diffutils/src/context_diff.rs

// This file is part of the uutils diffutils package.
//
// For the full copyright and license information, please view the LICENSE-*
// files that was distributed with this source code.

use std::collections::VecDeque;
use std::io::Write;

use crate::utils::do_write_line;

#[derive(Debug, PartialEq)]
pub enum DiffLine {
    Context(Vec<u8>),
    Change(Vec<u8>),
    Add(Vec<u8>),
}

#[derive(Debug, PartialEq)]
struct Mismatch {
    pub line_number_expected: usize,
    pub line_number_actual: usize,
    pub expected: Vec<DiffLine>,
    pub actual: Vec<DiffLine>,
    pub expected_missing_nl: bool,
    pub actual_missing_nl: bool,
    pub expected_all_context: bool,
    pub actual_all_context: bool,
}

impl Mismatch {
    fn new(line_number_expected: usize, line_number_actual: usize) -> Mismatch {
        Mismatch {
            line_number_expected,
            line_number_actual,
            expected: Vec::new(),
            actual: Vec::new(),
            expected_missing_nl: false,
            actual_missing_nl: false,
            expected_all_context: false,
            actual_all_context: false,
        }
    }
}

// Produces a diff between the expected output and actual output.
fn make_diff(
    expected: &[u8],
    actual: &[u8],
    context_size: usize,
    stop_early: bool,
) -> Vec<Mismatch> {
    let mut line_number_expected = 1;
    let mut line_number_actual = 1;
    let mut context_queue: VecDeque<&[u8]> = VecDeque::with_capacity(context_size);
    let mut lines_since_mismatch = context_size + 1;
    let mut results = Vec::new();
    let mut mismatch = Mismatch::new(0, 0);

    let mut expected_lines: Vec<&[u8]> = expected.split(|&c| c == b'\n').collect();
    let mut actual_lines: Vec<&[u8]> = actual.split(|&c| c == b'\n').collect();

    debug_assert_eq!(b"".split(|&c| c == b'\n').count(), 1);
    // ^ means that underflow here is impossible
    let expected_lines_count = expected_lines.len() - 1;
    let actual_lines_count = actual_lines.len() - 1;

    if expected_lines.last() == Some(&&b""[..]) {
        expected_lines.pop();
    }

    if actual_lines.last() == Some(&&b""[..]) {
        actual_lines.pop();
    }

    // Rust only allows allocations to grow to isize::MAX, and this is bigger than that.
    let mut expected_lines_change_idx: usize = !0;

    for result in diff::slice(&expected_lines, &actual_lines) {
        match result {
            diff::Result::Left(str) => {
                if lines_since_mismatch > context_size && lines_since_mismatch > 0 {
                    results.push(mismatch);
                    mismatch = Mismatch::new(
                        line_number_expected - context_queue.len(),
                        line_number_actual - context_queue.len(),
                    );
                }

                while let Some(line) = context_queue.pop_front() {
                    mismatch.expected.push(DiffLine::Context(line.to_vec()));
                    mismatch.actual.push(DiffLine::Context(line.to_vec()));
                }

                expected_lines_change_idx = mismatch.expected.len();
                mismatch.expected.push(DiffLine::Add(str.to_vec()));
                if line_number_expected > expected_lines_count {
                    mismatch.expected_missing_nl = true;
                }
                line_number_expected += 1;
                lines_since_mismatch = 0;
            }
            diff::Result::Right(str) => {
                if lines_since_mismatch > context_size && lines_since_mismatch > 0 {
                    results.push(mismatch);
                    mismatch = Mismatch::new(
                        line_number_expected - context_queue.len(),
                        line_number_actual - context_queue.len(),
                    );
                    expected_lines_change_idx = !0;
                }

                while let Some(line) = context_queue.pop_front() {
                    mismatch.expected.push(DiffLine::Context(line.to_vec()));
                    mismatch.actual.push(DiffLine::Context(line.to_vec()));
                }

