Avoid enforcing extra-only constraints (#4570)

## Summary

In the dependency refactor (https://github.com/astral-sh/uv/pull/4430),
the logic for requirements and constraints was combined. Specifically,
we were applying constraints _before_ filtering on markers and extras,
and then applying that same filtering to the constraints. As a result,
constraints that should only be activated when an extra is enabled were
being enabled unconditionally.

Closes https://github.com/astral-sh/uv/issues/4569.

crates/uv-resolver/src/resolver/mod.rs

@@ -1302,15 +1302,6 @@ impl<InstalledPackages: InstalledPackagesProvider> ResolverState<InstalledPackag
     ) -> impl Iterator<Item = &'a Requirement> {
         self.overrides
             .apply(dependencies)
-            .flat_map(|requirement| {
-                iter::once(requirement).chain(
-                    // If the requirement was constrained, add those constraints.
-                    self.constraints
-                        .get(&requirement.name)
-                        .into_iter()
-                        .flatten(),
-                )
-            })
             .filter(move |requirement| {
                 // If the requirement would not be selected with any Python version
                 // supported by the root, skip it.
@@ -1353,8 +1344,50 @@ impl<InstalledPackages: InstalledPackagesProvider> ResolverState<InstalledPackag
                         }
                     }
                 }
+
                 true
             })
+            .flat_map(move |requirement| {
+                iter::once(requirement).chain(
+                    self.constraints
+                        .get(&requirement.name)
+                        .into_iter()
+                        .flatten()
+                        .filter(move |constraint| {
+                            if !satisfies_requires_python(self.requires_python.as_ref(), constraint) {
+                                trace!(
+                                    "skipping {constraint} because of Requires-Python {requires_python}",
+                                    requires_python = self.requires_python.as_ref().unwrap()
+                                );
+                                return false;
+                            }
+
+                            if !possible_to_satisfy_markers(markers, constraint) {
+                                trace!("skipping {constraint} because of context resolver markers {markers}");
+                                return false;
+                            }
+
+                            // If the constraint isn't relevant for the current platform, skip it.
+                            match extra {
+                                Some(source_extra) => {
+                                    if !constraint.evaluate_markers(
+                                        self.markers.as_ref(),
+                                        std::slice::from_ref(source_extra),
+                                    ) {
+                                        return false;
+                                    }
+                                }
+                                None => {
+                                    if !constraint.evaluate_markers(self.markers.as_ref(), &[]) {
+                                        return false;
+                                    }
+                                }
+                            }
+
+                            true
+                        }),
+                )
+            })
     }
 
     /// Fetch the metadata for a stream of packages and versions.

crates/uv/tests/pip_compile.rs

@@ -9731,3 +9731,38 @@ fn no_binary_only_binary() -> Result<()> {
 
     Ok(())
 }
+
+/// `gunicorn` only depends on `eventlet` via an extra, so the resolution should succeed despite
+/// the nonsensical extra.
+#[test]
+fn ignore_invalid_constraint() -> Result<()> {
+    let context = TestContext::new("3.12");
+
+    let requirements_in = context.temp_dir.child("requirements.in");
+    requirements_in.write_str("gunicorn>=20")?;
+
+    let constraints_txt = context.temp_dir.child("constraints.txt");
+    constraints_txt.write_str("eventlet==9999.0.1.2.3.4.5")?;
+
+    uv_snapshot!(context
+        .pip_compile()
+        .arg("requirements.in")
+        .arg("-c")
+        .arg("constraints.txt"), @r###"
+    success: true
+    exit_code: 0
+    ----- stdout -----
+    # This file was autogenerated by uv via the following command:
+    #    uv pip compile --cache-dir [CACHE_DIR] requirements.in -c constraints.txt
+    gunicorn==21.2.0
+        # via -r requirements.in
+    packaging==24.0
+        # via gunicorn
+
+    ----- stderr -----
+    Resolved 2 packages in [TIME]
+    "###
+    );
+
+    Ok(())
+}

req.txt

@@ -1,3 +0,0 @@
---index-url file:///Users/crmarsh/workspace/packse/index/simple-html/
-
-example-a-961b4c22