Add brew specific message for `uv self update` (#16838)

Resolves https://github.com/astral-sh/uv/issues/16833

`uv self update` could error with a better message if it knows the user
has installed it with brew. This diff adds an `InstallSource` we can use
the detect where a `uv` binary comes from and augment error messages
with better context. We're only adding brew for now, but it could easily
be extend with other detection heuristics.

crates/uv/src/install_source.rs

@@ -0,0 +1,74 @@
+#![cfg(not(feature = "self-update"))]
+
+use std::{
+    ffi::OsStr,
+    path::{Path, PathBuf},
+};
+
+/// Known sources for uv installations.
+#[derive(Debug, Clone, Copy, PartialEq, Eq)]
+pub(crate) enum InstallSource {
+    Homebrew,
+}
+
+impl InstallSource {
+    /// Attempt to infer the install source for the given executable path.
+    fn from_path(path: &Path) -> Option<Self> {
+        let canonical = path.canonicalize().unwrap_or_else(|_| PathBuf::from(path));
+
+        let components = canonical
+            .components()
+            .map(|component| component.as_os_str().to_owned())
+            .collect::<Vec<_>>();
+
+        let cellar = OsStr::new("Cellar");
+        let formula = OsStr::new("uv");
+
+        if components
+            .windows(2)
+            .any(|window| window[0] == cellar && window[1] == formula)
+        {
+            return Some(Self::Homebrew);
+        }
+
+        None
+    }
+
+    /// Detect how uv was installed by inspecting the current executable path.
+    pub(crate) fn detect() -> Option<Self> {
+        Self::from_path(&std::env::current_exe().ok()?)
+    }
+
+    pub(crate) fn description(self) -> &'static str {
+        match self {
+            Self::Homebrew => "Homebrew",
+        }
+    }
+
+    pub(crate) fn update_instructions(self) -> &'static str {
+        match self {
+            Self::Homebrew => "brew update && brew upgrade uv",
+        }
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn detects_homebrew_cellar() {
+        assert_eq!(
+            InstallSource::from_path(Path::new("/opt/homebrew/Cellar/uv/0.9.11/bin/uv")),
+            Some(InstallSource::Homebrew)
+        );
+    }
+
+    #[test]
+    fn ignores_non_cellar_paths() {
+        assert_eq!(
+            InstallSource::from_path(Path::new("/usr/local/bin/uv")),
+            None
+        );
+    }
+}

crates/uv/src/lib.rs

@@ -21,6 +21,8 @@ use settings::PipTreeSettings;
 use tokio::task::spawn_blocking;
 use tracing::{debug, instrument, trace};
 
+#[cfg(not(feature = "self-update"))]
+use crate::install_source::InstallSource;
 use uv_cache::{Cache, Refresh};
 use uv_cache_info::Timestamp;
 #[cfg(feature = "self-update")]
@@ -59,6 +61,8 @@ use crate::settings::{
 
 pub(crate) mod child;
 pub(crate) mod commands;
+#[cfg(not(feature = "self-update"))]
+mod install_source;
 pub(crate) mod logging;
 pub(crate) mod printer;
 pub(crate) mod settings;
@@ -1249,10 +1253,22 @@ async fn run(mut cli: Cli) -> Result<ExitStatus> {
         }
         #[cfg(not(feature = "self-update"))]
         Commands::Self_(_) => {
-            anyhow::bail!(
-                "uv was installed through an external package manager, and self-update \
-                is not available. Please use your package manager to update uv."
-            );
+            const BASE_MESSAGE: &str =
+                "uv was installed through an external package manager and cannot update itself.";
+
+            let message = match InstallSource::detect() {
+                Some(source) => format!(
+                    "{base}\n\n{hint}{colon} You installed uv using {}. To update uv, run `{}`",
+                    source.description(),
+                    source.update_instructions().green(),
+                    hint = "hint".bold().cyan(),
+                    colon = ":".bold(),
+                    base = BASE_MESSAGE
+                ),
+                None => format!("{BASE_MESSAGE} Please use your package manager to update uv."),
+            };
+
+            anyhow::bail!(message);
         }
         Commands::GenerateShellCompletion(args) => {
             args.shell.generate(&mut Cli::command(), &mut stdout());