Enable writing module code directly to file

libcst/_nodes/internal.py

@@ -4,6 +4,7 @@
 # LICENSE file in the root directory of this source tree.
 
 
+import io
 from contextlib import contextmanager
 from dataclasses import dataclass, field
 from typing import Iterable, Iterator, List, Optional, Sequence, TYPE_CHECKING, Union
@@ -70,6 +71,30 @@
         yield
 
 
+@add_slots
+@dataclass(frozen=False)
+class CodegenWriter(CodegenState):
+    """
+    A CodegenState that writes to a file-like object.
+    """
+
+    writer: io.TextIOBase = None  # need a default value for dataclass
+
+    def __post_init__(self) -> None:
+        if self.writer is None:
+            raise TypeError("writer must be provided")
+
+    def add_indent_tokens(self) -> None:
+        for token in self.indent_tokens:
+            self.writer.write(token)
+
+    def add_token(self, value: str) -> None:
+        self.writer.write(value)
+
+    def pop_trailing_newline(self) -> None:
+        pass
+
+
 def visit_required(
     parent: "CSTNode", fieldname: str, node: CSTNodeT, visitor: "CSTVisitorT"
 ) -> CSTNodeT:

libcst/_nodes/module.py

@@ -3,12 +3,18 @@
 # This source code is licensed under the MIT license found in the
 # LICENSE file in the root directory of this source tree.
 
+import io
 from dataclasses import dataclass
 from typing import cast, Optional, Sequence, TYPE_CHECKING, TypeVar, Union
 
 from libcst._add_slots import add_slots
 from libcst._nodes.base import CSTNode
-from libcst._nodes.internal import CodegenState, visit_body_sequence, visit_sequence
+from libcst._nodes.internal import (
+    CodegenState,
+    CodegenWriter,
+    visit_body_sequence,
+    visit_sequence,
+)
 from libcst._nodes.statement import (
     BaseCompoundStatement,
     get_docstring_impl,
@@ -136,6 +142,24 @@
         node._codegen(state)
         return "".join(state.tokens)
 
+    def write_code(self, writer: io.TextIOBase):
+        """
+        Like :meth:`code`, but writes the code to the given file-like object.
+        """
+        self.write_code_for_node(self, writer)
+
+    def write_code_for_node(self, node: CSTNode, writer: io.TextIOBase):
+        """
+        Like :meth:`code_for_node`, but writes the code to the given file-like object.
+        """
+
+        state = CodegenWriter(
+            default_indent=self.default_indent,
+            default_newline=self.default_newline,
+            writer=writer,
+        )
+        node._codegen(state)
+
     @property
     def config_for_parsing(self) -> "PartialParserConfig":
         """