Add Python language support (#6508)

Author: jkschneider

.context/metaprogramming_options.py

@@ -0,0 +1,243 @@
+"""
+Exploring compile-time metaprogramming options for typed replace() methods.
+
+Goal: Keep LST source clean and readable, but provide IDE autocomplete for replace().
+"""
+
+from dataclasses import dataclass, fields, replace
+from typing import Optional, Self, dataclass_transform, TypeVar, get_type_hints
+from uuid import UUID
+import functools
+
+
+# =============================================================================
+# OPTION 1: Custom decorator that adds a typed replace() method at import time
+# =============================================================================
+# The decorator inspects fields and dynamically creates a replace() method
+# with the correct signature. BUT - IDEs won't see the generated signature.
+
+def add_replace_method(cls):
+    """Decorator that adds a replace() method to a frozen dataclass."""
+    def _replace(self, **changes):
+        return replace(self, **changes)
+    cls.replace = _replace
+    return cls
+
+
+# =============================================================================
+# OPTION 2: .pyi stub files (RECOMMENDED)
+# =============================================================================
+# Generate .pyi stub files that declare the typed replace() signature.
+# The runtime code uses plain replace(), but IDEs read the .pyi for types.
+#
+# tree.py (runtime - clean and simple):
+#
+#     @dataclass(frozen=True, slots=True)
+#     class Await(Py, Expression):
+#         id: UUID
+#         prefix: Space
+#         markers: Markers
+#         expression: Expression
+#         type: Optional[JavaType] = None
+#
+# tree.pyi (stub file - provides IDE autocomplete):
+#
+#     class Await(Py, Expression):
+#         id: UUID
+#         prefix: Space
+#         markers: Markers
+#         expression: Expression
+#         type: Optional[JavaType]
+#
+#         def replace(
+#             self,
+#             *,
+#             id: UUID = ...,
+#             prefix: Space = ...,
+#             markers: Markers = ...,
+#             expression: Expression = ...,
+#             type: Optional[JavaType] = ...,
+#         ) -> Self: ...
+#
+# The stub generator script reads tree.py and generates tree.pyi automatically.
+
+
+# =============================================================================
+# OPTION 3: __init_subclass__ with dataclass_transform
+# =============================================================================
+# Use PEP 681 dataclass_transform to tell type checkers about our pattern.
+# This is how attrs, pydantic, and other libraries get IDE support.
+
+@dataclass_transform(frozen_default=True)
+class LstBase:
+    """Base class for all LST types that adds replace() method."""
+
+    def __init_subclass__(cls, **kwargs):
+        super().__init_subclass__(**kwargs)
+        # Apply dataclass decorator
+        dataclass(frozen=True, slots=True, eq=False)(cls)
+
+    def replace(self, **changes) -> Self:
+        """Create a copy with the specified fields replaced."""
+        return replace(self, **changes)
+
+
+# Usage would be:
+# class Await(LstBase, Py, Expression):
+#     id: UUID
+#     prefix: Space
+#     ...
+#
+# BUT: dataclass_transform alone doesn't give us typed kwargs on replace()
+
+
+# =============================================================================
+# OPTION 4: Protocol + stub file hybrid
+# =============================================================================
+# Define a Protocol that declares replace() exists, generate stubs for specifics
+
+from typing import Protocol
+
+class Replaceable(Protocol):
+    def replace(self, **kwargs) -> Self: ...
+
+
+# =============================================================================
+# OPTION 5: Use typing.overload in stub files
+# =============================================================================
+# In .pyi files, we can use @overload to provide multiple typed signatures.
+# This is the most IDE-friendly approach.
+#
+# tree.pyi:
+#
+#     from typing import overload
+#
+#     class Await(Py, Expression):
+#         @overload
+#         def replace(self) -> Await: ...
+#         @overload
+#         def replace(self, *, id: UUID) -> Await: ...
+#         @overload
+#         def replace(self, *, prefix: Space) -> Await: ...
