Swift: some restructuring of codegen

Loading of the schema and dbscheme has been moved to a separate
`loaders` package for better separation of concerns.

swift/codegen/lib/dbscheme.py

@@ -105,54 +105,3 @@ class Scheme:
     src: str
     includes: List[SchemeInclude]
     declarations: List[Decl]
-
-
-class Re:
-    entity = re.compile(
-        "(?m)"
-        r"(?:^#keyset\[(?P<tablekeys>[\w\s,]+)\][\s\n]*)?^(?P<table>\w+)\("
-        r"(?:\s*//dir=(?P<tabledir>\S*))?(?P<tablebody>[^\)]*)"
-        r"\);?"
-        "|"
-        r"^(?P<union>@\w+)\s*=\s*(?P<unionbody>@\w+(?:\s*\|\s*@\w+)*)\s*;?"
-    )
-    field = re.compile(r"(?m)[\w\s]*\s(?P<field>\w+)\s*:\s*(?P<type>@?\w+)(?P<ref>\s+ref)?")
-    key = re.compile(r"@\w+")
-    comment = re.compile(r"(?m)(?s)/\*.*?\*/|//(?!dir=)[^\n]*$")  # lookahead avoid ignoring metadata like //dir=foo
-
-
-def get_column(match):
-    return Column(
-        schema_name=match["field"].rstrip("_"),
-        type=match["type"],
-        binding=not match["ref"],
-    )
-
-
-def get_table(match):
-    keyset = None
-    if match["tablekeys"]:
-        keyset = KeySet(k.strip() for k in match["tablekeys"].split(","))
-    return Table(
-        name=match["table"],
-        columns=[get_column(f) for f in Re.field.finditer(match["tablebody"])],
-        keyset=keyset,
-        dir=pathlib.PosixPath(match["tabledir"]) if match["tabledir"] else None,
-    )
-
-
-def get_union(match):
-    return Union(
-        lhs=match["union"],
-        rhs=(d[0] for d in Re.key.finditer(match["unionbody"])),
-    )
-
-
-def iterload(file):
-    with open(file) as file:
-        data = Re.comment.sub("", file.read())
-    for e in Re.entity.finditer(data):
-        if e["table"]:
-            yield get_table(e)
-        elif e["union"]:
-            yield get_union(e)