[Imports] Fix many import bugs and make sure that doc builder CI test works correctly (#5176)

* [Doc builder] Ensure slow import for doc builder

* Apply suggestions from code review

* env for doc builder

* fix more

* [Diffusers] Set import to slow as env variable

* fix docs

* fix docs

* Apply suggestions from code review

* Apply suggestions from code review

* fix docs

* fix docs

src/diffusers/pipelines/text_to_video_synthesis/__init__.py

 from typing import TYPE_CHECKING
 
 from ...utils import (
+    DIFFUSERS_SLOW_IMPORT,
     OptionalDependencyNotAvailable,
     _LazyModule,
     get_objects_from_module,
@@ -26,7 +27,7 @@ else:
     _import_structure["pipeline_text_to_video_zero"] = ["TextToVideoZeroPipeline"]
 
 
-if TYPE_CHECKING:
+if TYPE_CHECKING or DIFFUSERS_SLOW_IMPORT:
     try:
         if not (is_transformers_available() and is_torch_available()):
             raise OptionalDependencyNotAvailable()

src/diffusers/pipelines/unclip/__init__.py

 from typing import TYPE_CHECKING
 
 from ...utils import (
+    DIFFUSERS_SLOW_IMPORT,
     OptionalDependencyNotAvailable,
     _LazyModule,
     is_torch_available,
@@ -27,7 +28,7 @@ else:
     _import_structure["text_proj"] = ["UnCLIPTextProjModel"]
 
 
-if TYPE_CHECKING:
+if TYPE_CHECKING or DIFFUSERS_SLOW_IMPORT:
     try:
         if not (is_transformers_available() and is_torch_available() and is_transformers_version(">=", "4.25.0")):
             raise OptionalDependencyNotAvailable()

src/diffusers/pipelines/unidiffuser/__init__.py

 from typing import TYPE_CHECKING
 
 from ...utils import (
+    DIFFUSERS_SLOW_IMPORT,
     OptionalDependencyNotAvailable,
     _LazyModule,
     is_torch_available,
@@ -29,7 +30,7 @@ else:
     _import_structure["pipeline_unidiffuser"] = ["ImageTextPipelineOutput", "UniDiffuserPipeline"]
 
 
-if TYPE_CHECKING:
+if TYPE_CHECKING or DIFFUSERS_SLOW_IMPORT:
     try:
         if not (is_transformers_available() and is_torch_available()):
             raise OptionalDependencyNotAvailable()

src/diffusers/pipelines/versatile_diffusion/__init__.py

 from typing import TYPE_CHECKING
 
 from ...utils import (
+    DIFFUSERS_SLOW_IMPORT,
     OptionalDependencyNotAvailable,
     _LazyModule,
     is_torch_available,
@@ -39,7 +40,7 @@ else:
     _import_structure["pipeline_versatile_diffusion_text_to_image"] = ["VersatileDiffusionTextToImagePipeline"]
 
 
-if TYPE_CHECKING:
+if TYPE_CHECKING or DIFFUSERS_SLOW_IMPORT:
     try:
         if not (is_transformers_available() and is_torch_available() and is_transformers_version(">=", "4.25.0")):
             raise OptionalDependencyNotAvailable()

src/diffusers/pipelines/vq_diffusion/__init__.py

 from typing import TYPE_CHECKING
 
 from ...utils import (
+    DIFFUSERS_SLOW_IMPORT,
     OptionalDependencyNotAvailable,
     _LazyModule,
     is_torch_available,
@@ -30,7 +31,7 @@ else:
     _import_structure["pipeline_vq_diffusion"] = ["LearnedClassifierFreeSamplingEmbeddings", "VQDiffusionPipeline"]
 
