Clean up dead code and outdated terminology

Code cleanup:
- Remove backward compatibility aliases (ObjectType, AttachType, etc.)
- Remove misleading comments about non-existent DJBlobType/ContentType
- Remove unused build_foreign_key_parser_old function
- Remove unused feature switches (ADAPTED_TYPE_SWITCH, FILEPATH_FEATURE_SWITCH)
- Remove unused os import from errors.py
- Rename ADAPTED type category to CODEC

Documentation fixes:
- Update mkdocs.yaml nav: customtype.md → codecs.md
- Fix dead links in attributes.md pointing to customtype.md

Terminology updates:
- Replace "AttributeType" with "Codec" in all comments
- Replace "Adapter" with "Codec" in docstrings
- Fix SHA256 → MD5 in content_registry.py docstring

Version bump to 2.0.0a6

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

Author: dimitri-yatsenko

docs/mkdocs.yaml

@@ -33,7 +33,7 @@ nav:
       - Blobs: design/tables/blobs.md
       - Attachments: design/tables/attach.md
       - Filepaths: design/tables/filepath.md
-      - Custom Datatypes: design/tables/customtype.md
+      - Custom Codecs: design/tables/codecs.md
       - Dependencies: design/tables/dependencies.md
       - Indexes: design/tables/indexes.md
       - Master-Part Relationships: design/tables/master-part.md

docs/src/design/tables/attributes.md

@@ -96,7 +96,7 @@ The `@` character indicates **external storage** (object store vs database):
 
 - `<blob>`: DataJoint's native serialization format for Python objects. Supports
   NumPy arrays, dicts, lists, datetime objects, and nested structures. Stores in
-  database. Compatible with MATLAB. See [custom types](customtype.md) for details.
+  database. Compatible with MATLAB. See [custom codecs](codecs.md) for details.
 
 - `<blob@>` / `<blob@store>`: Like `<blob>` but stores externally with hash-
   addressed deduplication. Use for large arrays that may be duplicated across rows.
@@ -125,7 +125,7 @@ The `@` character indicates **external storage** (object store vs database):
 
 ### User-defined codecs
 
-- `<custom_type>`: Define your own [custom codec](customtype.md) with
+- `<custom_type>`: Define your own [custom codec](codecs.md) with
   bidirectional conversion between Python objects and database storage. Use for
   graphs, domain-specific objects, or custom data structures.
 

src/datajoint/builtin_codecs.py

@@ -119,9 +119,6 @@ def decode(self, stored: bytes, *, key: dict | None = None) -> Any:
         return blob.unpack(stored, squeeze=False)
 
 
-# Note: DJBlobType is defined at end of file as DJBlobCodec (not BlobCodec)
-
-
 # =============================================================================
 # Hash-Addressed Storage Codec
 # =============================================================================
@@ -203,9 +200,6 @@ def validate(self, value: Any) -> None:
             raise TypeError(f"<hash> expects bytes, got {type(value).__name__}")
 
 
-# Note: ContentType is defined at end of file as ContentCodec (not HashCodec)
-
-
 # =============================================================================
 # Path-Addressed Storage Codec (OAS - Object-Augmented Schema)
 # =============================================================================
@@ -419,10 +413,6 @@ def validate(self, value: Any) -> None:
         raise TypeError(f"<object> expects bytes or path, got {type(value).__name__}")
 
 
-# Backward compatibility alias
-ObjectType = ObjectCodec
-
-
 # =============================================================================
 # File Attachment Codecs
 # =============================================================================
@@ -544,11 +534,6 @@ def validate(self, value: Any) -> None:
             raise TypeError(f"<attach> expects a file path, got {type(value).__name__}")
 
 
-# Backward compatibility aliases
-AttachType = AttachCodec
-XAttachType = AttachCodec  # <attach@> is now just AttachCodec with external storage
-
-
 # =============================================================================
 # Filepath Reference Codec
 # =============================================================================
@@ -664,7 +649,3 @@ def validate(self, value: Any) -> None:
 
         if not isinstance(value, (str, Path)):
             raise TypeError(f"<filepath> expects a path string or Path, got {type(value).__name__}")
-
-
-# Backward compatibility alias
-FilepathType = FilepathCodec

src/datajoint/content_registry.py

@@ -2,8 +2,8 @@
 Content-addressed storage registry for DataJoint.
 
