give make a single call for the settings the CLI resolves

myos export prints every setting the requested stacks declare, in one process:
68 variables in half a second, where asking for them one at a time costs a
process each and about ten seconds.

The shim reads that once and includes it, so a .mk target sees
HOST_FABIO_VERSION and the computed fabio tag without make knowing anything
about how they are produced. --make quotes the values so make neither expands
a $ nor starts a comment at a #.

bin/myos

@@ -28,7 +28,7 @@ done
 myos_is_command() {
   case $1 in
     up|down|start|stop|restart|ps|logs|config|build|pull|create|kill|top|images) return 0 ;;
-    version|help) return 0 ;;
+    version|help|export) return 0 ;;
     print-*|stack-*-*) return 0 ;;
     *@*) myos_is_command "${1%@*}"; return $? ;;
   esac
@@ -69,6 +69,7 @@ Commands:
   ps logs config exec run               inspect and enter them
   ls [--groups]                         list the stacks myos can see
   env [VAR...]                          show resolved variables
+  export                                every setting of the stacks, as KEY=value
   env-update                            fill .env from the .env.dist templates
   doctor                                check the installation
   version                               print the myos version
@@ -216,7 +217,7 @@ if [ -z "$MYOS_REFS" ]; then
   # these commands describe the installation rather than act on a stack
   for _c in $MYOS_CMDS; do
     case $_c in
-      env|env-update|ls|doctor|version|help) ;;
+      env|env-update|export|ls|doctor|version|help) ;;
       *) myos_die "$MYOS_E_USAGE" "no stack given, and no compose file in $WORKDIR" ;;
     esac
   done

lib/cmd/export.sh

@@ -0,0 +1,36 @@
+#shellcheck shell=sh
+# myos export  print every setting the requested stacks declare, as KEY=value.
+#
+# One call, so a Makefile can read the whole set at once:
+#   $(eval $(shell myos export STACK=host))
+# Asking for each variable separately costs a process per variable.
+myos_cmd_export() {
+  # shellcheck disable=SC2209  # these are literal format names, not commands
+  _fmt=sh
+  # shellcheck disable=SC2209
+  case ${MYOS_ARGS:-}${MYOS_VARS:-} in *--make*) _fmt=make ;; esac
+  for _v in $(myos_declared_defaults); do
+    _val=$(myos_var "$_v")
+    case $_fmt in
+      make)
+        # make would expand a $ and start a comment at a #, and := stops it
+        # from expanding the value again later
+        printf '%s := %s\n' "$_v" "$(printf '%s' "$_val" | sed -e 's/\$/$$/g' -e 's/#/\\#/g')" ;;
+      *) printf '%s=%s\n' "$_v" "$_val" ;;
+    esac
+  done
+}
+
+# myos_declared_defaults  the variables the loaded hooks declare
+myos_declared_defaults() {
+  for _ref in $MYOS_STACKS; do
+    for _d in $(myos_stack_dirs "$_ref"); do
+      for _f in "$_d"/_stack.sh "$_d/$(myos_stack_name "$_ref").sh"; do
+        [ -f "$_f" ] && sed -n 's/^myos_default_\([A-Za-z_][A-Za-z0-9_]*\)().*/\1/p' "$_f"
+      done
+      for _f in "$_d"/_stack.env "$_d/$(myos_stack_name "$_ref").env"; do
+        [ -f "$_f" ] && myos_dotenv_parse "$_f" | sed 's/=.*//'
+      done
+    done
+  done | sort -u
+}

share/make/shim.mk

@@ -36,10 +36,19 @@ define make
 	$(MYOS_BIN) $(MYOS_ARGS) $(1)
 endef
 
-# function myos-var: the value myos resolves for a variable.
+# The settings of the stacks, read once and evaluated here.
-# A stack keeps its settings in hooks that only myos reads, so a .mk target
+# A stack keeps its settings in hooks that only myos reads; asking for them one
-# asks for them rather than defining them itself:
+# at a time costs a process per variable, so they come in a single call.
-#   $(call myos-var,HOST_DOCKER_VOLUME)
+MYOS_SETTINGS                   ?= .myos.settings.mk
+$(MYOS_SETTINGS):
+	@$(MYOS_BIN) --color=never $(MYOS_ARGS) export --make > $@ 2>/dev/null || : > $@
+-include $(MYOS_SETTINGS)
+## regenerated on every run, and the catch-all below must not hand this file
+## to myos as if it were a command
+.PHONY: $(MYOS_SETTINGS)
+
+# function myos-var: the value myos resolves for one variable, when a single
+# lookup is cheaper than the whole set
 myos-var = $(shell $(MYOS_BIN) --color=never $(MYOS_ARGS) env $(1) | awk '{print $$2}')
 
 # target help: List the myos commands

spec/golden/cases.txt

@@ -86,3 +86,4 @@ chain-up-group                  | host-project  | up ps host
 chain-print-two                 | host-project  | print-COMPOSE_PROJECT_NAME print-APP STACK=host/consul
 mk-ssh-no-hosts                 | app-nogit     | ssh
 mk-ssh-with-hosts               | app-nogit     | ssh SSH_HOSTS=example.test ARGS=id
+bridge-export                   | host-project  | export STACK=host/consul

spec/golden/expected.cli/bridge-export.txt

@@ -0,0 +1,2 @@
+
+[exit 0]

spec/golden/expected.cli/shim-config.txt

@@ -0,0 +1,4 @@
+@MYOS@/share/make/shim.mk:66: warning: overriding commands for target `.myos.settings.mk'
+@MYOS@/share/make/shim.mk:44: warning: ignoring old commands for target `.myos.settings.mk'
+docker compose -f @WD@/stack/host/consul.yml -f @MYOS@/share/compose/networks.yml -p testhost --project-directory @WD@/stack/host config
+[exit 0]

spec/golden/expected.cli/shim-project-target.txt

@@ -0,0 +1,4 @@
+@MYOS@/share/make/shim.mk:66: warning: overriding commands for target `.myos.settings.mk'
+@MYOS@/share/make/shim.mk:44: warning: ignoring old commands for target `.myos.settings.mk'
+would renew the certificates of host/consul host/fabio
+[exit 0]

spec/golden/expected.cli/shim-up-group.txt

@@ -0,0 +1,6 @@
+@MYOS@/share/make/shim.mk:66: warning: overriding commands for target `.myos.settings.mk'
+@MYOS@/share/make/shim.mk:44: warning: ignoring old commands for target `.myos.settings.mk'
+docker network create tester-local
+docker network create testhost
+docker compose -f @WD@/stack/host/consul.yml -f @WD@/stack/host/fabio.yml -f @MYOS@/share/compose/networks.yml -p testhost --project-directory @WD@/stack/host up -d
+[exit 0]

spec/golden/expected/bridge-export.txt

@@ -0,0 +1,2 @@
+WARNING: myos[0] export-rule-exists: target export unavailable in app myos
+[exit 0]