pmb.config/install: add flexible provider selection for "pmbootstrap init" (MR 2132)

The provider selection for "pmbootstrap init" added in this commit
is a flexible way to offer UI/device-specific configuration options
in "pmbootstrap init", without hardcoding them in pmbootstrap.
Instead, the options are defined entirely in pmaports using APK's
virtual package provider mechanism. The code in pmbootstrap searches
for available providers and displays them together with their pkgdesc.

There are many possible use cases for this but I have tested two so far:

  1. Selecting root provider (sudo vs doas). This can be defined entirely
     in postmarketos-base, without having to handle this specifically in
     pmbootstrap.

     $ pmbootstrap init
     [...]
     Available providers for postmarketos-root (2):
      * sudo: Use sudo to run root commands (**default**)
      * doas: Use doas (minimal replacement for sudo) to run root commands
              (Note: Does not support all functionality of sudo)
     Provider [default]: doas

  2. Device-specific options. My main motivation for working on this
     feature is a new configuration option for the MSM8916-based devices.
     It allows more control about which firmware to enable:

     $ pmbootstrap init
     [...]
     Available providers for soc-qcom-msm8916-rproc (3):
      * all: Enable all remote processors (audio goes through modem) (default)
      * no-modem: Disable only modem (audio bypasses modem, ~80 MiB more RAM)
      * none: Disable all remote processors (no WiFi/BT/modem, ~90 MiB more RAM)
     Provider [default]: no-modem

The configuration prompts show up dynamically by defining
_pmb_select="<virtual packages>" in postmarketos-base, a UI PKGBUILD
or the device APKBUILD. Selecting "default" (just pressing enter)
means that no provider is selected. This allows APK to choose it
automatically based on the "provider_priority". It also provides
compatibility with existing installation; APK will just choose the
default provider when upgrading. The selection can still be changed
after installation by installing another provider using "apk".

Note that at the end this is just a more convenient interface for the
already existing "extra packages" prompt. When using pmbootstrap in
automated scripts the providers (e.g. "postmarketos-root-doas") can be
simply selected through the existing "extra_packages" option.

pmb/config/init.py

@@ -14,6 +14,7 @@ import pmb.helpers.devices
 import pmb.helpers.http
 import pmb.helpers.logging
 import pmb.helpers.other
+import pmb.helpers.pmaports
 import pmb.helpers.run
 import pmb.helpers.ui
 import pmb.chroot.zap
@@ -206,6 +207,80 @@ def ask_for_timezone(args):
     return "GMT"
 
 
+def ask_for_provider_select(args, apkbuild, providers_cfg):
+    """
+    Ask for selectable providers that are specified using "_pmb_select"
+    in a APKBUILD.
+
+    :param apkbuild: the APKBUILD with the _pmb_select
+    :param providers_cfg: the configuration section with previously selected
+                          providers. Updated with new providers after selection
+    """
+    for select in apkbuild["_pmb_select"]:
+        providers = pmb.helpers.pmaports.find_providers(args, select)
+        logging.info(f"Available providers for {select} ({len(providers)}):")
+
+        has_default = False
+        providers_short = {}
+        last_selected = providers_cfg.get(select, 'default')
+
+        for pkgname, pkg in providers:
+            # Strip provider prefix if possible
+            short = pkgname
+            if short.startswith(f'{select}-'):
+                short = short[len(f"{select}-"):]
+
+            # Allow selecting the package using both short and long name
+            providers_short[pkgname] = pkgname
+            providers_short[short] = pkgname
+
+            if pkgname == last_selected:
+                last_selected = short
+
+            if not has_default and pkg.get('provider_priority', 0) != 0:
+                # Display as default provider
+                styles = pmb.config.styles
+                logging.info(f"* {short}: {pkg['pkgdesc']} "
+                             f"{styles['BOLD']}(default){styles['END']}")
+                has_default = True
+            else:
+                logging.info(f"* {short}: {pkg['pkgdesc']}")
+
+        while True:
+            ret = pmb.helpers.cli.ask("Provider", None, last_selected, True,
+                                      complete=providers_short.keys())
+
+            if has_default and ret == 'default':
+                # Selecting default means to not select any provider explicitly
+                # In other words, apk chooses it automatically based on
+                # "provider_priority"
+                if select in providers_cfg:
+                    del providers_cfg[select]
+                break
+            if ret in providers_short:
+                providers_cfg[select] = providers_short[ret]
+                break
+            logging.fatal("ERROR: Invalid provider specified, please type in"
+                          " one from the list above.")
+
+
+def ask_for_provider_select_pkg(args, pkgname, providers_cfg):
+    """
+    Look up the APKBUILD for the specified pkgname and ask for selectable
+    providers that are specified using "_pmb_select".
+
+    :param pkgname: name of the package to search APKBUILD for
+    :param providers_cfg: the configuration section with previously selected
+                          providers. Updated with new providers after selection
+    """
+    apkbuild = pmb.helpers.pmaports.get(args, pkgname,
+                                        subpackages=False, must_exist=False)
+    if not apkbuild:
+        return
+
+    ask_for_provider_select(args, apkbuild, providers_cfg)
+
+
 def ask_for_device_kernel(args, device):
     """
     Ask for the kernel that should be used with the device.
@@ -567,6 +642,10 @@ def frontend(args):
     cfg["pmbootstrap"]["nonfree_userland"] = str(nonfree["userland"])
 
     info = pmb.parse.deviceinfo(args, device)
+    apkbuild_path = pmb.helpers.devices.find_path(args, device, 'APKBUILD')
+    if apkbuild_path:
+        apkbuild = pmb.parse.apkbuild(args, apkbuild_path)
+        ask_for_provider_select(args, apkbuild, cfg["providers"])
 
     # Device keymap
     if device_exists:
@@ -576,10 +655,15 @@ def frontend(args):
     cfg["pmbootstrap"]["user"] = pmb.helpers.cli.ask("Username", None,
                                                      args.user, False,
                                                      "[a-z_][a-z0-9_-]*")
+
+    ask_for_provider_select_pkg(args, "postmarketos-base", cfg["providers"])
+
     # UI and various build options
     ui = ask_for_ui(args, info)
     cfg["pmbootstrap"]["ui"] = ui
     cfg["pmbootstrap"]["ui_extras"] = str(ask_for_ui_extras(args, ui))
+    ask_for_provider_select_pkg(args, f"postmarketos-ui-{ui}",
+                                cfg["providers"])
     ask_for_additional_options(args, cfg)
 
     # Extra packages to be installed to rootfs