make: 'go build' does not run when TAGS change

[silverwind]

TAGS=bindata make build
make build

The intentions is to first build with bindata, then without.

I still observe a bindata executable after the second build becausego build never ran (make thinks the executable is already up to date). We somehow need to trigger go build when the value of TAGS differs from the previous build.

I'm not exactly sure how to best achieve that except writing out the last TAGS to a evidence file after build and only write the file again when TAGS differs from the file's content. If there are other environment variables that can affect the build, they would need the same treatment.

cc: @guillep2k

[guillep2k]

Yes, it's a good point. I'd write the tags to an evidence file, but only if different. Something like:

mkdir -p "`dirname "$EVIDENCE"`" ; # Just make sure the directory exists
if [ "`cat "$EVIDENCE" 2>/dev/null`" != "$TAGS" ] ; then echo "$TAGS" > "$EVIDENCE" ; fi

[silverwind]

I wonder if it is safe to skip the go generate step if the bindata tag is absent.

[zeripath]

No. Do not skip generate. Even if it does nothing at present - we should start using generate more.