[rush] Add 'myrush' binary that invokes globally installed Rush version

[darsi-an]

I bypass version selector just checking if command name is 'myrush'. If not it continues with its expected behavior. Let me know if i'm going about it correctly.

WIP (Please comment if I need to add any more)

• Print errors for 'rush' init if not latest rush

Questions

• Running rush init --overwrite-existing will still use an older version from rush.json. Is this necessary?
• Init action with --overwrite-existing, overwrites everything. What if you just want to update versions in the rush.json to the globally installed Rush version, without overwriting other properties?

Also am I debugging correctly? Below are my launch configs for rush and myrush binaries

{
	"type": "node",
	"request": "launch",
	"name": "myrush install",
	"program": "${workspaceRoot}/apps/rush/bin/myrush",
	"cwd": "C:\\dev\\rush-example",			
	"args": ["install"]
},
{
	"type": "node",
	"request": "launch",
	"name": "rush install",
	"program": "${workspaceRoot}/apps/rush/bin/rush",
	"cwd": "C:\\dev\\rush-example",
	"args": [ "install"]
}

This PR will close #1475

[iclanton]

Running rush init --overwrite-existing will still use an older version from rush.json. Is this necessary?

You mean if you have an older version installed globally? We should probably print a warning in that case. Maybe we just shouldn't let that happen? However, I could see someone wanting to be able to easily downgrade a repo. @octogonz - what do you think?

Init action with --overwrite-existing, overwrites everything. What if you just want to update versions in the rush.json to the globally installed Rush version, without overwriting other properties?

I think for this, we'd want to consider putting together a formal upgrader. Unfortunately, there are tons of cases to consider. It currently overwrites everything because an upgrader would be difficult to write and we weren't sure how much use it would get.

Also am I debugging correctly?

Yeah that looks right to me, assuming your VSCode window is open to the repo root.

I usually run node --inspect-brk <path-to-start.js> <args> and then attach the debugger, but that's probably more complex than is actually necessary.

[darsi-an]

You mean if you have an older version installed globally?

Currently if rush.json version is higher than the globally installed version, Rush will install it for you.

In the case where your rush.json version is lower than that installed globally, rush init --overwrite-existing would use the older version when it overwrites the rush.json b/c of the variable expansion.

Are there any other cases for the rush init --overwrite-existing other than just for upgrading a repo to a newer release of Rush (based off the CLI help)? If we do want to support downgrading It would be best to print a warning. We should also probably update the CLI help, so users don't get confused.

[octogonz]

FYI we recently reformatted the master branch using Prettier, which creates merge conflicts for existing PRs. We'll try to fix up the existing PRs for people, but if you want to do it yourself, here's the steps:

1. Run "npm install -g prettier@2.0.5" to install Prettier.
2. Merge the "release/master-before-prettier" branch into your PR branch. This is the state of the world before Prettier was applied.
3. Merge the "release/master-after-prettier" branch into your PR branch. This will create a merge conflict with the Prettier changes, and nothing else.
4. Resolve all the merge conflicts by discarding "origin", and overwriting with your branch's changes.
5. BEFORE committing the merge, run "prettier . --write" from the repo root to reapply the formatting (that you discarded in step 4).
6. Make sure to restage everything.
7. Commit the merge
8. Now you should be able to merge from the real "master" without any (Prettier-related) merge conflicts

[darsi-an]

Rush init was updated with #1956

[darsi-an]

1. When the repos rush.json version is greater than the globally installed rush version

• The "rush" binary will install it (if it is not already) and use the version specified in the repos rush.json
• The "myrush" binary will throw errors and suggest upgrading the library.

2. When the repos rush.json version is lower than the globally installed rush version

• The "rush" binary will use the repos rush.json version
• The "myrush" binary will use the globally installed version

As suggested in #1475 I have updated the error messages a bit.

@octogonz is there any thing else I should consider?