The topological sort in the SAT solver was messed up by a refactor

Author: Eh2406

src/cargo/core/resolver/context.rs

@@ -57,7 +57,7 @@ pub type Activations =
 /// A type that represents when cargo treats two Versions as compatible.
 /// Versions `a` and `b` are compatible if their left-most nonzero digit is the
 /// same.
-#[derive(Clone, Copy, Eq, PartialEq, Hash)]
+#[derive(Clone, Copy, Eq, PartialEq, Hash, Debug)]
 pub enum SemverCompatibility {
     Major(NonZeroU64),
     Minor(NonZeroU64),

tests/testsuite/resolve.rs

@@ -380,6 +380,20 @@ fn public_dependency_skipping_in_backtracking() {
     resolve(pkg_id("root"), vec![dep("C")], &reg).unwrap();
 }
 
+#[test]
+fn public_sat_topological_order() {
+    let input = vec![
+        pkg!(("a", "0.0.1")),
+        pkg!(("a", "0.0.0")),
+        pkg!(("b", "0.0.1") => [dep_req_kind("a", "= 0.0.1", Kind::Normal, true),]),
+        pkg!(("b", "0.0.0") => [dep("bad"),]),
+        pkg!("A" => [dep_req("a", "= 0.0.0"),dep_req_kind("b", "*", Kind::Normal, true)]),
+    ];
+
+    let reg = registry(input);
+    assert!(resolve_and_validated(pkg_id("root"), vec![dep("A")], &reg, None).is_err());
+}
+
 #[test]
 #[should_panic(expected = "assertion failed: !name.is_empty()")]
 fn test_dependency_with_empty_name() {

tests/testsuite/support/resolver.rs

@@ -203,10 +203,12 @@ fn sat_at_most_one(solver: &mut impl varisat::ExtendFormula, vars: &[varisat::Va
         return;
     } else if vars.len() == 2 {
         solver.add_clause(&[vars[0].negative(), vars[1].negative()]);
+        return;
     } else if vars.len() == 3 {
         solver.add_clause(&[vars[0].negative(), vars[1].negative()]);
         solver.add_clause(&[vars[0].negative(), vars[2].negative()]);
         solver.add_clause(&[vars[1].negative(), vars[2].negative()]);
+        return;
     }
     // use the "Binary Encoding" from
     // https://www.it.uu.se/research/group/astra/ModRef10/papers/Alan%20M.%20Frisch%20and%20Paul%20A.%20Giannoros.%20SAT%20Encodings%20of%20the%20At-Most-k%20Constraint%20-%20ModRef%202010.pdf
@@ -305,6 +307,7 @@ impl SatResolve {
                     .iter()
                     .filter(|&p| dep.matches_id(*p))
                 {
+                    graph.link(p.package_id(), m);
                     by_key
                         .entry(m.as_activations_key())
                         .or_default()