fix OS detection for Alpine Linux (#1545)

This PR fixes the OS detection for Alpine Linux such that the version
of musl available is correctly determined. The issue boiled down to
a regex that required 2 digits for each version component. But a
valid musl version is 1.2.4, which only has a single digit for each
component.

It's unclear how this was working for musl before this change. My
theory is that our other methods of OS detection were somehow working.

The first commit in this PR cleans up our Linux detection logic and adds
lots of tracing calls to make debugging issues like this easier in the
future. To do so, one can run:

    $ RUST_LOG=trace uv pip install -v whatever

The second commit has the actual fix.

Fixes #1427

crates/platform-host/src/linux.rs

@@ -8,41 +8,85 @@ use fs_err as fs;
 use goblin::elf::Elf;
 use once_cell::sync::Lazy;
 use regex::Regex;
-use tracing::trace;
 
 use crate::{Os, PlatformError};
 
+pub(crate) fn detect_linux_libc() -> Result<Os, PlatformError> {
+    let ld_path = find_ld_path()?;
+
+    tracing::trace!("trying to detect musl version by running `{ld_path:?}`");
+    match detect_musl_version(&ld_path) {
+        Ok(os) => return Ok(os),
+        Err(err) => tracing::trace!("tried to find musl version, but failed: {err}"),
+    }
+    tracing::trace!("trying to detect libc version from possible symlink at {ld_path:?}");
+    match detect_linux_libc_from_ld_symlink(&ld_path) {
+        Ok(os) => return Ok(os),
+        Err(err) => {
+            tracing::trace!("tried to find libc version from ld symlink, but failed: {err}");
+        }
+    }
+    tracing::trace!("trying to run `ldd --version` to detect glibc version");
+    match detect_glibc_version_from_ldd() {
+        Ok(os_version) => return Ok(os_version),
+        Err(err) => {
+            tracing::trace!("tried to find glibc version from `ldd --version`, but failed: {err}");
+        }
+    }
+    let msg = "\
+          could not detect either glibc version nor musl libc version, \
+          at least one of which is required\
+      ";
+    Err(PlatformError::OsVersionDetectionError(msg.to_string()))
+}
+
 // glibc version is taken from std/sys/unix/os.rs
-fn glibc_version_from_ldd() -> Result<Os, PlatformError> {
-    trace!("Falling back to `ldd --version` to detect OS libc version");
+fn detect_glibc_version_from_ldd() -> Result<Os, PlatformError> {
     let output = Command::new("ldd")
         .args(["--version"])
         .output()
         .map_err(|err| {
-            PlatformError::OsVersionDetectionError(format!("Failed to execute ldd: {err}"))
+            PlatformError::OsVersionDetectionError(format!(
+                "failed to execute `ldd --version` for glibc: {err}"
+            ))
         })?;
-    let output_str = std::str::from_utf8(&output.stdout).map_err(|err| {
-        PlatformError::OsVersionDetectionError(format!(
-            "Failed to parse ldd output as UTF-8: {err}"
-        ))
-    })?;
-    let version_str = ldd_output_to_version_str(output_str)?;
-
-    parse_glibc_version(version_str).ok_or_else(|| {
-        PlatformError::OsVersionDetectionError(format!(
-            "Invalid version string from ldd output: {version_str}"
-        ))
-    })
+    match glibc_ldd_output_to_version("stdout", &output.stdout) {
+        Ok(os) => return Ok(os),
+        Err(err) => {
+            tracing::trace!("failed to parse glibc version from stdout of `ldd --version`: {err}");
+        }
+    }
+    match glibc_ldd_output_to_version("stderr", &output.stderr) {
+        Ok(os) => return Ok(os),
+        Err(err) => {
+            tracing::trace!("failed to parse glibc version from stderr of `ldd --version`: {err}");
+        }
+    }
+    Err(PlatformError::OsVersionDetectionError(
+        "could not find glibc version from stdout or stderr of `ldd --version`".to_string(),
+    ))
 }
 
