From f8cac4acf95ae91f26edb1ce32dbd36558964710 Mon Sep 17 00:00:00 2001
From: Damien Picard <dam.pic@free.fr>
Date: Mon, 29 Jan 2024 22:04:52 +0100
Subject: [PATCH] Node Wrangler: Add more specific poll methods

Since it is useful to set a poll message to tell the user why an
operator cannot be called, decompose poll conditions into basic
functions and make every operator use them.

- Make the basic nw_check report issues.
- Add functions to check that:
  - the node tree is not empty,
  - a node is active,
  - a specified number of nodes are selected,
  - the active node is of a specific type,
  - it has visible outputs,
  - there is a viewer image.
- These functions report the issue to the poll message otherwise.
- Go through operators and add or update poll methods using those
  various functions.
- In a few operators, remove obsolete error reports that are now
  caught at the poll stage.

Fixes a few issues:
- PreviewNode would not work immediately when the active node was a
  material or world output.
- ReloadImages needed an active node.
---
 node_wrangler/__init__.py    |   2 +-
 node_wrangler/interface.py   |  77 +++++++++++--------
 node_wrangler/operators.py   | 177 ++++++++++++++++++++++++++-----------------
 node_wrangler/utils/nodes.py |  89 +++++++++++++++++++---
 4 files changed, 231 insertions(+), 114 deletions(-)

diff --git a/node_wrangler/__init__.py b/node_wrangler/__init__.py
index 13a3178b..b1baa24c 100644
--- a/node_wrangler/__init__.py
+++ b/node_wrangler/__init__.py
@@ -5,7 +5,7 @@
 bl_info = {
     "name": "Node Wrangler",
     "author": "Bartek Skorupa, Greg Zaal, Sebastian Koenig, Christian Brinkmann, Florian Meyer",
-    "version": (3, 51),
+    "version": (3, 52),
     "blender": (4, 0, 0),
     "location": "Node Editor Toolbar or Shift-W",
     "description": "Various tools to enhance and speed up node-based workflow",
diff --git a/node_wrangler/interface.py b/node_wrangler/interface.py
index e28e947a..d0131d28 100644
--- a/node_wrangler/interface.py
+++ b/node_wrangler/interface.py
@@ -10,7 +10,7 @@ from nodeitems_utils import node_categories_iter, NodeItemCustom
 from . import operators
 
 from .utils.constants import blend_types, geo_combine_operations, operations
-from .utils.nodes import get_nodes_links, nw_check, NWBase
+from .utils.nodes import get_nodes_links, NWBaseMenu
 
 
 def drawlayout(context, layout, mode='non-panel'):
@@ -71,7 +71,7 @@ def drawlayout(context, layout, mode='non-panel'):
     col.separator()
 
 
-class NodeWranglerPanel(Panel, NWBase):
+class NodeWranglerPanel(Panel, NWBaseMenu):
     bl_idname = "NODE_PT_nw_node_wrangler"
     bl_space_type = 'NODE_EDITOR'
     bl_label = "Node Wrangler"
@@ -92,7 +92,7 @@ class NodeWranglerPanel(Panel, NWBase):
 #
 #  M E N U S
 #
-class NodeWranglerMenu(Menu, NWBase):
+class NodeWranglerMenu(Menu, NWBaseMenu):
     bl_idname = "NODE_MT_nw_node_wrangler_menu"
     bl_label = "Node Wrangler"
 
@@ -101,7 +101,7 @@ class NodeWranglerMenu(Menu, NWBase):
         drawlayout(context, self.layout)
 
 
-class NWMergeNodesMenu(Menu, NWBase):
+class NWMergeNodesMenu(Menu, NWBaseMenu):
     bl_idname = "NODE_MT_nw_merge_nodes_menu"
     bl_label = "Merge Selected Nodes"
 
@@ -124,7 +124,7 @@ class NWMergeNodesMenu(Menu, NWBase):
             props.merge_type = 'ALPHAOVER'
 
