feat: support multi-base platform recipes (#2054)

Adds support for multi-base recipes with the `platforms` keyword.

Internally, this moves to a new practice where the application stops modifying project data before passing the it to craft-platforms.  This will ensure consistent processing by charmcraft and by launchpad.

Documentation is coming soon via canonical/craft-platforms#75 and #2009.

To summarize the usage, `base` and `build-base` are removed from the project and the base is encoded into the platform.

Platforms can be defined in a shorthand notation:
```yaml
platforms:
  ubuntu@22.04:amd64:
  ubuntu@24.04:amd64:
```

Or they can be defined in standard form:
```yaml
platforms:
  jammy:
    build-on: [ubuntu@22.04:amd64]
    build-for: [ubuntu@22.04:amd64]
  noble:
    build-on: [ubuntu@24.04:amd64]
    build-for: [ubuntu@24.04:amd64]
```


Fixes #1789 
Fixes #2008 
Creates canonical/craft-platforms#85
Found during implementation canonical/craft-platforms#80
(CRAFT-3718)

charmcraft/models/project.py

@@ -38,7 +38,7 @@
 from craft_platforms import charm
 from craft_providers import bases
 from pydantic import dataclasses
-from typing_extensions import Self
+from typing_extensions import Self, override
 
 from charmcraft import const, preprocess, utils
 from charmcraft.const import (
@@ -323,6 +323,15 @@ class CharmcraftBuildPlanner(models.BuildPlanner):
     build_base: str | None = None
     platforms: dict[str, models.Platform | None] | None = None  # type: ignore[assignment]
 
+    @override
+    @pydantic.field_validator("platforms", mode="before")
+    @classmethod
+    def _populate_platforms(cls, platforms: dict[str, Any]) -> dict[str, Any]:
+        """Overrides the validator to prevent platforms from being modified.
+
+        Modifying the platforms field can break multi-base builds."""
+        return platforms
+
     def get_build_plan(self) -> list[models.BuildInfo]:
         """Get build bases for this charm.
 
@@ -346,13 +355,9 @@ def get_build_plan(self) -> list[models.BuildInfo]:
                     ),
                 )
             ]
-        if not self.base:
+        if not self.base and not self.platforms:
             return list(CharmBuildInfo.gen_from_bases_configurations(*self.bases))
 
-        build_base = self.build_base or self.base
-        base_name, _, base_version = build_base.partition("@")
-        base = bases.BaseName(name=base_name, version=base_version)
-
         if self.platforms is None:
             raise CraftError("Must define at least one platform.")
         platforms = cast(
@@ -373,7 +378,9 @@ def get_build_plan(self) -> list[models.BuildInfo]:
                 platform=info.platform,
                 build_on=str(info.build_on),
                 build_for=str(info.build_for),
-                base=base,
+                base=bases.BaseName(
+                    name=info.build_base.distribution, version=info.build_base.series
+                ),
             )
             for info in build_infos
         ]
@@ -1064,7 +1071,7 @@ class PlatformCharm(CharmProject):
     """Model for defining a charm using Platforms."""
 
     # Silencing pyright because it complains about missing default value
-    base: BaseStr  # pyright: ignore[reportGeneralTypeIssues]
+    base: BaseStr | None = None
     build_base: BuildBaseStr | None = None
     platforms: dict[str, models.Platform | None]  # type: ignore[assignment]
 
@@ -1076,6 +1083,15 @@ def _validate_dev_base_needs_build_base(self) -> Self:
             )
         return self
 
+    @override
+    @pydantic.field_validator("platforms", mode="before")
+    @classmethod
+    def _populate_platforms(cls, platforms: dict[str, Any]) -> dict[str, Any]:
+        """Overrides the validator to prevent platforms from being modified.
+
+        Modifying the platforms field can break multi-base builds."""
+        return platforms
+
 
