modules: find module with TT_CLI_MODULES_PATH

[dmyger]

Closes #1013

@TarantoolBot document
Title: Use environment variable to find modules.

The TT_CLI_MODULES_PATH environment variable specifies a list of
module's paths separated by a colon “:”.
It can be set externally from tt and must contain a list of
folders where modules are located.
The logic of working with this variable is similar to the PATH
system variable.

Lists of modules are combined into one common list:

• The modules declared in the configuration file tt.yaml come first
• then the modules defined via the environment variable are added.
  Any duplicates must be removed, while maintaining the original
  order of module declarations.

Usage example
Set variable:

export TT_CLI_MODULES_PATH=/ext/path/modules:${TT_CLI_MODULES_PATH}

[oleg-jukovec]

Please, add a description to the commit messages, see:

#1030
tarantool/doc#4661

It will help to notify a doc team about changes.

[oleg-jukovec]

We can't break backward compatibility. So old tests should work.

[oleg-jukovec]

I think we could add an integration test that a module could be found in a path passed with the variable, not just in "modules". Could we?

[dmyger]

I think we could add an integration test

Yes, integration tests will need to be added. But they won't work at the current stage, as there is nothing to run to test yet. There is a task assigned to the tests #1039.

[oleg-jukovec]

I think we could add an integration test

Yes, integration tests will need to be added. But they won't work at the current stage, as there is nothing to run to test yet. There is a task assigned to the tests #1039.

Why not? In theory, the directory should add a module path, so we could add a test in which modules (in the current implementation) will be located at the path. Or am I missed something?

[dmyger]

Or am I missed something?

Creating an integration test requires that there should be a difference in external behaviour in the operation of the utility, and this has not yet been implemented.

Unit testing, in theory, allows for such verification. But we don't test implementation of private methods, while public methods don't have implementation until #1014 will be done.