1use collections::HashMap;
2use ordered_float::OrderedFloat;
3use std::{
4 cmp,
5 fmt::{self, Debug},
6 ops::Range,
7};
8
9struct Matrix {
10 cells: Vec<f64>,
11 rows: usize,
12 cols: usize,
13}
14
15impl Matrix {
16 fn new() -> Self {
17 Self {
18 cells: Vec::new(),
19 rows: 0,
20 cols: 0,
21 }
22 }
23
24 fn resize(&mut self, rows: usize, cols: usize) {
25 self.cells.resize(rows * cols, 0.);
26 self.rows = rows;
27 self.cols = cols;
28 }
29
30 fn get(&self, row: usize, col: usize) -> f64 {
31 if row >= self.rows {
32 panic!("row out of bounds")
33 }
34
35 if col >= self.cols {
36 panic!("col out of bounds")
37 }
38 self.cells[col * self.rows + row]
39 }
40
41 fn set(&mut self, row: usize, col: usize, value: f64) {
42 if row >= self.rows {
43 panic!("row out of bounds")
44 }
45
46 if col >= self.cols {
47 panic!("col out of bounds")
48 }
49
50 self.cells[col * self.rows + row] = value;
51 }
52}
53
54impl Debug for Matrix {
55 fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
56 writeln!(f)?;
57 for i in 0..self.rows {
58 for j in 0..self.cols {
59 write!(f, "{:5}", self.get(i, j))?;
60 }
61 writeln!(f)?;
62 }
63 Ok(())
64 }
65}
66
67#[derive(Debug)]
68pub enum Hunk {
69 Insert { text: String },
70 Remove { len: usize },
71 Keep { len: usize },
72}
73
74pub struct StreamingDiff {
75 old: Vec<char>,
76 new: Vec<char>,
77 scores: Matrix,
78 old_text_ix: usize,
79 new_text_ix: usize,
80 equal_runs: HashMap<(usize, usize), u32>,
81}
82
83impl StreamingDiff {
84 const INSERTION_SCORE: f64 = -1.;
85 const DELETION_SCORE: f64 = -20.;
86 const EQUALITY_BASE: f64 = 1.8;
87 const MAX_EQUALITY_EXPONENT: i32 = 16;
88
89 pub fn new(old: String) -> Self {
90 let old = old.chars().collect::<Vec<_>>();
91 let mut scores = Matrix::new();
92 scores.resize(old.len() + 1, 1);
93 for i in 0..=old.len() {
94 scores.set(i, 0, i as f64 * Self::DELETION_SCORE);
95 }
96 Self {
97 old,
98 new: Vec::new(),
99 scores,
100 old_text_ix: 0,
101 new_text_ix: 0,
102 equal_runs: Default::default(),
103 }
104 }
105
106 pub fn push_new(&mut self, text: &str) -> Vec<Hunk> {
107 self.new.extend(text.chars());
108 self.scores.resize(self.old.len() + 1, self.new.len() + 1);
109
110 for j in self.new_text_ix + 1..=self.new.len() {
111 self.scores.set(0, j, j as f64 * Self::INSERTION_SCORE);
112 for i in 1..=self.old.len() {
113 let insertion_score = self.scores.get(i, j - 1) + Self::INSERTION_SCORE;
114 let deletion_score = self.scores.get(i - 1, j) + Self::DELETION_SCORE;
115 let equality_score = if self.old[i - 1] == self.new[j - 1] {
116 let mut equal_run = self.equal_runs.get(&(i - 1, j - 1)).copied().unwrap_or(0);
117 equal_run += 1;
118 self.equal_runs.insert((i, j), equal_run);
119
120 let exponent = cmp::min(equal_run as i32 / 4, Self::MAX_EQUALITY_EXPONENT);
121 self.scores.get(i - 1, j - 1) + Self::EQUALITY_BASE.powi(exponent)
122 } else {
123 f64::NEG_INFINITY
124 };
125
126 let score = insertion_score.max(deletion_score).max(equality_score);
127 self.scores.set(i, j, score);
128 }
129 }
130
131 let mut max_score = f64::NEG_INFINITY;
132 let mut next_old_text_ix = self.old_text_ix;
133 let next_new_text_ix = self.new.len();
134 for i in self.old_text_ix..=self.old.len() {
135 let score = self.scores.get(i, next_new_text_ix);
136 if score > max_score {
137 max_score = score;
138 next_old_text_ix = i;
139 }
140 }
141
142 let hunks = self.backtrack(next_old_text_ix, next_new_text_ix);
143 self.old_text_ix = next_old_text_ix;
144 self.new_text_ix = next_new_text_ix;
145 hunks
146 }
147
148 fn backtrack(&self, old_text_ix: usize, new_text_ix: usize) -> Vec<Hunk> {
149 let mut pending_insert: Option<Range<usize>> = None;
150 let mut hunks = Vec::new();
