[OpenWrt-Devel] Why does perl get compiled even if it not selected by any package?

[Hannu Nyman]

Why does the presence of perl in a larger multi-package Makefile force the 
compilation of perl even if the specific package depending on perl is not 
even selected. (compilation of perl takes long, so it is rather annoying...)

I have stumbled into two cases, where my package selection leads into perl 
compilation during build, although perl is not a dependency of my package 
selection, and the final perl package .ipk is not even produced.

* xtables-addons Makefile has geoip components that depend on perl, but even 
if those are not selected and only e.g. rstp is selected, perl is still 
compiled for the xtables-addons.

* lm-sensors Makefile defines several packages, of which only 
"lm-sensors-detect" depends on perl. Selecting only some other package like 
libsensors still leads into perl compilation.

My hunch is that this is related to perl having a host build component. That 
apparently gets evaluated in any case, regardless of the package needing perl 
actually being selected, or something like that.

Is this just a limitation of the dependency parsing, and is caused by the 
presence of a host build in the package Makefile  ??

Could this be mitigated somehow?

E.g. by saying  " +PACKAGE_lm-sensors-detect:perl " instead of just "+perl"  ???

Any input from the dependency gurus?

https://github.com/openwrt/packages/blob/master/utils/lm-sensors/Makefile

Looking at the tmp/.packagedeps, perl likely gets into the dependency tree 
this way:

package-$(CONFIG_PACKAGE_lm-sensors) += feeds/packages/lm-sensors
package-$(CONFIG_PACKAGE_lm-sensors-detect) += feeds/packages/lm-sensors
package-$(CONFIG_PACKAGE_libsensors) += feeds/packages/lm-sensors

$(curdir)/feeds/packages/lm-sensors/compile += 
$(curdir)/feeds/packages/perl/compile $(curdir)/libs/sysfsutils/compile 
$(curdir)/libs/toolchain/compile $(if 
$(CONFIG_GCC_LIBSSP),$(curdir)/libs/toolchain/compile) $(if 
$(CONFIG_USE_GLIBC),$(curdir)/libs/toolchain/compile)



perus at ub1810:/Openwrt/wrt3200$ grep sensor .config
# CONFIG_PACKAGE_libupm-pulsensor is not set
CONFIG_PACKAGE_libsensors=y
CONFIG_PACKAGE_collectd-mod-sensors=y
# CONFIG_PACKAGE_lm-sensors is not set

# CONFIG_PACKAGE_lm-sensors-detect is not set
perus at ub1810:/Openwrt/wrt3200$ grep perl .config# CONFIG_PACKAGE_perl is not set



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