Add suggestion of similar macro names to `macro undefined` error message

1 files changed, 63 insertions, 0 deletions

diff --git a/src/libsyntax/util/lev_distance.rs b/src/libsyntax/util/lev_distance.rs
new file mode 100644
index 00000000000..28f8510ce3f
--- /dev/null
+++ b/src/libsyntax/util/lev_distance.rs
@@ -0,0 +1,63 @@
+// Copyright 2012-2014 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+use std::cmp;
+
+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(); }
+
+    let mut dcol: Vec<_> = (0..t.len() + 1).collect();
+    let mut t_last = 0;
+
+    for (i, sc) in me.chars().enumerate() {
+
+        let mut current = i;
+        dcol[0] = current + 1;
+
+        for (j, tc) in t.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]
+}
+
+#[test]
+fn test_lev_distance() {
+    use std::char::{ from_u32, MAX };
+    // Test bytelength agnosticity
+    for c in (0..MAX as u32)
+             .filter_map(|i| from_u32(i))
+             .map(|i| i.to_string()) {
+        assert_eq!(lev_distance(&c[..], &c[..]), 0);
+    }
+
+    let a = "\nMäry häd ä little lämb\n\nLittle lämb\n";
+    let b = "\nMary häd ä little lämb\n\nLittle lämb\n";
+    let c = "Mary häd ä little lämb\n\nLittle lämb\n";
+    assert_eq!(lev_distance(a, b), 1);
+    assert_eq!(lev_distance(b, a), 1);
+    assert_eq!(lev_distance(a, c), 2);
+    assert_eq!(lev_distance(c, a), 2);
+    assert_eq!(lev_distance(b, c), 1);
+    assert_eq!(lev_distance(c, b), 1);
+}