craft-update: a failed check for a running attach is reported on macOS (#803)

detach_unmounted leaves a disk image's attachments alone when the check
for a running `hdiutil attach` of the image gets no answer, and it
returned Ok in that case. A failed install then ended with no note that
the image may still be attached. It now returns the check's reason as
an error, so the install's error says "the disk image may still be
attached" with that reason, and craft-update logs it at warn level.

crates/update/src/install.rs

@@ -1716,7 +1716,8 @@ pub mod macos {
     /// Detaches the image file `dmg` where it is attached with no volume mounted, which a failed
     /// attach can leave. An attachment with a mounted volume is left alone: another install may
     /// be using it. So is every attachment while a program started with `dmg` in its arguments
-    /// (another process's `hdiutil attach`) is running, or while the check for one gets no answer.
+    /// (another process's `hdiutil attach`) is running, or while the check for one gets no answer;
+    /// in that case the error gives the check's reason.
     fn detach_unmounted(dmg: &Path) -> Result<(), String> {
         detach_unmounted_with(dmg, process::running, process::run)
     }
@@ -1728,8 +1729,10 @@ pub mod macos {
         running: impl FnOnce(&Path) -> Result<bool, String>,
         run: impl Fn(&str, &[&str], Duration) -> Result<String, String>,
     ) -> Result<(), String> {
-        if running(dmg) != Ok(false) {
-            return Ok(());
+        match running(dmg) {
+            Ok(false) => {}
+            Ok(true) => return Ok(()),
+            Err(why) => return Err(format!("couldn't check for a running attach of the image ({why})")),
         }
         let info = run(HDIUTIL, &["info", "-plist"], Duration::from_secs(30))?;
         let image = [Some(dmg.to_path_buf()), std::fs::canonicalize(dmg).ok()];
@@ -4288,11 +4291,16 @@ esac
                 "<?xml version=\"1.0\" encoding=\"UTF-8\"?><plist version=\"1.0\"><dict><key>images</key><array><dict><key>image-path</key><string>{}</string><key>system-entities</key><array><dict><key>dev-entry</key><string>/dev/disk5</string></dict></array></dict></array></dict></plist>",
                 dmg.display()
             );
-            for (answer, expected) in [
-                (Ok(true), vec![]),
-                // pgrep gave no answer: an attach of the image may still be running.
-                (Err("pgrep didn't finish within 30 seconds".to_string()), vec![]),
-                (Ok(false), vec!["info -plist".to_string(), "detach /dev/disk5 -force -quiet".to_string()]),
+            for (answer, expected, outcome) in [
+                (Ok(true), vec![], Ok(())),
+                // pgrep gave no answer: an attach of the image may still be running, and the image
+                // may still be attached.
+                (
+                    Err("pgrep didn't finish within 30 seconds".to_string()),
+                    vec![],
+                    Err("couldn't check for a running attach of the image (pgrep didn't finish within 30 seconds)".to_string()),
+                ),
+                (Ok(false), vec!["info -plist".to_string(), "detach /dev/disk5 -force -quiet".to_string()], Ok(())),
             ] {
                 let ran = std::cell::RefCell::new(Vec::new());
                 let result = super::macos::detach_unmounted_with(
@@ -4307,7 +4315,7 @@ esac
                         Ok(if args[0] == "info" { info.clone() } else { String::new() })
                     },
                 );
-                assert_eq!(result, Ok(()));
+                assert_eq!(result, outcome, "with the process check giving {answer:?}");
                 assert_eq!(ran.into_inner(), expected, "with the process check giving {answer:?}");
             }
         }