 This module provides content-addressed storage with deduplication for the <hash>
-AttributeType. Content is identified by its SHA256 hash and stored in a hierarchical
-directory structure: _content/{hash[:2]}/{hash[2:4]}/{hash}
+Codec. Content is identified by its MD5 hash and stored in a hierarchical
+directory structure: _hash/{hash[:2]}/{hash[2:4]}/{hash}
 
 The ContentRegistry tracks stored content for garbage collection purposes.
 """

src/datajoint/declare.py

@@ -76,16 +76,16 @@
         TEMPORAL=r"(time|timestamp|year)(\s*\(.+\))?$",  # time, timestamp, year (not date/datetime)
         NATIVE_BLOB=r"(tiny|small|medium|long)blob$",  # Specific blob variants
         NATIVE_TEXT=r"(tiny|small|medium|long)text$",  # Text variants (use plain 'text' instead)
-        # AttributeTypes use angle brackets
-        ADAPTED=r"<.+>$",
+        # Codecs use angle brackets
+        CODEC=r"<.+>$",
     ).items()
 }
 
 # Core types are stored in attribute comment for reconstruction
 CORE_TYPE_NAMES = {name.upper() for name in CORE_TYPES}
 
 # Special types that need comment storage (core types + adapted)
-SPECIAL_TYPES = CORE_TYPE_NAMES | {"ADAPTED"}
+SPECIAL_TYPES = CORE_TYPE_NAMES | {"CODEC"}
 
 # Native SQL types that pass through (with optional warning)
 NATIVE_TYPES = set(TYPE_PATTERN) - SPECIAL_TYPES
@@ -104,23 +104,6 @@ def match_type(attribute_type):
 logger = logging.getLogger(__name__.split(".")[0])
 
 
-def build_foreign_key_parser_old():
-    # old-style foreign key parser. Superseded by expression-based syntax. See issue #436
-    # This will be deprecated in a future release.
-    left = pp.Literal("(").suppress()
-    right = pp.Literal(")").suppress()
-    attribute_name = pp.Word(pp.srange("[a-z]"), pp.srange("[a-z0-9_]"))
-    new_attrs = pp.Optional(left + pp.DelimitedList(attribute_name) + right).set_results_name("new_attrs")
-    arrow = pp.Literal("->").suppress()
-    lbracket = pp.Literal("[").suppress()
-    rbracket = pp.Literal("]").suppress()
-    option = pp.Word(pp.srange("[a-zA-Z]"))
-    options = pp.Optional(lbracket + pp.DelimitedList(option) + rbracket).set_results_name("options")
-    ref_table = pp.Word(pp.alphas, pp.alphanums + "._").set_results_name("ref_table")
-    ref_attrs = pp.Optional(left + pp.DelimitedList(attribute_name) + right).set_results_name("ref_attrs")
-    return new_attrs + arrow + options + ref_table + ref_attrs
-
-
 def build_foreign_key_parser():
     arrow = pp.Literal("->").suppress()
     lbracket = pp.Literal("[").suppress()
@@ -144,7 +127,6 @@ def build_attribute_parser():
     return attribute_name + pp.Optional(default) + colon + data_type + comment
 
 
-foreign_key_parser_old = build_foreign_key_parser_old()
 foreign_key_parser = build_foreign_key_parser()
 attribute_parser = build_attribute_parser()
 
@@ -459,14 +441,14 @@ def substitute_special_type(match, category, foreign_key_sql, context):
 
     Special types are:
     - Core DataJoint types (float32 → float, uuid → binary(16), bytes → longblob, etc.)
-    - ADAPTED types (AttributeTypes in angle brackets)
+    - CODEC types (Codecs in angle brackets)
 