151 let mut i = old_text_ix;
152 let mut j = new_text_ix;
153 while (i, j) != (self.old_text_ix, self.new_text_ix) {
154 let insertion_score = if j > self.new_text_ix {
155 Some((i, j - 1))
156 } else {
157 None
158 };
159 let deletion_score = if i > self.old_text_ix {
160 Some((i - 1, j))
161 } else {
162 None
163 };
164 let equality_score = if i > self.old_text_ix && j > self.new_text_ix {
165 if self.old[i - 1] == self.new[j - 1] {
166 Some((i - 1, j - 1))
167 } else {
168 None
169 }
170 } else {
171 None
172 };
173
174 let (prev_i, prev_j) = [insertion_score, deletion_score, equality_score]
175 .iter()
176 .max_by_key(|cell| cell.map(|(i, j)| OrderedFloat(self.scores.get(i, j))))
177 .unwrap()
178 .unwrap();
179
180 if prev_i == i && prev_j == j - 1 {
181 if let Some(pending_insert) = pending_insert.as_mut() {
182 pending_insert.start = prev_j;
183 } else {
184 pending_insert = Some(prev_j..j);
185 }
186 } else {
187 if let Some(range) = pending_insert.take() {
188 hunks.push(Hunk::Insert {
189 text: self.new[range].iter().collect(),
190 });
191 }
192
193 let char_len = self.old[i - 1].len_utf8();
194 if prev_i == i - 1 && prev_j == j {
195 if let Some(Hunk::Remove { len }) = hunks.last_mut() {
196 *len += char_len;
197 } else {
198 hunks.push(Hunk::Remove { len: char_len })
199 }
200 } else if let Some(Hunk::Keep { len }) = hunks.last_mut() {
201 *len += char_len;
202 } else {
203 hunks.push(Hunk::Keep { len: char_len })
204 }
205 }
206
207 i = prev_i;
208 j = prev_j;
209 }
210
211 if let Some(range) = pending_insert.take() {
212 hunks.push(Hunk::Insert {
213 text: self.new[range].iter().collect(),
214 });
215 }
216
217 hunks.reverse();
218 hunks
219 }
220
221 pub fn finish(self) -> Vec<Hunk> {
222 self.backtrack(self.old.len(), self.new.len())
223 }
224}
225
226#[cfg(test)]
227mod tests {
228 use std::env;
229
230 use super::*;
231 use rand::prelude::*;
232
233 #[gpui::test(iterations = 100)]
234 fn test_random_diffs(mut rng: StdRng) {
235 let old_text_len = env::var("OLD_TEXT_LEN")
236 .map(|i| i.parse().expect("invalid `OLD_TEXT_LEN` variable"))
237 .unwrap_or(10);
238 let new_text_len = env::var("NEW_TEXT_LEN")
239 .map(|i| i.parse().expect("invalid `NEW_TEXT_LEN` variable"))
240 .unwrap_or(10);
241
242 let old = util::RandomCharIter::new(&mut rng)
243 .take(old_text_len)
244 .collect::<String>();
245 log::info!("old text: {:?}", old);
246
247 let mut diff = StreamingDiff::new(old.clone());
248 let mut hunks = Vec::new();
249 let mut new_len = 0;
250 let mut new = String::new();
251 while new_len < new_text_len {
252 let new_chunk_len = rng.gen_range(1..=new_text_len - new_len);
253 let new_chunk = util::RandomCharIter::new(&mut rng)
254 .take(new_len)
255 .collect::<String>();
256 log::info!("new chunk: {:?}", new_chunk);
257 new_len += new_chunk_len;
258 new.push_str(&new_chunk);
259 let new_hunks = diff.push_new(&new_chunk);
260 log::info!("hunks: {:?}", new_hunks);
261 hunks.extend(new_hunks);
262 }
263 let final_hunks = diff.finish();
264 log::info!("final hunks: {:?}", final_hunks);
265 hunks.extend(final_hunks);
266
267 log::info!("new text: {:?}", new);
268 let mut old_ix = 0;
269 let mut new_ix = 0;
270 let mut patched = String::new();
271 for hunk in hunks {
272 match hunk {
273 Hunk::Keep { len } => {
274 assert_eq!(&old[old_ix..old_ix + len], &new[new_ix..new_ix + len]);
275 patched.push_str(&old[old_ix..old_ix + len]);
276 old_ix += len;
277 new_ix += len;
278 }
279 Hunk::Remove { len } => {
280 old_ix += len;
281 }
282 Hunk::Insert { text } => {
283 assert_eq!(text, &new[new_ix..new_ix + text.len()]);
284 patched.push_str(&text);
285 new_ix += text.len();
286 }
287 }
288 }
289 assert_eq!(patched, new);
290 }
291}