Use restricted Damerau-Levenshtein algorithm

src/cargo/core/package_id_spec.rs

@@ -7,9 +7,9 @@ use serde::{de, ser};
 use url::Url;
 
 use crate::core::PackageId;
+use crate::util::edit_distance;
 use crate::util::errors::CargoResult;
 use crate::util::interning::InternedString;
-use crate::util::lev_distance;
 use crate::util::{validate_package_name, IntoUrl, ToSemver};
 
 /// Some or all of the data required to identify a package:
@@ -88,7 +88,7 @@ impl PackageIdSpec {
     {
         let i: Vec<_> = i.into_iter().collect();
         let spec = PackageIdSpec::parse(spec).with_context(|| {
-            let suggestion = lev_distance::closest_msg(spec, i.iter(), |id| id.name().as_str());
+            let suggestion = edit_distance::closest_msg(spec, i.iter(), |id| id.name().as_str());
             format!("invalid package ID specification: `{}`{}", spec, suggestion)
         })?;
         spec.query(i)
@@ -229,7 +229,7 @@ impl PackageIdSpec {
                     );
                 }
                 if suggestion.is_empty() {
-                    suggestion.push_str(&lev_distance::closest_msg(
+                    suggestion.push_str(&edit_distance::closest_msg(
                         &self.name,
                         all_ids.iter(),
                         |id| id.name().as_str(),

src/cargo/core/resolver/errors.rs

@@ -2,7 +2,7 @@ use std::fmt;
 use std::task::Poll;
 
 use crate::core::{Dependency, PackageId, QueryKind, Registry, Summary};
-use crate::util::lev_distance::lev_distance;
+use crate::util::edit_distance::edit_distance;
 use crate::util::{Config, VersionExt};
 use anyhow::Error;
 
@@ -308,8 +308,7 @@ pub(super) fn activation_error(
             candidates.dedup_by(|a, b| a.name() == b.name());
             let mut candidates: Vec<_> = candidates
                 .iter()
-                .map(|n| (lev_distance(&*new_dep.package_name(), &*n.name()), n))
-                .filter(|&(d, _)| d < 4)
+                .filter_map(|n| Some((edit_distance(&*new_dep.package_name(), &*n.name(), 3)?, n)))
                 .collect();
             candidates.sort_by_key(|o| o.0);
             let mut msg: String;

src/cargo/core/workspace.rs

@@ -19,9 +19,9 @@ use crate::core::{Dependency, FeatureValue, PackageId, PackageIdSpec};
 use crate::core::{EitherManifest, Package, SourceId, VirtualManifest};
 use crate::ops;
 use crate::sources::{PathSource, CRATES_IO_INDEX, CRATES_IO_REGISTRY};
+use crate::util::edit_distance;
 use crate::util::errors::{CargoResult, ManifestError};
 use crate::util::interning::InternedString;
-use crate::util::lev_distance;
 use crate::util::toml::{read_manifest, InheritableFields, TomlDependency, TomlProfiles};
 use crate::util::{config::ConfigRelativePath, Config, Filesystem, IntoUrl};
 use cargo_util::paths;
@@ -1245,8 +1245,9 @@ impl<'cfg> Workspace<'cfg> {
             optional_dependency_names_per_member.insert(member, optional_dependency_names_raw);
         }
 
-        let levenshtein_test =
-            |a: InternedString, b: InternedString| lev_distance(a.as_str(), b.as_str()) < 4;
+        let edit_distance_test = |a: InternedString, b: InternedString| {
+            edit_distance(a.as_str(), b.as_str(), 3).is_some()
+        };
 
         let suggestions: Vec<_> = cli_features
             .features
@@ -1257,12 +1258,12 @@ impl<'cfg> Workspace<'cfg> {
                     // Finds member features which are similar to the requested feature.
                     let summary_features = summary_features
                         .iter()
-                        .filter(move |feature| levenshtein_test(**feature, *typo));
+                        .filter(move |feature| edit_distance_test(**feature, *typo));
 