     :param match: dict containing with keys "type" and "comment" -- will be modified in place
     :param category: attribute type category from TYPE_PATTERN
     :param foreign_key_sql: list of foreign key declarations to add to
     :param context: context for looking up user-defined codecs (unused, kept for compatibility)
     """
-    if category == "ADAPTED":
+    if category == "CODEC":
         # Codec - resolve to underlying dtype
         codec, store_name = lookup_codec(match["type"])
         if store_name is not None:
@@ -540,7 +522,7 @@ def compile_attribute(line, in_key, foreign_key_sql, context):
     category = match_type(match["type"])
 
     if category in SPECIAL_TYPES:
-        # Core types and AttributeTypes are recorded in comment for reconstruction
+        # Core types and Codecs are recorded in comment for reconstruction
         match["comment"] = ":{type}:{comment}".format(**match)
         substitute_special_type(match, category, foreign_key_sql, context)
     elif category in NATIVE_TYPES:

src/datajoint/errors.py

@@ -2,8 +2,6 @@
 Exception classes for the DataJoint library
 """
 
-import os
-
 
 # --- Top Level ---
 class DataJointError(Exception):
@@ -87,43 +85,3 @@ class BucketInaccessible(DataJointError):
     """
     Error raised when a S3 bucket is inaccessible
     """
-
-
-# environment variables to control availability of experimental features
-
-ADAPTED_TYPE_SWITCH = "DJ_SUPPORT_ADAPTED_TYPES"
-FILEPATH_FEATURE_SWITCH = "DJ_SUPPORT_FILEPATH_MANAGEMENT"
-
-
-def _switch_adapted_types(on):
-    """
-    Enable (on=True) or disable (on=False) support for AttributeAdapter
-    """
-    if on:
-        os.environ[ADAPTED_TYPE_SWITCH] = "TRUE"
-    else:
-        del os.environ[ADAPTED_TYPE_SWITCH]
-
-
-def _support_adapted_types():
-    """
-    check if support for AttributeAdapter is enabled
-    """
-    return os.getenv(ADAPTED_TYPE_SWITCH, "FALSE").upper() == "TRUE"
-
-
-def _switch_filepath_types(on):
-    """
-    Enable (on=True) or disable (on=False) support for AttributeAdapter
-    """
-    if on:
-        os.environ[FILEPATH_FEATURE_SWITCH] = "TRUE"
-    else:
-        del os.environ[FILEPATH_FEATURE_SWITCH]
-
-
-def _support_filepath_types():
-    """
-    check if support for AttributeAdapter is enabled
-    """
-    return os.getenv(FILEPATH_FEATURE_SWITCH, "FALSE").upper() == "TRUE"

src/datajoint/heading.py

@@ -307,8 +307,8 @@ def _init_from_database(self):
                     # Store the original type name for display but keep db_type for SQL
                     attr["original_type"] = special["type"]
 
-            # process Codecs (adapted types in angle brackets)
-            if special and TYPE_PATTERN["ADAPTED"].match(attr["type"]):
+            # process Codecs (types in angle brackets)
+            if special and TYPE_PATTERN["CODEC"].match(attr["type"]):
                 # Context can be None for built-in types that are globally registered
                 codec_spec = special["type"]
                 try:

src/datajoint/migrate.py

@@ -2,7 +2,7 @@
 Migration utilities for DataJoint schema updates.
 
 This module provides tools for migrating existing schemas to use the new
-AttributeType system, particularly for upgrading blob columns to use
+Codec system, particularly for upgrading blob columns to use
 explicit `<blob>` type declarations.
 """
 

src/datajoint/table.py

@@ -732,7 +732,7 @@ def __make_placeholder(self, name, value, ignore_extra_fields=False, row=None):
         processing by mysql API.
 
         In the simplified type system:
-        - Adapters (AttributeTypes) handle all custom encoding via type chains
+        - Codecs handle all custom encoding via type chains
         - UUID values are converted to bytes
         - JSON values are serialized
         - Blob values pass through as bytes

src/datajoint/version.py

@@ -1,4 +1,4 @@
 # version bump auto managed by Github Actions:
 # label_prs.yaml(prep), release.yaml(bump), post_release.yaml(edit)
 # manually set this version will be eventually overwritten by the above actions
-__version__ = "2.0.0a5"
+__version__ = "2.0.0a6"