                if let Some(DiffLine::Add(content)) =
                    mismatch.expected.get_mut(expected_lines_change_idx)
                {
                    let content = std::mem::take(content);
                    mismatch.expected[expected_lines_change_idx] = DiffLine::Change(content);
                    expected_lines_change_idx = expected_lines_change_idx.wrapping_sub(1); // if 0, becomes !0
                    mismatch.actual.push(DiffLine::Change(str.to_vec()));
                } else {
                    mismatch.actual.push(DiffLine::Add(str.to_vec()));
                }
                if line_number_actual > actual_lines_count {
                    mismatch.actual_missing_nl = true;
                }
                line_number_actual += 1;
                lines_since_mismatch = 0;
            }
            diff::Result::Both(str, _) => {
                expected_lines_change_idx = !0;
                // if one of them is missing a newline and the other isn't, then they don't actually match
                if (line_number_actual > actual_lines_count)
                    && (line_number_expected > expected_lines_count)
                {
                    if context_queue.len() < context_size {
                        while let Some(line) = context_queue.pop_front() {
                            mismatch.expected.push(DiffLine::Context(line.to_vec()));
                            mismatch.actual.push(DiffLine::Context(line.to_vec()));
                        }
                        if lines_since_mismatch < context_size {
                            mismatch.expected.push(DiffLine::Context(str.to_vec()));
                            mismatch.actual.push(DiffLine::Context(str.to_vec()));
                            mismatch.expected_missing_nl = true;
                            mismatch.actual_missing_nl = true;
                        }
                    }
                    lines_since_mismatch = 0;
                } else if line_number_actual > actual_lines_count {
                    if lines_since_mismatch >= context_size && lines_since_mismatch > 0 {
                        results.push(mismatch);
                        mismatch = Mismatch::new(
                            line_number_expected - context_queue.len(),
                            line_number_actual - context_queue.len(),
                        );
                    }
                    while let Some(line) = context_queue.pop_front() {
                        mismatch.expected.push(DiffLine::Context(line.to_vec()));
                        mismatch.actual.push(DiffLine::Context(line.to_vec()));
                    }
                    mismatch.expected.push(DiffLine::Change(str.to_vec()));
                    mismatch.actual.push(DiffLine::Change(str.to_vec()));
                    mismatch.actual_missing_nl = true;
                    lines_since_mismatch = 0;
                } else if line_number_expected > expected_lines_count {
                    if lines_since_mismatch >= context_size && lines_since_mismatch > 0 {
                        results.push(mismatch);
                        mismatch = Mismatch::new(
                            line_number_expected - context_queue.len(),
                            line_number_actual - context_queue.len(),
                        );
                    }
                    while let Some(line) = context_queue.pop_front() {
                        mismatch.expected.push(DiffLine::Context(line.to_vec()));
                        mismatch.actual.push(DiffLine::Context(line.to_vec()));
                    }
                    mismatch.expected.push(DiffLine::Change(str.to_vec()));
                    mismatch.expected_missing_nl = true;
                    mismatch.actual.push(DiffLine::Change(str.to_vec()));
                    lines_since_mismatch = 0;
                } else {
                    debug_assert!(context_queue.len() <= context_size);
                    if context_queue.len() >= context_size {
                        let _ = context_queue.pop_front();
                    }
                    if lines_since_mismatch < context_size {
                        mismatch.expected.push(DiffLine::Context(str.to_vec()));
                        mismatch.actual.push(DiffLine::Context(str.to_vec()));
                    } else if context_size > 0 {
                        context_queue.push_back(str);
                    }
                    lines_since_mismatch += 1;
                }
                line_number_expected += 1;
                line_number_actual += 1;
            }
        }
        if stop_early && !results.is_empty() {
            // Optimization: stop analyzing the files as soon as there are any differences
            return results;
        }
    }

    results.push(mismatch);
    results.remove(0);

