fix(postgres.manage): only reload modules if needed; fixes #214

[alxwr]

Based on the great work of @RobRuana in #216.

Tested on FreeBSD 11.2 with Salt 2019.2.0.

• postgres-reload-modules only report changes (and reloads the modules) if necessary
  • uses test.configurable_test_state
• require is always present in the format_state macro, so we're just using it. (This part is not as clean as I want it to be, but I regard it as a trade-off. Maybe there are better ideas.)
• Changing Pillar data in a subsequent highstate run results in changed users, databases, etc., as requested in Makes postgres-reload-modules conditional #216 (comment).

[vutny]

@alxwr Thanks for picking up the issue.

I would like to explain the functionality which caused so many confusions. Below I will suggest a better way to handle this.

First of all, the postgres-reload-modules state changes is only required for one and only one thing:
set a flag that PG client binaries are now available. Because if they're not, all subsequent states would fail.
The main purpose is to be able to test Pillar values using state.apply mock=True call during initial state run. Since Salt will not do any job, there would be no binaries, and we'd get failures. No way to distinguish the failures caused by bad supplied data and missing requirements. So, to be able to verify that formula is reading your pillar data right, we need to have all states return True. And the only way to achieve that is trigger needed states only after some "fake" changes.

Depending on just reloading Salt modules doesn't make any difference, since Salt doesn't return any result back on that. It is always success. In my opinion, the proper way to fix it is to subscribe on changes only when the binaries aren't available on rendering time.

[vutny]

No need to have this configurable. We will make the default behavior correct, so there would be no undesired state changes.

[vutny]

Instead of making the hard requirement, I'd suggest to put a conditional like this:

    {%- if needs_client_binaries %}
    - onchanges:
       - test: postgres-reload-modules
    {%- endif %}

This would make changes only when the binaries were not available before, which is valid behavior.
Otherwise, there would not be any dependency on the test state, since it would actually do nothing.

[vutny]

Let's just make this very simple:

    - changes: {{ needs_client_binaries }}

Should work as expected.

[vutny]

Then, all requisite should be returned back.