Pytest-dependency reordering support (module and session scopes only)

conftest.py

import warnings
from typing import Optional, List, Dict
from collections import defaultdict, deque

from pytest import Module, Item


def pytest_collection_modifyitems(items: List[Item]):
    session_names: Set[str] = set()
    module_names: Dict[Module, Set[str]] = defaultdict(set)

    # gather dependency names
    for item in items:
        for marker in item.iter_markers("dependency"):
            scope = marker.kwargs.get("scope", "module")
            name = marker.kwargs.get("name")
            if not name:
                nodeid = item.nodeid.replace("::()::", "::")
                if scope == "session" or scope == "package":
                    name = nodeid
                elif scope == "module":
                    name = nodeid.split("::", 1)[1]
                elif scope == "class":
                    name = nodeid.split("::", 2)[2]

                original = item.originalname if item.originalname is not None else item.name
                # remove the parametrization part at the end
                if not name.endswith(original):
                    index = name.rindex(original) + len(original)
                    name = name[:index]

            if scope == "module":
                module_names[item.module].add(name)
            elif scope == "session":
                session_names.add(name)

    final_items: List[Item] = []
    session_deps: Dict[str, Item] = {}
    module_deps: Dict[Module, Dict[str, Item]] = defaultdict(dict)

    # group the dependencies by their scopes
    cycles = 0
    deque_items = deque(items)
    while deque_items:
        if cycles > len(deque_items):
            # seems like we're stuck in a loop now
            # just add the remaining items and finish up
            final_items.extend(deque_items)
            break
        item = deque_items.popleft()
        correct_order: Optional[bool] = True
        for marker in item.iter_markers("dependency"):
            depends = marker.kwargs.get("depends", [])
            scope = marker.kwargs.get("scope", "module")
            name = marker.kwargs.get("name")
            if not name:
                nodeid = item.nodeid.replace("::()::", "::")
                if scope == "session" or scope == "package":
                    name = nodeid
                elif scope == "module":
                    name = nodeid.split("::", 1)[1]
                elif scope == "class":
                    name = nodeid.split("::", 2)[2]

                original = item.originalname if item.originalname is not None else item.name
                # remove the parametrization part at the end
                if not name.endswith(original):
                    index = name.rindex(original) + len(original)
                    name = name[:index]
            # pick a scope
            if scope == "module":
                scope_deps = module_deps[item.module]
                scope_names = module_names[item.module]
            elif scope == "session":
                scope_deps = session_deps
                scope_names = session_names
            # check deps
            if not all(d in scope_deps for d in depends):
                # check to see if we're ever gonna see a dep like that
                for d in depends:
                    if d in scope_names:
                        if correct_order is not None:
                            correct_order = False
                    else:
                        correct_order = None
                        warnings.warn(
                            f"Dependency '{d}' of '{name}' doesn't exist, "
                            "or has incorrect scope!",
                            RuntimeWarning,
                        )
                break
            # save
            if scope == "module":
                module_deps[item.module][name] = item
            elif scope == "session":
                session_deps[name] = item  # use 'nodeid' instead of the name
        # 'correct_order' possible values:
        # None  - invalid dependency, add anyway
        # True  - add it to the final list
        # False - missing dependency, add it back to the processing deque
        if correct_order is None:
            # TODO: Take the config into account here
            final_items.append(item)
            cycles = 0
        elif correct_order:
            final_items.append(item)
            cycles = 0
        else:
            deque_items.append(item)
            cycles += 1

    assert len(items) == len(final_items) and all(i in items for i in final_items)
    items[:] = final_items