    if results.is_empty() && expected_lines_count != actual_lines_count {
        let mut mismatch = Mismatch::new(expected_lines.len(), actual_lines.len());
        // empty diff and only expected lines has a missing line at end
        if expected_lines_count != expected_lines.len() {
            mismatch.expected.push(DiffLine::Change(
                expected_lines
                    .pop()
                    .expect("can't be empty; produced by split()")
                    .to_vec(),
            ));
            mismatch.expected_missing_nl = true;
            mismatch.actual.push(DiffLine::Change(
                actual_lines
                    .pop()
                    .expect("can't be empty; produced by split()")
                    .to_vec(),
            ));
            results.push(mismatch);
        } else if actual_lines_count != actual_lines.len() {
            mismatch.expected.push(DiffLine::Change(
                expected_lines
                    .pop()
                    .expect("can't be empty; produced by split()")
                    .to_vec(),
            ));
            mismatch.actual.push(DiffLine::Change(
                actual_lines
                    .pop()
                    .expect("can't be empty; produced by split()")
                    .to_vec(),
            ));
            mismatch.actual_missing_nl = true;
            results.push(mismatch);
        }
    }

    // hunks with pure context lines get truncated to empty
    for mismatch in &mut results {
        if !mismatch
            .expected
            .iter()
            .any(|x| !matches!(&x, DiffLine::Context(_)))
        {
            mismatch.expected_all_context = true;
        }
        if !mismatch
            .actual
            .iter()
            .any(|x| !matches!(&x, DiffLine::Context(_)))
        {
            mismatch.actual_all_context = true;
        }
    }

    results
}

#[must_use]
#[allow(clippy::too_many_arguments)]
pub fn diff(
    expected: &[u8],
    expected_filename: &str,
    actual: &[u8],
    actual_filename: &str,
    context_size: usize,
    stop_early: bool,
    expand_tabs: bool,
    tabsize: usize,
) -> Vec<u8> {
    let mut output = format!("*** {expected_filename}\t\n--- {actual_filename}\t\n").into_bytes();
    let diff_results = make_diff(expected, actual, context_size, stop_early);
    if diff_results.is_empty() {
        return Vec::new();
    }
    if stop_early {
        return output;
    }
    for result in diff_results {
        let mut line_number_expected = result.line_number_expected;
        let mut line_number_actual = result.line_number_actual;
        let mut expected_count = result.expected.len();
        let mut actual_count = result.actual.len();
        if expected_count == 0 {
            line_number_expected -= 1;
            expected_count = 1;
        }
        if actual_count == 0 {
            line_number_actual -= 1;
            actual_count = 1;
        }
        let end_line_number_expected = expected_count + line_number_expected - 1;
        let end_line_number_actual = actual_count + line_number_actual - 1;
        let exp_start = if end_line_number_expected == line_number_expected {
            String::new()
        } else {
            format!("{line_number_expected},")
        };
        let act_start = if end_line_number_actual == line_number_actual {
            String::new()
        } else {
            format!("{line_number_actual},")
        };
        writeln!(
            output,
            "***************\n*** {exp_start}{end_line_number_expected} ****"
        )
        .expect("write to Vec is infallible");
        if !result.expected_all_context {
            for line in result.expected {
                match line {
                    DiffLine::Context(e) => {
                        write!(output, "  ").expect("write to Vec is infallible");
                        do_write_line(&mut output, &e, expand_tabs, tabsize)
                            .expect("write to Vec is infallible");
                        writeln!(output).unwrap();
                    }
                    DiffLine::Change(e) => {
                        write!(output, "! ").expect("write to Vec is infallible");
                        do_write_line(&mut output, &e, expand_tabs, tabsize)
                            .expect("write to Vec is infallible");
                        writeln!(output).unwrap();
                    }
                    DiffLine::Add(e) => {
                        write!(output, "- ").expect("write to Vec is infallible");
                        do_write_line(&mut output, &e, expand_tabs, tabsize)
                            .expect("write to Vec is infallible");
                        writeln!(output).unwrap();
                    }
                }
            }
            if result.expected_missing_nl {
                writeln!(output, r"\ No newline at end of file")
                    .expect("write to Vec is infallible");
            }
        }
        writeln!(output, "--- {act_start}{end_line_number_actual} ----")
            .expect("write to Vec is infallible");
        if !result.actual_all_context {
            for line in result.actual {
                match line {
                    DiffLine::Context(e) => {
                        write!(output, "  ").expect("write to Vec is infallible");
                        do_write_line(&mut output, &e, expand_tabs, tabsize)
                            .expect("write to Vec is infallible");
                        writeln!(output).unwrap();
                    }
                    DiffLine::Change(e) => {
                        write!(output, "! ").expect("write to Vec is infallible");
                        do_write_line(&mut output, &e, expand_tabs, tabsize)
                            .expect("write to Vec is infallible");
                        writeln!(output).unwrap();
                    }
                    DiffLine::Add(e) => {
                        write!(output, "+ ").expect("write to Vec is infallible");
                        do_write_line(&mut output, &e, expand_tabs, tabsize)
                            .expect("write to Vec is infallible");
                        writeln!(output).unwrap();
                    }
                }
            }
            if result.actual_missing_nl {
                writeln!(output, r"\ No newline at end of file")
                    .expect("write to Vec is infallible");
            }
        }
    }
    output
}

