lookup from O(files × projects) to O(files + projects).

Also:
- Replaced forEach with for...in/of loops
- Removed unused isPackageJsonAtProjectRoot function
- Removed unused ProjectConfiguration import
@adwait1290 adwait1290 requested a review from a team as a code owner December 8, 2025 07:30
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@JamesHenry
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JamesHenry commented Dec 8, 2025

Thank you @adwait1290 please make this the last one for now and give the team chance to review

@adwait1290
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adwait1290 commented Dec 8, 2025

@JamesHenry will pause for now; let me know what I can do to help get these reviewed.

@FrozenPandaz FrozenPandaz changed the title perf(js): use Set for O(1) package.json root lookup fix(js): use Set for O(1) package.json root lookup Dec 8, 2025
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☁️ Nx Cloud last updated this comment at 2025-12-08 20:57:08 UTC

FrozenPandaz
FrozenPandaz approved these changes Dec 8, 2025
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Thank you for your contribution! LGTM 🎉

@FrozenPandaz FrozenPandaz merged commit 5d597ee into nrwl:master Dec 8, 2025
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JamesHenry commented Dec 9, 2025

@adwait1290 We're grateful for the contributions, however no team/project is expecting 25 PRs from a single contributor in rapid succession and so rather than adding to a growing list, it makes sense to wait a few days to allow us to work through the existing ones. You can that including yours we have 150+ PRs open that all need to be reviewed and we're working on it

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github-actions bot commented Dec 15, 2025

This pull request has already been merged/closed. If you experience issues related to these changes, please open a new issue referencing this pull request.

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@adwait1290 @JamesHenry @FrozenPandaz