Allow earlier post releases with exclusive ordering (#16881)

## Summary

Given (e.g.) `<0.12.0.post2`, we need to omit pre-releases on `0.12.0`,
but include post-releases.

Closes https://github.com/astral-sh/uv/issues/16868.

crates/uv-pep440/src/version_ranges.rs

@@ -57,12 +57,30 @@ impl From<VersionSpecifier> for Ranges<Version> {
                 Self::from_range_bounds(version..upper)
             }
             Operator::LessThan => {
-                if version.any_prerelease() {
-                    Self::strictly_lower_than(version)
-                } else {
                 // Per PEP 440: "The exclusive ordered comparison <V MUST NOT allow a
                 // pre-release of the specified version unless the specified version is itself a
                 // pre-release."
+                if version.any_prerelease() {
+                    // If V is a pre-release, we allow pre-releases of the same version.
+                    Self::strictly_lower_than(version)
+                } else if let Some(post) = version.post() {
+                    // If V is a post-release (e.g., `<0.12.0.post2`), we want to:
+                    // - Exclude pre-releases of the base version (e.g., `0.12.0a1`)
+                    // - Include the final release (e.g., `0.12.0`)
+                    // - Include earlier post-releases (e.g., `0.12.0.post1`)
+                    //
+                    // The range is: `(-∞, base.min0) ∪ [base, V.post)`
+                    // where `base` is the version without the post-release component.
+                    let base = version.clone().with_post(None);
+                    // Everything below the base version's pre-releases
+                    let lower = Self::strictly_lower_than(base.clone().with_min(Some(0)));
+                    // From base (inclusive) up to but not including V
+                    let upper = Self::from_range_bounds(base..version.with_post(Some(post)));
+                    lower.union(&upper)
+                } else {
+                    // V is not a pre-release or post-release, so exclude pre-releases of the
+                    // specified version by using a "min" sentinel that sorts before all
+                    // pre-releases.
                     Self::strictly_lower_than(version.with_min(Some(0)))
                 }
             }
@@ -476,3 +494,131 @@ impl From<UpperBound> for Bound<Version> {
         bound.0
     }
 }
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    /// Test that `<V.postN` excludes pre-releases of the base version but includes
+    /// earlier post-releases and the final release.
+    ///
+    /// See: <https://github.com/astral-sh/uv/issues/16868>
+    #[test]
+    fn less_than_post_release() {
+        let specifier: VersionSpecifier = "<0.12.0.post2".parse().unwrap();
+        let range = Ranges::<Version>::from(specifier);
+
+        // Should include versions less than base release.
+        let v = "0.11.0".parse::<Version>().unwrap();
+        assert!(range.contains(&v), "should include 0.11.0");
+
+        // Should exclude pre-releases of the base release.
+        let v = "0.12.0a1".parse::<Version>().unwrap();
+        assert!(!range.contains(&v), "should exclude 0.12.0a1");
+
+        let v = "0.12.0b1".parse::<Version>().unwrap();
+        assert!(!range.contains(&v), "should exclude 0.12.0b1");
+
+        let v = "0.12.0rc1".parse::<Version>().unwrap();
+        assert!(!range.contains(&v), "should exclude 0.12.0rc1");
+
+        let v = "0.12.0.dev0".parse::<Version>().unwrap();
+        assert!(!range.contains(&v), "should exclude 0.12.0.dev0");
+
+        // Should also exclude post-releases of pre-releases.
+        let v = "0.12.0a1.post1".parse::<Version>().unwrap();
+        assert!(!range.contains(&v), "should exclude 0.12.0a1.post1");
+
+        let v = "0.12.0b1.post1".parse::<Version>().unwrap();
+        assert!(!range.contains(&v), "should exclude 0.12.0b1.post1");
+
+        // Should include the final release.
+        let v = "0.12.0".parse::<Version>().unwrap();
+        assert!(range.contains(&v), "should include 0.12.0");
+
+        // Should include earlier post-releases.
+        let v = "0.12.0.post1".parse::<Version>().unwrap();
+        assert!(range.contains(&v), "should include 0.12.0.post1");
+
+        // Should exclude the specified post-release.
+        let v = "0.12.0.post2".parse::<Version>().unwrap();
