Does this need to be CONFLICTS rather than CONFLICTS_INSTALL ? CONFLICTS says you can't even build this port if the conflicting software is installed.

You shouldn't assume the setting of $LOCALBASE as /usr/local here. That can be overridden in the same way that $PREFIX can. It's fairly common to set:

CPPFLAGS=-I${LOCALBASE}/include

in the port Makefile and then pass that to the build Makefile in the MAKEFLAGS, and make this line be

CFLAGS += $(CPPFLAGS)

You're right, CONFLICTS_INSTALL is better suited.

I agree, fixed.

Why not use direct CFLAGS+=-I${LOCALBASE}/include in port Makefile?

You don't need to patch the Makefile for that, adding it to CFLAGS will be enough, CFLAGS is added to MAKE_ENV, so it'll end up in there.

You should pass the version in MAKE_ENV and use it here, so that the patch doesn't have to change when updates are being made.

You don't need to patch uninstall, it will never be used.

That's wrong too, not respecting ${CC}, you should add to the Makefile:

MAKE_ARGS=CC=${CC}

use $(BSD_INSTALL_PROGRAM) instead of $(INSTALL) -s -m 0755

use $(BSD_INSTALL_MAN) instead of $(INSTALL) -c -m 0644

You don't need to remove the line.

It needs

BUILD_DEPENDS= a2x:textproc/asciidoc

Removing that line is not needed.

That line replace $CC from MAKE_ARGS with hardcoded gcc. gcc is not in BUILD_DEPENDS for this port and should not be there.

When you pass a variable as an argument to the make command, it overrides the variable defined in the Makefile.

You are right, reverted.