 Charm = BasesCharm | PlatformCharm
 

charmcraft/services/package.py

@@ -26,6 +26,7 @@
 from typing import TYPE_CHECKING, cast
 
 import craft_application
+import craft_platforms
 import yaml
 from craft_application import services, util
 from craft_cli import emit
@@ -213,20 +214,39 @@ def get_manifest_bases(self) -> list[models.Base]:
                 raise RuntimeError("Could not determine run-on bases.")
             return run_on_bases
         if isinstance(self._project, PlatformCharm):
-            if not self._platform:
-                architectures = [util.get_host_architecture()]
-            elif self._platform in (*const.SUPPORTED_ARCHITECTURES, "all"):
-                architectures = [self._platform]
-            elif platform := self._project.platforms.get(self._platform):
-                if platform.build_for:
-                    architectures = [str(arch) for arch in platform.build_for]
-                else:
-                    raise ValueError(
-                        f"Platform {self._platform} contains unknown build-for."
+            archs = [self._build_plan[0].build_for]
+
+            # single base recipes will have a base
+            if self._project.base:
+                return [models.Base.from_str_and_arch(self._project.base, archs)]
+
+            # multi-base recipes may have the base in the platform name
+            platform_label = self._build_plan[0].platform
+            if base := craft_platforms.parse_base_and_name(platform_label)[0]:
+                return [
+                    models.Base(
+                        name=base.distribution,
+                        channel=base.series,
+                        architectures=archs,
                     )
-            else:
-                architectures = [util.get_host_architecture()]
-            return [models.Base.from_str_and_arch(self._project.base, architectures)]
+                ]
+
+            # Otherwise, retrieve the build-for base from the platform in the project.
+            # This complexity arises from building on devel bases - the BuildInfo
+            # contains the devel base and not the compatibility base.
+            platform = self._project.platforms.get(platform_label)
+            if platform and platform.build_for:
+                if base := craft_platforms.parse_base_and_architecture(
+                    platform.build_for[0]
+                )[0]:
+                    return [
+                        models.Base(
+                            name=base.distribution,
+                            channel=base.series,
+                            architectures=archs,
+                        )
+                    ]
+
         raise TypeError(
             f"Unknown charm type {self._project.__class__}, cannot get bases."
         )

pyproject.toml

@@ -4,12 +4,12 @@ dynamic = ["version"]
 description = "The main tool to build, upload, and develop in general the Juju charms."
 readme = "README.md"
 dependencies = [
-    "craft-application~=4.2",
+    "craft-application~=4.7",
     "craft-cli>=2.3.0",
     "craft-grammar>=2.0.0",
     "craft-parts>=2.2.0",
     "craft-providers>=2.0.0",
-    "craft-platforms~=0.3",
+    "craft-platforms~=0.5",
     "craft-providers>=2.0.0",
     "craft-store>=3.1.0",
     "distro>=1.7.0",

requirements-dev.txt

@@ -8,12 +8,12 @@ cffi==1.17.1
 chardet==5.2.0
 charset-normalizer==3.4.0
 coverage==7.6.9
-craft-application==4.4.0
+craft-application==4.7.0
 craft-archives==2.0.2
-craft-cli==2.10.1
+craft-cli==2.13.0
 craft-grammar==2.0.1
 craft-parts==2.2.0
-craft-platforms==0.4.0
+craft-platforms==0.5.0
 craft-providers==2.0.4
 craft-store==3.1.0
 cryptography==43.0.3

tests/integration/commands/test_expand_extensions.py

@@ -69,11 +69,7 @@ def fake_extensions(stub_extensions):
                 description: test-description
                 base: ubuntu@22.04
                 platforms:
-                  amd64:
-                    build-on:
-                    - amd64
-                    build-for:
-                    - amd64
+                  amd64: null
                 parts: {}
                 type: charm
                 terms:

tests/integration/sample-charms/actions-included/expected.yaml

@@ -4,11 +4,7 @@ description: |
   A description for an example charm with platforms.
 base: ubuntu@22.04
 platforms:
-  amd64:
-    build-on:
-    - amd64
-    build-for:
-    - amd64
+  amd64: null
 parts:
   charm:
     plugin: charm

tests/integration/sample-charms/actions-separate/expected.yaml

@@ -4,11 +4,7 @@ description: |
   A description for an example charm with platforms.
 base: ubuntu@22.04
 platforms:
-  amd64:
-    build-on:
-    - amd64
-    build-for:
-    - amd64
+  amd64: null
 parts:
   charm:
     plugin: charm

tests/integration/sample-charms/basic-platforms/expected.yaml

@@ -4,11 +4,7 @@ description: |
   A description for an example charm with platforms.
 base: ubuntu@22.04
 platforms:
-  amd64:
-    build-on:
-    - amd64
-    build-for:
-    - amd64
+  amd64: null
 parts:
   charm:
     plugin: charm

tests/integration/sample-charms/config-included/expected.yaml

@@ -4,11 +4,7 @@ description: |
   A description for an example charm with platforms.
 base: ubuntu@22.04
 platforms:
-  amd64:
-    build-on:
-    - amd64
-    build-for:
-    - amd64
+  amd64: null
 parts:
   charm:
     plugin: charm

tests/integration/sample-charms/config-separate/expected.yaml

@@ -4,11 +4,7 @@ description: |
   A description for an example charm with platforms.
 base: ubuntu@22.04
 platforms:
-  amd64:
-    build-on:
-    - amd64
-    build-for:
-    - amd64
+  amd64: null
 parts:
   charm:
     plugin: charm

tests/spread/smoketests/multi-base/all/charmcraft.yaml

@@ -0,0 +1,20 @@
+name: test-charm
+type: charm
+title: test
+summary: test
+description: |
+  A charm recipe that uses a multi-base platform syntax to define
+  architecture independent charms for 22.04 and 24.04.
+
+platforms:
+  jammy:
+    build-on: [ubuntu@22.04:amd64]
+    build-for: [ubuntu@22.04:all]
+  noble:
+    build-on: [ubuntu@24.04:amd64]
+    build-for: [ubuntu@24.04:all]
+
+parts:
+  my-charm:
+    plugin: dump
+    source: .

