Makefile: Don't allow install{world,kernel} with pkgbase

Using these targets on a pkgbase system will cause the installed system
to become out of sync with the package database, which is almost certain
to cause issues the next time pkg(8) is used.

To prevent users doing this accidentally, disallow install* if we detect
that FreeBSD-runtime is installed in the target.  The check can be
overridden with DESTDIR=/ for users who are sure they want to do this.

MFC after:	3 days
Reviewed by:	emaste
Sponsored by:	https://www.patreon.com/bsdivy
Differential Revision:	https://reviews.freebsd.org/D52879

Makefile.inc1

@@ -587,7 +587,16 @@ PKG_VERSION:=	${_PKG_REVISION}${EXTRA_REVISION:C/[[:space:]]//g}
 
 .endif	# !defined(_MKSHOWCONFIG)
 
+PKG_NAME_PREFIX?=	FreeBSD
+PKG_MAINTAINER?=	[email protected]
+PKG_WWW?=		https://www.FreeBSD.org
+PKG_WORKERS_COUNT?=	1
+
 .if make(*package*)
+.export PKG_NAME_PREFIX
+.export PKG_MAINTAINER
+.export PKG_WWW
+
 .if !defined(PKG_TIMESTAMP)
 .if !empty(GIT_CMD) && exists(${GIT_CMD}) && exists(${SRCDIR}/.git)
 SOURCE_DATE_EPOCH!=	${GIT_CMD} -C ${SRCDIR} show -s --format=%ct HEAD
@@ -598,14 +607,6 @@ SOURCE_DATE_EPOCH=	${TIMEEPOCHNOW:gmtime}
 .else
 SOURCE_DATE_EPOCH=	${PKG_TIMESTAMP}
 .endif
-PKG_WORKERS_COUNT?=	1
-
-PKG_NAME_PREFIX?=	FreeBSD
-PKG_MAINTAINER?=	[email protected]
-PKG_WWW?=		https://www.FreeBSD.org
-.export PKG_NAME_PREFIX
-.export PKG_MAINTAINER
-.export PKG_WWW
 .endif
 
 .if !defined(_MKSHOWCONFIG)
@@ -1353,6 +1354,28 @@ __installcheck_DESTDIR: .PHONY
 .endif
 .endif
 
+#
+# Don't allow installworld or installkernel on a pkgbase system.  This avoids
+# accidentally updating a pkgbase system with install{world,kernel}, causing
+# the installed system to become out of date with the package database.
+#
+# Skip the check if DESTDIR is defined on the assumption the user knows what
+# they're doing.  This means the check can be disabled for the running system
+# using DESTDIR=/.
+#
+.if !make(distributeworld) && !defined(DESTDIR)
+_installcheck_world: __installcheck_PKG
+_installcheck_kernel: __installcheck_PKG
+__installcheck_PKG: .PHONY
+.if exists(${LOCALBASE}/sbin/pkg-static)
+	@if ${LOCALBASE}/sbin/pkg-static info -e ${PKG_NAME_PREFIX}-runtime; then \
+		echo >&2 "ERROR: This target should not be used on a system installed from packages." ; \
+		echo >&2 "       To override this check, set DESTDIR=/."; \
+		false; \
+	fi
+.endif
+.endif
+
 .if !defined(DB_FROM_SRC)
 #
 # Check for missing UIDs/GIDs.