Scope scratch OS empty-field defaults to ImageVersionOS

Move _OSLESS_NAMES and the scratch-aware default_factory out of
shared.py into version_os.py. The shared ExtensionField/
TagDisplayNameField are used by ImageVariant too; keeping the
scratch check there would silently produce empty extension/
tagDisplayName for any variant named "scratch", risking tag and
Containerfile collisions.

- shared.py: restore original default_factory and + patterns
- version_os.py: own _OSLESS_NAMES and * patterns locally

Author: bschwedler

posit-bakery/posit_bakery/config/image/version_os.py

@@ -5,10 +5,13 @@
 from pydantic import BaseModel, Field, field_validator, field_serializer
 from pydantic_core.core_schema import ValidationInfo
 
-from posit_bakery.config.shared import BakeryYAMLModel, ExtensionField, TagDisplayNameField
+from posit_bakery.config.shared import BakeryYAMLModel
+from posit_bakery.const import REGEX_IMAGE_TAG_SUFFIX_ALLOWED_CHARACTERS_PATTERN
 from .build_os import BuildOS, SUPPORTED_OS, ALTERNATE_NAMES, TargetPlatform, DEFAULT_PLATFORMS
 from .posit_product.const import URL_WITH_ENV_VARS_REGEX_PATTERN
 
+_OSLESS_NAMES = frozenset({"scratch"})
+
 log = logging.getLogger(__name__)
 
 _NAME_VERSION_PATTERN = re.compile(r"(?P<name>[\D]+)(?P<version>[\d.]*)")
@@ -63,16 +66,30 @@ class ImageVersionOS(BakeryYAMLModel):
         Field(default=DEFAULT_PLATFORMS, description="List of platforms to build for this image."),
     ]
     extension: Annotated[
-        ExtensionField,
+        str,
         Field(
+            default_factory=lambda data: (
+                ""
+                if data.get("name", "").lower().strip() in _OSLESS_NAMES
+                else re.sub(r"[^a-zA-Z0-9_-]", "", data.get("name", "").lower())
+            ),
+            pattern=r"^[a-zA-Z0-9_-]*$",
+            validate_default=True,
             description="File extension used in the Containerfile filename in the pattern "
             "Containerfile.<os>.<variant> for this OS. Set to an empty string if no extension is needed.",
             examples=["ubuntu2204", "debian12"],
         ),
     ]
     tagDisplayName: Annotated[
-        TagDisplayNameField,
+        str,
         Field(
+            default_factory=lambda data: (
+                ""
+                if data.get("name", "").lower().strip() in _OSLESS_NAMES
+                else re.sub(REGEX_IMAGE_TAG_SUFFIX_ALLOWED_CHARACTERS_PATTERN, "-", data.get("name", "").lower())
+            ),
+            pattern=r"^[a-zA-Z0-9_.-]*$",
+            validate_default=True,
             description="The name used in image tags for this OS. This is used to create the tag "
             "in the format <image>:<version>-<os>-<variant>.",
             examples=["ubuntu-22.04", "debian-12"],

posit-bakery/posit_bakery/config/shared.py

@@ -10,18 +10,12 @@
 
 from posit_bakery.const import REGEX_IMAGE_TAG_SUFFIX_ALLOWED_CHARACTERS_PATTERN
 
-_OSLESS_NAMES = frozenset({"scratch"})
-
 # Shared field configuration for file extensions.
 ExtensionField = Annotated[
     str,
     Field(
-        default_factory=lambda data: (
-            ""
-            if data.get("name", "").lower().strip() in _OSLESS_NAMES
-            else re.sub(r"[^a-zA-Z0-9_-]", "", data.get("name", "").lower())
-        ),
-        pattern=r"^[a-zA-Z0-9_-]*$",
+        default_factory=lambda data: re.sub(r"[^a-zA-Z0-9_-]", "", data.get("name", "").lower()),
+        pattern=r"^[a-zA-Z0-9_-]+$",
         validate_default=True,
     ),
 ]
@@ -31,12 +25,10 @@
 TagDisplayNameField = Annotated[
     str,
     Field(
-        default_factory=lambda data: (
-            ""
-            if data.get("name", "").lower().strip() in _OSLESS_NAMES
-            else re.sub(REGEX_IMAGE_TAG_SUFFIX_ALLOWED_CHARACTERS_PATTERN, "-", data.get("name", "").lower())
+        default_factory=lambda data: re.sub(
+            REGEX_IMAGE_TAG_SUFFIX_ALLOWED_CHARACTERS_PATTERN, "-", data.get("name", "").lower()
         ),
-        pattern=r"^[a-zA-Z0-9_.-]*$",
+        pattern=r"^[a-zA-Z0-9_.-]+$",
         validate_default=True,
     ),
 ]