Add powershell for installed binaries RFC

PR-URL: #20
Credit: @bterlson
Close: #20
Reviewed-by: @isaacs

Author: bterlson

accepted/0000-powershell-bins.md

@@ -0,0 +1,57 @@
+# Powershell for Installed Binaries
+
+AKA Terminate Terminate Batch Job
+
+## Summary
+
+Today, installing binaries using npm creates an executable bash script and a .cmd file with the same name. Unfortunately, terminating cmd scripts with SIGINT causes a useless prompt for windows users - "Terminate batch job (Y/N)". Also, Powershell is the default shell for Windows. By creating .ps1 scripts in addition to bash and .cmd, powershell users will have a better command line experience.
+
+## Motivation
+
+Windows users have three main options when it comes to shells:
+
+- cmd: essentially unchanged from early versions of Windows
+- powershell: the default Windows shell, under active development
+- unixy shell: for example git-bash, zsh via WSL
+
+WSL is growing in popularity, but isn't super common. Many Windows users need to use or prefer using a native shell. And for those using Powershell, we can make their experience better by creating powershell binary wrappers.
+
+## Detailed Explanation
+
+When installing binaries (e.g. `npm install -g typescript`), NPM should create `tsc.ps1` in addition to `tsc.cmd` and the executable `tsc` bash script. Powershell will prioritize `foo.ps1` over `foo.cmd` when users type `foo` on the command line. cmd users will have to continue living with it. Users of git-bash or WSL shells will be unaffected.
+
+## Rationale and Alternatives
+
+The main alternative is to maintain the status quo, but this leaves an annoying SIGINT prompt in Windows's default shell.
+
+Creating just .ps1 scripts isn't an option. cmd can't start treating .ps1 scripts as executables (at least not by default), and NPM can't drop support for cmd.
+
+## Implementation
+
+Here's an example of a functionally identical powershell wrapper:
+
+```powershell
+$myPath = Split-Path $myInvocation.MyCommand.Path -Parent
+$node = Join-Path $myPath 'node.exe'
+$binPath = Join-Path $myPath '[ path to node_module bin script, e.g. node_modules\typescript\bin\tsc]'
+if (Test-Path $node)
+{
+    & $node $binPath $args
+}
+else
+{
+    node $binPath $args
+}
+```
+
+The path to the bin script will have to be substituted into the right place.
+
+## Prior Art
+
+- [cmd-shim](https://www.npmjs.com/package/cmd-shim)
+- [yarn PR](https://github.com/yarnpkg/yarn/pull/6093)
+
+## Unresolved Questions and Bikeshedding
+
+- impact of additional scripts on install times, node_modules size, etc.
+- default powershell permissions: will powershell users need to toggle some settings so this works without permissions errors? Can the errors be worked around? (This PR will need testing on a fresh Windows install)