Introduce max_suggestion_distance function to avoid duplicating the heuristic

2 files changed, 10 insertions, 4 deletions

diff --git a/src/libsyntax/ext/base.rs b/src/libsyntax/ext/base.rs
index 09c98c3e547..cf6881ab650 100644
--- a/src/libsyntax/ext/base.rs
+++ b/src/libsyntax/ext/base.rs
@@ -24,7 +24,7 @@ use parse::token;
 use parse::token::{InternedString, intern, str_to_ident};
 use ptr::P;
 use util::small_vector::SmallVector;
-use util::lev_distance::lev_distance;
+use util::lev_distance::{lev_distance, max_suggestion_distance};
 use ext::mtwt;
 use fold::Folder;
 
@@ -779,10 +779,8 @@ impl<'a> ExtCtxt<'a> {
     }
 
     pub fn suggest_macro_name(&mut self, name: &str, span: Span) {
-        use std::cmp::max;
-
         let mut min: Option<(Name, usize)> = None;
-        let max_dist = max(name.len() / 3, 1);
+        let max_dist = max_suggestion_distance(name);
         for macro_name in self.syntax_env.names.iter() {
             let dist = lev_distance(name, &macro_name.as_str());
             if dist <= max_dist && (min.is_none() || min.unwrap().1 > dist) {
diff --git a/src/libsyntax/util/lev_distance.rs b/src/libsyntax/util/lev_distance.rs
index 28f8510ce3f..9bf96311122 100644
--- a/src/libsyntax/util/lev_distance.rs
+++ b/src/libsyntax/util/lev_distance.rs
@@ -41,6 +41,14 @@ pub fn lev_distance(me: &str, t: &str) -> usize {
     dcol[t_last + 1]
 }
 
+pub fn max_suggestion_distance(name: &str) -> usize {
+    use std::cmp::max;
+    // As a loose rule to avoid obviously incorrect suggestions, clamp the
+    // maximum edit distance we will accept for a suggestion to one third of
+    // the typo'd name's length.
+    max(name.len(), 3) / 3
+}
+
 #[test]
 fn test_lev_distance() {
     use std::char::{ from_u32, MAX };