This is a fix for canonical/charmcraft#1874

The spec (ST105) allows <list-of-arch> | <arch> in both build-on and
build-for on all craft apps. This change makes the Platform model accept
a string value, but doesn't specify that in the schema. This means
text editors using the schema will still suggest converting the build-on
and build-for values to lists.

This fix addresses cases like, for example, a project that only builds on `amd64`
being built on `riscv64`. Previously the call to run_managed() would loop over
the (empty) build plan and then finish "successfully". This new version will
raise an EmptyBuildPlanError indicating to the user that they should check the
project's 'platforms' declaration and the command-line parameters.

Fixes canonical#225

Fixes canonical#422

`--shell` and `--shell-after` are implemented for a) consistency with the other
lifecycle commands, and b) because it makes sense to want to inspect the build
environment at packing time, considering that there are packing-related steps,
like writing the metadata file, that the users don't have a way to inspect
otherwise (short of examining the final artefact).

`--debug` is improved to actually shell into the build environment when the
packing itself failed, as opposed to the previous behavior of only debugging
failures that happen during the lifecycle steps.

Fixes canonical#430

---------

Co-authored-by: Alex Lowe <alex.lowe@canonical.com>

…args (canonical#440)

Adds a configuration service that can be used to get application
configuration.

CRAFT_* environment variables are only used if the config item
is known to craft-application (not for app-specific config).

Co-authored-by: Dariusz Duda <dariusz.duda@canonical.com>

Co-authored-by: renovate[bot] <29139614+renovate[bot]@users.noreply.github.com>

…al#449)

Co-authored-by: renovate[bot] <29139614+renovate[bot]@users.noreply.github.com>

Co-authored-by: renovate[bot] <29139614+renovate[bot]@users.noreply.github.com>

Co-authored-by: renovate[bot] <29139614+renovate[bot]@users.noreply.github.com>

* docs: add changelog for 4.2.0

* docs: review changelog 4.2.0

* Update docs/reference/changelog.rst

Co-authored-by: Michael DuBelko <michael.dubelko@gmail.com>

* move command entry to subheader

---------

Co-authored-by: Michael DuBelko <michael.dubelko@gmail.com>

This allows applications to override the inner run logic, with the end
goal of capturing application specific exceptions and raise
appropriate ones for Craft Application to handle.

Without the logic split, overriding run to capture exceptions is
virtually impossible as the run method holds a generic Exception
handler.

Signed-off-by: Sergio Schvezov <sergio.schvezov@canonical.com>

Signed-off-by: Callahan Kovacs <callahankovacs@gmail.com>

Previously, if a value was in the passed Namespace, it would return
that. The correct behaviour however is to check the environment for
the value and return that instead.

Signed-off-by: Callahan Kovacs <callahankovacs@gmail.com>

Signed-off-by: Callahan Kovacs <callahankovacs@gmail.com>

Co-authored-by: Sergio Schvezov <sergio.schvezov@canonical.com>

See: albertodonato/snap-helpers#21 (comment)

Co-authored-by: renovate[bot] <29139614+renovate[bot]@users.noreply.github.com>

Co-authored-by: renovate[bot] <29139614+renovate[bot]@users.noreply.github.com>

This lets commands be able to always rely on `self.config` existing, even
when running `fill_parser()` for help output.

Fixes canonical#530

Signed-off-by: Callahan Kovacs <callahan.kovacs@canonical.com>

Signed-off-by: Callahan Kovacs <callahankovacs@gmail.com>
Co-authored-by: Dariusz Duda <dariusz.duda@canonical.com>

Fixes canonical#537

Add some steps under the "Configuring fetch-service integration :: " progress,
to give some feedback that things are happening without all of the noisy output
from Apt.

Fixes canonical#536

Craft Application will only add default commands in a group if the application
doesn't define the command. The order of command groups is now preserved.

Signed-off-by: Callahan Kovacs <callahan.kovacs@canonical.com>

Signed-off-by: Callahan Kovacs <callahan.kovacs@canonical.com>

Version 2.10.1 fixes the issue where the app greeting is shown twice when
running in managed mode, which happened because the Emitter was initialized in
"verbose" and then the Dispatcher set it to verbose again when parsing the
command line.

Fixes canonical#551

Signed-off-by: Dariusz Duda <dariusz.duda@canonical.com>

Signed-off-by: Callahan Kovacs <callahan.kovacs@canonical.com>

Both mypy and pyright complain that the "field.default_factory()" call has too
few arguments, even though its type is typing.Callable[[], Any]. It should be
fixed soon, and in the meantime we can ignore the spurious error.

Ref: pydantic/pydantic#10945

* Check that the provided "--name" is valid according to the standard name regex.

* If the user doesn't provide a "--name", *and* the project directory is *not*
  a valid project name, default to "my-project".

The issue with redirecting the fetch-service's output to a file via bash is
this: as a strict snap, the fetch-service cannot inherit the file descriptors
from the bash process if said process is spawned by a classic snap. This is
the case when the integration is controlled by a snapped craft tool:

```
+----------------------------+        +-------------+
|(snapped) craft-tool -> bash| -----> |fetch-service|
+----------------------------+        +-------------+
```

The solution here is to pass the path to the logfile to the fetch-service itself
through a new, recently implemented command-line option. We also update the
logpath to use tmp, and print the path when emitting the warning about the
integration being experimental.

Refs:

- https://bugs.launchpad.net/ubuntu/+source/snapd/+bug/1849753

Fixes canonical#550