+#         @overload
+#         def replace(self, *, id: UUID, prefix: Space) -> Await: ...
+#         # ... combinatorial explosion, not practical
+#
+# Better: Just use keyword-only args with defaults in stub:
+#
+#     def replace(
+#         self,
+#         *,
+#         id: UUID = ...,
+#         prefix: Space = ...,
+#     ) -> Await: ...
+
+
+# =============================================================================
+# STUB GENERATOR SCRIPT (for Option 2)
+# =============================================================================
+import ast
+import inspect
+from pathlib import Path
+
+
+def generate_stubs_for_module(source_path: Path) -> str:
+    """Generate .pyi stub content for a dataclass module with replace() methods."""
+    with open(source_path) as f:
+        source = f.read()
+
+    tree = ast.parse(source)
+    stub_lines = []
+
+    # Add imports
+    stub_lines.append("from typing import Optional, Self")
+    stub_lines.append("from uuid import UUID")
+    stub_lines.append("# ... other imports")
+    stub_lines.append("")
+
+    for node in ast.walk(tree):
+        if isinstance(node, ast.ClassDef):
+            # Check if it's a dataclass (has @dataclass decorator)
+            is_dataclass = any(
+                (isinstance(d, ast.Name) and d.id == 'dataclass') or
+                (isinstance(d, ast.Call) and isinstance(d.func, ast.Name) and d.func.id == 'dataclass')
+                for d in node.decorator_list
+            )
+
+            if is_dataclass:
+                # Extract fields (annotated assignments)
+                fields_info = []
+                for item in node.body:
+                    if isinstance(item, ast.AnnAssign) and isinstance(item.target, ast.Name):
+                        field_name = item.target.id
+                        # Get the annotation as string
+                        field_type = ast.unparse(item.annotation)
+                        has_default = item.value is not None
+                        fields_info.append((field_name, field_type, has_default))
+
+                # Generate stub class
+                bases = ", ".join(ast.unparse(b) for b in node.bases)
+                stub_lines.append(f"class {node.name}({bases}):")
+
+                # Add field declarations
+                for name, type_str, _ in fields_info:
+                    stub_lines.append(f"    {name}: {type_str}")
+
+                stub_lines.append("")
+
+                # Add typed replace() method
+                stub_lines.append("    def replace(")
+                stub_lines.append("        self,")
+                stub_lines.append("        *,")
+                for name, type_str, _ in fields_info:
+                    stub_lines.append(f"        {name}: {type_str} = ...,")
+                stub_lines.append("    ) -> Self: ...")
+                stub_lines.append("")
+
+    return "\n".join(stub_lines)
+
+
+# =============================================================================
+# DEMONSTRATION
+# =============================================================================
+
+if __name__ == "__main__":
+    # Example LST class (clean source)
+    @dataclass(frozen=True, slots=True, eq=False)
+    class Space:
+        whitespace: str = ""
+        comments: list = None
+
+    @dataclass(frozen=True, slots=True, eq=False)
+    class Markers:
+        id: UUID
+        markers: list = None
+
+    @dataclass(frozen=True, slots=True, eq=False)
+    class Await:
+        id: UUID
+        prefix: Space
+        markers: Markers
+        expression: object  # Would be Expression
+        type: Optional[str] = None
+
+        # Simple replace method - runtime works, but IDE doesn't know the kwargs
+        def replace(self, **changes) -> "Await":
+            return replace(self, **changes)
+
+    # Usage
+    a = Await(
+        id=UUID("12345678-1234-5678-1234-567812345678"),
+        prefix=Space(),
+        markers=Markers(id=UUID("12345678-1234-5678-1234-567812345678")),
+        expression=None
+    )
+
+    # This works at runtime, but IDE won't autocomplete 'expression'
+    a2 = a.replace(expression="new_expr")
+    print(f"Original: {a}")
+    print(f"Replaced: {a2}")
+
+    # Generate stub for this file
+    print("\n--- Generated Stub ---")
+    print(generate_stubs_for_module(Path(__file__)))