+        assert!(!range.contains(&v), "should exclude 0.12.0.post2");
+
+        // Should exclude later versions.
+        let v = "0.13.0".parse::<Version>().unwrap();
+        assert!(!range.contains(&v), "should exclude 0.13.0");
+    }
+
+    /// Test that `<V` (non-post-release) correctly excludes pre-releases.
+    #[test]
+    fn less_than_final_release() {
+        let specifier: VersionSpecifier = "<0.12.0".parse().unwrap();
+        let range = Ranges::<Version>::from(specifier);
+
+        // Should include versions less than base release.
+        let v = "0.11.0".parse::<Version>().unwrap();
+        assert!(range.contains(&v), "should include 0.11.0");
+
+        // Should exclude pre-releases of the specified version.
+        let v = "0.12.0a1".parse::<Version>().unwrap();
+        assert!(!range.contains(&v), "should exclude 0.12.0a1");
+
+        let v = "0.12.0.dev0".parse::<Version>().unwrap();
+        assert!(!range.contains(&v), "should exclude 0.12.0.dev0");
+
+        // Should exclude the specified version.
+        let v = "0.12.0".parse::<Version>().unwrap();
+        assert!(!range.contains(&v), "should exclude 0.12.0");
+
+        // Should exclude post-releases of the specified version.
+        let v = "0.12.0.post1".parse::<Version>().unwrap();
+        assert!(!range.contains(&v), "should exclude 0.12.0.post1");
+    }
+
+    /// Test that `<V.preN` allows earlier pre-releases of the same version.
+    #[test]
+    fn less_than_pre_release() {
+        let specifier: VersionSpecifier = "<0.12.0b1".parse().unwrap();
+        let range = Ranges::<Version>::from(specifier);
+
+        // Should include earlier pre-releases.
+        let v = "0.12.0a1".parse::<Version>().unwrap();
+        assert!(range.contains(&v), "should include 0.12.0a1");
+
+        let v = "0.12.0.dev0".parse::<Version>().unwrap();
+        assert!(range.contains(&v), "should include 0.12.0.dev0");
+
+        // Should exclude the specified pre-release and later.
+        let v = "0.12.0b1".parse::<Version>().unwrap();
+        assert!(!range.contains(&v), "should exclude 0.12.0b1");
+
+        let v = "0.12.0".parse::<Version>().unwrap();
+        assert!(!range.contains(&v), "should exclude 0.12.0");
+    }
+
+    /// Test the edge case where `<V.post0` still includes the final release.
+    #[test]
+    fn less_than_post_zero() {
+        let specifier: VersionSpecifier = "<0.12.0.post0".parse().unwrap();
+        let range = Ranges::<Version>::from(specifier);
+
+        // Should include versions less than base release.
+        let v = "0.11.0".parse::<Version>().unwrap();
+        assert!(range.contains(&v), "should include 0.11.0");
+
+        // Should exclude pre-releases of the base release.
+        let v = "0.12.0a1".parse::<Version>().unwrap();
+        assert!(!range.contains(&v), "should exclude 0.12.0a1");
+
+        // Should include the final release (0.12.0 < 0.12.0.post0).
+        let v = "0.12.0".parse::<Version>().unwrap();
+        assert!(range.contains(&v), "should include 0.12.0");
+
+        // Should exclude post0 and later.
+        let v = "0.12.0.post0".parse::<Version>().unwrap();
+        assert!(!range.contains(&v), "should exclude 0.12.0.post0");
+
+        let v = "0.12.0.post1".parse::<Version>().unwrap();
+        assert!(!range.contains(&v), "should exclude 0.12.0.post1");
+    }
+}

crates/uv/tests/it/pip_compile.rs

@@ -17850,3 +17850,36 @@ fn credentials_from_subdirectory() -> Result<()> {
 
     Ok(())
 }
+
+/// Install a package with a post-release version constraint.
+///
+/// `<V.postN` should include earlier post-releases but exclude pre-releases.
+///
+/// See: <https://github.com/astral-sh/uv/issues/16868>
+#[test]
+fn post_release_less_than() -> Result<()> {
+    let context = TestContext::new("3.10");
+
+    let requirements_in = context.temp_dir.child("requirements.in");
+    requirements_in.write_str("hidapi>=0.12.0.post1,<0.12.0.post2")?;
+
+    // The constraint `>=0.12.0.post1, <0.12.0.post2` should only match 0.12.0.post1.
+    uv_snapshot!(context.pip_compile()
+        .arg("requirements.in"), @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
+    hidapi==0.12.0.post1
+        # via -r requirements.in
+    setuptools==69.2.0
+        # via hidapi
+
+    ----- stderr -----
+    Resolved 2 packages in [TIME]
+    "
+    );
+
+    Ok(())
+}