fix: Prefer exact prefix/suffix matches when trimming replacements

src/renderer/source_map.rs

@@ -779,18 +779,24 @@ pub(crate) fn as_substr<'a>(
     original: &'a str,
     suggestion: &'a str,
 ) -> Option<(usize, &'a str, usize)> {
-    let common_prefix = original
-        .chars()
-        .zip(suggestion.chars())
-        .take_while(|(c1, c2)| c1 == c2)
-        .map(|(c, _)| c.len_utf8())
-        .sum();
-    let original = &original[common_prefix..];
-    let suggestion = &suggestion[common_prefix..];
-    if let Some(stripped) = suggestion.strip_suffix(original) {
-        let common_suffix = original.len();
-        Some((common_prefix, stripped, common_suffix))
+    if let Some(stripped) = suggestion.strip_prefix(original) {
+        Some((original.len(), stripped, 0))
+    } else if let Some(stripped) = suggestion.strip_suffix(original) {
+        Some((0, stripped, original.len()))
     } else {
-        None
+        let common_prefix = original
+            .chars()
+            .zip(suggestion.chars())
+            .take_while(|(c1, c2)| c1 == c2)
+            .map(|(c, _)| c.len_utf8())
+            .sum();
+        let original = &original[common_prefix..];
+        let suggestion = &suggestion[common_prefix..];
+        if let Some(stripped) = suggestion.strip_suffix(original) {
+            let common_suffix = original.len();
+            Some((common_prefix, stripped, common_suffix))
+        } else {
+            None
+        }
     }
 }

tests/formatter.rs

@@ -5015,3 +5015,52 @@ help: consider importing this module
     let renderer = renderer.decor_style(DecorStyle::Unicode);
     assert_data_eq!(renderer.render(input), expected_unicode);
 }
+
+#[test]
+fn original_matches_replacement_suffix() {
+    let source = r#"use sync;"#;
+    let input = &[
+        Group::with_level(Level::ERROR).element(
+            Snippet::source(source).path("/tmp/test.rs").annotation(
+                AnnotationKind::Primary
+                    .span(4..8)
+                    .label("no `sync` in the root"),
+            ),
+        ),
+        Level::HELP
+            .secondary_title("consider importing this module instead")
+            .element(
+                Snippet::source(source)
+                    .path("/tmp/test.rs")
+                    .patch(Patch::new(4..8, "std::sync")),
+            ),
+    ];
+
+    let expected_ascii = str![[r#"
+ --> /tmp/test.rs:1:5
+  |
+1 | use sync;
+  |     ^^^^ no `sync` in the root
+  |
+help: consider importing this module instead
+  |
+1 | use std::sync;
+  |     +++++
+"#]];
+    let renderer = Renderer::plain();
+    assert_data_eq!(renderer.render(input), expected_ascii);
+
+    let expected_unicode = str![[r#"
+  ╭▸ /tmp/test.rs:1:5
+  │
+1 │ use sync;
+  │     ━━━━ no `sync` in the root
+  ╰╴
+help: consider importing this module instead
+  ╭╴
+1 │ use std::sync;
+  ╰╴    +++++
+"#]];
+    let renderer = renderer.decor_style(DecorStyle::Unicode);
+    assert_data_eq!(renderer.render(input), expected_unicode);
+}