unsloth/studio/backend/tests/test_diffusion_cache.py

# SPDX-License-Identifier: AGPL-3.0-only
# Copyright 2026-present the Unsloth AI Inc. team. All rights reserved. See /studio/LICENSE.AGPL-3.0

"""Hermetic CPU tests for opt-in step caching (First-Block-Cache).

``diffusers`` is stubbed via ``sys.modules`` (the module under test imports
``FirstBlockCacheConfig`` lazily), and the pipeline is a fake that records the engaged config.
So normalisation, the CacheMixin (``enable_cache``) gating, threshold selection, and the
best-effort failure handling are all exercised without torch or a real diffusers model.
"""

from __future__ import annotations

import sys
import types

import pytest

from core.inference.diffusion_cache import (
    DEFAULT_FBCACHE_THRESHOLD,
    QUANT_FBCACHE_THRESHOLD,
    TC_FBCACHE,
    apply_step_cache,
    normalize_transformer_cache,
)


# ── normalize_transformer_cache ────────────────────────────────────────────────────
def test_normalize_disabled_values_are_none():
    for value in (None, "", "  ", "none", "off", "OFF", "None"):
        assert normalize_transformer_cache(value) is None


def test_normalize_fbcache_and_casing():
    assert normalize_transformer_cache("fbcache") == TC_FBCACHE
    assert normalize_transformer_cache("FBCache") == TC_FBCACHE
    assert normalize_transformer_cache("  fbcache  ") == TC_FBCACHE


def test_normalize_rejects_unknown():
    with pytest.raises(ValueError):
        normalize_transformer_cache("deepcache")


# ── apply_step_cache ───────────────────────────────────────────────────────────────
class _Config:
    def __init__(self, threshold):
        self.threshold = threshold


class _MixinTransformer:
    """A CacheMixin-style transformer: exposes ``enable_cache``."""

    def __init__(self, *, fail = False):
        self.fail = fail
        self.enabled_with = None

    def enable_cache(self, config):
        if self.fail:
            raise RuntimeError("block signature not recognised")
        self.enabled_with = config


class _NonCacheMixinTransformer:
    """A transformer with no ``enable_cache`` (not a CacheMixin) -> must run uncached.

    Its pipeline opens no ``cache_context``, so installing FBCache would crash at generation;
    the load runs uncached instead (e.g. Z-Image)."""


class _CtxPipe:
    """A pipeline whose denoise loop opens ``transformer.cache_context(...)`` (like FluxPipeline)
    -- the First-Block-Cache hook needs it, so FBCache may engage here."""

    def __init__(self, transformer):
        self.transformer = transformer

    def __call__(self, *args, **kwargs):
        with self.transformer.cache_context("cond"):
            return None


class _NoCtxPipe:
    """A pipeline that never enters a caching context (like FluxKontextPipeline / img2img /
    inpaint / controlnet, which reuse the CacheMixin FluxTransformer2DModel): FBCache must NOT
    engage or the hook raises "No context is set" on the first forward."""

    def __init__(self, transformer):
        self.transformer = transformer

    def __call__(self, *args, **kwargs):
        return None


def _pipe(transformer):
    return _CtxPipe(transformer)


def _stub_diffusers(monkeypatch, *, hook_recorder = None):
    diffusers = types.ModuleType("diffusers")
    diffusers.FirstBlockCacheConfig = _Config
    monkeypatch.setitem(sys.modules, "diffusers", diffusers)

    hooks = types.ModuleType("diffusers.hooks")

    def _apply_first_block_cache(transformer, config):
        if hook_recorder is not None:
            hook_recorder["transformer"] = transformer
            hook_recorder["config"] = config

    hooks.apply_first_block_cache = _apply_first_block_cache
    monkeypatch.setitem(sys.modules, "diffusers.hooks", hooks)


def test_disabled_mode_is_noop(monkeypatch):
    _stub_diffusers(monkeypatch)
    t = _MixinTransformer()
    assert apply_step_cache(_pipe(t), mode = None) is None
    assert apply_step_cache(_pipe(t), mode = "off") is None
    assert t.enabled_with is None


def test_enable_cache_path_default_threshold(monkeypatch):
    _stub_diffusers(monkeypatch)
    t = _MixinTransformer()
    engaged = apply_step_cache(_pipe(t), mode = "fbcache")
    assert engaged == TC_FBCACHE
    assert t.enabled_with.threshold == DEFAULT_FBCACHE_THRESHOLD
    assert t._unsloth_step_cache == f"fbcache@{DEFAULT_FBCACHE_THRESHOLD}"


