Avoid conflict set combinatorial explosion

crates/uv-pep508/src/marker/algebra.rs

@@ -558,27 +558,46 @@ impl InternerGuard<'_> {
     /// `((os_name == ... and extra == foo) or (sys_platform == ... and extra != foo))`,
     /// this would return a marker
     /// `os_name == ... or sys_platform == ...`.
-    pub(crate) fn without_extras(&mut self, mut i: NodeId) -> NodeId {
+    pub(crate) fn without_extras(&mut self, i: NodeId) -> NodeId {
+        let mut cache = FxHashMap::default();
+        self.without_extras_cached(i, &mut cache)
+    }
+
+    fn without_extras_cached(
+        &mut self,
+        mut i: NodeId,
+        cache: &mut FxHashMap<NodeId, NodeId>,
+    ) -> NodeId {
         if matches!(i, NodeId::TRUE | NodeId::FALSE) {
             return i;
         }
 
+        if let Some(&cached) = cache.get(&i) {
+            return cached;
+        }
+
+        let original = i;
         let parent = i;
         let node = self.shared.node(i);
-        if matches!(node.var, Variable::Extra(_)) {
+        let result = if matches!(node.var, Variable::Extra(_)) {
             i = NodeId::FALSE;
             for child in node.children.nodes() {
                 i = self.or(i, child.negate(parent));
             }
             if i.is_true() {
-                return NodeId::TRUE;
+                NodeId::TRUE
+            } else {
+                self.without_extras_cached(i, cache)
             }
-            self.without_extras(i)
         } else {
             // Restrict all nodes recursively.
-            let children = node.children.map(i, |node| self.without_extras(node));
+            let children = node
+                .children
+                .map(i, |node| self.without_extras_cached(node, cache));
             self.create_node(node.var.clone(), children)
-        }
+        };
+        cache.insert(original, result);
+        result
     }
 
     /// Returns a new tree where the only nodes remaining are `extra` nodes.

crates/uv/tests/it/lock_conflict.rs

@@ -1,3 +1,5 @@
+use std::time::Duration;
+
 use anyhow::Result;
 use assert_fs::prelude::*;
 use insta::assert_snapshot;
@@ -16568,3 +16570,103 @@ fn project_level_conflict_with_group() -> Result<()> {
 
     Ok(())
 }
+
+/// See: <https://github.com/astral-sh/uv/issues/16779>
+#[test]
+fn many_conflicts_with_requested_dependency_extra() -> Result<()> {
+    let context = uv_test::test_context!("3.12");
+
+    let root_pyproject_toml = context.temp_dir.child("pyproject.toml");
+    // 29 conflicts results in a reasonably short run-time after fixing, and a very long runtime
+    // without the fix. This is to attempt to ensure that this test won't fail sporadically on a
+    // slow machine, or succeed (while broken) on a super fast machine.
+    root_pyproject_toml.write_str(
+        r#"
+        [project]
+        name = "project"
+        version = "0.1.0"
+        requires-python = "==3.12.*"
+        dependencies = []
+
+        [project.optional-dependencies]
+        x00 = ["branch-package"]
+
+        [tool.uv.sources]
+        branch-package = { path = "branch-package" }
+
+        [tool.uv]
+        conflicts = [[
+            { extra = "x00" },
+            { extra = "x01" },
+            { extra = "x02" },
+            { extra = "x03" },
+            { extra = "x04" },
+            { extra = "x05" },
+            { extra = "x06" },
+            { extra = "x07" },
+            { extra = "x08" },
+            { extra = "x09" },
+            { extra = "x10" },
+            { extra = "x11" },
+            { extra = "x12" },
+            { extra = "x13" },
+            { extra = "x14" },
+            { extra = "x15" },
+            { extra = "x16" },
+            { extra = "x17" },
+            { extra = "x18" },
+            { extra = "x19" },
+            { extra = "x20" },
+            { extra = "x21" },
+            { extra = "x22" },
+            { extra = "x23" },
+            { extra = "x24" },
+            { extra = "x25" },
+            { extra = "x26" },
+            { extra = "x27" },
+            { extra = "x28" },
+        ]]
+        "#,
+    )?;
+
+    let branch_pyproject_toml = context
+        .temp_dir
+        .child("branch-package")
+        .child("pyproject.toml");
+    branch_pyproject_toml.write_str(
+        r#"
+        [project]
+        name = "branch-package"
+        version = "0.1.0"
+        requires-python = ">=3.12"
+        dependencies = ["leaf-package[easy]"]
+
+        [tool.uv.sources]
+        leaf-package = { path = "../leaf-package" }
+        "#,
+    )?;
+
+    let leaf_pyproject_toml = context
+        .temp_dir
+        .child("leaf-package")
+        .child("pyproject.toml");
+    leaf_pyproject_toml.write_str(
+        r#"
+        [project]
+        name = "leaf-package"
+        version = "0.1.0"
+        requires-python = ">=3.12"
+        dependencies = []
+
+        [project.optional-dependencies]
+        easy = []
+        "#,
+    )?;
+
+    assert_cmd::Command::from_std(context.lock())
+        .timeout(Duration::from_mins(1))
+        .assert()
+        .success();
+
+    Ok(())
+}