Go update all modules

[Steven Penny]

Using this module as an example (using a specific commit so others will see what I see):

~~~
git clone git://github.com/walles/moar
Set-Location moar
git checkout d24acdbf
~~~

I would like a way to tell Go to "update everything". Assume that the module will work with the newest version of everything. Below are five ways I found to do this, assume each is run on a clean clone. This results in a `go.mod` of 19 lines:

~~~
go get -u
~~~

This results in a `go.mod` of 14 lines:

~~~
go get -u
go mod tidy
~~~

This results in a `go.mod` of 13 lines:

~~~
go mod tidy
~~~

If I just manually delete everything in `require` and run `go mod tidy`, I get 12 lines. If I just manually delete everything in `require` and run `go get -u`, I get 11 lines. My question is, why are these methods producing different results, and what is the "right way" to do what I am trying to do?

~~~
go version go1.16.3 windows/amd64
~~~