#[cfg(test)]
mod tests {
    use super::*;
    use pretty_assertions::assert_eq;
    #[test]
    fn test_permutations() {
        // test all possible six-line files.
        let target = "target/context-diff/";
        let _ = std::fs::create_dir(target);
        for &a in &[0, 1, 2] {
            for &b in &[0, 1, 2] {
                for &c in &[0, 1, 2] {
                    for &d in &[0, 1, 2] {
                        for &e in &[0, 1, 2] {
                            for &f in &[0, 1, 2] {
                                use std::fs::{self, File};
                                use std::io::Write;
                                use std::process::Command;
                                let mut alef = Vec::new();
                                let mut bet = Vec::new();
                                alef.write_all(if a == 0 { b"a\n" } else { b"b\n" })
                                    .unwrap();
                                if a != 2 {
                                    bet.write_all(b"b\n").unwrap();
                                }
                                alef.write_all(if b == 0 { b"c\n" } else { b"d\n" })
                                    .unwrap();
                                if b != 2 {
                                    bet.write_all(b"d\n").unwrap();
                                }
                                alef.write_all(if c == 0 { b"e\n" } else { b"f\n" })
                                    .unwrap();
                                if c != 2 {
                                    bet.write_all(b"f\n").unwrap();
                                }
                                alef.write_all(if d == 0 { b"g\n" } else { b"h\n" })
                                    .unwrap();
                                if d != 2 {
                                    bet.write_all(b"h\n").unwrap();
                                }
                                alef.write_all(if e == 0 { b"i\n" } else { b"j\n" })
                                    .unwrap();
                                if e != 2 {
                                    bet.write_all(b"j\n").unwrap();
                                }
                                alef.write_all(if f == 0 { b"k\n" } else { b"l\n" })
                                    .unwrap();
                                if f != 2 {
                                    bet.write_all(b"l\n").unwrap();
                                }
                                // This test diff is intentionally reversed.
                                // We want it to turn the alef into bet.
                                let diff = diff(
                                    &alef,
                                    "a/alef",
                                    &bet,
                                    &format!("{target}/alef"),
                                    2,
                                    false,
                                    false,
                                    8,
                                );
                                File::create(&format!("{target}/ab.diff"))
                                    .unwrap()
                                    .write_all(&diff)
                                    .unwrap();
                                let mut fa = File::create(&format!("{target}/alef")).unwrap();
                                fa.write_all(&alef[..]).unwrap();
                                let mut fb = File::create(&format!("{target}/bet")).unwrap();
                                fb.write_all(&bet[..]).unwrap();
                                let _ = fa;
                                let _ = fb;
                                let output = Command::new("patch")
                                    .arg("-p0")
                                    .arg("--context")
                                    .stdin(File::open(&format!("{target}/ab.diff")).unwrap())
                                    .output()
                                    .unwrap();
                                assert!(output.status.success(), "{:?}", output);
                                //println!("{}", String::from_utf8_lossy(&output.stdout));
                                //println!("{}", String::from_utf8_lossy(&output.stderr));
                                let alef = fs::read(&format!("{target}/alef")).unwrap();
                                assert_eq!(alef, bet);
                            }
                        }
                    }
                }
            }
        }
    }

