Highlight diffs

Cargo.toml

@@ -14,6 +14,7 @@ readme = "README.md"
 travis-ci = { repository = "dtolnay/trybuild" }
 
 [dependencies]
+diffr-lib = "=0.1.3"
 glob = "0.3"
 lazy_static = "1.3"
 serde = { version = "1.0.103", features = ["derive"] }

src/diff.rs

@@ -0,0 +1,112 @@
+use diffr_lib::{diff, tokenize, DiffInput, HashedSpan, Snake, Tokenization};
+use std::cmp;
+use std::iter::Peekable;
+use std::slice;
+
+pub struct Diff<'a> {
+    pub worth_printing: bool,
+    expected: &'a str,
+    expected_tokens: Vec<HashedSpan>,
+    actual: &'a str,
+    actual_tokens: Vec<HashedSpan>,
+    common: Vec<Snake>,
+}
+
+impl<'a> Diff<'a> {
+    pub fn compute(expected: &'a str, actual: &'a str) -> Self {
+        let mut actual_tokens = Vec::new();
+        tokenize(actual.as_bytes(), 0, &mut actual_tokens);
+        let added = Tokenization::new(actual.as_bytes(), &actual_tokens);
+
+        let mut expected_tokens = Vec::new();
+        tokenize(expected.as_bytes(), 0, &mut expected_tokens);
+        let removed = Tokenization::new(expected.as_bytes(), &expected_tokens);
+
+        let input = DiffInput { added, removed };
+        let mut scratch = Vec::new();
+        let mut common = Vec::new();
+        diff(&input, &mut scratch, &mut common);
+
+        let min_len = cmp::max(expected_tokens.len(), actual_tokens.len());
+        let common_len = common.iter().map(|snake| snake.len).sum::<isize>() as usize;
+        let worth_printing = common_len / 4 >= min_len / 5;
+
+        Diff {
+            worth_printing,
+            expected,
+            expected_tokens,
+            actual,
+            actual_tokens,
+            common,
+        }
+    }
+
+    pub fn iter(&self, input: &str) -> Iter {
+        if input == self.expected {
+            Iter {
+                pos: 0,
+                input: self.expected,
+                tokens: &self.expected_tokens,
+                common: self.common.iter().peekable(),
+                token_index: |snake| snake.x0,
+            }
+        } else if input == self.actual {
+            Iter {
+                pos: 0,
+                input: self.actual,
+                tokens: &self.actual_tokens,
+                common: self.common.iter().peekable(),
+                token_index: |snake| snake.y0,
+            }
+        } else {
+            panic!("unrecognized input");
+        }
+    }
+}
+
+pub struct Iter<'a> {
+    pos: usize,
+    input: &'a str,
+    tokens: &'a [HashedSpan],
+    common: Peekable<slice::Iter<'a, Snake>>,
+    token_index: fn(&Snake) -> isize,
+}
+
+pub enum Chunk<'a> {
+    Common(&'a str),
+    Unique(&'a str),
+}
+
+impl<'a> Iterator for Iter<'a> {
+    type Item = Chunk<'a>;
+
+    fn next(&mut self) -> Option<Self::Item> {
+        match self.common.peek() {
+            Some(common) => {
+                let index = (self.token_index)(common);
+                let begin = &self.tokens[index as usize];
+                if self.pos < begin.lo {
+                    let chunk = &self.input[self.pos..begin.lo];
+                    self.pos = begin.lo;
+                    Some(Chunk::Unique(chunk))
+                } else {
+                    let index = (self.token_index)(common) + common.len - 1;
+                    let end = &self.tokens[index as usize];
+                    let chunk = &self.input[begin.lo..end.hi];
+                    self.common.next().unwrap();
+                    self.pos = end.hi;
+                    Some(Chunk::Common(chunk))
+                }
+            }
+            None => {
+                if self.pos < self.input.len() {
+                    let chunk = &self.input[self.pos..];
+                    self.pos = self.input.len();
+                    Some(Chunk::Unique(chunk))
+                } else {
+                    None
+                }
+            }
+        }
+    }
+}

src/lib.rs

@@ -208,6 +208,7 @@ mod path;
 
 mod cargo;
 mod dependencies;
+mod diff;
 mod env;
 mod error;
 mod features;

src/message.rs

@@ -1,6 +1,7 @@
 use termcolor::Color::{self, *};
 
 use super::{Expected, Test};
+use crate::diff::{Chunk, Diff};
 use crate::error::Error;
 use crate::normalize;
 use crate::term;
@@ -129,13 +130,14 @@ pub(crate) fn mismatch(expected: &str, actual: &str) {
     println!("mismatch");
     term::reset();
     println!();
+    let diff = Diff::compute(expected, actual);
     term::bold_color(Blue);
     println!("EXPECTED:");
-    snippet(Blue, expected);
+    snippet_diff(Blue, expected, Some(&diff));
     println!();
     term::bold_color(Red);
     println!("ACTUAL OUTPUT:");
-    snippet(Red, actual);
+    snippet_diff(Red, actual, Some(&diff));
     println!();
 }
 
@@ -203,13 +205,36 @@ pub(crate) fn warnings(warnings: &str) {
 }
 
 fn snippet(color: Color, content: &str) {
+    snippet_diff(color, content, None);
+}
+
+fn snippet_diff(color: Color, content: &str, diff: Option<&Diff>) {
     fn dotted_line() {
         println!("{}", "┈".repeat(60));
     }
 
     term::color(color);
     dotted_line();
-    print!("{}", content);
+
+    match diff {
+        Some(diff) if diff.worth_printing => {
+            for chunk in diff.iter(content) {
+                match chunk {
+                    Chunk::Common(s) => {
+                        term::color(color);
+                        print!("{}", s);
+                    }
+                    Chunk::Unique(s) => {
+                        term::bold_color(color);
+                        print!("\x1B[7m{}", s);
+                    }
+                }
+            }
+        }
+        _ => print!("{}", content),
+    }
+
+    term::color(color);
     dotted_line();
     term::reset();
 }