= Usage
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Zilch supports compiling any Go code incrementally using `zilch-cli-go`, with
no special configuration needed on the part of the Go module being built:

[,console]
----
$ git clone https://github.com/tailscale/tailscale

$ zilch-cli-go --module-dir tailscale/ <1>
tailscale.com/client/tailscale/example/servetls	/nix/store/727ci6sssga0pbi4aqb08vnhfvmh9nl0-tailscale.com_client_tailscale_example_servetls
tailscale.com/cmd/addlicense	/nix/store/ckc5bx4s0c29sancd05asvhz0dy43xj7-tailscale.com_cmd_addlicense
…
tailscale.com/cmd/xdpderper	/nix/store/8wn9w91mjipw1dzks4p3kcmkwcn18jp7-tailscale.com_cmd_xdpderper

$ zilch-cli-go --module-dir tailscale/ \
>  tailscale.com/cmd/tailscaled <2>
tailscale.com/cmd/tailscaled	/nix/store/hqrm0f8sd8sx54am921na25w8za67p3m-tailscale.com_cmd_tailscaled
----
<1> Building all binary packages in a module
<2> Building a specifically targeted package

Right now, the daemon has to be able to build `x86_64-linux` derivations,
and `zilch-cli-go` will only output statically linked amd64 binaries as well.


While running, all processing of the Go module, its dependencies, etc, are done
inside of Nix. Once all dependencies have been resolved, a series of Nix
derivations will be used to then build the requested packages. If any source
file's changes do not affect the way dependent packages use it, those packages
will not need rebuilding; only the final result will have to be re-linked.

== Replacing dependencies
As part of Zilch, it's also possible to quickly build a module with one of its
(transitive) dependencies replaced. This keeps the same guarantees as before:
Any changes made that do not involve the output changing will only need
relinking of the resulting binary. This is also very simple:

[,console]
----
$ git clone https://go.googlesource.com/net x-net   # golang.org/x/net
$ zilch-cli-go --module-dir tailscale --replace x-net/ tailscale.com/cmd/tailscaled
…
tailscale.com/cmd/tailscaled	/nix/store/hqrm0f8sd8sx54am921na25w8za67p3m-tailscale.com_cmd_tailscaled
----

After editing a file any of the replaced dependencies, if this package is used
in the final build, Zilch will apply early-cutoff where possible.