RFC: Add npm diff

[ruyadorno]

Quick overview:

See more in the rendered RFC

[ljharb]

Interesting - this is diffing between the file contents, but i'd also want to know the theoretical lockfile diff - iow, what transitive dep name/version changes have happened across that span.

[ljharb]

I also asked during the RFC call about whether the diff should be from "current to wanted" by default rather than "current to latest", so as to avoid breaking changes (matching what npm update does by default)

[ruyadorno]

btw we actually have a working prototype over at npm/cli#1319

[ruyadorno]

@coreyfarrell suggested in the tooling WG that it would be nice to have a pager config (similar to git) to go with that, to which I really like 😊

[coreyfarrell]

@ruyadorno have you considered if any standard diff CLI flags will be supported? Like pager support this is not critical but I very frequently use git diff --ignore-all-space. This is great when blocks of unconditional code gets moved into a condition:

diff --git a/lib/internal/main/worker_thread.js b/lib/internal/main/worker_thread.js
index 6e3935d138..e6ae3952f3 100644
--- a/lib/internal/main/worker_thread.js
+++ b/lib/internal/main/worker_thread.js
@@ -113,8 +113,9 @@ port.on('message', (message) => {
     initializeDeprecations();
     initializeWASI();
     initializeCJSLoader();
-    initializeESMLoader();
+    initializeESMLoader(loaderPort);
 
+    if (!internal) {
       const CJSLoader = require('internal/modules/cjs/loader');
       assert(!CJSLoader.hasLoadedAnyUserCJSModule);
       loadPreloadModules();
@@ -122,6 +123,7 @@ port.on('message', (message) => {
       if (argv !== undefined) {
         process.argv = process.argv.concat(argv);
       }
+    }
     publicWorker.parentPort = publicPort;
     publicWorker.workerData = workerData;
 

With or without support for standard diff flags this feature will be great!

[ljharb]

In general it’d be nice if it could defer to git diff - and all its options.

[juliangruber]

Quickly sharing my learnings from working on https://github.com/juliangruber/npm-diff:

• git diff plus colordiff works great, however colordiff isn't available everywhere. A JS replacement might not be hard to write
• If less is used with colordiff, need less -R
• In my tests it was useful to ignore any changed files with test/ and Makefile in their name, since as a consumer these don't change my situation. There could be false negatives ignoring test.
• In my tests it was also useful to ignore line changes containing readme, _id, _from and _resolved, as these were noise

[bnb]

Should this be merged?

[ruyadorno]

yes! I'll just finish cleaning it up and merge it as implemented 😊

[ruyadorno]

For future reference, this feature went out in npm@7.5.0 and I wrote a little overview in a blog post format over here: https://dev.to/ruyadorno/npm-diff-23dh