fix: reconcile update channel switches

2 files changed, 123 insertions, 10 deletions

diff --git a/src/cli.rs b/src/cli.rs
index b6e2fc94..f756b96f 100644
--- a/src/cli.rs
+++ b/src/cli.rs
@@ -77,6 +77,14 @@ fn channel_set(args: &[String]) -> std::io::Result<i32> {
         return Ok(2);
     };
 
+    if let Some(reason) = channel_set_preview_rejection(
+        channel,
+        crate::update::preview_channel_rejection_for_current_install(),
+    ) {
+        eprintln!("{reason}.");
+        return Ok(1);
+    }
+
     let path = crate::config::config_path();
     let content = if path.exists() {
         std::fs::read_to_string(&path)?
@@ -112,11 +120,23 @@ fn channel_set(args: &[String]) -> std::io::Result<i32> {
         "Herdr update channel set to {channel} in {}.",
         path.display()
     );
-    if channel == "preview" {
-        println!("Run `herdr update` to install the latest preview build when ready.");
-    } else {
-        println!("Run `herdr update` to install the latest stable release when ready.");
+
+    match channel_set_install_action(
+        crate::update::package_manager_channel_update_guidance_for_current_install(),
+    ) {
+        ChannelSetInstallAction::PrintGuidance(guidance) => {
+            println!("{guidance}");
+            return Ok(0);
+        }
+        ChannelSetInstallAction::RunSelfUpdate => {}
     }
+
+    if let Err(err) = crate::update::self_update(crate::update::SelfUpdateOptions::default()) {
+        eprintln!("update failed: {err}");
+        eprintln!("Run `herdr update` to retry.");
+        return Ok(1);
+    }
+
     Ok(0)
 }
 
@@ -129,6 +149,30 @@ fn parse_channel_set_arg(args: &[String]) -> Option<&str> {
     }
 }
 
+fn channel_set_preview_rejection(
+    channel: &str,
+    install_rejection: Option<&'static str>,
+) -> Option<&'static str> {
+    (channel == "preview")
+        .then_some(install_rejection)
+        .flatten()
+}
+
+#[derive(Debug, Clone, Copy, PartialEq, Eq)]
+enum ChannelSetInstallAction {
+    RunSelfUpdate,
+    PrintGuidance(&'static str),
+}
+
+fn channel_set_install_action(
+    package_manager_guidance: Option<&'static str>,
+) -> ChannelSetInstallAction {
+    match package_manager_guidance {
+        Some(guidance) => ChannelSetInstallAction::PrintGuidance(guidance),
+        None => ChannelSetInstallAction::RunSelfUpdate,
+    }
+}
+
 fn print_channel_help() {
     eprintln!("herdr channel commands:");
     eprintln!("  herdr channel show                  print the configured update channel");
@@ -848,4 +892,29 @@ mod tests {
             None
         );
     }
+
+    #[test]
+    fn channel_set_rejects_package_managed_preview_before_config_write() {
+        assert_eq!(
+            super::channel_set_preview_rejection("preview", Some("no preview")),
+            Some("no preview")
+        );
+        assert_eq!(
+            super::channel_set_preview_rejection("stable", Some("no preview")),
+            None
+        );
+        assert_eq!(super::channel_set_preview_rejection("preview", None), None);
+    }
+
+    #[test]
+    fn channel_set_skips_self_update_for_package_manager_guidance() {
+        assert_eq!(
+            super::channel_set_install_action(Some("use package manager")),
+            super::ChannelSetInstallAction::PrintGuidance("use package manager")
+        );
+        assert_eq!(
+            super::channel_set_install_action(None),
+            super::ChannelSetInstallAction::RunSelfUpdate
+        );
+    }
 }
diff --git a/src/update.rs b/src/update.rs
index 0d73b5b1..6d1ad49b 100644
--- a/src/update.rs
+++ b/src/update.rs
@@ -1662,6 +1662,37 @@ fn is_nix_managed_install() -> bool {
     is_nix_store_exe_path_following_links(&current_exe)
 }
 
+pub(crate) fn preview_channel_rejection_for_current_install() -> Option<&'static str> {
+    let Ok(current_exe) = env::current_exe() else {
+        return None;
+    };
+
+    preview_channel_rejection_for_exe_path(&current_exe)
+}
+
+pub(crate) fn package_manager_channel_update_guidance_for_current_install() -> Option<&'static str>
+{
+    if is_homebrew_managed_install() {
+        Some("Use `brew update && brew upgrade herdr` to update Homebrew installs.")
+    } else if is_nix_managed_install() {
+        Some("Update through Nix to update Nix-managed Herdr installs.")
+    } else {
+        None
+    }
+}
+
+fn preview_channel_rejection_for_exe_path(path: &Path) -> Option<&'static str> {
+    if is_homebrew_managed_exe_path_following_links(path) {
+        Some(
+            "preview channel is only available for direct Herdr installs; Homebrew installs update through `brew update && brew upgrade herdr`",
+        )
+    } else if is_nix_store_exe_path_following_links(path) {
+        Some("preview channel is only available for direct Herdr installs; Nix installs update through Nix")
+    } else {
+        None
+    }
+}
+
 pub(crate) fn is_package_manager_managed_exe_path(path: &Path) -> bool {
     is_homebrew_managed_exe_path_following_links(path)
         || is_nix_store_exe_path_following_links(path)
@@ -2155,6 +2186,19 @@ mod tests {
     }
 
     #[test]
+    fn preview_channel_is_rejected_for_package_manager_paths() {
+        let homebrew = Path::new("/opt/homebrew/Cellar/herdr/0.6.6/bin/herdr");
+        let nix = Path::new("/nix/store/abc123-herdr-0.6.6/bin/herdr");
+        let direct = Path::new("/home/user/.local/bin/herdr");
+
+        assert!(preview_channel_rejection_for_exe_path(homebrew)
+            .is_some_and(|message| message.contains("Homebrew")));
+        assert!(preview_channel_rejection_for_exe_path(nix)
+            .is_some_and(|message| message.contains("Nix")));
+        assert!(preview_channel_rejection_for_exe_path(direct).is_none());
+    }
+
+    #[test]
     fn non_nix_store_path_is_not_detected() {
         let path = Path::new("/usr/local/bin/herdr");
 
@@ -2984,16 +3028,16 @@ mod tests {
 
     #[test]
     fn stable_channel_installs_stable_asset_when_current_binary_is_preview() {
-        let older_stable = Version::parse("0.6.5").unwrap();
-        let preview_base = Version::parse("0.6.6").unwrap();
+        let latest_stable = Version::parse("0.6.6").unwrap();
+        let installed_base = Version::parse("0.6.6").unwrap();
         assert!(stable_channel_should_install(
-            &older_stable,
-            &preview_base,
+            &latest_stable,
+            &installed_base,
             true
         ));
         assert!(!stable_channel_should_install(
-            &older_stable,
-            &preview_base,
+            &latest_stable,
+            &installed_base,
             false
         ));
     }