do not try an exponential number of package names

src/cargo/sources/registry/index.rs

@@ -81,91 +81,6 @@ use std::path::Path;
 use std::str;
 use std::task::{ready, Poll};
 
-/// Crates.io treats hyphen and underscores as interchangeable, but the index and old Cargo do not.
-/// Therefore, the index must store uncanonicalized version of the name so old Cargo's can find it.
-/// This loop tries all possible combinations of switching hyphen and underscores to find the
-/// uncanonicalized one. As all stored inputs have the correct spelling, we start with the spelling
-/// as-provided.
-pub struct UncanonicalizedIter<'s> {
-    input: &'s str,
-    num_hyphen_underscore: u32,
-    hyphen_combination_num: u16,
-}
-
-impl<'s> UncanonicalizedIter<'s> {
-    pub fn new(input: &'s str) -> Self {
-        let num_hyphen_underscore = input.chars().filter(|&c| c == '_' || c == '-').count() as u32;
-        UncanonicalizedIter {
-            input,
-            num_hyphen_underscore,
-            hyphen_combination_num: 0,
-        }
-    }
-}
-
-impl<'s> Iterator for UncanonicalizedIter<'s> {
-    type Item = String;
-
-    fn next(&mut self) -> Option<Self::Item> {
-        if self.hyphen_combination_num > 0
-            && self.hyphen_combination_num.trailing_zeros() >= self.num_hyphen_underscore
-        {
-            return None;
-        }
-
-        let ret = Some(
-            self.input
-                .chars()
-                .scan(0u16, |s, c| {
-                    // the check against 15 here's to prevent
-                    // shift overflow on inputs with more than 15 hyphens
-                    if (c == '_' || c == '-') && *s <= 15 {
-                        let switch = (self.hyphen_combination_num & (1u16 << *s)) > 0;
-                        let out = if (c == '_') ^ switch { '_' } else { '-' };
-                        *s += 1;
-                        Some(out)
-                    } else {
-                        Some(c)
-                    }
-                })
-                .collect(),
-        );
-        self.hyphen_combination_num += 1;
-        ret
-    }
-}
-
-#[test]
-fn no_hyphen() {
-    assert_eq!(
-        UncanonicalizedIter::new("test").collect::<Vec<_>>(),
-        vec!["test".to_string()]
-    )
-}
-
-#[test]
-fn two_hyphen() {
-    assert_eq!(
-        UncanonicalizedIter::new("te-_st").collect::<Vec<_>>(),
-        vec![
-            "te-_st".to_string(),
-            "te__st".to_string(),
-            "te--st".to_string(),
-            "te_-st".to_string()
-        ]
-    )
-}
-
-#[test]
-fn overflow_hyphen() {
-    assert_eq!(
-        UncanonicalizedIter::new("te-_-_-_-_-_-_-_-_-st")
-            .take(100)
-            .count(),
-        100
-    )
-}
-
 /// Manager for handling the on-disk index.
 ///
 /// Note that local and remote registries store the index differently. Local

src/cargo/sources/registry/mod.rs

@@ -850,9 +850,15 @@ impl<'cfg> Source for RegistrySource<'cfg> {
                 // names to the original name. The resolver will later
                 // reject any candidates that have the wrong name, and with this it'll
                 // along the way produce helpful "did you mean?" suggestions.
-                for name_permutation in
-                    index::UncanonicalizedIter::new(&dep.package_name()).take(1024)
-                {
+                // For now we only try the canonical lysing `-` to `_` and vice versa.
+                // More advanced fuzzy searching become in the future.
+                for name_permutation in [
+                    dep.package_name().replace('-', "_"),
+                    dep.package_name().replace('_', "-"),
+                ] {
+                    if name_permutation.as_str() == dep.package_name().as_str() {
+                        continue;
+                    }
                     any_pending |= self
                         .index
                         .query_inner(

tests/testsuite/registry.rs

@@ -3166,7 +3166,7 @@ fn not_found_permutations() {
                 authors = []
 
                 [dependencies]
-                a-b-c = "1.0"
+                a-b_c = "1.0"
             "#,
         )
         .file("src/lib.rs", "")
@@ -3177,7 +3177,7 @@ fn not_found_permutations() {
         .with_stderr(
             "\
 [UPDATING] `dummy-registry` index
-error: no matching package named `a-b-c` found
+error: no matching package named `a-b_c` found
 location searched: registry `crates-io`
 required by package `foo v0.0.1 ([ROOT]/foo)`
 ",
@@ -3190,7 +3190,6 @@ required by package `foo v0.0.1 ([ROOT]/foo)`
         &[
             "/index/a-/b-/a-b-c",
             "/index/a-/b_/a-b_c",
-            "/index/a_/b-/a_b-c",
             "/index/a_/b_/a_b_c"
         ]
     );