Add support for dynamic musl Python distributions on x86-64 Linux (#12121)

Following the upstream release and #12120, removes gating preventing
installation of the managed musl Python versions.

Of note

- The filtering of musl Python distributions has moved from the Rust
runtime to the metadata fetcher
- The filtering is now conditional on the PBS release date, removing all
old static musl distributions
- We could support the `+static` musl downloads in the future; right
now, they are deprioritized when selecting a variant
- I added test to CI which uses Alpine and installs numpy

.github/workflows/ci.yml

@@ -737,6 +737,36 @@ jobs:
           eval "$(./uv generate-shell-completion bash)"
           eval "$(./uvx --generate-shell-completion bash)"
 
+  smoke-test-linux-musl:
+    timeout-minutes: 10
+    needs: build-binary-linux-musl
+    name: "check system | alpine"
+    runs-on: ubuntu-latest
+    container: alpine:latest
+    steps:
+      - uses: actions/checkout@v4
+
+      - name: "Download binary"
+        uses: actions/download-artifact@v4
+        with:
+          name: uv-linux-musl-${{ github.sha }}
+
+      - name: "Prepare binary"
+        run: |
+          chmod +x ./uv
+          chmod +x ./uvx
+
+      - name: "Smoke test"
+        run: |
+          # Overwrite the 3.13.0 pin from the project, there are not functional
+          # musl distributions for it
+          ./uv python pin 3.13
+          ./uv venv -v
+          ./uv pip install ruff -v
+          ./uvx -v ruff --version
+          ./uv pip install numpy -v
+          ./uv run python -c "import numpy; print(numpy.__version__)"
+
   smoke-test-macos:
     timeout-minutes: 10
     needs: build-binary-macos-x86_64

crates/uv-python/fetch-download-metadata.py

@@ -61,6 +61,10 @@ import httpx
 SELF_DIR = Path(__file__).parent
 VERSIONS_FILE = SELF_DIR / "download-metadata.json"
 
+# The date at which the default CPython musl builds became dynamically linked
+# instead of statically.
+CPYTHON_MUSL_STATIC_RELEASE_END = 20250311
+
 
 def batched(iterable: Iterable, n: int) -> Generator[tuple, None, None]:
     """Batch data into tuples of length n. The last batch may be shorter."""
@@ -142,6 +146,7 @@ class Variant(StrEnum):
 
 @dataclass
 class PythonDownload:
+    release: int
     version: Version
     triple: PlatformTriple
     flavor: str
@@ -253,6 +258,11 @@ class CPythonFinder(Finder):
                     download = self._parse_download_url(url)
                     if download is None:
                         continue
+                    if (
+                        download.release < CPYTHON_MUSL_STATIC_RELEASE_END
+                        and download.triple.libc == "musl"
+                    ):
+                        continue
                     logging.debug("Found %s (%s)", download.key(), download.filename)
                     downloads_by_version.setdefault(download.version, []).append(
                         download
@@ -341,6 +351,7 @@ class CPythonFinder(Finder):
         if url.endswith(".sha256"):
             return None
         filename = unquote(url.rsplit("/", maxsplit=1)[-1])
+        release = int(url.rsplit("/")[-2])
 
         match = self._filename_re.match(filename) or self._legacy_filename_re.match(
             filename
@@ -370,6 +381,7 @@ class CPythonFinder(Finder):
             return None
 
         return PythonDownload(
+            release=release,
             version=version,
             triple=triple,
             flavor=flavor,
@@ -490,6 +502,7 @@ class PyPyFinder(Finder):
                 platform = self._normalize_os(file["platform"])
                 libc = "gnu" if platform == "linux" else "none"
                 download = PythonDownload(
+                    release=0,
                     version=python_version,
                     triple=PlatformTriple(
                         platform=platform,

crates/uv-python/src/downloads.rs

@@ -466,11 +466,7 @@ impl ManagedPythonDownload {
 
     /// Iterate over all [`ManagedPythonDownload`]s.
     pub fn iter_all() -> impl Iterator<Item = &'static ManagedPythonDownload> {
-        PYTHON_DOWNLOADS
+        PYTHON_DOWNLOADS.iter()
-            .iter()
-            // TODO(konsti): musl python-build-standalone builds are currently broken (statically
-            // linked), so we pretend they don't exist. https://github.com/astral-sh/uv/issues/4242
-            .filter(|download| download.key.libc != Libc::Some(target_lexicon::Environment::Musl))
     }
 
     pub fn url(&self) -> &'static str {

crates/uv-python/src/platform.rs

@@ -126,6 +126,10 @@ impl Arch {
     pub fn family(&self) -> target_lexicon::Architecture {
         self.family
     }
+
+    pub fn is_arm(&self) -> bool {
+        matches!(self.family, target_lexicon::Architecture::Arm(_))
+    }
 }
 
 impl Display for Libc {

crates/uv/src/commands/python/install.rs

@@ -17,7 +17,7 @@ use uv_python::downloads::{self, DownloadResult, ManagedPythonDownload, PythonDo
 use uv_python::managed::{
     python_executable_dir, ManagedPythonInstallation, ManagedPythonInstallations,
 };
-use uv_python::platform::Libc;
+use uv_python::platform::{Arch, Libc};
 use uv_python::{
     PythonDownloads, PythonInstallationKey, PythonRequest, PythonVersionFile,
     VersionFileDiscoveryOptions, VersionFilePreference,
@@ -58,10 +58,11 @@ impl InstallRequest {
         let download = match ManagedPythonDownload::from_request(&download_request) {
             Ok(download) => download,
             Err(downloads::Error::NoDownloadFound(request))
-                if request.libc().is_some_and(Libc::is_musl) =>
+                if request.libc().is_some_and(Libc::is_musl)
+                    && request.arch().is_some_and(Arch::is_arm) =>
             {
                 return Err(anyhow::anyhow!(
-                    "uv does not yet provide musl Python distributions. See https://github.com/astral-sh/uv/issues/6890 to track support."
+                    "uv does not yet provide musl Python distributions on aarch64."
                 ));
             }
             Err(err) => return Err(err.into()),