def test_quant_active_raises_default_threshold(monkeypatch):
    _stub_diffusers(monkeypatch)
    t = _MixinTransformer()
    apply_step_cache(_pipe(t), mode = "fbcache", quant_active = True)
    assert t.enabled_with.threshold == QUANT_FBCACHE_THRESHOLD


def test_explicit_threshold_overrides_quant(monkeypatch):
    _stub_diffusers(monkeypatch)
    t = _MixinTransformer()
    apply_step_cache(_pipe(t), mode = "fbcache", threshold = 0.2, quant_active = True)
    assert t.enabled_with.threshold == 0.2


def test_non_cachemixin_runs_uncached(monkeypatch):
    # A transformer without enable_cache (e.g. Z-Image) must NOT install the standalone hook
    # -- its pipeline opens no cache_context, so it runs uncached instead of crashing at gen.
    rec: dict = {}
    _stub_diffusers(monkeypatch, hook_recorder = rec)
    t = _NonCacheMixinTransformer()
    assert apply_step_cache(_pipe(t), mode = "fbcache") is None
    assert rec == {}  # the standalone hook was never called


def test_pipeline_without_cache_context_runs_uncached(monkeypatch):
    # A CacheMixin transformer whose PIPELINE never opens a cache_context (Flux Kontext /
    # img2img / inpaint / controlnet reuse the CacheMixin FluxTransformer2DModel) must run
    # uncached -- otherwise the First-Block-Cache hook raises "No context is set" on the
    # first forward, crashing every default generation.
    _stub_diffusers(monkeypatch)
    t = _MixinTransformer()
    assert apply_step_cache(_NoCtxPipe(t), mode = "fbcache") is None
    assert t.enabled_with is None  # enable_cache was never called


def test_incompatible_model_runs_uncached(monkeypatch):
    # enable_cache raising (e.g. unrecognised block signature) must not fail the load.
    _stub_diffusers(monkeypatch)
    t = _MixinTransformer(fail = True)
    assert apply_step_cache(_pipe(t), mode = "fbcache") is None


def test_enable_cache_failure_rolls_back_partial_hooks(monkeypatch):
    # enable_cache can raise after hooking some blocks; the reported-uncached model
    # must not actually run half-cached, so the failure path calls disable_cache.
    _stub_diffusers(monkeypatch)
    t = _MixinTransformer(fail = True)
    t.disabled = False
    t.disable_cache = lambda: setattr(t, "disabled", True)
    assert apply_step_cache(_pipe(t), mode = "fbcache") is None
    assert t.disabled is True


def test_config_import_falls_back_to_hooks_module(monkeypatch):
    # Older diffusers exports FirstBlockCacheConfig only from diffusers.hooks.
    diffusers = types.ModuleType("diffusers")  # no FirstBlockCacheConfig attribute
    monkeypatch.setitem(sys.modules, "diffusers", diffusers)
    hooks = types.ModuleType("diffusers.hooks")
    hooks.FirstBlockCacheConfig = _Config
    monkeypatch.setitem(sys.modules, "diffusers.hooks", hooks)
    t = _MixinTransformer()
    assert apply_step_cache(_pipe(t), mode = "fbcache") == TC_FBCACHE
    assert t.enabled_with.threshold == DEFAULT_FBCACHE_THRESHOLD


def test_missing_transformer_is_none(monkeypatch):
    _stub_diffusers(monkeypatch)
    pipe = types.SimpleNamespace(transformer = None)
    assert apply_step_cache(pipe, mode = "fbcache") is None


def test_diffusers_unavailable_runs_uncached(monkeypatch):
    # no diffusers import -> best-effort returns None, load proceeds uncached. Block the
    # hooks module too: the config import falls back to diffusers.hooks, which a REAL
    # earlier import in the test session may have left cached in sys.modules.
    monkeypatch.setitem(sys.modules, "diffusers", None)
    monkeypatch.setitem(sys.modules, "diffusers.hooks", None)
    t = _MixinTransformer()
    assert apply_step_cache(_pipe(t), mode = "fbcache") is None


# ── the auto policy: normalize("auto") + generation-time toggling ──────────────────
from core.inference.diffusion_cache import (  # noqa: E402
    FBCACHE_MIN_STEPS,
    TC_AUTO,
    effective_denoise_steps,
    effective_request_strength,
    maybe_toggle_step_cache,
)


