Confusing configuration sources might lead to (more) development errors

Context and description

rustic has three complementary ways of being prompted a configuration.

the CLI arguments
the environment variables
the TOML configuration profile file

the current design of rustic makes it that the implementation of command (such as forget or webdav) has access to two different configurations:

a static global RUSTIC_APP.config() where all the sources were merged
a &self reference to the CLI (clap parsed) instance that only has the CLI

Example

issue: #1163 fix PR: #1241

code before the fix (https://github.com/rustic-rs/rustic/blob/abf1835cbdf5804806a1106cfb88b4cd3b20e0d9/src/commands/webdav.rs#L68C1-L104C1):

impl WebDavCmd {
    // [+] &self is a reference to a `WebDavCmd` where the fields are only representing the CLI args
    // we musn't use it because it lacks the config from `ENV` or `TOML`
    fn inner_run(&self) -> Result<()> {
        // [+] this config is complete, the TOML, ENV and CLI were merged to produce this config struct instance.
        // the correct `WebDavCmd` can be found in `RUSTIC_APP.config().webdav`
        let config = RUSTIC_APP.config();
        let repo = open_repository_indexed(&config.repository)?;

        // [+] this is the bugged code. 
        // Here by using `self` we ignore the `path_template` that could be defined in the `rustic.toml`
        let path_template = self
            .path_template
            .clone()
            .unwrap_or_else(|| "[{hostname}]/[{label}]/{time}".to_string());

        // [+] same here
        let time_template = self
            .time_template
            .clone()
            .unwrap_or_else(|| "%Y-%m-%d_%H-%M-%S".to_string());

       // ...

        // [+] same here
        let addr = self
            .address
            .clone()
            .unwrap_or_else(|| "localhost:8000".to_string())
            .to_socket_addrs()?
            .next()
            .ok_or_else(|| anyhow!("no address given"))?;

        // ....

To correct this, the #1241 PR came with changes similar to:

-        let path_template = self
+        let path_template = config
+            .webdav
             .path_template
             .clone()
             .unwrap_or_else(|| "[{hostname}]/[{label}]/{time}".to_string());

Why an issue, if this is fixed

This bug is purely a developers' problem. By the current design, the type system is not able to verify that we don't use self when we shouldn't. And sometimes we should (forget command for instance).

For this reason, we need to reflect on design updates and refactors that would solve this issue. The design reflection will include (but not only) the role of the abscissa framework, our usage of it, and how it fits to our needs.

This issue will track the related design change.

Do not hesitate if you have any prompt, question, advice and all.

rustic-rs / rustic