Support v1 recipes in CrossRBaseMigrator

Add support for v1 recipes in `CrossRBaseMigrator`.  Here the logic
made it easy to output a single combined condition:

```yaml
    - if: build_platform != target_platform
      then:
        - cross-r-base ${{ r_base }}
        - r-rlang
```

Part of bug regro#3642

Author: mgorny

conda_forge_tick/migrators/cross_compile.py

@@ -326,6 +326,7 @@ def migrate(self, recipe_dir: str, attrs: "AttrsTypedDict", **kwargs: Any) -> No
 
 
 class CrossRBaseMigrator(MiniMigrator):
+    allowed_schema_versions = {0, 1}
     post_migration = True
 
     def filter(self, attrs: "AttrsTypedDict", not_bad_str_start: str = "") -> bool:
@@ -340,7 +341,8 @@ def filter(self, attrs: "AttrsTypedDict", not_bad_str_start: str = "") -> bool:
 
     def migrate(self, recipe_dir: str, attrs: "AttrsTypedDict", **kwargs: Any) -> None:
         with pushd(recipe_dir):
-            with open("meta.yaml") as fp:
+            recipe_file = next(filter(os.path.exists, ("recipe.yaml", "meta.yaml")))
+            with open(recipe_file) as fp:
                 meta_yaml = fp.readlines()
 
             new_lines = []
@@ -349,10 +351,20 @@ def migrate(self, recipe_dir: str, attrs: "AttrsTypedDict", **kwargs: Any) -> No
             for line in meta_yaml:
                 if previous_was_build:
                     nspaces = len(line) - len(line.lstrip())
-                    new_lines.append(
-                        " " * nspaces
-                        + "- cross-r-base {{ r_base }}  # [build_platform != target_platform]\n",
-                    )
+                    if recipe_file == "recipe.yaml":
+                        new_lines.extend(
+                            [
+                                " " * nspaces
+                                + "- if: build_platform != target_platform\n",
+                                " " * nspaces + "  then:\n",
+                                " " * nspaces + "    - cross-r-base ${{ r_base }}\n",
+                            ]
+                        )
+                    else:
+                        new_lines.append(
+                            " " * nspaces
+                            + "- cross-r-base {{ r_base }}  # [build_platform != target_platform]\n",
+                        )
                     # Add host R requirements to build
                     host_reqs = attrs.get("requirements", {}).get("host", set())
                     r_host_reqs = [
@@ -361,15 +373,18 @@ def migrate(self, recipe_dir: str, attrs: "AttrsTypedDict", **kwargs: Any) -> No
                         if req.startswith("r-") and req != "r-base"
                     ]
                     for r_req in r_host_reqs:
-                        # Ensure nice formatting
-                        post_nspaces = max(0, 25 - len(r_req))
-                        new_lines.append(
-                            " " * nspaces
-                            + "- "
-                            + r_req
-                            + " " * post_nspaces
-                            + "  # [build_platform != target_platform]\n",
-                        )
+                        if recipe_file == "recipe.yaml":
+                            new_lines.append(" " * nspaces + f"    - {r_req}\n")
+                        else:
+                            # Ensure nice formatting
+                            post_nspaces = max(0, 25 - len(r_req))
+                            new_lines.append(
+                                " " * nspaces
+                                + "- "
+                                + r_req
+                                + " " * post_nspaces
+                                + "  # [build_platform != target_platform]\n",
+                            )
                     in_req = False
                     previous_was_build = False
                 if "requirements:" in line:
@@ -378,7 +393,7 @@ def migrate(self, recipe_dir: str, attrs: "AttrsTypedDict", **kwargs: Any) -> No
                     previous_was_build = True
                 new_lines.append(line)
 
-            with open("meta.yaml", "w") as f:
+            with open(recipe_file, "w") as f:
                 f.write("".join(new_lines))
 
             if os.path.exists("build.sh"):

tests/test_cross_compile.py

@@ -150,11 +150,14 @@ def test_cmake(tmp_path):
 
 
 @flaky
-def test_cross_rbase(tmp_path):
+@pytest.mark.parametrize("recipe_version", [0, 1])
+def test_cross_rbase(tmp_path, recipe_version: int):
     run_test_migration(
         m=version_migrator_rbase,
-        inp=YAML_PATH.joinpath("rbase_recipe.yaml").read_text(),
-        output=YAML_PATH.joinpath("rbase_recipe_correct.yaml").read_text(),
+        inp=YAML_PATHS[recipe_version].joinpath("rbase_recipe.yaml").read_text(),
+        output=YAML_PATHS[recipe_version]
+        .joinpath("rbase_recipe_correct.yaml")
+        .read_text(),
         prb="Dependencies have been updated if changed",
         kwargs={"new_version": "2.0.1"},
         mr_out={
@@ -163,18 +166,22 @@ def test_cross_rbase(tmp_path):
             "version": "2.0.1",
         },
         tmp_path=tmp_path,
+        recipe_version=recipe_version,
     )
 
 
 @flaky
-def test_cross_rbase_build_sh(tmp_path):
+@pytest.mark.parametrize("recipe_version", [0, 1])
+def test_cross_rbase_build_sh(tmp_path, recipe_version: int):
     tmp_path.joinpath("recipe").mkdir()
     with open(tmp_path / "recipe/build.sh", "w") as f:
         f.write("#!/bin/bash\nR CMD INSTALL --build .")
     run_test_migration(
         m=version_migrator_rbase,
-        inp=YAML_PATH.joinpath("rbase_recipe.yaml").read_text(),
-        output=YAML_PATH.joinpath("rbase_recipe_correct.yaml").read_text(),
+        inp=YAML_PATHS[recipe_version].joinpath("rbase_recipe.yaml").read_text(),
+        output=YAML_PATHS[recipe_version]
+        .joinpath("rbase_recipe_correct.yaml")
+        .read_text(),
         prb="Dependencies have been updated if changed",
         kwargs={"new_version": "2.0.1"},
         mr_out={
@@ -183,6 +190,7 @@ def test_cross_rbase_build_sh(tmp_path):
             "version": "2.0.1",
         },
         tmp_path=tmp_path,
+        recipe_version=recipe_version,
     )
     expected = [
         "#!/bin/bash\n",