improvement: customisable `docker build` command

This paves the way for `docker buildx build` and better caching.

For instance, with this change you can try out the following plugin,
which should make image building much faster in CI:
https://gist.github.com/regisb/4049622ec4b48cbd48c89ec708dc5252
(not ready for production just yet, we still need to build and push the
images)

changelog.d/20230313_172348_regis_docker_optimize.md

@@ -0,0 +1 @@
+- [Feature] Introduce the `DOCKER_BUILD_COMMAND` which makes it possible to customize the `docker build` command. (by @regisb)

tutor/commands/k8s.py

@@ -1,6 +1,6 @@
 from datetime import datetime
 from time import sleep
-from typing import Any, List, Optional, Type, Iterable
+from typing import Any, Iterable, List, Optional, Type
 
 import click
 

tutor/hooks/catalog.py

@@ -282,13 +282,20 @@ class Filters:
         "config:overrides"
     )
 
-    #: Declare uniqaue configuration settings that must be saved in the user ``config.yml`` file. This is where
+    #: Declare unique configuration settings that must be saved in the user ``config.yml`` file. This is where
     #: you should declare passwords and randomly-generated values that are different from one environment to the next.
     #:
     #: :parameter list[tuple[str, ...]] items: list of (name, value) new settings. All
     #:   names must be prefixed with the plugin name in all-caps.
     CONFIG_UNIQUE: Filter[list[tuple[str, Any]], []] = filters.get("config:unique")
 
+    #: Use this filter to modify the ``docker build`` command. For instance, to replace
+    #: the ``build`` subcommand by ``buildx build``.
+    #:
+    #: :parameter list[str] command: the full build command, including options and
+    #:   arguments. Note that these arguments do not include the leading ``docker`` command.
+    DOCKER_BUILD_COMMAND: Filter[list[str], []] = filters.get("docker:build:command")
+
     #: List of patches that should be inserted in a given location of the templates. The
     #: filter name must be formatted with the patch name.
     #: This filter is not so convenient and plugin developers will probably

tutor/images.py

@@ -1,5 +1,5 @@
-from . import fmt, utils
-from .types import Config, get_typed
+from tutor import fmt, hooks, utils
+from tutor.types import Config, get_typed
 
 
 def get_tag(config: Config, name: str) -> str:
@@ -9,7 +9,10 @@ def get_tag(config: Config, name: str) -> str:
 
 def build(path: str, tag: str, *args: str) -> None:
     fmt.echo_info(f"Building image {tag}")
-    utils.docker("build", "-t", tag, *args, path)
+    command = hooks.Filters.DOCKER_BUILD_COMMAND.apply(
+        ["build", "-t", tag, *args, path]
+    )
+    utils.docker(*command)
 
 
 def pull(tag: str) -> None: