*** OPNsense.localdomain: OPNsense 18.7.1_3 (amd64/OpenSSL) ***
# opnsense-code tools ports src
# cd /usr/ports/net/ntopng
# make
===> ntopng-3.4.d20180604,1 depends on executable: bash - not found
===> bash-4.4.23 depends on executable: bison - not found
===> bison-3.0.4,1 depends on package: m4>=1.4.16,1 - not found
===> bison-3.0.4,1 depends on package: m4>=1.4.16,1 - not found
*** Error code 1
Stop.
make[2]: stopped in /usr/ports/devel/bison
*** Error code 1
Stop.
make[1]: stopped in /usr/ports/shells/bash
*** Error code 1
Stop.
make: stopped in /usr/ports/net/ntopng
Problem solved.
I started to compile before doing "opnsense-code tools ports src".
I had to "make clean" to get in a proper state.