Support arch="" in APKBUILD to skip builds (MR 1985)

Alpine indicates with arch="", that a package should temporarily not be
built for any architecture. Support this in postmarketOS too by not
complaining in the APKBUILD parser if arch is empty.

Adjust pmb.build.autodetect.arch and pmb.build.menuconfig.get_arch, so
both don't fail with an IndexError when encountering a disabled package.

Co-Authored-By: Luca Weiss <luca@z3ntu.xyz>

pmb/build/autodetect.py

@@ -57,7 +57,10 @@ def arch(args, pkgname):
     if arch_device in arches:
         return arch_device
 
-    return apkbuild["arch"][0]
+    try:
+        return apkbuild["arch"][0]
+    except IndexError:
+        return None
 
 
 def suffix(args, apkbuild, arch):

pmb/build/menuconfig.py

@@ -25,6 +25,11 @@ def get_arch(args, apkbuild):
     """
     pkgname = apkbuild["pkgname"]
 
+    # Disabled package (arch="")
+    if not apkbuild["arch"]:
+        raise RuntimeError(f"'{pkgname}' is disabled (arch=\"\"). Please use"
+                           " '--arch' to specify the desired architecture.")
+
     # Multiple architectures
     if len(apkbuild["arch"]) > 1:
         raise RuntimeError(f"'{pkgname}' supports multiple architectures"

pmb/parse/_apkbuild.py

@@ -312,10 +312,6 @@ def apkbuild(args, path, check_pkgver=True, check_pkgname=True):
             raise RuntimeError("The pkgname must be equal to the name of"
                                " the folder, that contains the APKBUILD!")
 
-    # Sanity check: arch
-    if not len(ret["arch"]):
-        raise RuntimeError("Arch must not be empty: " + path)
-
     # Sanity check: pkgver
     if check_pkgver:
         if "-r" in ret["pkgver"] or not pmb.parse.version.validate(ret["pkgver"]):