cli pyproject updating (#12945)

`langchain app add` and `langchain app remove` will now keep the
dependencies list updated.

---------

Co-authored-by: Nuno Campos <nuno@boringbits.io>

libs/cli/langchain_cli/utils/packages.py

@@ -1,5 +1,7 @@
 from pathlib import Path
-from typing import Optional, Set
+from typing import Any, Dict, Optional, Set, TypedDict
+
+from tomlkit import load
 
 
 def get_package_root(cwd: Optional[Path] = None) -> Path:
@@ -14,3 +16,30 @@ def get_package_root(cwd: Optional[Path] = None) -> Path:
             return package_root
         package_root = package_root.parent
     raise FileNotFoundError("No pyproject.toml found")
+
+
+class LangServeExport(TypedDict):
+    """
+    Fields from pyproject.toml that are relevant to LangServe
+
+    Attributes:
+        module: The module to import from, tool.langserve.export_module
+        attr: The attribute to import from the module, tool.langserve.export_attr
+        package_name: The name of the package, tool.poetry.name
+    """
+
+    module: str
+    attr: str
+    package_name: str
+
+
+def get_langserve_export(filepath: Path) -> LangServeExport:
+    with open(filepath) as f:
+        data: Dict[str, Any] = load(f)
+    try:
+        module = data["tool"]["langserve"]["export_module"]
+        attr = data["tool"]["langserve"]["export_attr"]
+        package_name = data["tool"]["poetry"]["name"]
+    except KeyError as e:
+        raise KeyError("Invalid LangServe PyProject.toml") from e
+    return LangServeExport(module=module, attr=attr, package_name=package_name)