On Wed, Apr 15, 2020 at 4:55 AM Glen Huang <hey....@gmail.com> wrote:
>
> I have a makefile where upon a new go binary being built, it builds some
> other stuff that is not go related.
>
> The go binary is unconditionally built with a FORCE prerequisite, so the go
> build command always runs, but that command always updates the output binary,
> which leads to downstream being unnecessarily built.
>
> Is there a way to tell go not to touch the output file if it builds purely
> from the cache?
>
> Currently it prevents me from using a makefile, and I don't really feel like
> sidestepping go's cache system by manually listing all go files and have the
> makefile functions as a cache, besides, it's really difficult to correctly
> list dependencies if the module is big and the binary being built only
> depends on a subset.
Updating the binary is intentional, so that `go build` has consistent behavior.
The way to handle this in a Makefile is to use the move-if-change
dance, which looks more or less like
real-target: stamp-target; @true
stamp-target: ...
go build -o temporary-target ...
if cmp temporary-target real-target; then \
rm temporary-target; \
else \
mv temporary-target real-target
fi
touch stamp-target
With this technique stamp-target will be rebuilt if any of its
dependencies change, and real-target will be rebuilt only if the build
generated a file that was different in some way.
Ian
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