                     // Finds optional dependencies which name is similar to the feature
                     let optional_dependency_features = optional_dependency_names
                         .iter()
-                        .filter(move |feature| levenshtein_test(**feature, *typo));
+                        .filter(move |feature| edit_distance_test(**feature, *typo));
 
                     summary_features
                         .chain(optional_dependency_features)
@@ -1278,13 +1279,13 @@ impl<'cfg> Workspace<'cfg> {
                     // Finds set of `pkg/feat` that are very similar to current `pkg/feat`.
                     let pkg_feat_similar = dependencies_features
                         .iter()
-                        .filter(|(name, _)| levenshtein_test(**name, *dep_name))
+                        .filter(|(name, _)| edit_distance_test(**name, *dep_name))
                         .map(|(name, features)| {
                             (
                                 name,
                                 features
                                     .iter()
-                                    .filter(|feature| levenshtein_test(**feature, *dep_feature))
+                                    .filter(|feature| edit_distance_test(**feature, *dep_feature))
                                     .collect::<Vec<_>>(),
                             )
                         })
@@ -1298,12 +1299,12 @@ impl<'cfg> Workspace<'cfg> {
                     // Finds set of `member/optional_dep` features which name is similar to current `pkg/feat`.
                     let optional_dependency_features = optional_dependency_names_per_member
                         .iter()
-                        .filter(|(package, _)| levenshtein_test(package.name(), *dep_name))
+                        .filter(|(package, _)| edit_distance_test(package.name(), *dep_name))
                         .map(|(package, optional_dependencies)| {
                             optional_dependencies
                                 .into_iter()
                                 .filter(|optional_dependency| {
-                                    levenshtein_test(**optional_dependency, *dep_name)
+                                    edit_distance_test(**optional_dependency, *dep_name)
                                 })
                                 .map(move |optional_dependency| {
                                     format!("{}/{}", package.name(), optional_dependency)
@@ -1314,12 +1315,12 @@ impl<'cfg> Workspace<'cfg> {
                     // Finds set of `member/feat` features which name is similar to current `pkg/feat`.
                     let summary_features = summary_features_per_member
                         .iter()
-                        .filter(|(package, _)| levenshtein_test(package.name(), *dep_name))
+                        .filter(|(package, _)| edit_distance_test(package.name(), *dep_name))
                         .map(|(package, summary_features)| {
                             summary_features
                                 .into_iter()
                                 .filter(|summary_feature| {
-                                    levenshtein_test(**summary_feature, *dep_feature)
+                                    edit_distance_test(**summary_feature, *dep_feature)
                                 })
                                 .map(move |summary_feature| {
                                     format!("{}/{}", package.name(), summary_feature)

src/cargo/ops/cargo_clean.rs

@@ -2,9 +2,9 @@ use crate::core::compiler::{CompileKind, CompileMode, Layout, RustcTargetData};
 use crate::core::profiles::Profiles;
 use crate::core::{PackageIdSpec, TargetKind, Workspace};
 use crate::ops;
+use crate::util::edit_distance;
 use crate::util::errors::CargoResult;
 use crate::util::interning::InternedString;
-use crate::util::lev_distance;
 use crate::util::{Config, Progress, ProgressStyle};
 
 use anyhow::Context as _;
@@ -118,7 +118,7 @@ pub fn clean(ws: &Workspace<'_>, opts: &CleanOptions<'_>) -> CargoResult<()> {
         let matches: Vec<_> = resolve.iter().filter(|id| spec.matches(*id)).collect();
         if matches.is_empty() {
             let mut suggestion = String::new();
-            suggestion.push_str(&lev_distance::closest_msg(
+            suggestion.push_str(&edit_distance::closest_msg(
                 &spec.name(),
                 resolve.iter(),
                 |id| id.name().as_str(),