    #[test]
    fn test_permutations_empty_lines() {
        let target = "target/context-diff/";
        // test all possible six-line files with missing newlines.
        let _ = std::fs::create_dir(target);
        for &a in &[0, 1, 2] {
            for &b in &[0, 1, 2] {
                for &c in &[0, 1, 2] {
                    for &d in &[0, 1, 2] {
                        for &e in &[0, 1, 2] {
                            for &f in &[0, 1, 2] {
                                use std::fs::{self, File};
                                use std::io::Write;
                                use std::process::Command;
                                let mut alef = Vec::new();
                                let mut bet = Vec::new();
                                alef.write_all(if a == 0 { b"\n" } else { b"b\n" }).unwrap();
                                if a != 2 {
                                    bet.write_all(b"b\n").unwrap();
                                }
                                alef.write_all(if b == 0 { b"\n" } else { b"d\n" }).unwrap();
                                if b != 2 {
                                    bet.write_all(b"d\n").unwrap();
                                }
                                alef.write_all(if c == 0 { b"\n" } else { b"f\n" }).unwrap();
                                if c != 2 {
                                    bet.write_all(b"f\n").unwrap();
                                }
                                alef.write_all(if d == 0 { b"\n" } else { b"h\n" }).unwrap();
                                if d != 2 {
                                    bet.write_all(b"h\n").unwrap();
                                }
                                alef.write_all(if e == 0 { b"\n" } else { b"j\n" }).unwrap();
                                if e != 2 {
                                    bet.write_all(b"j\n").unwrap();
                                }
                                alef.write_all(if f == 0 { b"\n" } else { b"l\n" }).unwrap();
                                if f != 2 {
                                    bet.write_all(b"l\n").unwrap();
                                }
                                // This test diff is intentionally reversed.
                                // We want it to turn the alef into bet.
                                let diff = diff(
                                    &alef,
                                    "a/alef_",
                                    &bet,
                                    &format!("{target}/alef_"),
                                    2,
                                    false,
                                    false,
                                    8,
                                );
                                File::create(&format!("{target}/ab_.diff"))
                                    .unwrap()
                                    .write_all(&diff)
                                    .unwrap();
                                let mut fa = File::create(&format!("{target}/alef_")).unwrap();
                                fa.write_all(&alef[..]).unwrap();
                                let mut fb = File::create(&format!("{target}/bet_")).unwrap();
                                fb.write_all(&bet[..]).unwrap();
                                let _ = fa;
                                let _ = fb;
                                let output = Command::new("patch")
                                    .arg("-p0")
                                    .arg("--context")
                                    .stdin(File::open(&format!("{target}/ab_.diff")).unwrap())
                                    .output()
                                    .unwrap();
                                assert!(output.status.success(), "{:?}", output);
                                //println!("{}", String::from_utf8_lossy(&output.stdout));
                                //println!("{}", String::from_utf8_lossy(&output.stderr));
                                let alef = fs::read(&format!("{target}/alef_")).unwrap();
                                assert_eq!(alef, bet);
                            }
                        }
                    }
                }
            }
        }
    }