 
-class NWMergeGeometryMenu(Menu, NWBase):
+class NWMergeGeometryMenu(Menu, NWBaseMenu):
     bl_idname = "NODE_MT_nw_merge_geometry_menu"
     bl_label = "Merge Selected Nodes using Geometry Nodes"
 
@@ -137,7 +137,7 @@ class NWMergeGeometryMenu(Menu, NWBase):
             props.merge_type = 'GEOMETRY'
 
 
-class NWMergeShadersMenu(Menu, NWBase):
+class NWMergeShadersMenu(Menu, NWBaseMenu):
     bl_idname = "NODE_MT_nw_merge_shaders_menu"
     bl_label = "Merge Selected Nodes using Shaders"
 
@@ -150,7 +150,7 @@ class NWMergeShadersMenu(Menu, NWBase):
             props.merge_type = 'SHADER'
 
 
-class NWMergeMixMenu(Menu, NWBase):
+class NWMergeMixMenu(Menu, NWBaseMenu):
     bl_idname = "NODE_MT_nw_merge_mix_menu"
     bl_label = "Merge Selected Nodes using Mix"
 
@@ -162,7 +162,7 @@ class NWMergeMixMenu(Menu, NWBase):
             props.merge_type = 'MIX'
 
 
-class NWConnectionListOutputs(Menu, NWBase):
+class NWConnectionListOutputs(Menu, NWBaseMenu):
     bl_idname = "NODE_MT_nw_connection_list_out"
     bl_label = "From:"
 
@@ -180,7 +180,7 @@ class NWConnectionListOutputs(Menu, NWBase):
                     icon="RADIOBUT_OFF").from_socket = index
 
 
-class NWConnectionListInputs(Menu, NWBase):
+class NWConnectionListInputs(Menu, NWBaseMenu):
     bl_idname = "NODE_MT_nw_connection_list_in"
     bl_label = "To:"
 
@@ -201,7 +201,7 @@ class NWConnectionListInputs(Menu, NWBase):
                 op.to_socket = index
 
 
-class NWMergeMathMenu(Menu, NWBase):
+class NWMergeMathMenu(Menu, NWBaseMenu):
     bl_idname = "NODE_MT_nw_merge_math_menu"
     bl_label = "Merge Selected Nodes using Math"
 
@@ -213,7 +213,7 @@ class NWMergeMathMenu(Menu, NWBase):
             props.merge_type = 'MATH'
 
 
-class NWBatchChangeNodesMenu(Menu, NWBase):
+class NWBatchChangeNodesMenu(Menu, NWBaseMenu):
     bl_idname = "NODE_MT_nw_batch_change_nodes_menu"
     bl_label = "Batch Change Selected Nodes"
 
@@ -223,7 +223,7 @@ class NWBatchChangeNodesMenu(Menu, NWBase):
         layout.menu(NWBatchChangeOperationMenu.bl_idname)
 
 
-class NWBatchChangeBlendTypeMenu(Menu, NWBase):
+class NWBatchChangeBlendTypeMenu(Menu, NWBaseMenu):
     bl_idname = "NODE_MT_nw_batch_change_blend_type_menu"
     bl_label = "Batch Change Blend Type"
 
@@ -235,7 +235,7 @@ class NWBatchChangeBlendTypeMenu(Menu, NWBase):
             props.operation = 'CURRENT'
 
 
-class NWBatchChangeOperationMenu(Menu, NWBase):
+class NWBatchChangeOperationMenu(Menu, NWBaseMenu):
     bl_idname = "NODE_MT_nw_batch_change_operation_menu"
     bl_label = "Batch Change Math Operation"
 
@@ -247,7 +247,7 @@ class NWBatchChangeOperationMenu(Menu, NWBase):
             props.operation = type
 
 
-class NWCopyToSelectedMenu(Menu, NWBase):
+class NWCopyToSelectedMenu(Menu, NWBaseMenu):
     bl_idname = "NODE_MT_nw_copy_node_properties_menu"
     bl_label = "Copy to Selected"
 