# ── effective_denoise_steps (strength-aware step count for the auto policy) ─────────
def test_effective_steps_txt2img_is_full_count():
    # No strength (txt2img / reference) -> the full requested step count.
    assert effective_denoise_steps(28, None) == 28
    assert effective_denoise_steps(28, 1.0) == 28  # full redraw denoises every step


def test_effective_steps_low_strength_shrinks_below_the_bar():
    # A 28-step upscale at strength 0.35 denoises int(9.8) = 9 steps (diffusers get_timesteps
    # floors the product), which is below FBCACHE_MIN_STEPS -> the auto policy must NOT engage
    # FBCache there.
    eff = effective_denoise_steps(28, 0.35)
    assert eff == 9
    assert eff < FBCACHE_MIN_STEPS


def test_effective_request_strength_uses_pipe_default_when_omitted():
    import inspect

    # txt2img (no init image) or a pipe without the strength kwarg -> full trajectory (None).
    assert effective_request_strength(None, False, True, 0.6) is None
    assert effective_request_strength(0.5, True, False, None) is None
    # img2img with an explicit strength -> that value.
    assert effective_request_strength(0.2, True, True, 0.6) == 0.2
    # img2img with an OMITTED strength -> the pipe's own signature default (< 1), so the auto
    # policy keys on the real (short) trajectory, not the full step count. This is the fix:
    # int(28 * 0.6) = 16 real steps, not 28.
    s = effective_request_strength(None, True, True, 0.6)
    assert s == 0.6
    assert effective_denoise_steps(28, s) == 16
    # A non-numeric signature default (inspect.Parameter.empty) falls back to the full count.
    assert effective_request_strength(None, True, True, inspect.Parameter.empty) is None
    assert effective_request_strength(None, True, True, None) is None


def test_effective_steps_matches_diffusers_get_timesteps():
    # Mirror diffusers exactly: it denoises init_timestep = min(int(num_inference_steps *
    # strength), num_inference_steps) steps (the product is floored, not rounded).
    for steps, strength in [(28, 0.35), (28, 0.8), (50, 0.5), (20, 0.99), (30, 0.1)]:
        expected = max(1, min(int(steps * strength), steps))
        assert effective_denoise_steps(steps, strength) == expected


def test_toggle_stays_off_for_low_strength_workflow(monkeypatch):
    # End to end: a 28-step request would engage FBCache, but at strength 0.35 the
    # effective ~10 steps keep it uncached.
    _stub_diffusers(monkeypatch)
    t = _ToggleTransformer()
    mode = maybe_toggle_step_cache(_pipe(t), steps = effective_denoise_steps(28, 0.35))
    assert mode is None and t.enables == 0


class _ToggleTransformer(_MixinTransformer):
    """CacheMixin-style fake with the disable side too, counting transitions."""

    def __init__(self):
        super().__init__()
        self.enables = 0
        self.disables = 0

    def enable_cache(self, config):
        super().enable_cache(config)
        self.enables += 1

    def disable_cache(self):
        self.disables += 1


def test_normalize_auto_is_a_distinct_state():
    assert normalize_transformer_cache("auto") == TC_AUTO
    assert normalize_transformer_cache(" AUTO ") == TC_AUTO


def test_apply_treats_stray_auto_as_off(monkeypatch):
    # AUTO must be resolved by the loader; if it ever reaches the engage call the
    # load runs uncached instead of crashing.
    _stub_diffusers(monkeypatch)
    t = _MixinTransformer()
    assert apply_step_cache(_pipe(t), mode = "auto") is None
    assert t.enabled_with is None


def test_toggle_engages_at_the_step_bar(monkeypatch):
    _stub_diffusers(monkeypatch)
    t = _ToggleTransformer()
    mode = maybe_toggle_step_cache(_pipe(t), steps = FBCACHE_MIN_STEPS)
    assert mode == TC_FBCACHE and t.enables == 1
    assert t.enabled_with.threshold == DEFAULT_FBCACHE_THRESHOLD
    assert t._unsloth_step_cache


def test_toggle_uses_quant_threshold(monkeypatch):
    _stub_diffusers(monkeypatch)
    t = _ToggleTransformer()
    maybe_toggle_step_cache(_pipe(t), steps = 28, quant_active = True)
    assert t.enabled_with.threshold == QUANT_FBCACHE_THRESHOLD


def test_toggle_is_idempotent_when_engaged(monkeypatch):
    _stub_diffusers(monkeypatch)
    t = _ToggleTransformer()
    maybe_toggle_step_cache(_pipe(t), steps = 28)
    mode = maybe_toggle_step_cache(_pipe(t), steps = 28)
    assert mode == TC_FBCACHE and t.enables == 1 and t.disables == 0


