Avoid parsing dependency package.json's when searching for local bin to run

[rwjblue]

Currently (my understanding) is that when a binary is installed at the user/global level (e.g. notion install ember-cli), and then a bin script is invoked (e.g. ember build) within a project we do the following:

• Parse the project's own package.json
• Iterate the projects dependencies/devDependencies (should also do optionalDependencies but I don't know if we do?)
• Search each of those combined deps's package.json (e.g. node_modules/package-name/package.json) for bin scripts with the given name
• If found, use the local bin
• If not found, use the globally installed package's bin script

Having to open and parse all of the dependencies/devDependencies's package.json's adds additional overhead to launching, and I believe it can be avoided completely.

I propose:

• Parse the project's own package.json
• Look for the specific installed package (e.g. ember-cli from my example) in the dependencies/devDependencies
• If found, use the local bin
• If not found, use the globally installed package's bin script

This relies on the fact that we keep track of which package a given globally installed bin shim is provided by, so we can directly compare/look for that instead of manually searching.

Changing to this system would have a few benefits:

• Lower overall overhead for globally installed shims
• Better resilience to malformed package.json's (we no longer need to parse all of the dependencies/devDependencies package.json, only the projects itself and possibly the local installed version of the global package)
• Better alignment with PnP (the manually parsing the node_modules tree will have to branch when in a PnP project vs when not in one, IMHO better to remove the branching)

This idea originally came from the discussion in discord when #388 was reported.

[rwjblue]

Definitely not conclusive evidence of anything specific, but it appears that the global shims today are adding a bit of overhead (more than I would have expected):

• Average of 10 time ember version: 1.31s
• Average of 10 time node_modules/.bin/ember: 1.1s

[rwjblue]

While poking at the performance differences I mentioned in my last comment, I decided to test what the impact is of having many dependencies/devDependencies while using the global shim.

When I delete all dependencies and devDependencies other than ember-cli, the there is no measurable time difference between time ember v and time node_modules/.bin/ember v.

tldr; the extra dependency traversal and package.json parsing is likely to be the cause of the slower performance of global shim binaries compared to directly invoking their project local bins.

[charlespierce]

Out of curiosity, in the test you did above where there was a ~0.2s difference between the two invocations, how many dependencies did that project have?