Gohack: mutable checkouts of Go module dependencies
The new Go module system is awesome. It ensures repeatable, deterministic
builds of Go code. External module code is cached locally in a read-only
directory, which is great for reproducibility. But if you're used to the
global mutable namespace that is
$GOPATH, there's an obvious question:
what if I'm hacking on my program and I want to change one of those
You might want to put a sneaky
log.Printf statement to find out how
some internal data structure works, or perhaps try out a bug fix to see
if it solves your latest problem. But since all those external modules
are in read-only directories, it's hard to change them. And you really
don't want to change them anyway, because that will break the integrity
checking that the Go tool does when building.
Luckily the modules system provides a way around this: you can add a
replace statement to the
go.mod file which substitutes the contents
of a directory holding a module for the readonly cached copy. You can of
course do this manually, but gohack aims to make this process pain-free.
Install gohack with:
go get github.com/rogpeppe/gohack
To make a mutable checkout of a module, say
gohack get example.com/foo/bar
This will clone the module's repository to
$HOME/gohack/example.com/foo/bar, check out the correct version of the
source code there, and add a replace directive in the local
replace example.com/foo/bar /home/rog/gohack/example.com/foo/bar
Once you are done hacking and wish to revert to the immutable version, you can remove the replace statement with:
gohack undo example.com/foo/bar
or you can remove all gohack replace statements with:
Note that undoing a replace does not remove the external module's directory - that stays around so your changes are not lost. For example, you might wish to turn that bug fix into an upstream PR.
If you run gohack on a module that already has a directory, gohack will try to check out the current version without recreating the repository, but only if the directory is clean - it won't overwrite your changes until you've committed or undone them.