@@ -257,7 +257,7 @@ class NWCopyToSelectedMenu(Menu, NWBase):
         layout.menu(NWCopyLabelMenu.bl_idname)
 
 
-class NWCopyLabelMenu(Menu, NWBase):
+class NWCopyLabelMenu(Menu, NWBaseMenu):
     bl_idname = "NODE_MT_nw_copy_label_menu"
     bl_label = "Copy Label"
 
@@ -268,7 +268,7 @@ class NWCopyLabelMenu(Menu, NWBase):
         layout.operator(operators.NWCopyLabel.bl_idname, text="from Linked Output's Name").option = 'FROM_SOCKET'
 
 
-class NWAddReroutesMenu(Menu, NWBase):
+class NWAddReroutesMenu(Menu, NWBaseMenu):
     bl_idname = "NODE_MT_nw_add_reroutes_menu"
     bl_label = "Add Reroutes"
     bl_description = "Add Reroute Nodes to Selected Nodes' Outputs"
@@ -280,7 +280,7 @@ class NWAddReroutesMenu(Menu, NWBase):
         layout.operator(operators.NWAddReroutes.bl_idname, text="to Linked Outputs").option = 'LINKED'
 
 
-class NWLinkActiveToSelectedMenu(Menu, NWBase):
+class NWLinkActiveToSelectedMenu(Menu, NWBaseMenu):
     bl_idname = "NODE_MT_nw_link_active_to_selected_menu"
     bl_label = "Link Active to Selected"
 
@@ -291,7 +291,7 @@ class NWLinkActiveToSelectedMenu(Menu, NWBase):
         layout.menu(NWLinkUseOutputsNamesMenu.bl_idname)
 
 
-class NWLinkStandardMenu(Menu, NWBase):
+class NWLinkStandardMenu(Menu, NWBaseMenu):
     bl_idname = "NODE_MT_nw_link_standard_menu"
     bl_label = "To All Selected"
 
@@ -307,7 +307,7 @@ class NWLinkStandardMenu(Menu, NWBase):
         props.use_outputs_names = False
 
 
-class NWLinkUseNodeNameMenu(Menu, NWBase):
+class NWLinkUseNodeNameMenu(Menu, NWBaseMenu):
     bl_idname = "NODE_MT_nw_link_use_node_name_menu"
     bl_label = "Use Node Name/Label"
 
@@ -323,7 +323,7 @@ class NWLinkUseNodeNameMenu(Menu, NWBase):
         props.use_outputs_names = False
 
 
-class NWLinkUseOutputsNamesMenu(Menu, NWBase):
+class NWLinkUseOutputsNamesMenu(Menu, NWBaseMenu):
     bl_idname = "NODE_MT_nw_link_use_outputs_names_menu"
     bl_label = "Use Outputs Names"
 
@@ -345,7 +345,11 @@ class NWAttributeMenu(bpy.types.Menu):
 
     @classmethod
     def poll(cls, context):
-        return nw_check(context) and context.space_data.tree_type == 'ShaderNodeTree'
+        space = context.space_data
+        return (space.type == 'NODE_EDITOR'
+                and space.node_tree is not None
+                and space.node_tree.library is None
+                and space.tree_type == 'ShaderNodeTree')
 
     def draw(self, context):
         l = self.layout
@@ -372,7 +376,7 @@ class NWAttributeMenu(bpy.types.Menu):
             l.label(text="No attributes on objects with this material")
 
 
-class NWSwitchNodeTypeMenu(Menu, NWBase):
+class NWSwitchNodeTypeMenu(Menu, NWBaseMenu):
     bl_idname = "NODE_MT_nw_switch_node_type_menu"
     bl_label = "Switch Type to..."
 
