Prefer higher-priority similar paths

stack-graphs/src/cycles.rs

@@ -31,6 +31,7 @@
 
 use enumset::EnumSet;
 use smallvec::SmallVec;
+use std::cmp::Ordering;
 use std::collections::HashMap;
 
 use crate::arena::Arena;
@@ -97,22 +98,23 @@ where
     /// Determines whether we should process this path during the path-finding algorithm.  If we have seen
     /// a path with the same start and end node, and the same pre- and postcondition, then we return false.
     /// Otherwise, we return true.
-    pub fn has_similar_path<Eq>(
+    pub fn has_similar_path<Cmp>(
         &mut self,
         _graph: &StackGraph,
         arena: &mut P::Arena,
         path: &P,
-        eq: Eq,
+        cmp: Cmp,
     ) -> bool
     where
-        Eq: Fn(&mut P::Arena, &P, &P) -> bool,
+        Cmp: Fn(&mut P::Arena, &P, &P) -> Option<Ordering>,
     {
         let key = path.key();
 
         let possibly_similar_paths = self.paths.entry(key).or_default();
         for other_path in possibly_similar_paths.iter() {
-            if eq(arena, path, other_path) {
-                return true;
+            match cmp(arena, path, other_path) {
+                Some(ord) if ord != Ordering::Less => return true,
+                _ => continue,
             }
         }
 

stack-graphs/src/stitching.rs

@@ -35,6 +35,7 @@
 //! [`Database`]: struct.Database.html
 //! [`PathStitcher`]: struct.PathStitcher.html
 
+use std::cmp::Ordering;
 use std::collections::HashMap;
 use std::collections::VecDeque;
 #[cfg(feature = "copious-debugging")]
@@ -897,7 +898,19 @@ impl<H: Clone> ForwardPartialPathStitcher<H> {
                         graph,
                         partials,
                         &new_partial_path,
-                        |ps, left, right| left.equals(ps, right),
+                        |ps, left, right| {
+                            if !left.equals(ps, right) {
+                                None
+                            } else {
+                                if left.shadows(ps, right) {
+                                    Some(Ordering::Less)
+                                } else if right.shadows(ps, left) {
+                                    Some(Ordering::Greater)
+                                } else {
+                                    Some(Ordering::Equal)
+                                }
+                            }
+                        },
                     ) {
                         copious_debugging!("        is rejected: too many similar");
                         continue;