main: handle ManifestImportError from extensions better

The default west manifest file in zephyrproject-rtos/zephyr
recently added a project with an 'import'.

That means that 'west build' will fail with the confusing
'invalid choice: "build"' error if you pull zephyr without
running 'west update'. This is a worse experience than what happens
when you run e.g. 'west list': running a built-in command that needs
the manifest to do its work will happily tell you you need to run
'west update' to resolve the failed import.

This is confusing people who pull and run 'west build', and we do have
enough information to do better from WestArgumentParser.error(), which
is the official argparse callback API invoked when
parse_known_arguments() fails in this situation.

Extract the error message formatting for this situation into a helper
function and use it from error() to print the same message when we
get ManifestImportError in these situations.

Make the error message take up fewer lines while we are here.

Signed-off-by: Martí Bolívar <[email protected]>

src/west/app/main.py

@@ -200,26 +200,7 @@ def isinst(*args):
                 if args.command == 'update':
                     return      # that's fine
 
-                p, imp = self.mle.project, self.mle.imp
-                ctxt = f'  Failed importing "{imp}"'
-                if not isinstance(p, ManifestProject):
-                    # Try to be more helpful by explaining exactly
-                    # what west.manifest needs to happen before we can
-                    # resolve the missing import.
-                    rev = p.revision
-
-                    ctxt += f' from revision "{rev}"\n'
-                    ctxt += '  Hint: for this to work:\n'
-                    ctxt += f'          - {p.name} must be cloned\n'
-                    ctxt += (f'          - its {MANIFEST_REV_BRANCH} ref '
-                             'must point to a commit with the import data\n')
-                    ctxt += '        To fix, run:\n'
-                    ctxt += '          west update'
-
-                self.queued_io.append(
-                    lambda cmd:
-                    cmd.die(f'failed manifest import in {p.name_and_path}\n' +
-                            ctxt))
+                self.queued_io.append(lambda cmd: cmd.die(mie_msg(self.mle)))
             elif isinst(FileNotFoundError):
                 # This should ordinarily only happen when the top
                 # level manifest is not found.
@@ -860,21 +841,61 @@ def add_argument(self, *args, **kwargs):
         super().add_argument(*args, **kwargs)
 
     def error(self, message):
-        if (self.west_app and
-                self.west_app.mle and
-                isinstance(self.west_app.mle,
-                           ManifestVersionError) and
-                self.west_app.cmd):
-            self.west_app.cmd.die(mve_msg(self.west_app.mle))
+        if self.west_app and self.west_app.mle:
+            # If we have a known WestApp instance and the manifest
+            # failed to load, then try to specialize the error message
+            # to handle west-specific situations.
+
+            app = self.west_app
+            mle = self.west_app.mle
+            if app.cmd:
+                cmd = app.cmd
+            else:
+                # No app.cmd probably means that the user is
+                # running an extension command that they expected
+                # to work, but we don't know about because the
+                # import failed and thus we have no manifest to
+                # load extensions from.
+                #
+                # Just use the help command as a stand-in instead.
+                # We have to manually patch up its config
+                # attribute in order to do this outside of
+                # do_run().
+                cmd = app.builtins['help']
+                cmd.config = west.configuration.Configuration(
+                    topdir=app.topdir)
+            if isinstance(mle, ManifestVersionError):
+                cmd.die(mve_msg(mle))
+            elif isinstance(mle, ManifestImportFailed):
+                cmd.die(mie_msg(mle))
         super().error(message=message)
 
 def mve_msg(mve, suggest_upgrade=True):
+    # Helper for getting a message for a ManifestVersionError.
     return '\n  '.join(
         [f'west v{mve.version} or later is required by the manifest',
          f'West version: v{__version__}'] +
         ([f'Manifest file: {mve.file}'] if mve.file else []) +
         (['Please upgrade west and retry.'] if suggest_upgrade else []))
 
+def mie_msg(mie):
+    # Helper for getting a message for a ManifestImportError.
+
+    p, imp = mie.project, mie.imp
+    ret = (f'failed manifest import in {p.name_and_path}:\n'
+           f'  Failed importing "{imp}"')
+    if not isinstance(p, ManifestProject):
+        # Try to be more helpful by explaining exactly
+        # what west.manifest needs to happen before we can
+        # resolve the missing import.
+        ret += (f' from revision "{p.revision}"\n'
+                f'  Hint: {p.name} must be cloned and its '
+                f'{MANIFEST_REV_BRANCH} ref must point to a '
+                'commit with the import data\n'
+                '  To fix, run "west update"')
+
+    return ret
+
 def adjust_command_verbosity(command, args):
     command.verbosity = min(command.verbosity + args.verbose,
                             Verbosity.DBG_EXTREME)