From af84483c06896a346873a0aa122d1336cf540023 Mon Sep 17 00:00:00 2001
From: Gregory Petrosyan <pgregory@pgregory.net>
Date: Thu, 7 Dec 2023 21:14:12 +0300
Subject: [PATCH] fuzz: assert String equivalence

---
 fuzz/fuzz_targets/editing.rs | 18 ++++++++++++++----
 src/rope/rope.rs             | 10 +++++++---
 2 files changed, 21 insertions(+), 7 deletions(-)

diff --git a/fuzz/fuzz_targets/editing.rs b/fuzz/fuzz_targets/editing.rs
index d0926b8..10a3955 100644
--- a/fuzz/fuzz_targets/editing.rs
+++ b/fuzz/fuzz_targets/editing.rs
@@ -24,10 +24,12 @@ enum StartingText<'a> {
 fuzz_target!(|data: (StartingText, Vec<EditOp>)| {
     let (starting, ops) = data;
 
-    let mut rope = Rope::from(match starting {
+    let start = match starting {
         StartingText::Custom(s) => s,
         StartingText::NonAscii => NON_ASCII,
-    });
+    };
+    let mut rope = Rope::from(start);
+    let mut string = String::from(start);
 
     for op in ops {
         match op {
@@ -38,6 +40,7 @@ fuzz_target!(|data: (StartingText, Vec<EditOp>)| {
                     byte_offset += 1;
                 }
                 rope.insert(byte_offset, text);
+                string.insert_str(byte_offset, text);
             },
 
             EditOp::Delete { mut byte_range }
@@ -50,7 +53,8 @@ fuzz_target!(|data: (StartingText, Vec<EditOp>)| {
                 while !rope.is_char_boundary(byte_range.end) {
                     byte_range.end += 1;
                 }
-                rope.delete(byte_range);
+                rope.delete(byte_range.clone());
+                string.replace_range(byte_range, "");
             },
 
             EditOp::Replace { mut byte_range, text }
@@ -63,7 +67,8 @@ fuzz_target!(|data: (StartingText, Vec<EditOp>)| {
                 while !rope.is_char_boundary(byte_range.end) {
                     byte_range.end += 1;
                 }
-                rope.replace(byte_range, text);
+                rope.replace(byte_range.clone(), text);
+                string.replace_range(byte_range, text);
             },
 
             _ => continue,
@@ -71,4 +76,9 @@ fuzz_target!(|data: (StartingText, Vec<EditOp>)| {
     }
 
     rope.assert_invariants();
+    assert_eq!(rope, string);
+    assert_eq!(
+        rope.lines().collect::<Vec<_>>(),
+        string.lines().collect::<Vec<_>>(),
+    );
 });
diff --git a/src/rope/rope.rs b/src/rope/rope.rs
index 26cc4f3..27c767b 100644
--- a/src/rope/rope.rs
+++ b/src/rope/rope.rs
@@ -8,16 +8,20 @@ use super::RopeSlice;
 use crate::range_bounds_to_start_end;
 use crate::tree::Tree;
 
-#[cfg(any(test, feature = "arity_4"))]
+#[cfg(any(test, fuzzing, feature = "arity_4"))]
 const ARITY: usize = 4;
 
-#[cfg(not(any(test, feature = "arity_4")))]
+#[cfg(not(any(test, fuzzing, feature = "arity_4")))]
 const ARITY: usize = 16;
 
 #[cfg(any(test, feature = "small_chunks"))]
 const CHUNK_MAX_BYTES: usize = 4;
 
-#[cfg(not(any(test, feature = "small_chunks")))]
+// With 4-byte chunks, fuzzing is unbearably slow.
+#[cfg(fuzzing)]
+const CHUNK_MAX_BYTES: usize = 16;
+
+#[cfg(not(any(test, fuzzing, feature = "small_chunks")))]
 const CHUNK_MAX_BYTES: usize = 2048;
 
 pub(super) type RopeChunk = GapBuffer<CHUNK_MAX_BYTES>;