exa/src/options/mod.rs

//! Parsing command-line strings into exa options.
//!
//! This module imports exa’s configuration types, such as `View` (the details
//! of displaying multiple files) and `DirAction` (what to do when encountering
//! a directory), and implements `deduce` methods on them so they can be
//! configured using command-line options.
//!
//!
//! ## Useless and overridden options
//!
//! Let’s say exa was invoked with just one argument: `exa --inode`. The
//! `--inode` option is used in the details view, where it adds the inode
//! column to the output. But because the details view is *only* activated with
//! the `--long` argument, adding `--inode` without it would not have any
//! effect.
//!
//! For a long time, exa’s philosophy was that the user should be warned
//! whenever they could be mistaken like this. If you tell exa to display the
//! inode, and it *doesn’t* display the inode, isn’t that more annoying than
//! having it throw an error back at you?
//!
//! However, this doesn’t take into account *configuration*. Say a user wants
//! to configure exa so that it lists inodes in the details view, but otherwise
//! functions normally. A common way to do this for command-line programs is to
//! define a shell alias that specifies the details they want to use every
//! time. For the inode column, the alias would be:
//!
//! `alias exa="exa --inode"`
//!
//! Using this alias means that although the inode column will be shown in the
//! details view, you’re now *only* allowed to use the details view, as any
//! other view type will result in an error. Oops!
//!
//! Another example is when an option is specified twice, such as `exa
//! --sort=Name --sort=size`. Did the user change their mind about sorting, and
//! accidentally specify the option twice?
//!
//! Again, exa rejected this case, throwing an error back to the user instead
//! of trying to guess how they want their output sorted. And again, this
//! doesn’t take into account aliases being used to set defaults. A user who
//! wants their files to be sorted case-insensitively may configure their shell
//! with the following:
//!
//! `alias exa="exa --sort=Name"`
//!
//! Just like the earlier example, the user now can’t use any other sort order,
//! because exa refuses to guess which one they meant. It’s *more* annoying to
//! have to go back and edit the command than if there were no error.
//!
//! Fortunately, there’s a heuristic for telling which options came from an
//! alias and which came from the actual command-line: aliased options are
//! nearer the beginning of the options array, and command-line options are
//! nearer the end. This means that after the options have been parsed, exa
//! needs to traverse them *backwards* to find the last-most-specified one.
//!
//! For example, invoking exa with `exa --sort=size` when that alias is present
//! would result in a full command-line of:
//!
//! `exa --sort=Name --sort=size`
//!
//! `--sort=size` should override `--sort=Name` because it’s closer to the end
//! of the arguments array. In fact, because there’s no way to tell where the
//! arguments came from -- it’s just a heuristic -- this will still work even
//! if no aliases are being used!
//!
//! Finally, this isn’t just useful when options could override each other.
//! Creating an alias `exal=”exa --long --inode --header”` then invoking `exal
//! --grid --long` shouldn’t complain about `--long` being given twice when
//! it’s clear what the user wants.


use std::ffi::{OsStr, OsString};

use fs::dir_action::DirAction;
use fs::filter::FileFilter;
use output::{View, Mode, details, grid_details};

mod colours;
mod dir_action;
mod filter;
mod view;

mod help;
use self::help::HelpString;

mod version;
use self::version::VersionString;

mod misfire;
pub use self::misfire::Misfire;

mod parser;
mod flags;
use self::parser::MatchedFlags;


/// These **options** represent a parsed, error-checked versions of the
/// user’s command-line options.
#[derive(Debug)]
pub struct Options {

    /// The action to perform when encountering a directory rather than a
    /// regular file.
    pub dir_action: DirAction,

    /// How to sort and filter files before outputting them.
    pub filter: FileFilter,

    /// The type of output to use (lines, grid, or details).
    pub view: View,
}

impl Options {

    /// Parse the given iterator of command-line strings into an Options
    /// struct and a list of free filenames, using the environment variables
    /// for extra options.
    #[allow(unused_results)]
    pub fn parse<'args, I, V>(args: I, vars: &V) -> Result<(Options, Vec<&'args OsStr>), Misfire>
    where I: IntoIterator<Item=&'args OsString>,
          V: Vars {
        use options::parser::{Matches, Strictness};

        let strictness = match vars.get("EXA_STRICT") {
            None                         => Strictness::UseLastArguments,
            Some(ref t) if t.is_empty()  => Strictness::UseLastArguments,
            _                            => Strictness::ComplainAboutRedundantArguments,
        };

        let Matches { flags, frees } = match flags::ALL_ARGS.parse(args, strictness) {
            Ok(m)   => m,
            Err(e)  => return Err(Misfire::InvalidOptions(e)),
        };

