Improve handling of the default schema paths

[tobim]

This PR removes the baking to the install prefix from the binary.

• The path to the lowest priority schema files was already determined relative to the binary location at runtime. Now the help message properly reflects that.
• The fallback path to vast.conf is now also determined by the runtime location.

This fixes 2 bugs:

1. VAST_RELOCATABLE_INSTALL was not really relocatable because the paths above would not update on relocations.
2. The CMAKE_INSTALL_PREFIX leaked into the static binary, which is relocatable by definition.

In addition, this PR also adds /etc/vast/schema to the schema file lookup path.

[dominiklohmann]

Can you revert the change to the lookup order? PREFIX/etc/vast/vast.conf should come before /etc/vast/vast.conf in the ordering, and this PR changes that.

[tobim]

Can you revert the change to the lookup order? PREFIX/etc/vast/vast.conf should come before /etc/vast/vast.conf in the ordering, and this PR changes that.

That was intentional. As a user, I would intuitively edit /etc/vast/vast.conf and expect my changes to take effect, with the old ordering that expectation would not always be met. To me this is another small bump in the road that might negatively effect my evaluation of VAST.

[dominiklohmann]

That was intentional. As a user, I would intuitively edit /etc/vast/vast.conf and expect my changes to take effect, with the old ordering that expectation would not always be met.

I don't get it. The usual behavior for programs is that the more specific a path to a configuration file, the earlier it should be in the lookup path. I think we should discuss this separately within the team (including ops) and have a vote on the expected and desired user experience.

As a side note: if this change was intentional, it should be reflected as such in the changelog.

[mavam]

The usual behavior for programs is that the more specific a path to a configuration file, the earlier it should be in the lookup path.

That's also my understanding. A home config file takes precedence over system-wide installed version. In that sense, /etc/vast is system and if the prefix is not /, it's more specific than the system.

[tobim]

I can only speak of what I'm used to and to some extent expect:

The configuration of a program is normally composed of 3 parts in order of precedence:

1. The user level config, found in ~/.vast/vast.conf or ~/.config/vast/vast.conf (FSB scheme)
2. The system level config in /etc/vast/vast.conf
3. The defaults built into the application

What vast does at the moment:

1. $PWD/vast.conf (A)
2. <prefix>/share/vast/vast.conf (B)
3. /etc/vast/vast.conf
4. defaults

That's also my understanding. A home config file takes precedence over system-wide installed version. In that sense, /etc/vast is system and if the prefix is not /, it's more specific than the system.

This is not the way I think about the issue. <prefix>/share/vast/ contains settings defined by the upstream or vendor, thus they are the least specific. /etc/vast/ contains settings by the system administrator, thus they are more specific.

[tobim]

I think this change should be discussed in a separate thread though. I'm going to revert the change for this PR.

[dominiklohmann]

I verified in a Docker container that the additional schema paths get picked up.