feat(cli): Dry run mode ( --dry-run flag) (#156)

This change adds a new flag `--dry-run` that when
given, prevents otherwise destructive file
overwrite operations and instead prints a rich
diff. The diff contains names of files which would
be modified, and a git-like (word) diff of what
modifications *would* be made.

The diff is human-readable, and not designed to be
easily machine-readable. It leverages the existing
search mode.

Closes #152.

README.md

@@ -1457,6 +1457,13 @@ Options (global):
           Processing no files is not an error condition in itself, but might be an
           unexpected outcome in some contexts. This flag makes the condition explicit.
 
+      --dry-run
+          Do not destructively overwrite files, instead print rich diff only.
+          
+          The diff details the names of files which would be modified, alongside all
+          changes inside those files which would be performed outside of dry running.
+          It is similar to git diff with word diffing enabled.
+
   -i, --invert
           Undo the effects of passed actions, where applicable.
           

src/actions/style.rs

@@ -13,6 +13,28 @@ pub struct Style {
     pub styles: Vec<Styles>,
 }
 
+impl Style {
+    /// Creates a style with red foreground color and bold font weight.
+    #[must_use]
+    pub fn red_bold() -> Self {
+        Self {
+            fg: Some(Color::Red),
+            bg: None,
+            styles: vec![Styles::Bold],
+        }
+    }
+
+    /// Creates a style with green foreground color and bold font weight.
+    #[must_use]
+    pub fn green_bold() -> Self {
+        Self {
+            fg: Some(Color::Green),
+            bg: None,
+            styles: vec![Styles::Bold],
+        }
+    }
+}
+
 impl Action for Style {
     fn act(&self, input: &str) -> String {
         const NEWLINE: char = '\n';

src/iterext.rs

@@ -0,0 +1,105 @@
+/// Extension trait that adds parallel zipping functionality to iterators over iterators.
+pub trait ParallelZipExt: Iterator {
+    /// Zips multiple iterators in parallel, such that the nth invocation yields a
+    /// [`Vec`] of all nth items of the subiterators.
+    fn parallel_zip(self) -> ParallelZip<Self::Item>
+    where
+        Self: Sized,
+        Self::Item: Iterator;
+}
+
+/// An iterator similar to [`std::iter::zip`], but instead it zips over *multiple
+/// iterators* in parallel, such that the nth invocation yields a [`Vec`] of all
+/// nth items of its subiterators.
+#[derive(Debug)]
+pub struct ParallelZip<I>(Vec<I>);
+
+impl<I: Iterator> Iterator for ParallelZip<I> {
+    type Item = Vec<I::Item>;
+
+    fn next(&mut self) -> Option<Self::Item> {
+        if self.0.is_empty() {
+            return None;
+        }
+
+        self.0.iter_mut().map(Iterator::next).collect()
+    }
+}
+
+// Implement the extension trait for any iterator whose items are themselves iterators
+impl<T> ParallelZipExt for T
+where
+    T: Iterator,
+    T::Item: Iterator,
+{
+    fn parallel_zip(self) -> ParallelZip<T::Item> {
+        ParallelZip(self.collect())
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use itertools::Itertools;
+    use rstest::rstest;
+
+    use super::*;
+
+    #[rstest]
+    #[case::empty_once(
+        Vec::<Vec<i32>>::new(),
+        Vec::new(),
+    )]
+    #[case::empty_twice(
+        vec![
+            vec![],
+            vec![],
+        ],
+        vec![],
+    )]
+    #[case::zips_to_shortest(
+        vec![
+            vec![0, 1, 2],
+            vec![3, 4],
+        ],
+        vec![
+            vec![0, 3],
+            vec![1, 4],
+        ]
+    )]
+    #[case::base_case(
+        vec![
+            vec![1, 2],
+            vec![3, 4],
+            vec![5, 6]
+        ],
+        vec![
+            vec![1, 3, 5],
+            vec![2, 4, 6]
+        ]
+    )]
+    #[case::transpose_horizontal(
+        vec![
+            vec![1, 2, 3],
+        ],
+        vec![
+            vec![1],
+            vec![2],
+            vec![3],
+        ]
+    )]
+    #[case::transpose_vertical(
+        vec![
+            vec![1],
+            vec![2],
+            vec![3]
+        ],
+        vec![
+            vec![1, 2, 3]
+        ]
+    )]
+    fn test_parallel_zip(#[case] input: Vec<Vec<i32>>, #[case] expected: Vec<Vec<i32>>) {
+        let iters = input.into_iter().map(IntoIterator::into_iter).collect_vec();
+        let res = iters.into_iter().parallel_zip().collect_vec();
+        assert_eq!(res, expected);
+    }
+}

src/lib.rs

@@ -195,3 +195,6 @@ pub const GLOBAL_SCOPE: &str = r".*";
 /// The type of regular expression used throughout the crate. Abstracts away the
 /// underlying implementation.
 pub use fancy_regex::Regex as RegexPattern;
+
+/// Custom iterator extensions.
+pub mod iterext;