def test_toggle_disengages_below_the_bar(monkeypatch):
    _stub_diffusers(monkeypatch)
    t = _ToggleTransformer()
    maybe_toggle_step_cache(_pipe(t), steps = 28)
    mode = maybe_toggle_step_cache(_pipe(t), steps = 8)
    assert mode is None and t.disables == 1
    assert not t._unsloth_step_cache
    # and it stays off on repeat calls (no flapping disable calls).
    assert maybe_toggle_step_cache(_pipe(t), steps = 8) is None
    assert t.disables == 1


def test_toggle_reengages_after_a_disable(monkeypatch):
    _stub_diffusers(monkeypatch)
    t = _ToggleTransformer()
    maybe_toggle_step_cache(_pipe(t), steps = 28)
    maybe_toggle_step_cache(_pipe(t), steps = 8)
    mode = maybe_toggle_step_cache(_pipe(t), steps = 24)
    assert mode == TC_FBCACHE and t.enables == 2


def test_toggle_noop_without_cache_support(monkeypatch):
    _stub_diffusers(monkeypatch)
    t = _NonCacheMixinTransformer()
    assert maybe_toggle_step_cache(_pipe(t), steps = 28) is None
    assert maybe_toggle_step_cache(_pipe(t), steps = 8) is None


def test_toggle_noop_without_transformer():
    assert maybe_toggle_step_cache(types.SimpleNamespace(), steps = 28) is None


# ── compiled cache-hook inners (regional compile x step cache composition) ──────────
import functools  # noqa: E402

from core.inference.diffusion_cache import (  # noqa: E402
    _compile_hooked_block_inners,
    _invalidate_child_registry_cache,
    _restore_hooked_block_inners,
)


class _BoundInner:
    """Provides a plain bound method for fn_ref.original_forward (__self__ present)."""

    def forward(self, *args, **kwargs):
        return "eager"


def _hooked_block(
    *,
    compiled = True,
    hook_name = "fbc_block_hook",
    bound = True,
):
    inner = _BoundInner()
    orig = inner.forward if bound else functools.partial(_BoundInner.forward, inner)
    hook = types.SimpleNamespace(fn_ref = types.SimpleNamespace(original_forward = orig))
    block = types.SimpleNamespace(
        _diffusers_hook = types.SimpleNamespace(hooks = {hook_name: hook}),
        _compiled_call_impl = object() if compiled else None,
    )
    return block, hook, orig


def _fake_dit(blocks):
    return types.SimpleNamespace(modules = lambda: [types.SimpleNamespace()] + blocks)


def _stub_torch_compile(monkeypatch):
    compiled_calls = []

    def _compile(fn, **kwargs):
        compiled_calls.append((fn, kwargs))
        wrapper = lambda *a, **k: fn(*a, **k)  # noqa: E731
        wrapper._unsloth_test_compiled_of = fn
        return wrapper

    torch = types.ModuleType("torch")
    torch.compile = _compile
    monkeypatch.setitem(sys.modules, "torch", torch)
    return compiled_calls


def test_arming_swaps_inner_for_compiled_wrapper(monkeypatch):
    calls = _stub_torch_compile(monkeypatch)
    block, hook, orig = _hooked_block()
    assert _compile_hooked_block_inners(_fake_dit([block])) == 1
    assert hook.fn_ref.original_forward is not orig
    assert hook.fn_ref.original_forward._unsloth_test_compiled_of is orig
    assert hook._unsloth_orig_inner is orig
    # The inner compile must match the cache-active tier: graph-breakable + dynamic.
    assert calls[0][1] == {"fullgraph": False, "dynamic": True}


def test_arming_is_idempotent(monkeypatch):
    _stub_torch_compile(monkeypatch)
    block, hook, _ = _hooked_block()
    dit = _fake_dit([block])
    assert _compile_hooked_block_inners(dit) == 1
    once = hook.fn_ref.original_forward
    assert _compile_hooked_block_inners(dit) == 0  # marker short-circuits
    assert hook.fn_ref.original_forward is once


def test_arming_skips_uncompiled_blocks(monkeypatch):
    # An eager-tier load has no _compiled_call_impl: the hook must stay untouched
    # (compiling the inner would ADD compile where the user chose eager).
    _stub_torch_compile(monkeypatch)
    block, hook, orig = _hooked_block(compiled = False)
    assert _compile_hooked_block_inners(_fake_dit([block])) == 0
    assert hook.fn_ref.original_forward is orig


