Fix issue when there are multiple candidates for edit_distance_with_substrings

compiler/rustc_span/src/edit_distance.rs

@@ -174,10 +174,10 @@ pub fn find_best_match_for_name(
 fn find_best_match_for_name_impl(
     use_substring_score: bool,
     candidates: &[Symbol],
-    lookup: Symbol,
+    lookup_symbol: Symbol,
     dist: Option<usize>,
 ) -> Option<Symbol> {
-    let lookup = lookup.as_str();
+    let lookup = lookup_symbol.as_str();
     let lookup_uppercase = lookup.to_uppercase();
 
     // Priority of matches:
@@ -190,6 +190,8 @@ fn find_best_match_for_name_impl(
 
     let mut dist = dist.unwrap_or_else(|| cmp::max(lookup.len(), 3) / 3);
     let mut best = None;
+    // store the candidates with the same distance, only for `use_substring_score` current.
+    let mut next_candidates = vec![];
     for c in candidates {
         match if use_substring_score {
             edit_distance_with_substrings(lookup, c.as_str(), dist)
@@ -198,12 +200,36 @@ fn find_best_match_for_name_impl(
         } {
             Some(0) => return Some(*c),
             Some(d) => {
-                dist = d - 1;
+                if use_substring_score {
+                    if d < dist {
+                        dist = d;
+                        next_candidates.clear();
+                    } else {
+                        // `d == dist` here, we need to store the candidates with the same distance
+                        // so we won't decrease the distance in the next loop.
+                    }
+                    next_candidates.push(*c);
+                } else {
+                    dist = d - 1;
+                }
                 best = Some(*c);
             }
             None => {}
         }
     }
+
+    // We have a tie among several candidates, try to select the best among them ignoring substrings.
+    // For example, the candidates list `force_capture`, `capture`, and user inputed `forced_capture`,
+    // we select `force_capture` with a extra round of edit distance calculation.
+    if next_candidates.len() > 1 {
+        debug_assert!(use_substring_score);
+        best = find_best_match_for_name_impl(
+            false,
+            &next_candidates,
+            lookup_symbol,
+            Some(lookup.len()),
+        );
+    }
     if best.is_some() {
         return best;
     }

tests/ui/suggestions/issue-109291.rs

@@ -0,0 +1,4 @@
+fn main() {
+    println!("Custom backtrace: {}", std::backtrace::Backtrace::forced_capture());
+    //~^ ERROR no function or associated item name
+}

tests/ui/suggestions/issue-109291.stderr

@@ -0,0 +1,12 @@
+error[E0599]: no function or associated item named `forced_capture` found for struct `Backtrace` in the current scope
+  --> $DIR/issue-109291.rs:2:65
+   |
+LL |     println!("Custom backtrace: {}", std::backtrace::Backtrace::forced_capture());
+   |                                                                 ^^^^^^^^^^^^^^
+   |                                                                 |
+   |                                                                 function or associated item not found in `Backtrace`
+   |                                                                 help: there is an associated function with a similar name: `force_capture`
+
+error: aborting due to previous error
+
+For more information about this error, try `rustc --explain E0599`.