assertr 0.5.2

Fluent assertions for the Rust programming language.
Documentation 
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use alloc::string::String;
use alloc::vec::Vec;
use core::fmt::{Arguments, Write};

use crate::{
    AssertThat,
    details::{DetailMessages, WithDetail},
    prelude::Mode,
};

pub trait Failure {
    /// Writes the failure message to the target string.
    ///
    /// # Errors
    ///
    /// Returns a `core::fmt::Error` if writing to the target string fails.
    fn write_to(self, target: &mut String) -> std::fmt::Result;
}

impl Failure for &str {
    fn write_to(self, target: &mut String) -> core::fmt::Result {
        target.write_str(self)
    }
}

impl Failure for Arguments<'_> {
    fn write_to(self, target: &mut String) -> core::fmt::Result {
        target.write_fmt(self)
    }
}

impl<F> Failure for F
where
    F: FnOnce(&mut String) -> core::fmt::Result,
{
    fn write_to(self, target: &mut String) -> core::fmt::Result {
        self(target)
    }
}

pub(crate) trait Fallible {
    fn store_failure(&self, failure: String);
}

impl<T, M: Mode> Fallible for AssertThat<'_, T, M> {
    fn store_failure(&self, failure: String) {
        match &self.parent {
            Some(parent) => parent.store_failure(failure),
            None => self.failures.borrow_mut().push(failure),
        }
    }
}

impl<T, M: Mode> AssertThat<'_, T, M> {
    /// Records or raises a failure message.
    ///
    /// # Panics
    ///
    /// Panics with the formatted failure message when not in capture mode.
    #[track_caller]
    pub fn fail(&self, failure: impl Failure) {
        let mut detail_messages = Vec::new();
        self.collect_messages(&mut detail_messages);

        let msg = build_failure_message(
            self.print_location,
            self.subject_name.as_deref(),
            &detail_messages,
            failure,
        )
        .expect("no write error");

        // TODO: Check is_capture in root! Do not allow with_capture() on derived asserts.
        if self.mode.borrow().is_capture() {
            self.store_failure(msg);
        } else {
            panic!("{msg}");
        }
    }
}

#[track_caller]
fn build_failure_message(
    print_location: bool,
    subject_name: Option<&str>,
    detail_messages: &[String],
    failure: impl Failure,
) -> Result<String, core::fmt::Error> {
    let mut err = String::new();

    err.write_str("-------- assertr --------\n")?;

    if print_location {
        let caller_location = core::panic::Location::caller();
        let _ = err.write_fmt(format_args!(
            "Assertion failed at {file}:{line}:{column}\n\n",
            file = caller_location.file(),
            line = caller_location.line(),
            column = caller_location.column(),
        ));
    }

    if let Some(subject_name) = subject_name {
        err.write_fmt(format_args!("Subject: {subject_name}\n\n"))?;
    }

    failure.write_to(&mut err)?;

    if !detail_messages.is_empty() {
        err.write_str("\n")?;
        let detail_messages = DetailMessages(detail_messages);
        err.write_fmt(format_args!("Details: {detail_messages:#?}\n"))?;
    }

    err.write_str("-------- assertr --------\n")?;

    Ok(err)
}