 
-if TYPE_CHECKING:
+if TYPE_CHECKING or DIFFUSERS_SLOW_IMPORT:
     try:
         if not (is_transformers_available() and is_torch_available()):
             raise OptionalDependencyNotAvailable()

src/diffusers/pipelines/wuerstchen/__init__.py

 from typing import TYPE_CHECKING
 
 from ...utils import (
+    DIFFUSERS_SLOW_IMPORT,
     OptionalDependencyNotAvailable,
     _LazyModule,
     get_objects_from_module,
@@ -28,7 +29,7 @@ else:
     _import_structure["pipeline_wuerstchen_prior"] = ["DEFAULT_STAGE_C_TIMESTEPS", "WuerstchenPriorPipeline"]
 
 
-if TYPE_CHECKING:
+if TYPE_CHECKING or DIFFUSERS_SLOW_IMPORT:
     try:
         if not (is_transformers_available() and is_torch_available()):
             raise OptionalDependencyNotAvailable()

src/diffusers/schedulers/__init__.py

@@ -15,6 +15,7 @@
 from typing import TYPE_CHECKING
 
 from ..utils import (
+    DIFFUSERS_SLOW_IMPORT,
     OptionalDependencyNotAvailable,
     _LazyModule,
     get_objects_from_module,
@@ -111,7 +112,7 @@ except OptionalDependencyNotAvailable:
 else:
     _import_structure["scheduling_dpmsolver_sde"] = ["DPMSolverSDEScheduler"]
 
-if TYPE_CHECKING:
+if TYPE_CHECKING or DIFFUSERS_SLOW_IMPORT:
     from ..utils import (
         OptionalDependencyNotAvailable,
         is_flax_available,
@@ -162,6 +163,7 @@ if TYPE_CHECKING:
         from .scheduling_ddim_flax import FlaxDDIMScheduler
         from .scheduling_ddpm_flax import FlaxDDPMScheduler
         from .scheduling_dpmsolver_multistep_flax import FlaxDPMSolverMultistepScheduler
+        from .scheduling_euler_discrete_flax import FlaxEulerDiscreteScheduler
         from .scheduling_karras_ve_flax import FlaxKarrasVeScheduler
         from .scheduling_lms_discrete_flax import FlaxLMSDiscreteScheduler
         from .scheduling_pndm_flax import FlaxPNDMScheduler

src/diffusers/utils/__init__.py

@@ -45,6 +45,7 @@ from .hub_utils import (
 )
 from .import_utils import (
     BACKENDS_MAPPING,
+    DIFFUSERS_SLOW_IMPORT,
     ENV_VARS_TRUE_AND_AUTO_VALUES,
     ENV_VARS_TRUE_VALUES,
     USE_JAX,

src/diffusers/utils/import_utils.py

@@ -46,6 +46,8 @@ USE_TF = os.environ.get("USE_TF", "AUTO").upper()
 USE_TORCH = os.environ.get("USE_TORCH", "AUTO").upper()
 USE_JAX = os.environ.get("USE_FLAX", "AUTO").upper()
 USE_SAFETENSORS = os.environ.get("USE_SAFETENSORS", "AUTO").upper()
+DIFFUSERS_SLOW_IMPORT = os.environ.get("DIFFUSERS_SLOW_IMPORT", "FALSE").upper()
+DIFFUSERS_SLOW_IMPORT = DIFFUSERS_SLOW_IMPORT in ENV_VARS_TRUE_VALUES
 
 STR_OPERATION_TO_FUNC = {">": op.gt, ">=": op.ge, "==": op.eq, "!=": op.ne, "<=": op.le, "<": op.lt}
 

src/diffusers/utils/peft_utils.py

@@ -17,11 +17,10 @@ PEFT utilities: Utilities related to peft library
 from .import_utils import is_torch_available
 
 
-if is_torch_available():
+def recurse_remove_peft_layers(model):
+    if is_torch_available():
         import torch
 
-
-def recurse_remove_peft_layers(model):
     r"""
     Recursively replace all instances of `LoraLayer` with corresponding new layers in `model`.
     """