@@ -411,8 +415,11 @@ def bgreset_menu_func(self, context):
 
 
 def save_viewer_menu_func(self, context):
-    if (nw_check(context)
-            and context.space_data.tree_type == 'CompositorNodeTree'
+    space = context.space_data
+    if (space.type == 'NODE_EDITOR'
+            and space.node_tree is not None
+            and space.node_tree.library is None
+            and space.tree_type == 'CompositorNodeTree'
             and context.scene.node_tree.nodes.active
             and context.scene.node_tree.nodes.active.type == "VIEWER"):
         self.layout.operator(operators.NWSaveViewer.bl_idname, icon='FILE_IMAGE')
@@ -421,18 +428,22 @@ def save_viewer_menu_func(self, context):
 def reset_nodes_button(self, context):
     node_active = context.active_node
     node_selected = context.selected_nodes
-    node_ignore = ["FRAME", "REROUTE", "GROUP"]
 
-    # Check if active node is in the selection and respective type
-    if (len(node_selected) == 1) and node_active and node_active.select and node_active.type not in node_ignore:
-        row = self.layout.row()
-        row.operator(operators.NWResetNodes.bl_idname, text="Reset Node", icon="FILE_REFRESH")
-        self.layout.separator()
+    # Check if active node is in the selection, ignore some node types
+    if (len(node_selected) != 1
+            or node_active is None
+            or not node_active.select
+            or node_active.type in {"REROUTE", "GROUP"}):
+        return
+
+    row = self.layout.row()
 
-    elif (len(node_selected) == 1) and node_active and node_active.select and node_active.type == "FRAME":
-        row = self.layout.row()
+    if node_active.type == "FRAME":
         row.operator(operators.NWResetNodes.bl_idname, text="Reset Nodes in Frame", icon="FILE_REFRESH")
-        self.layout.separator()
+    else:
+        row.operator(operators.NWResetNodes.bl_idname, text="Reset Node", icon="FILE_REFRESH")
+
+    self.layout.separator()
 
 
 classes = (
diff --git a/node_wrangler/operators.py b/node_wrangler/operators.py
index 9de22a07..d719925a 100644
--- a/node_wrangler/operators.py
+++ b/node_wrangler/operators.py
@@ -29,7 +29,9 @@ from .utils.draw import draw_callback_nodeoutline
 from .utils.paths import match_files_to_socket_names, split_into_components
 from .utils.nodes import (node_mid_pt, autolink, node_at_pos, get_nodes_links, is_viewer_socket, is_viewer_link,
                           get_group_output_node, get_output_location, force_update, get_internal_socket, nw_check,
-                          nw_check_space_type, NWBase, get_first_enabled_output, is_visible_socket, viewer_socket_name)
+                          nw_check_not_empty, nw_check_selected, nw_check_active, nw_check_space_type,
+                          nw_check_node_type, nw_check_visible_outputs, nw_check_viewer_node, NWBase,
+                          get_first_enabled_output, is_visible_socket, viewer_socket_name)
 
 class NWLazyMix(Operator, NWBase):
     """Add a Mix RGB/Shader node by interactively drawing lines between nodes"""
@@ -37,6 +39,10 @@ class NWLazyMix(Operator, NWBase):
     bl_label = "Mix Nodes"
     bl_options = {'REGISTER', 'UNDO'}
 
+    @classmethod
+    def poll(cls, context):
+        return nw_check(cls, context) and nw_check_not_empty(cls, context)
+
     def modal(self, context, event):
         context.area.tag_redraw()
         nodes, links = get_nodes_links(context)
@@ -115,6 +121,10 @@ class NWLazyConnect(Operator, NWBase):
     bl_options = {'REGISTER', 'UNDO'}
     with_menu: BoolProperty()
 
+    @classmethod
+    def poll(cls, context):
+        return nw_check(cls, context) and nw_check_not_empty(cls, context)
+
     def modal(self, context, event):
         context.area.tag_redraw()
         nodes, links = get_nodes_links(context)
@@ -244,10 +254,10 @@ class NWDeleteUnused(Operator, NWBase):
     @classmethod
     def poll(cls, context):
         """Disabled for custom nodes as we do not know which nodes are supported."""
-        return (nw_check(context)
-                and nw_check_space_type(cls, context, 'ShaderNodeTree', 'CompositorNodeTree',
-                                        'TextureNodeTree', 'GeometryNodeTree')
-                and context.space_data.node_tree.nodes)
+        return (nw_check(cls, context)
+                and nw_check_not_empty(cls, context)
+                and nw_check_space_type(cls, context, {'ShaderNodeTree', 'CompositorNodeTree',
+                                        'TextureNodeTree', 'GeometryNodeTree'}))
 
     def execute(self, context):
         nodes, links = get_nodes_links(context)
@@ -334,7 +344,7 @@ class NWSwapLinks(Operator, NWBase):
 
