istanbuljs/nyc

Add a new `profile` option.

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#144 opened on Jan 19, 2016

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Great First Contributionenhancementhelp wanted

Description

Since stumbling into this process while trying to improve NYC's performance, I have continued to discover ways that coverage data can answer questions beyond "is it tested?".

I think it would be really interesting to add a new profile command.

The signature would be:

nyc profile <profiled-dependency> <command ...>

It would not add coverage for the local library, but the dependency.

Assume some module uses AVA as it's test runner:

$ nyc profile ava ./node_modules/.bin/ava test/*.js

This executes ava ./node_modules/.bin/ava test/*.js using NYC's spawn-wrap goodness, but instead of excluding node_modules, our require hook hooks everything in node_modules/ava/ (but not node_modules/ava/node_modules).

This basically turns nyc into a quick and dirty profiling tool, allowing you to identify hot loops in your code and identify lines that are only used by your test suite.

Contributor guide

Tech stack
javascriptnodejs
Domain
clitooling
Issue type
feature
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.
1-2 days
Activity statusHow available the issue appears right now: fresh, active, stale, blocked, or waiting on maintainer input.
stale
ClarityHow clearly the issue explains the expected change, acceptance criteria, and next step.
mostly clear
Prerequisites
Node.js basicsUnderstanding of NYC's spawn wrapFamiliarity with require hooks
Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.
45
Research direction
Examine the NYC codebase, particularly the spawn wrap and require hook mechanisms in the 'bin' and 'lib' directories. Look at how existing commands like 'report' and 'check coverage' are structured to model the new 'profile' command. Review the linked PR #143 and the discussion around profiling to understand the desired behavior. The 'profile' command should hook only the specified dependency's module and exclude its sub dependencies, similar to how NYC excludes node modules by default.