Fix source_text treating span.lo as byte offset not char index

dtolnay · dtolnay · commit 137ae0a341be · 2023-10-08T16:33:09.000-07:00
diff --git a/src/fallback.rs b/src/fallback.rs
@@ -364,7 +364,10 @@ impl FileInfo {
 
     fn source_text(&self, span: Span) -> String {
         let lo = (span.lo - self.span.lo) as usize;
-        let trunc_lo = &self.source_text[lo..];
+        let trunc_lo = match self.source_text.char_indices().nth(lo) {
+            Some((offset, _ch)) => &self.source_text[offset..],
+            None => return String::new(),
+        };
         let char_len = (span.hi - span.lo) as usize;
         let source_text = match trunc_lo.char_indices().nth(char_len) {
             Some((offset, _ch)) => &trunc_lo[..offset],
diff --git a/tests/test.rs b/tests/test.rs
@@ -338,7 +338,7 @@ fn source_text() {
     assert_eq!("𓀕", ident.span().source_text().unwrap());
 
     let ident = tokens.next().unwrap();
-    assert_eq!("c", ident.span().source_text().unwrap()); // FIXME
+    assert_eq!("c", ident.span().source_text().unwrap());
 }
 
 #[test]

Original file line number	Diff line number	Diff line change
`@@ -338,7 +338,7 @@ fn source_text() {`
`338`	`338`	`assert_eq!("𓀕", ident.span().source_text().unwrap());`
`339`	`339`
`340`	`340`	`let ident = tokens.next().unwrap();`
`341`		`- assert_eq!("c", ident.span().source_text().unwrap()); // FIXME`
	`341`	`+ assert_eq!("c", ident.span().source_text().unwrap());`
`342`	`342`	`}`
`343`	`343`
`344`	`344`	`#[test]`