Modify the Levenshtein-based suggestions to include imports

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, max_suggestion_distance};
+use util::lev_distance::find_best_match_for_name;
 use ext::mtwt;
 use fold::Folder;
 
@@ -780,15 +780,8 @@ impl<'a> ExtCtxt<'a> {
     }
 
     pub fn suggest_macro_name(&mut self, name: &str, span: Span) {
-        let mut min: Option<(Name, usize)> = None;
-        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) {
-                min = Some((*macro_name, dist));
-            }
-        }
-        if let Some((suggestion, _)) = min {
+        let names = &self.syntax_env.names;
+        if let Some(suggestion) = find_best_match_for_name(names.iter(), name, None) {
             self.fileline_help(span, &format!("did you mean `{}!`?", suggestion));
         }
     }

src/libsyntax/util/lev_distance.rs

@@ -8,50 +8,64 @@
 // option. This file may not be copied, modified, or distributed
 // except according to those terms.
 
+use ast::Name;
 use std::cmp;
+use parse::token::InternedString;
 
-pub fn lev_distance(me: &str, t: &str) -> usize {
-    if me.is_empty() { return t.chars().count(); }
-    if t.is_empty() { return me.chars().count(); }
+/// To find the Levenshtein distance between two strings
+pub fn lev_distance(a: &str, b: &str) -> usize {
+    // cases which don't require further computation
+    if a.is_empty() {
+        return b.chars().count();
+    } else if b.is_empty() {
+        return a.chars().count();
+    }
 
-    let mut dcol: Vec<_> = (0..t.len() + 1).collect();
+    let mut dcol: Vec<_> = (0..b.len() + 1).collect();
     let mut t_last = 0;
 
-    for (i, sc) in me.chars().enumerate() {
-
+    for (i, sc) in a.chars().enumerate() {
         let mut current = i;
         dcol[0] = current + 1;
 
-        for (j, tc) in t.chars().enumerate() {
-
+        for (j, tc) in b.chars().enumerate() {
             let next = dcol[j + 1];
-
             if sc == tc {
                 dcol[j + 1] = current;
             } else {
                 dcol[j + 1] = cmp::min(current, next);
                 dcol[j + 1] = cmp::min(dcol[j + 1], dcol[j]) + 1;
             }
-
             current = next;
             t_last = j;
         }
-    }
-
-    dcol[t_last + 1]
+    } 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
+/// To find the best match for a given string from an iterator of names
+/// As a loose rule to avoid the obviously incorrect suggestions, it takes
+/// an optional limit for the maximum allowable edit distance, which defaults
+/// to one-third of the given word
+pub fn find_best_match_for_name<'a, T>(iter_names: T,
+                                       lookup: &str,
+                                       dist: Option<usize>) -> Option<InternedString>
+    where T: Iterator<Item = &'a Name> {
+    let max_dist = dist.map_or_else(|| cmp::max(lookup.len(), 3) / 3, |d| d);
+    iter_names
+    .filter_map(|name| {
+        let dist = lev_distance(lookup, &name.as_str());
+        match dist <= max_dist {    // filter the unwanted cases
+            true => Some((name.as_str(), dist)),
+            false => None,
+        }
+    })
+    .min_by_key(|&(_, val)| val)    // extract the tuple containing the minimum edit distance
+    .map(|(s, _)| s)                // and return only the string
 }
 
 #[test]
 fn test_lev_distance() {
-    use std::char::{ from_u32, MAX };
+    use std::char::{from_u32, MAX};
     // Test bytelength agnosticity
     for c in (0..MAX as u32)
              .filter_map(|i| from_u32(i))