fix: merge nodes more aggressively when unsat (#27)

Author: aochagavia

src/problem.rs

@@ -248,7 +248,6 @@ pub enum ConflictCause {
 /// - They all have the same name
 /// - They all have the same predecessor nodes
 /// - They all have the same successor nodes
-/// - None of them have incoming conflicting edges
 pub(crate) struct MergedProblemNode {
     pub ids: Vec<SolvableId>,
 }
@@ -370,14 +369,6 @@ impl ProblemGraph {
                 }
             };
 
-            if graph
-                .edges_directed(node_id, Direction::Incoming)
-                .any(|e| matches!(e.weight(), ProblemEdge::Conflict(..)))
-            {
-                // Nodes that are the target of a conflict should never be merged
-                continue;
-            }
-
             let predecessors: Vec<_> = graph
                 .edges_directed(node_id, Direction::Incoming)
                 .map(|e| e.source())

tests/snapshots/solver__merge_installable.snap

@@ -0,0 +1,10 @@
+---
+source: tests/solver.rs
+expression: "solve_snapshot(provider, &[\"a 0..3\", \"a 3..5\"])"
+---
+The following packages are incompatible
+|-- a >=3, <5 can be installed with any of the following options:
+    |-- a 3 | 4
+|-- a >=0, <3 cannot be installed because there are no viable options:
+    |-- a 1 | 2, which conflicts with the versions reported above.
+

tests/snapshots/solver__unsat_constrains_2.snap

@@ -1,21 +1,10 @@
 ---
 source: tests/solver.rs
-assertion_line: 703
 expression: error
 ---
 The following packages are incompatible
 |-- a * cannot be installed because there are no viable options:
-    |-- a 2 would require
-        |-- b *, which cannot be installed because there are no viable options:
-            |-- b 2 would require
-                |-- c >=2, <3, which cannot be installed because there are no viable options:
-                    |-- c 2 would constrain
-                        |-- a >=3, <4 , which conflicts with any installable versions previously reported
-            |-- b 1 would require
-                |-- c >=1, <2, which cannot be installed because there are no viable options:
-                    |-- c 1 would constrain
-                        |-- a >=3, <4 , which conflicts with any installable versions previously reported
-    |-- a 1 would require
+    |-- a 1 | 2 would require
         |-- b *, which cannot be installed because there are no viable options:
             |-- b 2 would require
                 |-- c >=2, <3, which cannot be installed because there are no viable options:

tests/solver.rs

@@ -912,6 +912,17 @@ fn test_merge_excluded() {
     insta::assert_snapshot!(solve_snapshot(provider, &["a"]));
 }
 
+#[test]
+fn test_merge_installable() {
+    let provider = BundleBoxProvider::from_packages(&[
+        ("a", 1, vec![]),
+        ("a", 2, vec![]),
+        ("a", 3, vec![]),
+        ("a", 4, vec![]),
+    ]);
+    insta::assert_snapshot!(solve_snapshot(provider, &["a 0..3", "a 3..5"]));
+}
+
 #[test]
 fn test_root_excluded() {
     let mut provider = BundleBoxProvider::from_packages(&[("a", 1, vec![])]);