# Allow user to configure things that only effect src tree builds.
SRCCONF?= /etc/src.conf
.if (exists(${SRCCONF}) || ${SRCCONF} != "/etc/src.conf") && !target(_srcconf_included_)
+
+# Validate that the user didn't try setting an env-only variable in
+# their src.conf. This benefits from already including bsd.mkopt.mk.
+.for var in ${__ENV_ONLY_OPTIONS}
+__presrcconf_${var}:= ${MK_${var}:U-}${WITHOUT_${var}:Uno:Dyes}${WITH_${var}:Uno:Dyes}
+.endfor
+
.sinclude "${SRCCONF}"
_srcconf_included_: .NOTMAIN
+
+# Validate the env-only variables.
+.for var in ${__ENV_ONLY_OPTIONS}
+__postrcconf_${var}:= ${MK_${var}:U-}${WITHOUT_${var}:Uno:Dyes}${WITH_${var}:Uno:Dyes}
+.if ${__presrcconf_${var}} != ${__postrcconf_${var}}
+.error Option ${var} may only be defined in ${SRC_ENV_CONF}, environment, or make argument, not ${SRCCONF}.
.endif
+.undef __presrcconf_${var}
+.undef __postrcconf_${var}
+.endfor
+
+.endif # SRCCONF
# tempting, but bsd.compiler.mk causes problems this early
# probably need to remove dependence on bsd.own.mk