     @classmethod
     def poll(cls, context):
-        return nw_check(context) and context.selected_nodes and len(context.selected_nodes) <= 2
+        return nw_check(cls, context) and nw_check_selected(cls, context, max=2)
 
     def execute(self, context):
         nodes, links = get_nodes_links(context)
@@ -448,8 +458,7 @@ class NWResetBG(Operator, NWBase):
 
     @classmethod
     def poll(cls, context):
-        return (nw_check(context)
-                and nw_check_space_type(cls, context, 'CompositorNodeTree'))
+        return nw_check(cls, context) and nw_check_space_type(cls, context, {'CompositorNodeTree'})
 
     def execute(self, context):
         context.space_data.backdrop_zoom = 1
@@ -468,8 +477,7 @@ class NWAddAttrNode(Operator, NWBase):
 
     @classmethod
     def poll(cls, context):
-        return (nw_check(context)
-                and nw_check_space_type(cls, context, 'ShaderNodeTree'))
+        return nw_check(cls, context) and nw_check_space_type(cls, context, {'ShaderNodeTree'})
 
     def execute(self, context):
         bpy.ops.node.add_node('INVOKE_DEFAULT', use_transform=True, type="ShaderNodeAttribute")
@@ -495,10 +503,8 @@ class NWPreviewNode(Operator, NWBase):
     @classmethod
     def poll(cls, context):
         """Already implemented natively for compositing nodes."""
-        return (nw_check(context)
-                and nw_check_space_type(cls, context, 'ShaderNodeTree', 'GeometryNodeTree')
-                and (not context.active_node
-                     or context.active_node.type not in {"OUTPUT_MATERIAL", "OUTPUT_WORLD"}))
+        return (nw_check(cls, context)
+                and nw_check_space_type(cls, context, {'ShaderNodeTree', 'GeometryNodeTree'}))
 
     @staticmethod
     def get_output_sockets(node_tree):
@@ -845,11 +851,10 @@ class NWReloadImages(Operator):
 
     @classmethod
     def poll(cls, context):
-        return (nw_check(context)
-                and nw_check_space_type(cls, context, 'ShaderNodeTree', 'CompositorNodeTree',
-                                        'TextureNodeTree', 'GeometryNodeTree')
-                and context.active_node is not None
-                and any(is_visible_socket(out) for out in context.active_node.outputs))
+        """Disabled for custom nodes."""
+        return (nw_check(cls, context)
+                and nw_check_space_type(cls, context, {'ShaderNodeTree', 'CompositorNodeTree',
+                                        'TextureNodeTree', 'GeometryNodeTree'}))
 
     def execute(self, context):
         nodes, links = get_nodes_links(context)
@@ -975,9 +980,10 @@ class NWMergeNodes(Operator, NWBase):
 
     @classmethod
     def poll(cls, context):
-        return (nw_check(context)
-                and nw_check_space_type(cls, context, 'ShaderNodeTree', 'CompositorNodeTree',
-                                        'TextureNodeTree', 'GeometryNodeTree'))
+        return (nw_check(cls, context)
+                and nw_check_space_type(cls, context, {'ShaderNodeTree', 'CompositorNodeTree',
+                                        'TextureNodeTree', 'GeometryNodeTree'})
+                and nw_check_selected(cls, context))
 
     def execute(self, context):
         settings = context.preferences.addons[__package__].preferences
@@ -1298,9 +1304,10 @@ class NWBatchChangeNodes(Operator, NWBase):
 
