add stack resolution: search path, references, overlays, groups

Replaces the 500-character stack_path expression of
make/apps/def.docker.mk:159 and its leaked $(stackz) loop variable with
three readable functions, covered by 20 assertions.

spec/unit/stack_spec.sh

@@ -0,0 +1,136 @@
+#shellcheck shell=sh
+Include lib/str.sh
+Include lib/core.sh
+Include lib/tags.sh
+Include lib/stack.sh
+
+Describe 'lib/stack.sh'
+  setup() {
+    MYOS_SANDBOX=$(myos_sandbox host-project)
+    WORKDIR=$MYOS_SANDBOX/wd
+    HOME=$MYOS_SANDBOX/home
+    MYOS_PATH=
+    ENV=local
+    unset COMPOSE_FILE_WWW COMPOSE_FILE_DNS 2>/dev/null || true
+  }
+  cleanup() { rm -rf "$MYOS_SANDBOX"; }
+  BeforeEach setup
+  AfterEach cleanup
+
+  Describe 'myos_path'
+    It 'puts the project stacks before the shared catalogue'
+      When call myos_path
+      The output should equal "$WORKDIR/stack:$HOME/.local/share/myos/stack"
+    End
+    It 'is overridable'
+      MYOS_PATH=/opt/stacks
+      When call myos_path
+      The output should equal "/opt/stacks"
+    End
+  End
+
+  Describe 'myos_stack_resolve'
+    It 'resolves a stack of the project'
+      When call myos_stack_resolve host/consul
+      The output should equal "$WORKDIR/stack/host"
+    End
+    It 'resolves a stack of the shared catalogue'
+      When call myos_stack_resolve postgres
+      The output should equal "$HOME/.local/share/myos/stack/postgres"
+    End
+    It 'resolves a versioned reference'
+      When run source spec/unit/stack_version_helper.sh
+      The output should equal "postgres 9.6"
+    End
+    It 'resolves a directory reference'
+      When call myos_stack_resolve "$WORKDIR/stack/host"
+      The output should equal "$WORKDIR/stack/host"
+    End
+    It 'fails loudly on an unknown stack'
+      When run myos_stack_resolve nosuchstack
+      The status should equal 3
+      The stderr should include "stack not found: nosuchstack"
+    End
+  End
+
+  Describe 'myos_compose_files'
+    It 'loads the stack file and its env overlay'
+      When call myos_compose_files "$HOME/.local/share/myos/stack/postgres" "docker-compose postgres" "" local
+      The line 1 should equal "$HOME/.local/share/myos/stack/postgres/postgres.yml"
+      The line 2 should equal "$HOME/.local/share/myos/stack/postgres/postgres.local.yml"
+      The lines of output should equal 2
+    End
+    It 'skips the env overlay of another env'
+      When call myos_compose_files "$HOME/.local/share/myos/stack/postgres" "docker-compose postgres" "" master
+      The output should equal "$HOME/.local/share/myos/stack/postgres/postgres.yml"
+    End
+    It 'loads the version overlay as a suffix'
+      When call myos_compose_files "$HOME/.local/share/myos/stack/postgres" "docker-compose postgres" "9.6" master
+      The line 2 should equal "$HOME/.local/share/myos/stack/postgres/postgres.9.6.yml"
+    End
+    It 'loads the suffix overlays in order'
+      When call myos_compose_files "$HOME/.local/share/myos/stack/host" "docker-compose nginx" "www dns" master
+      The line 1 should equal "$HOME/.local/share/myos/stack/host/nginx.yml"
+      The line 2 should equal "$HOME/.local/share/myos/stack/host/nginx.www.yml"
+      The line 3 should equal "$HOME/.local/share/myos/stack/host/nginx.dns.yml"
+    End
+    It 'is empty for a directory without compose files'
+      When call myos_compose_files "$WORKDIR" "docker-compose nothing" "" local
+      The output should equal ""
+    End
+  End
+
+  Describe 'myos_compose_suffixes'
+    It 'keeps the enabled suffixes and drops the false ones'
+      COMPOSE_FILE_LABELS=true; COMPOSE_FILE_WWW=false; COMPOSE_FILE_DNS=true
+      When call myos_compose_suffixes
+      The output should include "labels"
+      The output should include "dns"
+      The output should not include "www"
+    End
+    It 'adds <suffix>.<value> when the value is not a boolean'
+      COMPOSE_FILE_WWW=nginx
+      When call myos_compose_suffixes
+      The output should include "www"
+      The output should include "www.nginx"
+    End
+  End
+
+  Describe 'myos_group_expand'
+    It 'expands a group defined in the environment'
+      host="host/consul host/fabio"
+      When call myos_group_expand host
+      The line 1 should equal "host/consul"
+      The line 2 should equal "host/fabio"
+    End
+    It 'expands a group defined in a legacy .mk of the project'
+      When call myos_group_expand host
+      The line 1 should equal "host/consul"
+      The line 3 should equal "host/registrator"
+      The lines of output should equal 3
+    End
+    It 'expands a group of the shared catalogue'
+      When call myos_group_expand testing
+      The line 1 should equal "drone/drone"
+      The line 2 should equal "redis"
+    End
+    It 'expands recursively'
+      # shellcheck disable=SC2034
+      all="testing extra"; extra="redis"
+      When call myos_group_expand all
+      The lines of output should equal 3
+    End
+    It 'leaves a plain stack reference alone'
+      When call myos_group_expand postgres host/fabio
+      The line 1 should equal "postgres"
+      The line 2 should equal "host/fabio"
+    End
+    It 'refuses an endless group loop'
+      # shellcheck disable=SC2034
+      loop="loop"
+      When run myos_group_expand loop
+      The status should equal 2
+      The stderr should include "nested too deep"
+    End
+  End
+End