Make < exclusive for non-prerelease markers

crates/uv-resolver/src/pubgrub/specifier.rs

@@ -1,7 +1,7 @@
 use anyhow::Result;
 use pubgrub::range::Range;
 
-use pep440_rs::{Operator, PreRelease, Version, VersionSpecifier};
+use pep440_rs::{Operator, PreRelease, PreReleaseKind, Version, VersionSpecifier};
 
 use crate::ResolveError;
 
@@ -38,15 +38,22 @@ impl TryFrom<&VersionSpecifier> for PubGrubSpecifier {
                 let [rest @ .., last, _] = specifier.version().release() else {
                     return Err(ResolveError::InvalidTildeEquals(specifier.clone()));
                 };
-                let upper = pep440_rs::Version::new(rest.iter().chain([&(last + 1)]))
+                let upper = Version::new(rest.iter().chain([&(last + 1)]))
                     .with_epoch(specifier.version().epoch())
                     .with_dev(Some(0));
                 let version = specifier.version().clone();
                 Range::from_range_bounds(version..upper)
             }
             Operator::LessThan => {
                 let version = specifier.version().clone();
-                Range::strictly_lower_than(version)
+                if version.any_prerelease() {
+                    Range::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.
+                    Range::strictly_lower_than(version.with_pre(Some(PreRelease { kind: PreReleaseKind::Alpha, number: 0 })))
+                }
             }
             Operator::LessThanEqual => {
                 let version = specifier.version().clone();

crates/uv/tests/pip_compile.rs

@@ -2075,12 +2075,17 @@ fn compile_yanked_version_indirect() -> Result<()> {
       ╰─▶ Because only the following versions of attrs are available:
               attrs<=20.3.0
               attrs==21.1.0
-              attrs>=21.2.0
+              attrs>=21.2.0a0
           and attrs==21.1.0 is unusable because it was yanked (reason:
           Installable but not importable on Python 3.4), we can conclude that
-          attrs>20.3.0,<21.2.0 cannot be used.
-          And because you require attrs>20.3.0,<21.2.0, we can conclude that the
+          attrs>20.3.0,<21.2.0a0 cannot be used.
+          And because you require attrs>20.3.0,<21.2.0a0, we can conclude that the
           requirements are unsatisfiable.
+
+          hint: attrs was requested with a pre-release marker (e.g., any of:
+              attrs>20.3.0,<21.1.0
+              attrs>21.1.0,<21.2.0a0
+          ), but pre-releases weren't enabled (try: `--prerelease=allow`)
     "###
     );
 
@@ -3857,8 +3862,11 @@ fn compile_constraints_incompatible_url() -> Result<()> {
 
     ----- stderr -----
       × No solution found when resolving dependencies:
-      ╰─▶ Because only anyio>=4 is available and you require anyio<4, we can
+      ╰─▶ Because only anyio>=4a0 is available and you require anyio<4a0, we can
           conclude that the requirements are unsatisfiable.
+
+          hint: anyio was requested with a pre-release marker (e.g., anyio<4a0),
+          but pre-releases weren't enabled (try: `--prerelease=allow`)
     "###
     );
 
@@ -3881,8 +3889,11 @@ fn index_url_in_requirements() -> Result<()> {
 
     ----- stderr -----
       × No solution found when resolving dependencies:
-      ╰─▶ Because anyio<4 was not found in the package registry and you require
-          anyio<4, we can conclude that the requirements are unsatisfiable.
+      ╰─▶ Because anyio<4a0 was not found in the package registry and you require
+          anyio<4a0, we can conclude that the requirements are unsatisfiable.
+
+          hint: anyio was requested with a pre-release marker (e.g., anyio<4a0),
+          but pre-releases weren't enabled (try: `--prerelease=allow`)
     "###
     );
 
@@ -4285,7 +4296,7 @@ fn override_with_incompatible_constraint() -> Result<()> {
 
     ----- stderr -----
       × No solution found when resolving dependencies:
-      ╰─▶ Because you require anyio>=3.0.0 and you require anyio<3.0.0, we can
+      ╰─▶ Because you require anyio>=3.0.0 and you require anyio<3.0.0a0, we can
           conclude that the requirements are unsatisfiable.
     "###
     );