     @classmethod
     def poll(cls, context):
-        return (nw_check(context)
-                and nw_check_space_type(cls, context, 'ShaderNodeTree', 'CompositorNodeTree',
-                                        'TextureNodeTree', 'GeometryNodeTree'))
+        return (nw_check(cls, context)
+                and nw_check_space_type(cls, context, {'ShaderNodeTree', 'CompositorNodeTree',
+                                        'TextureNodeTree', 'GeometryNodeTree'})
+                and nw_check_selected(cls, context))
 
     def execute(self, context):
         blend_type = self.blend_type
@@ -1354,6 +1361,10 @@ class NWChangeMixFactor(Operator, NWBase):
     bl_description = "Change Factors of Mix Nodes and Mix Shader Nodes"
     bl_options = {'REGISTER', 'UNDO'}
 
+    @classmethod
+    def poll(cls, context):
+        return nw_check(cls, context) and nw_check_selected(cls, context)
+
     # option: Change factor.
     # If option is 1.0 or 0.0 - set to 1.0 or 0.0
     # Else - change factor by option value.
@@ -1387,24 +1398,15 @@ class NWCopySettings(Operator, NWBase):
 
     @classmethod
     def poll(cls, context):
-        return (nw_check(context)
-                and context.active_node is not None
-                and context.active_node.type != 'FRAME')
+        return (nw_check(cls, context)
+                and nw_check_active(cls, context)
+                and nw_check_selected(cls, context, min=2)
+                and nw_check_node_type(cls, context, 'FRAME', invert=True))
 
     def execute(self, context):
         node_active = context.active_node
         node_selected = context.selected_nodes
-
-        # Error handling
-        if not (len(node_selected) > 1):
-            self.report({'ERROR'}, "2 nodes must be selected at least")
-            return {'CANCELLED'}
-
-        # Check if active node is in the selection
         selected_node_names = [n.name for n in node_selected]
-        if node_active.name not in selected_node_names:
-            self.report({'ERROR'}, "No active node")
-            return {'CANCELLED'}
 
         # Get nodes in selection by type
         valid_nodes = [n for n in node_selected if n.type == node_active.type]
@@ -1498,6 +1500,7 @@ class NWCopyLabel(Operator, NWBase):
     bl_idname = "node.nw_copy_label"
     bl_label = "Copy Label"
     bl_options = {'REGISTER', 'UNDO'}
+    bl_description = "Copy label from active to selected nodes"
 
     option: EnumProperty(
         name="option",
@@ -1509,6 +1512,10 @@ class NWCopyLabel(Operator, NWBase):
         )
     )
 
+    @classmethod
+    def poll(cls, context):
+        return nw_check(cls, context) and nw_check_selected(cls, context, min=2)
+
     def execute(self, context):
         nodes, links = get_nodes_links(context)
         option = self.option
@@ -1542,9 +1549,14 @@ class NWClearLabel(Operator, NWBase):
     bl_idname = "node.nw_clear_label"
     bl_label = "Clear Label"
     bl_options = {'REGISTER', 'UNDO'}
+    bl_description = "Clear labels on selected nodes"
 
     option: BoolProperty()
 
+    @classmethod
+    def poll(cls, context):
+        return nw_check(cls, context) and nw_check_selected(cls, context)
+
     def execute(self, context):
         nodes, links = get_nodes_links(context)
         for node in [n for n in nodes if n.select]:
@@ -1560,7 +1572,7 @@ class NWClearLabel(Operator, NWBase):
 
 
 class NWModifyLabels(Operator, NWBase):
-    """Modify Labels of all selected nodes"""
+    """Modify labels of all selected nodes"""
     bl_idname = "node.nw_modify_labels"
     bl_label = "Modify Labels"
     bl_options = {'REGISTER', 'UNDO'}
@@ -1578,6 +1590,10 @@ class NWModifyLabels(Operator, NWBase):
         name="Replace with"
     )
 
