proposal: go/cmd: install should assume @latest in most cases

[ConradIrwin]

As a go programmer I create command line tools that I want to download and use on various machines. I'd like it to be as easy as possible to install those tools when I need them.

Until go1.18 it was possible to run go get github.com/superhuman/url64. This feature was moved to go install, and as part of that the syntax was changed to require @latest on the end, otherwise you (usually) get one of two possible error messages:

# in a module
$ go install github.com/superhuman/url64
no required module provides package github.com/superhuman/url64; to add it:
	go get github.com/superhuman/url64

# not in a module
$ go install github.com/superhuman/url64
go: 'go install' requires a version when current directory is not in a module
	Try 'go install github.com/superhuman/url64@latest' to install the latest version

I propose that:

• In a module that has a specific version of github.com/superhuman/url64 in its go.mod: go install github.com/superhuman/url64 would act as it does today.
• Otherwise (outside of a module, or in a module that does not have it as a dependency): go install github.com/superhuman/url64 should be equivalent to go install github.com/superhuman/url64@latest

This gives you the same behaviour as following the instructions in the current error messages, automatically.

[seankhliao]

I believe this was addressed in #40276 under "Why require a version suffix when outside a module"

The inconsistency isn't something that we want.

[ConradIrwin]

Thanks! Sorry for missing that