bumpdiff

bumpdiff

A patch bump that starts spawning shells looks exactly like one that fixes a typo.

npx bumpdiff chalk 4.1.2 5.0.0

  chalk 4.1.2 to 5.0.0

  ! it now reads machine and user details, and the previous version did not
      import os from 'node:os';
      source/vendor/supports-color/index.js
  . published 119 days after the previous version

  12 files, 40 kB, published by sindresorhus

  1 change(s) worth reading before you upgrade.
  These are changes, not verdicts. Most have an ordinary explanation.

A version number tells you what the author intended. It tells you nothing about what changed in what the package can do.

What it looks at

Install scripts	A postinstall appearing is the loudest thing here, because it runs on every machine that types npm install, before anyone has read a line.
Capabilities	Spawning processes, opening sockets, writing files, evaluating code at runtime, reading the environment. Gained, not merely present.
Hosts	A new domain in the source, ignoring the ones every package mentions.
The publisher	A release published by somebody who has never published this package before. No amount of reading the code gives you that.
Provenance	A package that carried npm provenance and stopped is now being published by hand rather than from a workflow.
Shape	New binaries, files that became single enormous lines, a patch that doubled in size.

Nothing runs, nothing lands on disk

The tarballs are fetched into memory, gunzipped, and read with a tar parser written by hand in this repository. No install script is ever given the chance to execute, and nothing is written anywhere.

That is also why it has no dependencies. A tool whose job is to inspect packages you have not decided to trust should not install a tree of its own to do the inspecting. A supply chain inspector with a supply chain is an argument in a circle.

Changes, never verdicts

It will never call a package malicious. That word requires knowing intent, and a tool that guesses at intent is the tool people stop reading.

Severity ranks how much a change deserves your attention, not how dangerous it is:

• ! worth reading before you upgrade
• ~ worth knowing, usually fine
• . background

Most ! findings have an ordinary explanation. The point is that you get thirty seconds to decide, rather than finding out later.

It is lexical, and says so

Capabilities are found by looking for the shapes that reach outside the process. A commented-out require('child_process') matches. A parser would be more precise and would mean shipping one.

The cost is low because nothing here produces a verdict, and because the line it was found on is printed underneath, so a false positive is obvious in one second rather than after you open the package:

  ! it now runs other programs, and the previous version did not
      // const cp = require('child_process'); // removed in v2

Documentation is never scanned. The first live run of this tool reported four findings on a chalk upgrade and three were badge URLs in the readme. That is how a tool gets uninstalled in a week: a reader wrong-footed three times stops reading the fourth line, which was the one that mattered. There is a test for it now.

In CI

- uses: catidegla/bumpdiff@v0.1.1
  with:
    lockfile: package-lock.json

On a pull request it diffs against the base automatically. A base it cannot reach, a lockfile that did not move, and a registry that is down all pass quietly rather than blocking a merge on something that is not about your dependencies.

Or in one line, which is all the action does:

git diff origin/main -- package-lock.json | npx bumpdiff lockfile

git diff origin/main -- package-lock.json | npx bumpdiff lockfile

Every version change in the diff, checked. Exit codes:

0	nothing worth stopping for
1	something worth reading
2	the command or the package was wrong
3	the registry could not be reached

Three is separate on purpose. A job that treats could not check as nothing changed is worse than no check at all.

What it cannot do

It cannot see what a package does at runtime, only what its source reaches for. Code fetched after install is invisible to it, which is precisely why a new host and a new install script are the two loudest findings.

It cannot read minified or obfuscated code usefully. It reports that a file became one enormous line and leaves the reading to you.

It cannot tell you a change is safe. It tells you a change happened.

Testing

npm test    # 67 tests, nothing to install

The suite never touches the registry: tarballs are built in memory so the tests cannot fail because somebody published something, and cannot pass because a network was down. CI has a separate job that runs against real packages and is allowed to fail, because a registry outage is not a defect in this repository.

Requirements

Node 20 or later. No other dependency, which is the whole point.

License

MIT.