Filter out markers based on Python requirement (#4912)

## Summary

In marker normalization, we now remove any markers that are redundant
with the `requires-python` specifier (i.e., always true for the given
Python requirement).

For example, given `iniconfig ; python_version >= '3.7'`, we can remove
the `python_version >= '3.7'` marker when resolving with
`--python-version 3.8`.

Closes #4852.

crates/uv-resolver/src/lock.rs

@@ -1892,7 +1892,7 @@ impl Dependency {
     ) -> Dependency {
         let distribution_id = DistributionId::from_annotated_dist(annotated_dist);
         let extra = annotated_dist.extra.clone();
-        let marker = marker.cloned().and_then(crate::marker::normalize);
+        let marker = marker.cloned();
         Dependency {
             distribution_id,
             extra,

crates/uv-resolver/src/marker.rs

@@ -4,7 +4,7 @@ use std::collections::HashMap;
 use std::ops::Bound::{self, *};
 use std::ops::RangeBounds;
 
-use pubgrub::range::Range as PubGrubRange;
+use pubgrub::range::{Range as PubGrubRange, Range};
 
 use pep440_rs::{Operator, Version, VersionSpecifier};
 use pep508_rs::{
@@ -82,35 +82,41 @@ fn string_is_disjoint(this: &MarkerExpression, other: &MarkerExpression) -> bool
     true
 }
 
-/// Returns the minimum Python version that can satisfy the [`MarkerTree`], if it's constrained.
-pub(crate) fn requires_python_marker(tree: &MarkerTree) -> Option<RequiresPythonBound> {
-    match tree {
-        MarkerTree::Expression(MarkerExpression::Version {
+pub(crate) fn python_range(expr: &MarkerExpression) -> Option<Range<Version>> {
+    match expr {
+        MarkerExpression::Version {
             key: MarkerValueVersion::PythonFullVersion,
             specifier,
-        }) => {
+        } => {
             // Simplify using PEP 440 semantics.
             let specifier = PubGrubSpecifier::from_pep440_specifier(specifier).ok()?;
 
-            // Convert to PubGrub range and perform a union.
-            let range = PubGrubRange::from(specifier);
-            let (lower, _) = range.iter().next()?;
-
-            // Extract the lower bound.
-            Some(RequiresPythonBound::new(lower.clone()))
+            // Convert to PubGrub.
+            Some(PubGrubRange::from(specifier))
         }
-        MarkerTree::Expression(MarkerExpression::Version {
+        MarkerExpression::Version {
             key: MarkerValueVersion::PythonVersion,
             specifier,
-        }) => {
+        } => {
             // Simplify using release-only semantics, since `python_version` is always `major.minor`.
             let specifier = PubGrubSpecifier::from_release_specifier(specifier).ok()?;
 
-            // Convert to PubGrub range and perform a union.
-            let range = PubGrubRange::from(specifier);
-            let (lower, _) = range.iter().next()?;
+            // Convert to PubGrub.
+            Some(PubGrubRange::from(specifier))
+        }
+        _ => None,
+    }
+}
+
+/// Returns the minimum Python version that can satisfy the [`MarkerTree`], if it's constrained.
+pub(crate) fn requires_python_marker(tree: &MarkerTree) -> Option<RequiresPythonBound> {
+    match tree {
+        MarkerTree::Expression(expr) => {
+            // Extract the supported Python range.
+            let range = python_range(expr)?;
 
             // Extract the lower bound.
+            let (lower, _) = range.iter().next()?;
             Some(RequiresPythonBound::new(lower.clone()))
         }
         MarkerTree::And(trees) => {
@@ -129,42 +135,47 @@ pub(crate) fn requires_python_marker(tree: &MarkerTree) -> Option<RequiresPython
             }
             min_version
         }
-        MarkerTree::Expression(_) => None,
     }
 }
 
