rust/rhg/src/commands/debugrequirements.rs

rust: replace most "operation" structs with functions

The hg-core crate has a partially-formed concept of "operation",
represented as structs with constructors and a `run` method.

Each struct’s contructor takes different parameters,
and each `run` has a different return type.
Constructors typically don’t do much more than store parameters
for `run` to access them.

There was a comment about adding an `Operation` trait
when the language supports expressing something so general,
but it’s hard to imagine how operations with such different APIs
could be used in a generic context.

This commit starts removing the concept of "operation",
since those are pretty much just functions.

Differential Revision: https://phab.mercurial-scm.org/D9595

use crate::commands::Command;
use crate::error::CommandError;
use crate::ui::Ui;
use hg::operations::find_root;
use hg::requirements;

pub const HELP_TEXT: &str = "
Print the current repo requirements.
";

pub struct DebugRequirementsCommand {}

impl DebugRequirementsCommand {
    pub fn new() -> Self {
        DebugRequirementsCommand {}
    }
}

impl Command for DebugRequirementsCommand {
    fn run(&self, ui: &Ui) -> Result<(), CommandError> {
        let root = find_root()?;
        let mut output = String::new();
        for req in requirements::load(&root)? {
            output.push_str(&req);
            output.push('\n');
        }
        ui.write_stdout(output.as_bytes())?;
        Ok(())
    }
}