+    @classmethod
+    def poll(cls, context):
+        return nw_check(cls, context) and nw_check_selected(cls, context)
+
     def execute(self, context):
         nodes, links = get_nodes_links(context)
         for node in [n for n in nodes if n.select]:
@@ -1605,8 +1621,9 @@ class NWAddTextureSetup(Operator, NWBase):
 
     @classmethod
     def poll(cls, context):
-        return (nw_check(context)
-                and nw_check_space_type(cls, context, 'ShaderNodeTree'))
+        return (nw_check(cls, context)
+                and nw_check_space_type(cls, context, {'ShaderNodeTree'})
+                and nw_check_selected(cls, context))
 
     def execute(self, context):
         nodes, links = get_nodes_links(context)
@@ -1708,23 +1725,22 @@ class NWAddPrincipledSetup(Operator, NWBase, ImportHelper):
 
     @classmethod
     def poll(cls, context):
-        return (nw_check(context)
-                and nw_check_space_type(cls, context, 'ShaderNodeTree'))
+        return (nw_check(cls, context)
+                and nw_check_active(cls, context)
+                and nw_check_space_type(cls, context, {'ShaderNodeTree'})
+                and nw_check_node_type(cls, context, 'BSDF_PRINCIPLED'))
 
     def execute(self, context):
         # Check if everything is ok
         if not self.directory:
-            self.report({'INFO'}, 'No Folder Selected')
+            self.report({'INFO'}, 'No folder selected')
             return {'CANCELLED'}
         if not self.files[:]:
-            self.report({'INFO'}, 'No Files Selected')
+            self.report({'INFO'}, 'No files selected')
             return {'CANCELLED'}
 
         nodes, links = get_nodes_links(context)
         active_node = nodes.active
-        if not (active_node and active_node.bl_idname == 'ShaderNodeBsdfPrincipled'):
-            self.report({'INFO'}, 'Select Principled BSDF')
-            return {'CANCELLED'}
 
         # Filter textures names for texturetypes in filenames
         # [Socket Name, [abbreviations and keyword list], Filename placeholder]
@@ -1982,6 +1998,10 @@ class NWAddReroutes(Operator, NWBase):
         ]
     )
 
+    @classmethod
+    def poll(cls, context):
+        return nw_check(cls, context) and nw_check_selected(cls, context)
+
     def execute(self, context):
         nodes, _links = get_nodes_links(context)
         post_select = []  # Nodes to be selected after execution.
@@ -2063,9 +2083,9 @@ class NWLinkActiveToSelected(Operator, NWBase):
 
     @classmethod
     def poll(cls, context):
-        return (nw_check(context)
-                and context.active_node is not None
-                and context.active_node.select)
+        return (nw_check(cls, context)
+                and nw_check_active(cls, context)
+                and nw_check_selected(cls, context, min=2))
 
     def execute(self, context):
         nodes, links = get_nodes_links(context)
@@ -2136,6 +2156,10 @@ class NWAlignNodes(Operator, NWBase):
     bl_options = {'REGISTER', 'UNDO'}
     margin: IntProperty(name='Margin', default=50, description='The amount of space between nodes')
 
+    @classmethod
+    def poll(cls, context):
+        return nw_check(cls, context) and nw_check_not_empty(cls, context)
+
     def execute(self, context):
         nodes, links = get_nodes_links(context)
         margin = self.margin
@@ -2214,6 +2238,10 @@ class NWSelectParentChildren(Operator, NWBase):
         )
     )
 
+    @classmethod
+    def poll(cls, context):
+        return nw_check(cls, context) and nw_check_selected(cls, context)
+
     def execute(self, context):
         nodes, links = get_nodes_links(context)
         option = self.option
@@ -2238,6 +2266,10 @@ class NWDetachOutputs(Operator, NWBase):
     bl_label = "Detach Outputs"
     bl_options = {'REGISTER', 'UNDO'}
 
