pmb.config.chroot_home_symlinks: cache rust dirs (!1850)

Rust packaging is new and still a bit weird in Alpine and postmarketOS.
As of writing, we only have one package (squeekboard), and use cargo to
download the source of all dependencies at build time (several git
repositories!) and compile it. Usually, this is a no-go, but at least
until this is resolved properly, let's cache the downloads as suggested
in: https://doc.rust-lang.org/cargo/guide/cargo-home.html

Related: #1861

pmb/chroot/zap.py

@@ -28,7 +28,8 @@ import pmb.parse.apkindex
 
 
 def zap(args, confirm=True, dry=False, pkgs_local=False, http=False,
-        pkgs_local_mismatch=False, pkgs_online_mismatch=False, distfiles=False):
+        pkgs_local_mismatch=False, pkgs_online_mismatch=False, distfiles=False,
+        rust=False):
     """
     Shutdown everything inside the chroots (e.g. distccd, adb), umount
     everything and then safely remove folders from the work-directory.
@@ -41,6 +42,7 @@ def zap(args, confirm=True, dry=False, pkgs_local=False, http=False,
     :param pkgs_online_mismatch: Clean out outdated binary packages downloaded from
                      mirrors (e.g. from Alpine)
     :param distfiles: Clear the downloaded files cache
+    :param rust: Remove rust related caches
 
     NOTE: This function gets called in pmb/config/init.py, with only args.work
     and args.device set!
@@ -73,6 +75,8 @@ def zap(args, confirm=True, dry=False, pkgs_local=False, http=False,
         patterns += ["cache_http"]
     if distfiles:
         patterns += ["cache_distfiles"]
+    if rust:
+        patterns += ["cache_rust"]
 
     # Delete everything matching the patterns
     for pattern in patterns:

pmb/config/__init__.py

@@ -127,6 +127,7 @@ chroot_mount_bind = {
     "$WORK/cache_ccache_$ARCH": "/mnt/pmbootstrap-ccache",
     "$WORK/cache_distfiles": "/var/cache/distfiles",
     "$WORK/cache_git": "/mnt/pmbootstrap-git",
+    "$WORK/cache_rust": "/mnt/pmbootstrap-rust",
     "$WORK/config_abuild": "/mnt/pmbootstrap-abuild-config",
     "$WORK/config_apk_keys": "/etc/apk/keys",
     "$WORK/packages": "/mnt/pmbootstrap-packages",
@@ -134,10 +135,19 @@ chroot_mount_bind = {
 
 # Building chroots (all chroots, except for the rootfs_ chroot) get symlinks in
 # the "pmos" user's home folder pointing to mountfolders from above.
+# Rust packaging is new and still a bit weird in Alpine and postmarketOS. As of
+# writing, we only have one package (squeekboard), and use cargo to download
+# the source of all dependencies at build time and compile it. Usually, this is
+# a no-go, but at least until this is resolved properly, let's cache the
+# dependencies and downloads as suggested in "Caching the Cargo home in CI":
+# https://doc.rust-lang.org/cargo/guide/cargo-home.html
 chroot_home_symlinks = {
     "/mnt/pmbootstrap-abuild-config": "/home/pmos/.abuild",
     "/mnt/pmbootstrap-ccache": "/home/pmos/.ccache",
     "/mnt/pmbootstrap-packages": "/home/pmos/packages/pmos",
+    "/mnt/pmbootstrap-rust/registry/index": "/home/pmos/.cargo/registry/index",
+    "/mnt/pmbootstrap-rust/registry/cache": "/home/pmos/.cargo/registry/cache",
+    "/mnt/pmbootstrap-rust/git/db": "/home/pmos/.cargo/git/db",
 }
 
 # Device nodes to be created in each chroot. Syntax for each entry:

pmb/helpers/frontend.py

@@ -375,7 +375,8 @@ def zap(args):
     pmb.chroot.zap(args, dry=args.dry, http=args.http,
                    distfiles=args.distfiles, pkgs_local=args.pkgs_local,
                    pkgs_local_mismatch=args.pkgs_local_mismatch,
-                   pkgs_online_mismatch=args.pkgs_online_mismatch)
+                   pkgs_online_mismatch=args.pkgs_online_mismatch,
+                   rust=args.rust)
 
     # Don't write the "Done" message
     pmb.helpers.logging.disable()

pmb/parse/arguments.py

@@ -402,6 +402,8 @@ def arguments():
                      dest="pkgs_online_mismatch",
                      help="also delete outdated packages from online mirrors"
                      " (that have been downloaded to the apk cache)")
+    zap.add_argument("-r", "--rust", action="store_true",
+                     help="also delete rust related caches")
 
     # Action: stats
     stats = sub.add_parser("stats", help="show ccache stats")