Add proper error message when using conflicting flags (e.g. --yes --no)

[vrmiguel]

No description provided.

[marcospb19]

This should definitely be a FinalError crashing at src/cli.rs

ouch/src/cli.rs

Lines 28 to 50 in 17d8959

	/// Calls parse_args_and_flags_from using argv (std::env::args_os)
	///
	/// This function is also responsible for treating and checking the command-line input,
	/// such as calling [`canonicalize`](std::fs::canonicalize), checking if it the given files exists, etc.
	pub fn parse_args() -> crate::Result<ParsedArgs> {
	// From argv, but ignoring empty arguments
	let args = env::args_os().skip(1).filter(|arg| !arg.is_empty()).collect();
	let mut parsed_args = parse_args_from(args)?;
	// If has a list of files, canonicalize them, reporting error if they do not exist
	match &mut parsed_args.command {
	Command::Compress { files, .. } | Command::Decompress { files, .. } => {
	*files = canonicalize_files(files)?;
	}
	_ => {}
	}
	if parsed_args.flags.is_present("yes") && parsed_args.flags.is_present("no") {
	todo!("conflicting flags, better error message.");
	}
	Ok(parsed_args)
	}

[SpyrosRoum]

Would it be better to use Error::Custom for this or create a new OofError variant like OofError::ConflictedFlag?
There already is OofError::FlagValueConflict but I don't think it's suitable for this

[marcospb19]

@SpyrosRoum I think that Error::Custom would require less effort, and OofError is weird. However, we are planing on migrating to clap, and with clap we will be able to specify that those flags conflict, no need to manually add error variants.

The reasons why we chose to go with custom argparsing are now looking less important than the features we will get by using that crate, like shell completions and man pages (Also, editing the help message manually is painful).

That's a recent decision, so maybe I should create a issue for that.

Do you prefer closing this issue now or waiting for clap to solve it?

[SpyrosRoum]

I can push the implementation I have with Error::Custom since it's just a couple of lines and could be included in 0.2.1 and then it can be replaced with clap.