    #[test]
    fn test_permutations_missing_lines() {
        let target = "target/context-diff/";
        // test all possible six-line files.
        let _ = std::fs::create_dir(target);
        for &a in &[0, 1, 2] {
            for &b in &[0, 1, 2] {
                for &c in &[0, 1, 2] {
                    for &d in &[0, 1, 2] {
                        for &e in &[0, 1, 2] {
                            for &f in &[0, 1, 2] {
                                use std::fs::{self, File};
                                use std::io::Write;
                                use std::process::Command;
                                let mut alef = Vec::new();
                                let mut bet = Vec::new();
                                alef.write_all(if a == 0 { b"a\n" } else { b"" }).unwrap();
                                if a != 2 {
                                    bet.write_all(b"b\n").unwrap();
                                }
                                alef.write_all(if b == 0 { b"c\n" } else { b"" }).unwrap();
                                if b != 2 {
                                    bet.write_all(b"d\n").unwrap();
                                }
                                alef.write_all(if c == 0 { b"e\n" } else { b"" }).unwrap();
                                if c != 2 {
                                    bet.write_all(b"f\n").unwrap();
                                }
                                alef.write_all(if d == 0 { b"g\n" } else { b"" }).unwrap();
                                if d != 2 {
                                    bet.write_all(b"h\n").unwrap();
                                }
                                alef.write_all(if e == 0 { b"i\n" } else { b"" }).unwrap();
                                if e != 2 {
                                    bet.write_all(b"j\n").unwrap();
                                }
                                alef.write_all(if f == 0 { b"k\n" } else { b"" }).unwrap();
                                if f != 2 {
                                    bet.write_all(b"l\n").unwrap();
                                }
                                if alef.is_empty() && bet.is_empty() {
                                    continue;
                                };
                                // This test diff is intentionally reversed.
                                // We want it to turn the alef into bet.
                                let diff = diff(
                                    &alef,
                                    "a/alefx",
                                    &bet,
                                    &format!("{target}/alefx"),
                                    2,
                                    false,
                                    false,
                                    8,
                                );
                                File::create(&format!("{target}/abx.diff"))
                                    .unwrap()
                                    .write_all(&diff)
                                    .unwrap();
                                let mut fa = File::create(&format!("{target}/alefx")).unwrap();
                                fa.write_all(&alef[..]).unwrap();
                                let mut fb = File::create(&format!("{target}/betx")).unwrap();
                                fb.write_all(&bet[..]).unwrap();
                                let _ = fa;
                                let _ = fb;
                                let output = Command::new("patch")
                                    .arg("-p0")
                                    .arg("--context")
                                    .stdin(File::open(&format!("{target}/abx.diff")).unwrap())
                                    .output()
                                    .unwrap();
                                assert!(output.status.success(), "{:?}", output);
                                //println!("{}", String::from_utf8_lossy(&output.stdout));
                                //println!("{}", String::from_utf8_lossy(&output.stderr));
                                let alef = fs::read(&format!("{target}/alefx")).unwrap();
                                assert_eq!(alef, bet);
                            }
                        }
                    }
                }
            }
        }
    }