-fn ldd_output_to_version_str(output_str: &str) -> Result<&str, PlatformError> {
+fn glibc_ldd_output_to_version(kind: &str, output: &[u8]) -> Result<Os, PlatformError> {
     static RE: Lazy<Regex> = Lazy::new(|| Regex::new(r"ldd \(.+\) ([0-9]+\.[0-9]+)").unwrap());
-    let Some((_, [version])) = RE.captures(output_str).map(|c| c.extract()) else {
+
+    let output = std::str::from_utf8(output).map_err(|err| {
+        PlatformError::OsVersionDetectionError(format!(
+            "failed to parse `ldd --version` {kind} as UTF-8: {err}"
+        ))
+    })?;
+    tracing::trace!("{kind} output from `ldd --version`: {output:?}");
+    let Some((_, [version])) = RE.captures(output).map(|c| c.extract()) else {
+        return Err(PlatformError::OsVersionDetectionError(
+            "failed to detect glibc version on {kind}".to_string(),
+        ));
+    };
+    let Some(os) = parse_glibc_version(version) else {
         return Err(PlatformError::OsVersionDetectionError(format!(
-            "ERROR: failed to detect glibc version. ldd output: {output_str}",
+            "failed to parse glibc version on {kind} from: {version:?}",
         )));
     };
-    Ok(version)
+    Ok(os)
 }
 
 // Returns Some((major, minor)) if the string is a valid "x.y" version,
@@ -55,46 +99,33 @@ fn parse_glibc_version(version: &str) -> Option<Os> {
     }
 }
 
-pub(crate) fn detect_linux_libc() -> Result<Os, PlatformError> {
-    let libc = find_libc()?;
-    let linux = if let Ok(Some((major, minor))) = get_musl_version(&libc) {
-        Os::Musllinux { major, minor }
-    } else if let Some(os_version) = detect_linux_libc_from_ld_symlink(&libc) {
-        return Ok(os_version);
-    } else if let Ok(os_version) = glibc_version_from_ldd() {
-        return Ok(os_version);
-    } else {
-        let msg = "\
-            Couldn't detect either glibc version nor musl libc version, \
-            at least one of which is required\
-        ";
-        return Err(PlatformError::OsVersionDetectionError(msg.to_string()));
-    };
-    Ok(linux)
-}
-
-fn detect_linux_libc_from_ld_symlink(path: &Path) -> Option<Os> {
+fn detect_linux_libc_from_ld_symlink(path: &Path) -> Result<Os, PlatformError> {
     static RE: Lazy<Regex> =
         Lazy::new(|| Regex::new(r"^ld-([0-9]{1,3})\.([0-9]{1,3})\.so$").unwrap());
 
-    let target = fs::read_link(path).ok()?;
+    let target = fs::read_link(path).map_err(|err| {
+        PlatformError::OsVersionDetectionError(format!(
+            "failed to read {path:?} as a symbolic link: {err}",
+        ))
+    })?;
     let Some(filename) = target.file_name() else {
-        trace!("expected dynamic linker symlink {target:?} to have a filename");
-        return None;
+        return Err(PlatformError::OsVersionDetectionError(format!(
+            "failed to get base name of symbolic link path {target:?}",
+        )));
     };
     let filename = filename.to_string_lossy();
     let Some((_, [major, minor])) = RE.captures(&filename).map(|c| c.extract()) else {
-        trace!(
-            "couldn't find major/minor version in dynamic linker symlink \
-             filename {filename:?} from its path {target:?}"
-        );
-        return None;
+        return Err(PlatformError::OsVersionDetectionError(format!(
+            "failed to find major/minor version in dynamic linker symlink \
+             filename {filename:?} from its path {target:?} via regex {regex}",
+            regex = RE.as_str(),
+        )));
     };
     // OK since we are guaranteed to have between 1 and 3 ASCII digits and the
     // maximum possible value, 999, fits into a u16.
     let major = major.parse().expect("valid major version");
     let minor = minor.parse().expect("valid minor version");
-    Some(Os::Manylinux { major, minor })
+    Ok(Os::Manylinux { major, minor })
 }
 