 /// Normalizes this marker tree.
 ///
 /// This function does a number of operations to normalize a marker tree recursively:
 /// - Sort and flatten all nested expressions.
-/// - Simplify expressions. This includes combining overlapping version ranges and removing duplicate
-///   expressions.
+/// - Simplify expressions. This includes combining overlapping version ranges, removing duplicate
+///   expressions, and removing redundant expressions.
 /// - Normalize the order of version expressions to the form `<version key> <version op> <version>`
-///  (i.e. not the reverse).
+///   (i.e., not the reverse).
 ///
 /// This is useful in cases where creating conjunctions or disjunctions might occur in a non-deterministic
 /// order. This routine will attempt to erase the distinction created by such a construction.
-pub(crate) fn normalize(mut tree: MarkerTree) -> Option<MarkerTree> {
+pub(crate) fn normalize(
+    mut tree: MarkerTree,
+    bound: Option<&RequiresPythonBound>,
+) -> Option<MarkerTree> {
     // Filter out redundant expressions that show up before and after normalization.
     filter_all(&mut tree);
-    let mut tree = normalize_all(tree)?;
+    let mut tree = normalize_all(tree, bound)?;
     filter_all(&mut tree);
     Some(tree)
 }
 
 /// Normalize the marker tree recursively.
-pub(crate) fn normalize_all(tree: MarkerTree) -> Option<MarkerTree> {
+pub(crate) fn normalize_all(
+    tree: MarkerTree,
+    bound: Option<&RequiresPythonBound>,
+) -> Option<MarkerTree> {
     match tree {
         MarkerTree::And(trees) => {
             let mut reduced = Vec::new();
             let mut versions: HashMap<_, Vec<_>> = HashMap::new();
 
             for subtree in trees {
-                // Simplify nested expressions as much as possible first.
+                // Normalize nested expressions as much as possible first.
                 //
                 // If the expression gets normalized out (e.g., `version < '3.8' and version >= '3.8'`),
                 // omit it.
-                let Some(subtree) = normalize_all(subtree) else {
+                let Some(subtree) = normalize_all(subtree, bound) else {
                     continue;
                 };
 
@@ -206,11 +217,11 @@ pub(crate) fn normalize_all(tree: MarkerTree) -> Option<MarkerTree> {
             let mut versions: HashMap<_, Vec<_>> = HashMap::new();
 
             for subtree in trees {
-                // Simplify nested expressions as much as possible first.
+                // Normalize nested expressions as much as possible first.
                 //
                 // If the expression gets normalized out (e.g., `version < '3.8' and version >= '3.8'`),
                 // return `true`.
-                let subtree = normalize_all(subtree)?;
+                let subtree = normalize_all(subtree, bound)?;
 
                 match subtree {
                     MarkerTree::And(_) => reduced.push(subtree),
@@ -260,6 +271,19 @@ pub(crate) fn normalize_all(tree: MarkerTree) -> Option<MarkerTree> {
             }
         }
 
+        // If the marker is redundant given the supported Python range, remove it.
+        //
+        // For example, `python_version >= '3.7'` is redundant with `requires-python: '>=3.8'`.
+        MarkerTree::Expression(expr)
+            if bound.is_some_and(|bound| {
+                python_range(&expr).is_some_and(|supported_range| {
+                    Range::from(bound.clone()).subset_of(&supported_range)
+                })
+            }) =>
+        {
+            None
+        }
+
         MarkerTree::Expression(ref expr) => {
             if let Some((key, range)) = keyed_range(expr) {
                 // If multiple terms are required to express the range, flatten them into an `Or`
@@ -681,8 +705,8 @@ mod tests {
     #[test]
     fn simplify() {
         assert_marker_equal(
-            "python_version == '3.1' or python_version == '3.1'",
-            "python_version == '3.1'",
+            "python_version == '3.9' or python_version == '3.9'",
+            "python_version == '3.9'",
         );
 
         assert_marker_equal(
@@ -827,6 +851,21 @@ mod tests {
         );
     }
 
+    #[test]
+    fn requires_python() {
+        assert_normalizes_out("python_version >= '3.8'");
+        assert_normalizes_out("python_version >= '3.8' or sys_platform == 'win32'");
+
+        assert_normalizes_to(
+            "python_version >= '3.8' and sys_platform == 'win32'",
+            "sys_platform == 'win32'",
+        );
+
+        assert_normalizes_to("python_version == '3.8'", "python_version == '3.8'");
+
+        assert_normalizes_to("python_version <= '3.10'", "python_version <= '3.10'");
+    }
+
     #[test]
     fn extra_disjointness() {
         assert!(!is_disjoint("extra == 'a'", "python_version == '1'"));
@@ -987,8 +1026,9 @@ mod tests {
     }
 
