Implement specific errors for parser types

[mara-schulke]

          This is a nitpick, feel free to ignore.

I would add a proper error type here. It is not too much work, and you have the benefit of having more readable code, because you are not mixing business logic and error messages. Additionally, it is much easier to use miette's advanced features such as error codes that way without cluttering the code itself too much.

Example:

#[derive(thiserror::Error, miette::Diagnostic, Debug)]
pub enum DependencyLocatorError {
    #[error("locator {dependency} is missing a repository delimiter")]
    #[diagnostic(
        code = "locator_missing_dependency",
        help = "try to check your dependencies to ensure they are properly formatted"
    )]
    MissingDelimiter {
        dependency: String,
    },

    #[error("locator {dependency} is missing a repository delimiter")]
    #[diagnostic(
        code = "locator_missing_version",
        help = "make sure you specify the version you want"
    )]
    MissingVersion {
        dependency: String,
    },

    #[error("invalid package name")]
    InvalidPackageName(#[from] #[diagnostic_source] PackageNameError),
}

And then you use this in the code like this:

let (repository, dependency) = dependency
    .trim()
    .split_once('/')
    .ok_or_else(|| DependencyLocatorError::MissingDelimiter { dependency })?;

Only when you tie them all together (for example, in the main function) you should use miette::Report instead.

My feeling is that I would not allow using miette::Report in FromStr implementations. It is perfectly fine to use for the main function, where you are tying together errors from various sources. But in things such as FromStr or TryFrom, I generally don't allow the use of non-structured errors.

Originally posted by @xfbs in #131 (comment)