When using Go as part of a multi-step, multi-languages project, a naive makefile calling go build in rules without prerequisite is wasteful: each invocation of go build creates a new binary, which in turn triggers all dependent steps (e.g. binary compression, inclusion in a disk image, …).
Instead, we need to inform make about our precise dependencies to only trigger the build when needed.
This tool is a small script which, given a list of main packages, creates a correct and minimal dependency tree, ready for inclusion in a larger Makefile.
Running from the directory containing both prog1 and prog2:
PACKAGES := example.com/prog1 example.com/prog2
deps.mkd: $(wildcard **/*.go)
godeps $(PACKAGES) > deps.mkd
include deps.mkd
bin/prog1: example.com/prog1 go.mod
go build $@ $<
bin/prog2: example.com/prog2 go.mod
go build $@ $<
A few things of note in this makefile:
- packages are defined using a fully qualified name (so no conflict)
- dependencies are re-generated whenever any Go file changes (tracking possible import changes)
- module versioning is handled through the
gocommand-line tool for accuracy
The output is a set of rules defining dependencies between Go packages and files on disk: https://www.gnu.org/software/make/manual/html_node/Multiple-Rules.html
If a dependency is included twice, a single rule is created for both targets: https://www.gnu.org/software/make/manual/html_node/Multiple-Targets.html
In order to use Go packages as rules (without a corresponding file on disk), they are created as intermediate rules (so the transitive dependencies are used to rebuild): https://www.gnu.org/software/make/manual/html_node/Chained-Rules.html