     fn assert_marker_equal(one: impl AsRef<str>, two: impl AsRef<str>) {
+        let bound = RequiresPythonBound::new(Included(Version::new([3, 8])));
         let tree1 = MarkerTree::parse_reporter(one.as_ref(), &mut TracingReporter).unwrap();
-        let tree1 = normalize(tree1).unwrap();
+        let tree1 = normalize(tree1, Some(&bound)).unwrap();
         let tree2 = MarkerTree::parse_reporter(two.as_ref(), &mut TracingReporter).unwrap();
         assert_eq!(
             tree1.to_string(),
@@ -999,17 +1039,19 @@ mod tests {
     }
 
     fn assert_normalizes_to(before: impl AsRef<str>, after: impl AsRef<str>) {
+        let bound = RequiresPythonBound::new(Included(Version::new([3, 8])));
         let normalized = MarkerTree::parse_reporter(before.as_ref(), &mut TracingReporter)
             .unwrap()
             .clone();
-        let normalized = normalize(normalized).unwrap();
+        let normalized = normalize(normalized, Some(&bound)).unwrap();
         assert_eq!(normalized.to_string(), after.as_ref());
     }
 
     fn assert_normalizes_out(before: impl AsRef<str>) {
+        let bound = RequiresPythonBound::new(Included(Version::new([3, 8])));
         let normalized = MarkerTree::parse_reporter(before.as_ref(), &mut TracingReporter)
             .unwrap()
             .clone();
-        assert!(normalize(normalized).is_none());
+        assert!(normalize(normalized, Some(&bound)).is_none());
     }
 }

crates/uv-resolver/src/requires_python.rs

@@ -155,6 +155,11 @@ impl RequiresPython {
         self.bound.as_ref() == Bound::Unbounded
     }
 
+    /// Returns the [`RequiresPythonBound`] for the `Requires-Python` specifier.
+    pub fn bound(&self) -> &RequiresPythonBound {
+        &self.bound
+    }
+
     /// Returns this `Requires-Python` specifier as an equivalent marker
     /// expression utilizing the `python_version` marker field.
     ///
@@ -254,6 +259,16 @@ impl RequiresPythonBound {
     }
 }
 
+impl From<RequiresPythonBound> for Range<Version> {
+    fn from(value: RequiresPythonBound) -> Self {
+        match value.0 {
+            Bound::Included(version) => Range::higher_than(version),
+            Bound::Excluded(version) => Range::strictly_higher_than(version),
+            Bound::Unbounded => Range::full(),
+        }
+    }
+}
+
 impl Deref for RequiresPythonBound {
     type Target = Bound<Version>;
 

crates/uv-resolver/src/resolution/display.rs

@@ -406,7 +406,7 @@ fn propagate_markers(mut graph: IntermediatePetGraph) -> IntermediatePetGraph {
         }
 
         if let DisplayResolutionGraphNode::Dist(node) = &mut graph[index] {
-            node.markers = marker_tree.and_then(marker::normalize);
+            node.markers = marker_tree.and_then(|marker| marker::normalize(marker, None));
         };
     }
 

crates/uv-resolver/src/resolution/graph.rs

@@ -291,6 +291,16 @@ impl ResolutionGraph {
             .and_then(PythonTarget::as_requires_python)
             .cloned();
 
+        // Normalize any markers.
+        for edge in petgraph.edge_indices() {
+            if let Some(marker) = petgraph[edge].take() {
+                petgraph[edge] = crate::marker::normalize(
+                    marker,
+                    requires_python.as_ref().map(RequiresPython::bound),
+                );
+            }
+        }
+
         Ok(Self {
             petgraph,
             requires_python,
@@ -318,7 +328,7 @@ impl ResolutionGraph {
 
     /// Return `true` if there are no packages in the graph.
     pub fn is_empty(&self) -> bool {
-        self.dists().any(super::AnnotatedDist::is_base)
+        self.dists().any(AnnotatedDist::is_base)
     }
 
     /// Returns `true` if the graph contains the given package.