        HelpString::deduce(&flags).map_err(Misfire::Help)?;
        VersionString::deduce(&flags).map_err(Misfire::Version)?;

        let options = Options::deduce(&flags, vars)?;
        Ok((options, frees))
    }

    /// Whether the View specified in this set of options includes a Git
    /// status column. It’s only worth trying to discover a repository if the
    /// results will end up being displayed.
    pub fn should_scan_for_git(&self) -> bool {
        match self.view.mode {
            Mode::Details(details::Options { table: Some(ref table), .. }) |
            Mode::GridDetails(grid_details::Options { details: details::Options { table: Some(ref table), .. }, .. }) => table.extra_columns.should_scan_for_git(),
            _ => false,
        }
    }

    /// Determines the complete set of options based on the given command-line
    /// arguments, after they’ve been parsed.
    fn deduce<V: Vars>(matches: &MatchedFlags, vars: &V) -> Result<Options, Misfire> {
        let dir_action = DirAction::deduce(matches)?;
        let filter = FileFilter::deduce(matches)?;
        let view = View::deduce(matches, vars)?;

        Ok(Options { dir_action, view, filter })
    }
}


/// Mockable wrapper for `std::env::var_os`.
pub trait Vars {
    fn get(&self, name: &'static str) -> Option<OsString>;
}




#[cfg(test)]
pub mod test {
    use super::{Options, Misfire, Vars, flags};
    use options::parser::{Arg, MatchedFlags};
    use std::ffi::OsString;

    // Test impl that just returns the value it has.
    impl Vars for Option<OsString> {
        fn get(&self, _name: &'static str) -> Option<OsString> {
            self.clone()
        }
    }


    #[derive(PartialEq, Debug)]
    pub enum Strictnesses {
        Last,
        Complain,
        Both,
    }

    /// This function gets used by the other testing modules.
    /// It can run with one or both strictness values: if told to run with
    /// both, then both should resolve to the same result.
    ///
    /// It returns a vector with one or two elements in.
    /// These elements can then be tested with assert_eq or what have you.
    pub fn parse_for_test<T, F>(inputs: &[&str], args: &'static [&'static Arg], strictnesses: Strictnesses, get: F) -> Vec<T>
    where F: Fn(&MatchedFlags) -> T
    {
        use self::Strictnesses::*;
        use options::parser::{Args, Strictness};
        use std::ffi::OsString;

        let bits = inputs.into_iter().map(|&o| os(o)).collect::<Vec<OsString>>();
        let mut rezzies = Vec::new();

        if strictnesses == Last || strictnesses == Both {
            let results = Args(args).parse(bits.iter(), Strictness::UseLastArguments);
            rezzies.push(get(&results.unwrap().flags));
        }

        if strictnesses == Complain || strictnesses == Both {
            let results = Args(args).parse(bits.iter(), Strictness::ComplainAboutRedundantArguments);
            rezzies.push(get(&results.unwrap().flags));
        }

        rezzies
    }

    /// Creates an `OSStr` (used in tests)
    #[cfg(test)]
    fn os(input: &str) -> OsString {
        let mut os = OsString::new();
        os.push(input);
        os
    }

    #[test]
    fn files() {
        let args = [ os("this file"), os("that file") ];
        let outs = Options::parse(&args, &None).unwrap().1;
        assert_eq!(outs, vec![ &os("this file"), &os("that file") ])
    }

    #[test]
    fn no_args() {
        let nothing: Vec<OsString> = Vec::new();
        let outs = Options::parse(&nothing, &None).unwrap().1;
        assert!(outs.is_empty());  // Listing the `.` directory is done in main.rs
    }

    #[test]
    fn long_across() {
        let args = [ os("--long"), os("--across") ];
        let opts = Options::parse(&args, &None);
        assert_eq!(opts.unwrap_err(), Misfire::Useless(&flags::ACROSS, true, &flags::LONG))
    }

    #[test]
    fn oneline_across() {
        let args = [ os("--oneline"), os("--across") ];
        let opts = Options::parse(&args, &None);
        assert_eq!(opts.unwrap_err(), Misfire::Useless(&flags::ACROSS, true, &flags::ONE_LINE))
    }
}