 /// Read the musl version from libc library's output. Taken from maturin.
@@ -106,27 +137,57 @@ fn detect_linux_libc_from_ld_symlink(path: &Path) -> Option<Os> {
 /// Version 1.2.2
 /// Dynamic Program Loader
 /// ```
-fn get_musl_version(ld_path: impl AsRef<Path>) -> std::io::Result<Option<(u16, u16)>> {
-    static RE: Lazy<Regex> =
-        Lazy::new(|| Regex::new(r"Version ([0-9]{2,4})\.([0-9]{2,4})").unwrap());
-
-    let output = Command::new(ld_path.as_ref())
+fn detect_musl_version(ld_path: impl AsRef<Path>) -> Result<Os, PlatformError> {
+    let ld_path = ld_path.as_ref();
+    let output = Command::new(ld_path)
         .stdout(Stdio::null())
         .stderr(Stdio::piped())
-        .output()?;
-    let stderr = String::from_utf8_lossy(&output.stderr);
-    let Some((_, [major, minor])) = RE.captures(&stderr).map(|c| c.extract()) else {
-        return Ok(None);
+        .output()
+        .map_err(|err| {
+            PlatformError::OsVersionDetectionError(format!(
+                "failed to execute `{ld_path:?}` for musl: {err}"
+            ))
+        })?;
+    match musl_ld_output_to_version("stdout", &output.stdout) {
+        Ok(os) => return Ok(os),
+        Err(err) => {
+            tracing::trace!("failed to parse musl version from stdout of `{ld_path:?}`: {err}");
+        }
+    }
+    match musl_ld_output_to_version("stderr", &output.stderr) {
+        Ok(os) => return Ok(os),
+        Err(err) => {
+            tracing::trace!("failed to parse musl version from stderr of `{ld_path:?}`: {err}");
+        }
+    }
+    Err(PlatformError::OsVersionDetectionError(format!(
+        "could not find musl version from stdout or stderr of `{ld_path:?}`",
+    )))
+}
+
+fn musl_ld_output_to_version(kind: &str, output: &[u8]) -> Result<Os, PlatformError> {
+    static RE: Lazy<Regex> =
+        Lazy::new(|| Regex::new(r"Version ([0-9]{1,4})\.([0-9]{1,4})").unwrap());
+
+    let output = std::str::from_utf8(output).map_err(|err| {
+        PlatformError::OsVersionDetectionError(format!("failed to parse {kind} as UTF-8: {err}"))
+    })?;
+    tracing::trace!("{kind} output from `ld`: {output:?}");
+    let Some((_, [major, minor])) = RE.captures(output).map(|c| c.extract()) else {
+        return Err(PlatformError::OsVersionDetectionError(format!(
+            "could not find musl version from on {kind} via regex: {}",
+            RE.as_str(),
+        )));
     };
-    // OK since we are guaranteed to have between 2 and 4 ASCII digits and the
+    // OK since we are guaranteed to have between 1 and 4 ASCII digits and the
     // maximum possible value, 9999, fits into a u16.
     let major = major.parse().expect("valid major version");
     let minor = minor.parse().expect("valid minor version");
-    Ok(Some((major, minor)))
+    Ok(Os::Musllinux { major, minor })
 }
 
 /// Find musl libc path from executable's ELF header.
-fn find_libc() -> Result<PathBuf, PlatformError> {
+fn find_ld_path() -> Result<PathBuf, PlatformError> {
     let buffer = fs::read("/bin/sh")?;
     let error_str = "Couldn't parse /bin/sh for detecting the ld version";
     let elf = Elf::parse(&buffer)
@@ -146,24 +207,55 @@ mod tests {
 
     #[test]
     fn parse_ldd_output() {
-        let ver_str = ldd_output_to_version_str(
-            r"ldd (GNU libc) 2.12
+        let ver_str = glibc_ldd_output_to_version(
+            "stdout",
+            br"ldd (GNU libc) 2.12
 Copyright (C) 2010 Free Software Foundation, Inc.
 This is free software; see the source for copying conditions.  There is NO
 warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
 Written by Roland McGrath and Ulrich Drepper.",
         )
         .unwrap();
-        assert_eq!(ver_str, "2.12");
+        assert_eq!(
+            ver_str,
+            Os::Manylinux {
+                major: 2,
+                minor: 12
+            }
+        );
 
-        let ver_str = ldd_output_to_version_str(
-            r"ldd (Ubuntu GLIBC 2.31-0ubuntu9.2) 2.31
+        let ver_str = glibc_ldd_output_to_version(
+            "stderr",
+            br"ldd (Ubuntu GLIBC 2.31-0ubuntu9.2) 2.31
   Copyright (C) 2020 Free Software Foundation, Inc.
   This is free software; see the source for copying conditions.  There is NO
   warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
   Written by Roland McGrath and Ulrich Drepper.",
         )
         .unwrap();
-        assert_eq!(ver_str, "2.31");
+        assert_eq!(
+            ver_str,
+            Os::Manylinux {
+                major: 2,
+                minor: 31
+            }
+        );
+    }
+
+    #[test]
+    fn parse_musl_ld_output() {
+        // This output was generated by running `/lib/ld-musl-x86_64.so.1`
+        // in an Alpine Docker image. The Alpine version:
+        //
+        // # cat /etc/alpine-release
+        // 3.19.1
+        let output = b"\
+musl libc (x86_64)
+Version 1.2.4_git20230717
+Dynamic Program Loader
+Usage: /lib/ld-musl-x86_64.so.1 [options] [--] pathname [args]\
+        ";
+        let got = musl_ld_output_to_version("stderr", output).unwrap();
+        assert_eq!(got, Os::Musllinux { major: 1, minor: 2 });
     }
 }