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

@@ -578,7 +578,7 @@ impl<InstalledPackages: InstalledPackagesProvider> ResolverState<InstalledPackag
                                 }
 
                                 forked_state.markers.and(fork.markers);
-                                forked_state.markers = normalize(forked_state.markers)
+                                forked_state.markers = normalize(forked_state.markers, None)
                                     .unwrap_or(MarkerTree::And(Vec::new()));
 
                                 // If the fork contains a narrowed Python requirement, apply it.

crates/uv/tests/edit.rs

@@ -1405,9 +1405,9 @@ fn update() -> Result<()> {
         version = "0.1.0"
         source = { editable = "." }
         dependencies = [
-            { name = "requests", marker = "python_version > '3.7'" },
-            { name = "requests", extra = "socks", marker = "python_version > '3.7'" },
-            { name = "requests", extra = "use-chardet-on-py3", marker = "python_version > '3.7'" },
+            { name = "requests" },
+            { name = "requests", extra = "socks" },
+            { name = "requests", extra = "use-chardet-on-py3" },
         ]
 
         [[distribution]]

crates/uv/tests/pip_compile.rs

@@ -6366,23 +6366,23 @@ fn universal() -> Result<()> {
     ----- stdout -----
     # This file was autogenerated by uv via the following command:
     #    uv pip compile --cache-dir [CACHE_DIR] requirements.in --universal
-    attrs==23.2.0 ; python_version > '3.11' or sys_platform == 'win32'
+    attrs==23.2.0
         # via
         #   outcome
         #   trio
-    cffi==1.16.0 ; implementation_name != 'pypy' and os_name == 'nt' and (python_version > '3.11' or sys_platform == 'win32')
+    cffi==1.16.0 ; implementation_name != 'pypy' and os_name == 'nt'
         # via trio
-    idna==3.6 ; python_version > '3.11' or sys_platform == 'win32'
+    idna==3.6
         # via trio
-    outcome==1.3.0.post0 ; python_version > '3.11' or sys_platform == 'win32'
+    outcome==1.3.0.post0
         # via trio
-    pycparser==2.21 ; implementation_name != 'pypy' and os_name == 'nt' and (python_version > '3.11' or sys_platform == 'win32')
+    pycparser==2.21 ; implementation_name != 'pypy' and os_name == 'nt'
         # via cffi
-    sniffio==1.3.1 ; python_version > '3.11' or sys_platform == 'win32'
+    sniffio==1.3.1
         # via trio
-    sortedcontainers==2.4.0 ; python_version > '3.11' or sys_platform == 'win32'
+    sortedcontainers==2.4.0
         # via trio
-    trio==0.25.0 ; python_version > '3.11' or sys_platform == 'win32'
+    trio==0.25.0
         # via -r requirements.in
 
     ----- stderr -----
@@ -6780,6 +6780,37 @@ fn universal_no_repeated_unconditional_distributions() -> Result<()> {
     Ok(())
 }
 
+/// Remove `python_version` markers that are always true.
+#[test]
+fn universal_unnecessary_python() -> Result<()> {
+    let context = TestContext::new("3.12");
+    let requirements_in = context.temp_dir.child("requirements.in");
+    requirements_in.write_str(indoc::indoc! {r"
+        iniconfig ; python_version >= '3.7'
+    "})?;
+
+    uv_snapshot!(context.filters(), windows_filters=false, context.pip_compile()
+            .arg("requirements.in")
+            .arg("-p")
+            .arg("3.8")
+            .arg("--universal"), @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 -p 3.8 --universal
+    iniconfig==2.0.0
+        # via -r requirements.in
+
+    ----- stderr -----
+    warning: The requested Python version 3.8 is not available; 3.12.[X] will be used to build dependencies instead.
+    Resolved 1 package in [TIME]
+    "###
+    );
+
+    Ok(())
+}
+
 /// Resolve a package from a `requirements.in` file, with a `constraints.txt` file pinning one of
 /// its transitive dependencies to a specific version.
 #[test]