Support `cp3-none-any`

According to https://packaging.python.org/en/latest/specifications/platform-compatibility-tags/, `cp3-none-any` is a valid tag, even though you shouldn't use it. We should accept it.

crates/uv-distribution-types/src/prioritized_distribution.rs

@@ -930,7 +930,7 @@ fn implied_python_markers(filename: &WheelFilename) -> MarkerTree {
                 // No Python tag means no Python version requirement.
                 return MarkerTree::TRUE;
             }
-            LanguageTag::Python { major, minor: None } => {
+            LanguageTag::Python { major, minor: None } | LanguageTag::CPythonMajor { major } => {
                 MarkerTree::expression(MarkerExpression::Version {
                     key: uv_pep508::MarkerValueVersion::PythonVersion,
                     specifier: VersionSpecifier::equals_star_version(Version::new([u64::from(

crates/uv-platform-tags/src/language_tag.rs

@@ -32,6 +32,8 @@ pub enum LanguageTag {
     GraalPy { python_version: (u8, u8) },
     /// Ex) `pyston38`
     Pyston { python_version: (u8, u8) },
+    /// Ex) `cp3`
+    CPythonMajor { major: u8 },
 }
 
 impl LanguageTag {
@@ -58,6 +60,7 @@ impl LanguageTag {
             Self::Pyston {
                 python_version: (major, minor),
             } => Some(format!("Pyston {major}.{minor}")),
+            Self::CPythonMajor { major } => Some(format!("CPython {major}")),
         }
     }
 }
@@ -94,6 +97,9 @@ impl std::fmt::Display for LanguageTag {
             } => {
                 write!(f, "pyston{major}{minor}")
             }
+            Self::CPythonMajor { major } => {
+                write!(f, "cp{major}")
+            }
         }
     }
 }
@@ -181,11 +187,36 @@ impl FromStr for LanguageTag {
                 }
             }
         } else if let Some(cp) = s.strip_prefix("cp") {
-            // Ex) `cp39`
-            let (major, minor) = parse_python_version(cp, "CPython", s)?;
-            Ok(Self::CPython {
-                python_version: (major, minor),
-            })
+            match cp.len() {
+                0 => Err(ParseLanguageTagError::MissingMajorVersion {
+                    implementation: "CPython",
+                    tag: s.to_string(),
+                }),
+                1 => {
+                    // Ex) `cp3`
+                    let major = cp
+                        .chars()
+                        .next()
+                        .ok_or_else(|| ParseLanguageTagError::MissingMajorVersion {
+                            implementation: "CPython",
+                            tag: s.to_string(),
+                        })?
+                        .to_digit(10)
+                        .ok_or_else(|| ParseLanguageTagError::InvalidMajorVersion {
+                            implementation: "CPython",
+                            tag: s.to_string(),
+                        })? as u8;
+                    Ok(Self::CPythonMajor { major })
+                }
+                2 | 3 => {
+                    // Ex) `cp39`, `cp310`
+                    let (major, minor) = parse_python_version(cp, "CPython", s)?;
+                    Ok(Self::CPython {
+                        python_version: (major, minor),
+                    })
+                }
+                _ => Err(ParseLanguageTagError::UnknownFormat(s.to_string())),
+            }
         } else if let Some(pp) = s.strip_prefix("pp") {
             // Ex) `pp39`
             let (major, minor) = parse_python_version(pp, "PyPy", s)?;
@@ -290,6 +321,10 @@ mod tests {
         assert_eq!(LanguageTag::from_str("cp39"), Ok(tag));
         assert_eq!(tag.to_string(), "cp39");
 
+        let tag = LanguageTag::CPythonMajor { major: 3 };
+        assert_eq!(LanguageTag::from_str("cp3"), Ok(tag));
+        assert_eq!(tag.to_string(), "cp3");
+
         assert_eq!(
             LanguageTag::from_str("cp"),
             Err(ParseLanguageTagError::MissingMajorVersion {

crates/uv-platform-tags/src/tags.rs

@@ -401,7 +401,10 @@ impl Implementation {
     fn language_tag(self, python_version: (u8, u8)) -> LanguageTag {
         match self {
             // Ex) `cp39`
-            Self::CPython { .. } => LanguageTag::CPython { python_version },
+            Self::CPython { .. } => LanguageTag::CPython {
+                major: python_version.0,
+                minor: Some(python_version.1),
+            },
             // Ex) `pp39`
             Self::PyPy => LanguageTag::PyPy { python_version },
             // Ex) `graalpy310`