From 3fe5f0179220dc8f27a1454e701b1cf49e878770 Mon Sep 17 00:00:00 2001
From: Bas Zalmstra <4995967+baszalmstra@users.noreply.github.com>
Date: Wed, 3 Jun 2026 16:56:01 +0200
Subject: [PATCH] fix: don't merge conflict nodes with distinct requirements

Versions of a package that require different versions of a missing dependency are no longer collapsed into a single node in the conflict report. Previously only one of those requirements was shown and the rest were hidden, producing a misleading error message.

See conda/rattler#2476.
---
 src/conflict.rs                                    |  6 ++++--
 tests/solver/main.rs                               | 14 ++++++++++++++
 ..._unsat_no_candidates_distinct_requirements.snap | 11 +++++++++++
 3 files changed, 29 insertions(+), 2 deletions(-)
 create mode 100644 tests/solver/snapshots/solver__unsat_no_candidates_distinct_requirements.snap

diff --git a/src/conflict.rs b/src/conflict.rs
index 32d22c4b..e363313b 100644
--- a/src/conflict.rs
+++ b/src/conflict.rs
@@ -440,14 +440,16 @@ impl<S: SolverId> ConflictGraph<S> {
                 | ConflictNode::Excluded(_) => continue,
             };
 
+            // Candidates that require different version sets stay separate so each
+            // distinct requirement is reported to the user (conda/rattler#2476).
             let predecessors: Vec<_> = graph
                 .edges_directed(node_id, Direction::Incoming)
-                .map(|e| e.source())
+                .map(|e| (e.weight().try_requires(), e.source()))
                 .sorted_unstable()
                 .collect();
             let successors: Vec<_> = graph
                 .edges(node_id)
-                .map(|e| e.target())
+                .map(|e| (e.weight().try_requires(), e.target()))
                 .sorted_unstable()
                 .collect();
 
diff --git a/tests/solver/main.rs b/tests/solver/main.rs
index a1d16f8d..856e281c 100644
--- a/tests/solver/main.rs
+++ b/tests/solver/main.rs
@@ -450,6 +450,20 @@ fn test_unsat_no_candidates_for_child_2() {
     insta::assert_snapshot!(error);
 }
 
+// Versions requiring different versions of a missing dependency are each
+// reported (conda/rattler#2476).
+#[test]
+fn test_unsat_no_candidates_distinct_requirements() {
+    let provider = BundleBoxProvider::from_packages(&[
+        ("a", 1, vec!["b 41..42"]),
+        ("a", 2, vec!["b 41..42"]),
+        ("a", 3, vec!["b 42..43"]),
+        ("a", 4, vec!["b 43..44"]),
+    ]);
+    let error = solve_unsat(provider, &["a"]);
+    insta::assert_snapshot!(error);
+}
+
 #[test]
 fn test_unsat_missing_top_level_dep_1() {
     let provider = BundleBoxProvider::from_packages(&[("asdf", 1, vec![])]);
diff --git a/tests/solver/snapshots/solver__unsat_no_candidates_distinct_requirements.snap b/tests/solver/snapshots/solver__unsat_no_candidates_distinct_requirements.snap
new file mode 100644
index 00000000..877b2f04
--- /dev/null
+++ b/tests/solver/snapshots/solver__unsat_no_candidates_distinct_requirements.snap
@@ -0,0 +1,11 @@
+---
+source: tests/solver/main.rs
+expression: error
+---
+a * cannot be installed because there are no viable options:
+├─ a 4 would require
+│  └─ b >=43, <44, for which no candidates were found.
+├─ a 3 would require
+│  └─ b >=42, <43, for which no candidates were found.
+└─ a 1 | 2 would require
+   └─ b >=41, <42, for which no candidates were found.