feat(report): Diff output mode

Cargo.toml

@@ -47,6 +47,7 @@ log = "0.4"
 env_logger = "0.8"
 bstr = "0.2"
 ahash = "0.5.8"
+difflib = "0.4"
 
 [dev-dependencies]
 assert_fs = "1.0"

src/args.rs

@@ -54,6 +54,10 @@ pub(crate) struct Args {
     /// Ignore implicit configuration files.
     pub(crate) isolated: bool,
 
+    #[structopt(long)]
+    /// Print a diff of what would change
+    pub(crate) diff: bool,
+
     #[structopt(long, short = "w")]
     /// Write corrections out
     pub(crate) write_changes: bool,

src/diff.rs

@@ -0,0 +1,93 @@
+use std::collections::BTreeMap;
+use std::sync;
+
+use bstr::ByteSlice;
+
+pub struct Diff<'r> {
+    reporter: &'r dyn typos::report::Report,
+    deferred: sync::Mutex<crate::replace::Deferred>,
+}
+
+impl<'r> Diff<'r> {
+    pub(crate) fn new(reporter: &'r dyn typos::report::Report) -> Self {
+        Self {
+            reporter,
+            deferred: sync::Mutex::new(crate::replace::Deferred::default()),
+        }
+    }
+
+    pub fn show(&self) -> Result<(), std::io::Error> {
+        let deferred = self.deferred.lock().unwrap();
+
+        for (path, corrections) in deferred.content.iter() {
+            let buffer = std::fs::read(path)?;
+
+            let mut original = Vec::new();
+            let mut corrected = Vec::new();
+            for (line_idx, line) in buffer.lines_with_terminator().enumerate() {
+                original.push(String::from_utf8_lossy(line).into_owned());
+
+                let line_num = line_idx + 1;
+                let line = if let Some(corrections) = corrections.get(&line_num) {
+                    let line = line.to_vec();
+                    crate::replace::correct(line, &corrections)
+                } else {
+                    line.to_owned()
+                };
+                corrected.push(String::from_utf8_lossy(&line).into_owned())
+            }
+
+            let display_path = path.display().to_string();
+            let diff = difflib::unified_diff(
+                &original,
+                &corrected,
+                display_path.as_str(),
+                display_path.as_str(),
+                "original",
+                "corrected",
+                0,
+            );
+            for line in diff {
+                print!("{}", line);
+            }
+        }
+
+        Ok(())
+    }
+}
+
+impl<'r> typos::report::Report for Diff<'r> {
+    fn report(&self, msg: typos::report::Message<'_>) -> bool {
+        let typo = match &msg {
+            typos::report::Message::Typo(typo) => typo,
+            _ => return self.reporter.report(msg),
+        };
+
+        let corrections = match &typo.corrections {
+            typos::Status::Corrections(corrections) if corrections.len() == 1 => corrections,
+            _ => return self.reporter.report(msg),
+        };
+
+        match &typo.context {
+            Some(typos::report::Context::File(file)) => {
+                let path = file.path.to_owned();
+                let line_num = file.line_num;
+                let correction = crate::replace::Correction::new(
+                    typo.byte_offset,
+                    typo.typo,
+                    corrections[0].as_ref(),
+                );
+                let mut deferred = self.deferred.lock().unwrap();
+                let content = deferred
+                    .content
+                    .entry(path)
+                    .or_insert_with(BTreeMap::new)
+                    .entry(line_num)
+                    .or_insert_with(Vec::new);
+                content.push(correction);
+                false
+            }
+            _ => msg.is_correction(),
+        }
+    }
+}

src/main.rs

@@ -10,6 +10,7 @@ mod args;
 mod checks;
 mod config;
 mod dict;
+mod diff;
 mod replace;
 
 fn main() {
@@ -86,7 +87,10 @@ fn run() -> Result<i32, anyhow::Error> {
 
         let mut reporter = args.format.reporter();
         let replace_reporter = replace::Replace::new(reporter);
-        if args.write_changes {
+        let diff_reporter = diff::Diff::new(reporter);
+        if args.diff {
+            reporter = &diff_reporter;
+        } else if args.write_changes {
             reporter = &replace_reporter;
         }
 
@@ -129,7 +133,9 @@ fn run() -> Result<i32, anyhow::Error> {
             errors_found = true;
         }
 
-        if args.write_changes {
+        if args.diff {
+            diff_reporter.show()?;
+        } else if args.write_changes {
             replace_reporter.write()?;
         }
     }

src/replace.rs

@@ -97,20 +97,20 @@ impl<'r> typos::report::Report for Replace<'r> {
 }
 
 #[derive(Clone, Debug, Default)]
-struct Deferred {
-    content: BTreeMap<path::PathBuf, BTreeMap<usize, Vec<Correction>>>,
-    paths: BTreeMap<path::PathBuf, Vec<Correction>>,
+pub(crate) struct Deferred {
+    pub(crate) content: BTreeMap<path::PathBuf, BTreeMap<usize, Vec<Correction>>>,
+    pub(crate) paths: BTreeMap<path::PathBuf, Vec<Correction>>,
 }
 
 #[derive(Clone, Debug, PartialOrd, Ord, PartialEq, Eq)]
-struct Correction {
+pub(crate) struct Correction {
     pub byte_offset: usize,
     pub typo: Vec<u8>,
     pub correction: Vec<u8>,
 }
 
 impl Correction {
-    fn new(byte_offset: usize, typo: &str, correction: &str) -> Self {
+    pub(crate) fn new(byte_offset: usize, typo: &str, correction: &str) -> Self {
         Self {
             byte_offset,
             typo: typo.as_bytes().to_vec(),
@@ -119,7 +119,7 @@ impl Correction {
     }
 }
 
-fn correct(mut line: Vec<u8>, corrections: &[Correction]) -> Vec<u8> {
+pub(crate) fn correct(mut line: Vec<u8>, corrections: &[Correction]) -> Vec<u8> {
     let mut corrections: Vec<_> = corrections.iter().collect();
     corrections.sort_unstable();
     corrections.reverse();