def test_arming_skips_partial_captured_inner(monkeypatch):
    # A stacked hook chain (e.g. group offload) captures a functools.partial, not the
    # plain bound method; arming would compile the wrong layer of the chain.
    _stub_torch_compile(monkeypatch)
    block, hook, orig = _hooked_block(bound = False)
    assert _compile_hooked_block_inners(_fake_dit([block])) == 0
    assert hook.fn_ref.original_forward is orig


def test_arming_covers_every_cache_hook_family(monkeypatch):
    # FBCache is the image cache today, but the hook-name table already covers the
    # MagCache layout too (same fn_ref shape), so a future mode arms for free.
    _stub_torch_compile(monkeypatch)
    names = (
        "mag_cache_leader_block_hook",
        "mag_cache_block_hook",
        "fbc_leader_block_hook",
        "fbc_block_hook",
    )
    blocks = [_hooked_block(hook_name = n)[0] for n in names]
    assert _compile_hooked_block_inners(_fake_dit(blocks)) == len(names)


def test_restore_puts_the_exact_original_back(monkeypatch):
    _stub_torch_compile(monkeypatch)
    block, hook, orig = _hooked_block()
    dit = _fake_dit([block])
    _compile_hooked_block_inners(dit)
    _restore_hooked_block_inners(dit)
    assert hook.fn_ref.original_forward is orig
    assert hook._unsloth_orig_inner is None


def test_restore_tolerates_fakes_without_modules():
    _restore_hooked_block_inners(_MixinTransformer())  # no .modules(): no-op


def test_apply_step_cache_arms_compiled_blocks_on_toggle(monkeypatch):
    # The generation-time toggle engages the cache AFTER the load already compiled the
    # blocks; apply_step_cache must arm the fresh hooks itself.
    _stub_diffusers(monkeypatch)
    _stub_torch_compile(monkeypatch)
    block, hook, orig = _hooked_block()

    class _T(_MixinTransformer):
        def modules(self):
            return [block]

    t = _T()
    engaged = apply_step_cache(_pipe(t), mode = "fbcache")
    assert engaged == TC_FBCACHE
    assert hook.fn_ref.original_forward is not orig
    assert hook._unsloth_orig_inner is orig


def test_toggle_disable_restores_inners_before_disable(monkeypatch):
    # remove_hook splices fn_ref.original_forward back into module.forward, so the
    # compiled wrapper must be swapped out BEFORE disable_cache runs.
    _stub_diffusers(monkeypatch)
    order = []

    class _T(_ToggleTransformer):
        def disable_cache(self):
            super().disable_cache()
            order.append("disable")

        def modules(self):
            order.append("restore-walk")
            return []

    t = _T()
    maybe_toggle_step_cache(_pipe(t), steps = 28)
    mode = maybe_toggle_step_cache(_pipe(t), steps = 8)
    assert mode is None and t.disables == 1
    assert order[-2:] == ["restore-walk", "disable"]


def test_enable_failure_restores_inners_before_partial_disable(monkeypatch):
    # enable_cache can fail after hooking (and arming) some blocks; the partial-hook
    # cleanup must un-arm them before disable_cache splices original_forward back.
    _stub_diffusers(monkeypatch)
    order = []

    class _T(_ToggleTransformer):
        def enable_cache(self, config):
            raise RuntimeError("block signature not recognised")

        def disable_cache(self):
            super().disable_cache()
            order.append("disable")

        def modules(self):
            order.append("restore-walk")
            return []

    t = _T()
    assert apply_step_cache(_pipe(t), mode = "fbcache") is None
    assert order == ["restore-walk", "disable"]


# ── stale child-registry cache invalidation (mid-session enable) ────────────────────


def test_enable_invalidates_stale_child_registry_cache(monkeypatch):
    # diffusers 0.39 caches the child-registry list on first cache_context use; an
    # UNCACHED generation already populates it (empty), so a later toggle-time
    # enable_cache would install hooks the context never reaches ("No context is set").
    _stub_diffusers(monkeypatch)
    t = _MixinTransformer()
    t._diffusers_hook = types.SimpleNamespace(_child_registries_cache = ["stale"])
    assert apply_step_cache(_pipe(t), mode = "fbcache") == TC_FBCACHE
    assert t._diffusers_hook._child_registries_cache is None


def test_invalidate_child_registry_cache_tolerates_absence():
    _invalidate_child_registry_cache(types.SimpleNamespace())  # no registry: no-op
    reg = types.SimpleNamespace(_child_registries_cache = None)
    _invalidate_child_registry_cache(types.SimpleNamespace(_diffusers_hook = reg))
    assert reg._child_registries_cache is None