src/cargo/util/edit_distance.rs

@@ -0,0 +1,143 @@
+use std::{cmp, mem};
+
+/// Finds the [edit distance] between two strings.
+///
+/// Returns `None` if the distance exceeds the limit.
+///
+/// [edit distance]: https://en.wikipedia.org/wiki/Edit_distance
+pub fn edit_distance(a: &str, b: &str, limit: usize) -> Option<usize> {
+    // Comparing the strings lowercased will result in a difference in capitalization being less distance away
+    // than being a completely different letter. Otherwise `CHECK` is as far away from `check` as it
+    // is from `build` (both with a distance of 5). For a single letter shortcut (e.g. `b` or `c`), they will
+    // all be as far away from any capital single letter entry (all with a distance of 1).
+    // By first lowercasing the strings, `C` and `c` are closer than `C` and `b`, for example.
+    let a = a.to_lowercase();
+    let b = b.to_lowercase();
+
+    let mut a = &a.chars().collect::<Vec<_>>()[..];
+    let mut b = &b.chars().collect::<Vec<_>>()[..];
+
+    // Ensure that `b` is the shorter string, minimizing memory use.
+    if a.len() < b.len() {
+        mem::swap(&mut a, &mut b);
+    }
+
+    let min_dist = a.len() - b.len();
+    // If we know the limit will be exceeded, we can return early.
+    if min_dist > limit {
+        return None;
+    }
+
+    // Strip common prefix.
+    while let Some(((b_char, b_rest), (a_char, a_rest))) = b.split_first().zip(a.split_first()) {
+        if a_char != b_char {
+            break;
+        }
+        a = a_rest;
+        b = b_rest;
+    }
+    // Strip common suffix.
+    while let Some(((b_char, b_rest), (a_char, a_rest))) = b.split_last().zip(a.split_last()) {
+        if a_char != b_char {
+            break;
+        }
+        a = a_rest;
+        b = b_rest;
+    }
+
+    // If either string is empty, the distance is the length of the other.
+    // We know that `b` is the shorter string, so we don't need to check `a`.
+    if b.len() == 0 {
+        return Some(min_dist);
+    }
+
+    let mut prev_prev = vec![usize::MAX; b.len() + 1];
+    let mut prev = (0..=b.len()).collect::<Vec<_>>();
+    let mut current = vec![0; b.len() + 1];
+
+    // row by row
+    for i in 1..=a.len() {
+        current[0] = i;
+        let a_idx = i - 1;
+
+        // column by column
+        for j in 1..=b.len() {
+            let b_idx = j - 1;
+
+            // There is no cost to substitute a character with itself.
+            let substitution_cost = if a[a_idx] == b[b_idx] { 0 } else { 1 };
+
+            current[j] = cmp::min(
+                // deletion
+                prev[j] + 1,
+                cmp::min(
+                    // insertion
+                    current[j - 1] + 1,
+                    // substitution
+                    prev[j - 1] + substitution_cost,
+                ),
+            );
+
+            if (i > 1) && (j > 1) && (a[a_idx] == b[b_idx - 1]) && (a[a_idx - 1] == b[b_idx]) {
+                // transposition
+                current[j] = cmp::min(current[j], prev_prev[j - 2] + 1);
+            }
+        }
+
+        // Rotate the buffers, reusing the memory.
+        [prev_prev, prev, current] = [prev, current, prev_prev];
+    }
+
+    // `prev` because we already rotated the buffers.
+    let distance = prev[b.len()];
+    (distance <= limit).then_some(distance)
+}
+
+/// Find the closest element from `iter` matching `choice`. The `key` callback
+/// is used to select a `&str` from the iterator to compare against `choice`.
+pub fn closest<'a, T>(
+    choice: &str,
+    iter: impl Iterator<Item = T>,
+    key: impl Fn(&T) -> &'a str,
+) -> Option<T> {
+    // Only consider candidates with an edit distance of 3 or less so we don't
+    // suggest out-of-the-blue options.
+    iter.filter_map(|e| Some((edit_distance(choice, key(&e), 3)?, e)))
+        .min_by_key(|t| t.0)
+        .map(|t| t.1)
+}
+
+/// Version of `closest` that returns a common "suggestion" that can be tacked
+/// onto the end of an error message.
+pub fn closest_msg<'a, T>(
+    choice: &str,
+    iter: impl Iterator<Item = T>,
+    key: impl Fn(&T) -> &'a str,
+) -> String {
+    match closest(choice, iter, &key) {
+        Some(e) => format!("\n\n\tDid you mean `{}`?", key(&e)),
+        None => String::new(),
+    }
+}
+
+#[test]
+fn test_edit_distance() {
+    use std::char::{from_u32, MAX};
+    // Test bytelength agnosticity
+    for c in (0u32..MAX as u32)
+        .filter_map(from_u32)
+        .map(|i| i.to_string())
+    {
+        assert_eq!(edit_distance(&c, &c, usize::MAX), Some(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!(edit_distance(a, b, usize::MAX), Some(1));
+    assert_eq!(edit_distance(b, a, usize::MAX), Some(1));
+    assert_eq!(edit_distance(a, c, usize::MAX), Some(2));
+    assert_eq!(edit_distance(c, a, usize::MAX), Some(2));
+    assert_eq!(edit_distance(b, c, usize::MAX), Some(1));
+    assert_eq!(edit_distance(c, b, usize::MAX), Some(1));
+}