feat(aura): detect the Pacman DB lockfile

Closes #918

CHANGELOG.md

@@ -2,6 +2,13 @@
 
 ## Unreleased
 
+#### Changed
+
+- Installation attempts will now pause if a Pacman database lockfile is detected
+  (usually found at `/var/lib/pacman/db.lck`). Aura will repeatedly sleep and
+  reattempt for up to 1 minute before failing; this is to prevent an infinite
+  loop in scripts.
+
 #### Fixed
 
 - Restore support for `-Qtt`.

rust/aura-core/src/aur/dependencies.rs

@@ -338,7 +338,7 @@ where
                     // FIXME Fri Feb 18 2022 Same here as above.
                     drop(alpm);
 
-                    debug!("{} is may be an AUR package.", pr);
+                    debug!("{} may be an AUR package.", pr);
                     let path = pull_or_clone(fetch, clone_d, parent, &pkg)?;
                     debug!("Parsing .SRCINFO for {}", pkg);
                     let full = path.join(".SRCINFO");

rust/aura-pm/src/command/cache.rs

@@ -120,7 +120,8 @@ pub(crate) fn downgrade(
         return Err(Error::NothingToDo);
     }
 
-    crate::pacman::sudo_pacman(env, "-U", NOTHING, to_downgrade).map_err(Error::Pacman)?;
+    crate::pacman::pacman_install_from_tarball(env, NOTHING, to_downgrade)
+        .map_err(Error::Pacman)?;
     green!(fll, "common-done");
     Ok(())
 }

rust/aura-pm/src/command/snapshot.rs

@@ -182,7 +182,8 @@ fn restore_snapshot(
             })
             .map(|pp| pp.into_pathbuf().into_os_string());
 
-        crate::pacman::sudo_pacman(env, "-U", NOTHING, tarballs).map_err(Error::Pacman)?;
+        crate::pacman::pacman_install_from_tarball(env, NOTHING, tarballs)
+            .map_err(Error::Pacman)?;
     }
 
     // Remove packages that weren't installed within the chosen snapshot.

rust/aura-pm/src/env.rs

@@ -208,6 +208,11 @@ impl Env {
 
         Ok(())
     }
+
+    /// The location of the Pacman database lockfile.
+    pub(crate) fn lock_file(&self) -> PathBuf {
+        Path::new(&self.pacman.db_path).join("db.lck")
+    }
 }
 
 #[derive(Debug, Deserialize)]

rust/aura-pm/src/pacman.rs

@@ -4,9 +4,11 @@ use crate::env::Env;
 use crate::error::Nested;
 use crate::localization::Localised;
 use i18n_embed_fl::fl;
+use log::debug;
 use log::error;
 use std::ffi::OsStr;
 use std::process::Command;
+use std::time::Duration;
 
 pub(crate) enum Error {
     ExternalCmd(std::io::Error),
@@ -105,6 +107,16 @@ where
     S: AsRef<OsStr>,
     T: AsRef<OsStr>,
 {
+    let lock = env.lock_file();
+    let secs = Duration::from_secs(3);
+    let mut tries = 0;
+
+    while lock.exists() && tries < 20 {
+        tries += 1;
+        debug!("{} exists. Sleeping... ({})", lock.display(), tries);
+        std::thread::sleep(secs);
+    }
+
     sudo_pacman(env, "-U", flags, args).map_err(|_| Error::InstallFromTarball)
 }