Add diff write mode https://github.com/nrc/rustfmt/issues/261

4 files changed, 129 insertions, 2 deletions

diff --git a/src/bin/rustfmt.rs b/src/bin/rustfmt.rs
index 86a4faa05f5..9f2387f5c2c 100644
--- a/src/bin/rustfmt.rs
+++ b/src/bin/rustfmt.rs
@@ -82,7 +82,7 @@ fn main() {
 }
 
 fn print_usage<S: Into<String>>(reason: S) {
-    println!("{}\n\r usage: rustfmt [-h Help] [--write-mode=[replace|overwrite|display]] <file_name>", reason.into());
+    println!("{}\n\r usage: rustfmt [-h Help] [--write-mode=[replace|overwrite|display|diff]] <file_name>", reason.into());
 }
 
 fn determine_params<I>(args: I) -> Option<(Vec<String>, WriteMode)>
diff --git a/src/filemap.rs b/src/filemap.rs
index 8bb5a7285bb..91aaece6558 100644
--- a/src/filemap.rs
+++ b/src/filemap.rs
@@ -14,10 +14,11 @@
 use strings::string_buffer::StringBuffer;
 use std::collections::HashMap;
 use std::fs::{self, File};
-use std::io::{self, Write, stdout};
+use std::io::{self, Write, Read, stdout};
 use WriteMode;
 use NewlineStyle;
 use config::Config;
+use rustfmt_diff::{make_diff, print_diff};
 
 // A map of the files of a crate, with their new content
 pub type FileMap = HashMap<String, StringBuffer>;
@@ -104,6 +105,17 @@ fn write_file(text: &StringBuffer,
             let stdout_lock = stdout.lock();
             try!(write_system_newlines(stdout_lock, text, config));
         }
+        WriteMode::Diff => {
+            println!("Diff of {}:\n", filename);
+            let mut f = try!(File::open(filename));
+            let mut ori_text = String::new();
+            try!(f.read_to_string(&mut ori_text));
+            let mut v = Vec::new();
+            try!(write_system_newlines(&mut v, text, config));
+            let fmt_text = String::from_utf8(v).unwrap();
+            let diff = make_diff(&ori_text, &fmt_text, 3);
+            print_diff(diff, |line_num| format!("\nDiff at line {}:", line_num));
+        }
         WriteMode::Return(_) => {
             // io::Write is not implemented for String, working around with
             // Vec<u8>
diff --git a/src/lib.rs b/src/lib.rs
index ab748f62a95..7975c77e06d 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -30,6 +30,8 @@ extern crate strings;
 
 extern crate unicode_segmentation;
 extern crate regex;
+extern crate diff;
+extern crate term;
 
 use rustc::session::Session;
 use rustc::session::config as rustc_config;
@@ -67,6 +69,7 @@ mod rewrite;
 mod string;
 mod comment;
 mod modules;
+pub mod rustfmt_diff;
 
 const MIN_STRING: usize = 10;
 // When we get scoped annotations, we should have rustfmt::skip.
@@ -82,6 +85,8 @@ pub enum WriteMode {
     NewFile(&'static str),
     // Write the output to stdout.
     Display,
+    // Write the diff to stdout.
+    Diff,
     // Return the result as a mapping from filenames to Strings.
     Return(&'static Fn(HashMap<String, String>)),
 }
@@ -94,6 +99,7 @@ impl FromStr for WriteMode {
             "replace" => Ok(WriteMode::Replace),
             "display" => Ok(WriteMode::Display),
             "overwrite" => Ok(WriteMode::Overwrite),
+            "diff" => Ok(WriteMode::Diff),
             _ => Err(()),
         }
     }
diff --git a/src/rustfmt_diff.rs b/src/rustfmt_diff.rs
new file mode 100644
index 00000000000..375cfd661fa
--- /dev/null
+++ b/src/rustfmt_diff.rs
@@ -0,0 +1,109 @@
+use std::collections::VecDeque;
+use diff;
+use term;
+
+pub enum DiffLine {
+    Context(String),
+    Expected(String),
+    Resulting(String),
+}
+
+pub struct Mismatch {
+    pub line_number: u32,
+    pub lines: Vec<DiffLine>,
+}
+
+impl Mismatch {
+    fn new(line_number: u32) -> Mismatch {
+        Mismatch { line_number: line_number, lines: Vec::new() }
+    }
+}
+
+// Produces a diff between the expected output and actual output of rustfmt.
+pub fn make_diff(expected: &str, actual: &str, context_size: usize) -> Vec<Mismatch> {
+    let mut line_number = 1;
+    let mut context_queue: VecDeque<&str> = VecDeque::with_capacity(context_size);
+    let mut lines_since_mismatch = context_size + 1;
+    let mut results = Vec::new();
+    let mut mismatch = Mismatch::new(0);
+
+    for result in diff::lines(expected, actual) {
+        match result {
+            diff::Result::Left(str) => {
+                if lines_since_mismatch >= context_size {
+                    results.push(mismatch);
+                    mismatch = Mismatch::new(line_number - context_queue.len() as u32);
+                }
+
+                while let Some(line) = context_queue.pop_front() {
+                    mismatch.lines.push(DiffLine::Context(line.to_owned()));
+                }
+
+                mismatch.lines.push(DiffLine::Resulting(str.to_owned()));
+                lines_since_mismatch = 0;
+            }
+            diff::Result::Right(str) => {
+                if lines_since_mismatch >= context_size {
+                    results.push(mismatch);
+                    mismatch = Mismatch::new(line_number - context_queue.len() as u32);
+                }
+
+                while let Some(line) = context_queue.pop_front() {
+                    mismatch.lines.push(DiffLine::Context(line.to_owned()));
+                }
+
+                mismatch.lines.push(DiffLine::Expected(str.to_owned()));
+                line_number += 1;
+                lines_since_mismatch = 0;
+            }
+            diff::Result::Both(str, _) => {
+                if context_queue.len() >= context_size {
+                    let _ = context_queue.pop_front();
+                }
+
+                if lines_since_mismatch < context_size {
+                    mismatch.lines.push(DiffLine::Context(str.to_owned()));
+                } else {
+                    context_queue.push_back(str);
+                }
+
+                line_number += 1;
+                lines_since_mismatch += 1;
+            }
+        }
+    }
+
+    results.push(mismatch);
+    results.remove(0);
+
+    results
+}
+
+pub fn print_diff<F>(diff: Vec<Mismatch>, get_section_title: F)
+    where F: Fn(u32) -> String
+{
+    let mut t = term::stdout().unwrap();
+    for mismatch in diff {
+        t.fg(term::color::BRIGHT_WHITE).unwrap();
+        let title = get_section_title(mismatch.line_number);
+        writeln!(t, "{}", title).unwrap();
+
+        for line in mismatch.lines {
+            match line {
+                DiffLine::Context(ref str) => {
+                    t.fg(term::color::WHITE).unwrap();
+                    writeln!(t, " {}⏎", str).unwrap();
+                }
+                DiffLine::Expected(ref str) => {
+                    t.fg(term::color::GREEN).unwrap();
+                    writeln!(t, "+{}⏎", str).unwrap();
+                }
+                DiffLine::Resulting(ref str) => {
+                    t.fg(term::color::RED).unwrap();
+                    writeln!(t, "-{}⏎", str).unwrap();
+                }
+            }
+        }
+    }
+    t.reset().unwrap();
+}