Check for for word boundaries.

txtlang/Cargo.toml

@@ -6,6 +6,7 @@ edition = "2018"
 build = "build.rs"
 
 [dependencies]
+bstr = "0.2"
 fst = "0.4"
 isolang = "1.0"
 once_cell = "1.4"

txtlang/src/lib.rs

@@ -1,5 +1,6 @@
 use std::str;
 
+use bstr::ByteSlice;
 use fst::raw::{Fst, Output};
 pub use isolang::Language;
 use once_cell::sync::Lazy;
@@ -15,9 +16,14 @@ pub struct Match {
     pub end: usize,
 }
 
-pub fn scan(input: impl AsRef<str>) -> Vec<Match> {
+pub fn scan(input: impl AsRef<[u8]>) -> Vec<Match> {
     let input = input.as_ref().to_lowercase();
 
+    let (start_indices, end_indices): (Vec<_>, Vec<_>) = input
+        .word_indices()
+        .map(|(start, end, _)| (start, end))
+        .unzip();
+
     let mut result = Vec::new();
 
     let mut stack = vec![None; N];
@@ -44,11 +50,13 @@ pub fn scan(input: impl AsRef<str>) -> Vec<Match> {
                         let bytes = value.to_be_bytes();
                         let code = str::from_utf8(&bytes[5..]).unwrap();
 
-                        result.push(Match {
-                            language: Language::from_639_3(code).unwrap(),
-                            start: idx,
-                            end: idx + len,
-                        });
+                        if start_indices.contains(&idx) && end_indices.contains(&(idx + len)) {
+                            result.push(Match {
+                                language: Language::from_639_3(code).unwrap(),
+                                start: idx,
+                                end: idx + len,
+                            });
+                        }
                     }
 
                     *entry = Some((node, out));
@@ -77,4 +85,9 @@ mod tests {
             }]
         );
     }
+
+    #[test]
+    fn test_bug_001() {
+        assert_eq!(scan("ampersand"), vec![]);
+    }
 }