API idea: JSON Diff

[orta]

We care a lot about JSON files in the JS community, so pretty often I think to myself "hrm, I'd like to do a diff to know whether the package version had changes, or dependencies" - it's pretty tough to do

It's definitely a bunch of code in a Dangerfile, that so far I've been hesitant to write. Perhaps it could be a new function inside the danger.utils class?

Here's some examples of what I'd imagine this could look like:

Promise vs callback API is worth a discussion, for my vote TBH I'm a promises, mainly because I use async/await but for now I'll just write a callback

danger.utils.jsonDiff("package.json", (diff) => {
  // diff could look something like
  // {
  //   "version" : {
  //     "before": 0.0.5,
  //     "after": 0.0.6
  //   }
  // }
  if (diff && diff.version && diff.version.before < diff.version.after) {
    fail("No retreat, no surrender.")
  }
}) 

The nullability aspect is interesting, initially I thought of passing null instead of an empty object to the params, but maybe it makes more sense to just not run the closure at all if there are no changes?

[orta]

Could have a much more fine grained check so that things like this don't happen

[orta]

That could look more like

danger.utils.jsonDiff("package.json", (diff) => {
  const depChanges = diff.dependencies || diff.devDependencies
  const lockfileChanges = danger.git.modified_files.include("yarn.lock")
  if (depChanges && !lockfileChanges) {
    fail("No lock file changes - yada yadda")
  }
}) 

Or you can start picking out the specific deps that are changed and do something like http://pkgsize.com on those locally

[orta]

I bet @wtgtybhertgeghgtwtg would love that have that on each dep changes 💯

[wtgtybhertgeghgtwtg]

I hadn't realized that I had been making a name for myself. The implementation might not be that complex.

1. Generate a JSON Patch from the original package.json to the proposed package.json (only add, replace, and remove, one entry per key).
2. Iterate over the patch, expand the key and create an object per path. a. If op is add, before is undefined, after is value. b. If op is replace, before is the value from the original package.json, after is value. c. If op is remove, before is the value from the original package.json, after is value.

[wtgtybhertgeghgtwtg]

Actually, you could probably ignore op altogether.

import {createPatch} from 'rfc6902';
import jsonpointer from 'jsonpointer';

function getDiff(beforePackage, afterPackage) {
  const patch = createPatch(beforePackage, afterPackage);
  return patch.reduce((accumulator, {path, value}) => {
    const diff = {
      after: value,
      before: jsonpointer.get(beforePackage, path),
    };
    jsonpointer.set(accumulator, path, diff);
    return accumulator.
  }, Object.create(null));
}

[orta]

Interesting, I've never heard of these two dependencies, and there is a standard for JSON patching - perfect. Better to work on existing infra. Thanks @wtgtybhertgeghgtwtg

[orta]

PR landing tomorrow

[orta]

Shipped.