fix: Fix struct definitions in notebooks (#374)

Fixes #373.

Trying to do `inspect.getsourclines` for a class defined in a notebook
yields an `OSError: source code not available`. See
* ipython/ipython#11249
* https://bugs.python.org/issue33826

The fix suggested in ipython/ipython#11249
only works for classes with methods. Instead, I'm using a solution
inspired by wandb/weave#1864 that retrieves the
cell sources of the active IPython session and searches them one by one.

guppylang/definition/struct.py

@@ -4,7 +4,7 @@
 from collections.abc import Sequence
 from dataclasses import dataclass
 from functools import cached_property
-from typing import Any
+from typing import Any, cast
 
 from guppylang.ast_util import AstNode, annotate_location
 from guppylang.checker.core import Globals
@@ -223,19 +223,62 @@ def compile(self, args: list[OutPortV]) -> list[OutPortV]:
         return [constructor_def]
 
 
+def is_running_ipython() -> bool:
+    """Checks if we are currently running in IPython"""
+    try:
+        return get_ipython() is not None  # type: ignore[name-defined]
+    except NameError:
+        return False
+
+
+def get_ipython_cell_sources() -> list[str]:
+    """Returns the source code of all cells in the running IPython session.
+
+    See https://github.com/wandb/weave/pull/1864
+    """
+    shell = get_ipython()  # type: ignore[name-defined]  # noqa: F821
+    if not hasattr(shell, "user_ns"):
+        raise AttributeError("Cannot access user namespace")
+    cells = cast(list[str], shell.user_ns["In"])
+    # First cell is always empty
+    return cells[1:]
+
+
 def parse_py_class(cls: type) -> ast.ClassDef:
     """Parses a Python class object into an AST."""
-    source_lines, line_offset = inspect.getsourcelines(cls)
-    source = "".join(source_lines)  # Lines already have trailing \n's
-    source = textwrap.dedent(source)
-    cls_ast = ast.parse(source).body[0]
-    file = inspect.getsourcefile(cls)
-    if file is None:
-        raise GuppyError("Couldn't determine source file for class")
-    annotate_location(cls_ast, source, file, line_offset)
-    if not isinstance(cls_ast, ast.ClassDef):
-        raise GuppyError("Expected a class definition", cls_ast)
-    return cls_ast
+    # We cannot use `inspect.getsourcelines` if we're running in IPython. See
+    #  - https://bugs.python.org/issue33826
+    #  - https://github.com/ipython/ipython/issues/11249
+    #  - https://github.com/wandb/weave/pull/1864
+    if is_running_ipython():
+        cell_sources = get_ipython_cell_sources()
+        # Search cells in reverse order to find the most recent version of the class
+        for i, cell_source in enumerate(reversed(cell_sources)):
+            try:
+                cell_ast = ast.parse(cell_source)
+            except SyntaxError:
+                continue
+            # Search body in reverse order to find the most recent version of the class
+            for node in reversed(cell_ast.body):
+                if getattr(node, "name", None) == cls.__name__:
+                    cell_name = f"<In [{len(cell_sources) - i}]>"
+                    annotate_location(node, cell_source, cell_name, 1)
+                    if not isinstance(node, ast.ClassDef):
+                        raise GuppyError("Expected a class definition", node)
+                    return node
+        raise ValueError(f"Couldn't find source for class `{cls.__name__}`")
+    else:
+        source_lines, line_offset = inspect.getsourcelines(cls)
+        source = "".join(source_lines)  # Lines already have trailing \n's
+        source = textwrap.dedent(source)
+        cls_ast = ast.parse(source).body[0]
+        file = inspect.getsourcefile(cls)
+        if file is None:
+            raise GuppyError("Couldn't determine source file for class")
+        annotate_location(cls_ast, source, file, line_offset)
+        if not isinstance(cls_ast, ast.ClassDef):
+            raise GuppyError("Expected a class definition", cls_ast)
+        return cls_ast
 
 
 def try_parse_generic_base(node: ast.expr) -> list[ast.expr] | None: