Swift: dbscheme generator

This patch introduces the basic infrastructure of the code generation
suite and the `dbscheme` generator.

Notice that the checked in `schema.yml` should reflect swift 5.6 but
might need some tweaking.

Closes https://github.com/github/codeql-c-team/issues/979

swift/codegen/lib/schema.py

@@ -0,0 +1,98 @@
+import pathlib
+from dataclasses import dataclass, field
+from enum import Enum, auto
+from typing import List, Set, Dict
+import re
+
+import yaml
+
+
+class Cardinality(Enum):
+    ONE = auto()
+    OPTIONAL = auto()
+    MANY = auto()
+
+
+@dataclass
+class Field:
+    name: str
+    type: str
+    cardinality: Cardinality = Cardinality.ONE
+
+    def is_single(self):
+        return self.cardinality == Cardinality.ONE
+
+    def is_optional(self):
+        return self.cardinality == Cardinality.OPTIONAL
+
+    def is_repeated(self):
+        return self.cardinality == Cardinality.MANY
+
+
+@dataclass
+class Class:
+    name: str
+    bases: Set[str] = field(default_factory=set)
+    derived: Set[str] = field(default_factory=set)
+    fields: List[Field] = field(default_factory=list)
+    dir: pathlib.Path = pathlib.Path()
+
+
+@dataclass
+class Schema:
+    classes: Dict[str, Class]
+    includes: Set[str] = field(default_factory=set)
+
+
+def _parse_field(name, type):
+    if type.endswith("*"):
+        cardinality = Cardinality.MANY
+        type = type[:-1]
+    elif type.endswith("?"):
+        cardinality = Cardinality.OPTIONAL
+        type = type[:-1]
+    else:
+        cardinality = Cardinality.ONE
+    return Field(name, type, cardinality)
+
+
+root_class_name = "Element"
+
+
+class DirSelector:
+    def __init__(self, dir_to_patterns):
+        self.selector = [(re.compile(p), pathlib.Path(d)) for d, p in dir_to_patterns]
+        self.selector.append((re.compile(""), pathlib.Path()))
+
+    def get(self, name):
+        return next(d for p, d in self.selector if p.search(name))
+
+
+def load(file):
+    data = yaml.load(file, Loader=yaml.SafeLoader)
+    grouper = DirSelector(data.get("_directories", {}).items())
+    ret = Schema(classes={cls: Class(cls, dir=grouper.get(cls)) for cls in data if not cls.startswith("_")},
+                 includes=set(data.get("_includes", [])))
+    assert root_class_name not in ret.classes
+    ret.classes[root_class_name] = Class(root_class_name)
+    for name, info in data.items():
+        if name.startswith("_"):
+            continue
+        assert name[0].isupper()
+        cls = ret.classes[name]
+        for k, v in info.items():
+            if not k.startswith("_"):
+                cls.fields.append(_parse_field(k, v))
+            elif k == "_extends":
+                if not isinstance(v, list):
+                    v = [v]
+                for base in v:
+                    cls.bases.add(base)
+                    ret.classes[base].derived.add(name)
+            elif k == "_dir":
+                cls.dir = pathlib.Path(v)
+        if not cls.bases:
+            cls.bases.add(root_class_name)
+            ret.classes[root_class_name].derived.add(name)
+
+    return ret