tests/spread/smoketests/multi-base/all/expected-charms.txt

@@ -0,0 +1,2 @@
+test-charm_jammy.charm
+test-charm_noble.charm

tests/spread/smoketests/multi-base/basic/charmcraft.yaml

@@ -0,0 +1,28 @@
+name: test-charm
+type: charm
+title: test
+summary: test
+description: |
+  A charm recipe that uses a multi-base platform syntax to define
+  6 charms across different bases and architectures.
+
+platforms:
+  # shorthand syntax
+  ubuntu@20.04:amd64:
+  ubuntu@20.04:riscv64:
+
+  ubuntu@22.04:amd64:
+  ubuntu@22.04:riscv64:
+
+  # standard syntax
+  noble-amd64:
+    build-on: [ubuntu@24.04:amd64]
+    build-for: [ubuntu@24.04:amd64]
+  noble-riscv64:
+    build-on: [ubuntu@24.04:riscv64]
+    build-for: [ubuntu@24.04:riscv64]
+
+parts:
+  my-charm:
+    plugin: charm
+    source: .

tests/spread/smoketests/multi-base/basic/expected-charms.txt

@@ -0,0 +1,3 @@
+test-charm_ubuntu@20.04:amd64.charm
+test-charm_ubuntu@22.04:amd64.charm
+test-charm_noble-amd64.charm

tests/spread/smoketests/multi-base/one-platform/arguments.txt

@@ -0,0 +1 @@
+--platform ubuntu@22.04:amd64

tests/spread/smoketests/multi-base/one-platform/charmcraft.yaml

@@ -0,0 +1,29 @@
+name: test-charm
+type: charm
+title: test
+summary: test
+description: |
+  A charm recipe that uses a multi-base platform syntax to define
+  6 charms across different bases and architectures.
+  This test builds one of the charms using the `--platform` argument.
+
+platforms:
+  # shorthand syntax
+  ubuntu@20.04:amd64:
+  ubuntu@20.04:riscv64:
+
+  ubuntu@22.04:amd64:
+  ubuntu@22.04:riscv64:
+
+  # standard syntax
+  noble-amd64:
+    build-on: [ubuntu@24.04:amd64]
+    build-for: [ubuntu@24.04:amd64]
+  noble-riscv64:
+    build-on: [ubuntu@24.04:riscv64]
+    build-for: [ubuntu@24.04:riscv64]
+
+parts:
+  my-charm:
+    plugin: charm
+    source: .

tests/spread/smoketests/multi-base/one-platform/expected-charms.txt

@@ -0,0 +1 @@
+test-charm_ubuntu@22.04:amd64.charm

tests/spread/smoketests/multi-base/task.yaml

@@ -0,0 +1,52 @@
+summary: pack charm using multi-base notation
+kill-timeout: 30m  # These sometimes take a while to download bases.
+priority: 50  # Because these can take a while, run them early.
+
+environment:
+  CHARM/all: all
+  CHARM/basic: basic
+  CHARM/one_platform: one-platform
+
+# test only on amd64
+systems:
+  - ubuntu-22.04-64
+  - ubuntu-22.04-amd64
+
+include:
+  - tests/
+
+prepare: |
+  # '--force' because charmcraft.yaml already exists
+  charmcraft init --force --project-dir="$CHARM"
+
+restore: |
+  cd $CHARM
+  charmcraft clean
+
+execute: |
+  cd $CHARM
+
+  if [[ -e "arguments.txt" ]]; then
+    call_args=$(cat "arguments.txt")
+  else
+    call_args=""
+  fi
+
+  # shellcheck disable=SC2046 (quote to prevent word splitting)
+  charmcraft pack $call_args
+
+  # assert charms were built
+  while read -r charm_file; do
+    if [[ ! -e ${charm_file} ]]; then
+      echo "Could not find charm '${charm_file}'"
+      exit 1
+    fi
+  done < "expected-charms.txt"
+
+  # assert no other charms were built
+  expected_num=$(wc -l < "expected-charms.txt")
+  actual_num=$(find . -wholename "./*.charm" | wc -l)
+  if [[ $expected_num -ne $actual_num ]]; then
+    echo "Expected $expected_num charms, but found $actual_num."
+    exit 1
+  fi