    #[test]
    fn test_permutations_reverse() {
        let target = "target/context-diff/";
        // test all possible six-line files.
        let _ = std::fs::create_dir(target);
        for &a in &[0, 1, 2] {
            for &b in &[0, 1, 2] {
                for &c in &[0, 1, 2] {
                    for &d in &[0, 1, 2] {
                        for &e in &[0, 1, 2] {
                            for &f in &[0, 1, 2] {
                                use std::fs::{self, File};
                                use std::io::Write;
                                use std::process::Command;
                                let mut alef = Vec::new();
                                let mut bet = Vec::new();
                                alef.write_all(if a == 0 { b"a\n" } else { b"f\n" })
                                    .unwrap();
                                if a != 2 {
                                    bet.write_all(b"a\n").unwrap();
                                }
                                alef.write_all(if b == 0 { b"b\n" } else { b"e\n" })
                                    .unwrap();
                                if b != 2 {
                                    bet.write_all(b"b\n").unwrap();
                                }
                                alef.write_all(if c == 0 { b"c\n" } else { b"d\n" })
                                    .unwrap();
                                if c != 2 {
                                    bet.write_all(b"c\n").unwrap();
                                }
                                alef.write_all(if d == 0 { b"d\n" } else { b"c\n" })
                                    .unwrap();
                                if d != 2 {
                                    bet.write_all(b"d\n").unwrap();
                                }
                                alef.write_all(if e == 0 { b"e\n" } else { b"b\n" })
                                    .unwrap();
                                if e != 2 {
                                    bet.write_all(b"e\n").unwrap();
                                }
                                alef.write_all(if f == 0 { b"f\n" } else { b"a\n" })
                                    .unwrap();
                                if f != 2 {
                                    bet.write_all(b"f\n").unwrap();
                                }
                                // This test diff is intentionally reversed.
                                // We want it to turn the alef into bet.
                                let diff = diff(
                                    &alef,
                                    "a/alefr",
                                    &bet,
                                    &format!("{target}/alefr"),
                                    2,
                                    false,
                                    false,
                                    8,
                                );
                                File::create(&format!("{target}/abr.diff"))
                                    .unwrap()
                                    .write_all(&diff)
                                    .unwrap();
                                let mut fa = File::create(&format!("{target}/alefr")).unwrap();
                                fa.write_all(&alef[..]).unwrap();
                                let mut fb = File::create(&format!("{target}/betr")).unwrap();
                                fb.write_all(&bet[..]).unwrap();
                                let _ = fa;
                                let _ = fb;
                                let output = Command::new("patch")
                                    .arg("-p0")
                                    .arg("--context")
                                    .stdin(File::open(&format!("{target}/abr.diff")).unwrap())
                                    .output()
                                    .unwrap();
                                assert!(output.status.success(), "{:?}", output);
                                //println!("{}", String::from_utf8_lossy(&output.stdout));
                                //println!("{}", String::from_utf8_lossy(&output.stderr));
                                let alef = fs::read(&format!("{target}/alefr")).unwrap();
                                assert_eq!(alef, bet);
                            }
                        }
                    }
                }
            }
        }
    }

    #[test]
    fn test_stop_early() {
        let from_filename = "foo";
        let from = ["a", "b", "c", ""].join("\n");
        let to_filename = "bar";
        let to = ["a", "d", "c", ""].join("\n");
        let context_size: usize = 3;

        let diff_full = diff(
            from.as_bytes(),
            from_filename,
            to.as_bytes(),
            to_filename,
            context_size,
            false,
            false,
            8,
        );
        let expected_full = [
            "*** foo\t",
            "--- bar\t",
            "***************",
            "*** 1,3 ****",
            "  a",
            "! b",
            "  c",
            "--- 1,3 ----",
            "  a",
            "! d",
            "  c",
            "",
        ]
        .join("\n");
        assert_eq!(diff_full, expected_full.as_bytes());

        let diff_brief = diff(
            from.as_bytes(),
            from_filename,
            to.as_bytes(),
            to_filename,
            context_size,
            true,
            false,
            8,
        );
        let expected_brief = ["*** foo\t", "--- bar\t", ""].join("\n");
        assert_eq!(diff_brief, expected_brief.as_bytes());

        let nodiff_full = diff(
            from.as_bytes(),
            from_filename,
            from.as_bytes(),
            to_filename,
            context_size,
            false,
            false,
            8,
        );
        assert!(nodiff_full.is_empty());

        let nodiff_brief = diff(
            from.as_bytes(),
            from_filename,
            from.as_bytes(),
            to_filename,
            context_size,
            true,
            false,
            8,
        );
        assert!(nodiff_brief.is_empty());
    }
}