+    @classmethod
+    def poll(cls, context):
+        return nw_check(cls, context) and nw_check_selected(cls, context)
+
     def execute(self, context):
         nodes, links = get_nodes_links(context)
         selected = context.selected_nodes
@@ -2263,11 +2295,11 @@ class NWLinkToOutputNode(Operator):
     @classmethod
     def poll(cls, context):
         """Disabled for custom nodes as we do not know which nodes are outputs."""
-        return (nw_check(context)
-                and nw_check_space_type(cls, context, 'ShaderNodeTree', 'CompositorNodeTree',
-                                        'TextureNodeTree', 'GeometryNodeTree')
-                and context.active_node is not None
-                and any(is_visible_socket(out) for out in context.active_node.outputs))
+        return (nw_check(cls, context)
+                and nw_check_space_type(cls, context, {'ShaderNodeTree', 'CompositorNodeTree',
+                                        'TextureNodeTree', 'GeometryNodeTree'})
+                and nw_check_active(cls, context)
+                and nw_check_visible_outputs(cls, context))
 
     def execute(self, context):
         nodes, links = get_nodes_links(context)
@@ -2387,6 +2419,11 @@ class NWAddSequence(Operator, NWBase, ImportHelper):
         default=True
     )
 
+    @classmethod
+    def poll(cls, context):
+        return (nw_check(cls, context)
+                and nw_check_space_type(cls, context, {'ShaderNodeTree', 'CompositorNodeTree'}))
+
     def draw(self, context):
         layout = self.layout
         layout.alignment = 'LEFT'
@@ -2499,6 +2536,11 @@ class NWAddMultipleImages(Operator, NWBase, ImportHelper):
         options={'HIDDEN', 'SKIP_SAVE'}
     )
 
+    @classmethod
+    def poll(cls, context):
+        return (nw_check(cls, context)
+                and nw_check_space_type(cls, context, {'ShaderNodeTree', 'CompositorNodeTree'}))
+
     def execute(self, context):
         nodes, links = get_nodes_links(context)
 
@@ -2548,8 +2590,8 @@ class NWViewerFocus(bpy.types.Operator):
 
     @classmethod
     def poll(cls, context):
-        return (nw_check(context)
-                and nw_check_space_type(cls, context, 'CompositorNodeTree'))
+        return (nw_check(cls, context)
+                and nw_check_space_type(cls, context, {'CompositorNodeTree'}))
 
     def execute(self, context):
         return {'FINISHED'}
@@ -2619,12 +2661,9 @@ class NWSaveViewer(bpy.types.Operator, ExportHelper):
 
     @classmethod
     def poll(cls, context):
-        return (nw_check(context)
-                and nw_check_space_type(cls, context, 'CompositorNodeTree')
-                and any(img.source == 'VIEWER'
-                        and img.render_slots == 0
-                        for img in bpy.data.images)
-                and sum(bpy.data.images["Viewer Node"].size) > 0)  # False if not connected or connected but no image
+        return (nw_check(cls, context)
+                and nw_check_space_type(cls, context, {'CompositorNodeTree'})
+                and nw_check_viewer_node(cls))
 
     def execute(self, context):
         fp = self.filepath
@@ -2662,19 +2701,15 @@ class NWResetNodes(bpy.types.Operator):
 
     @classmethod
     def poll(cls, context):
-        space = context.space_data
-        return space.type == 'NODE_EDITOR'
+        return (nw_check(cls, context)
+                and nw_check_selected(cls, context)
+                and nw_check_active(cls, context))
 
     def execute(self, context):
         node_active = context.active_node
         node_selected = context.selected_nodes
         node_ignore = ["FRAME", "REROUTE", "GROUP", "SIMULATION_INPUT", "SIMULATION_OUTPUT"]
 
-        # Check if one node is selected at least
-        if not (len(node_selected) > 0):
-            self.report({'ERROR'}, "1 node must be selected at least")
-            return {'CANCELLED'}
-
         active_node_name = node_active.name if node_active.select else None
         valid_nodes = [n for n in node_selected if n.type not in node_ignore]
 
diff --git a/node_wrangler/utils/nodes.py b/node_wrangler/utils/nodes.py
index fd2782af..29c0046f 100644
--- a/node_wrangler/utils/nodes.py
+++ b/node_wrangler/utils/nodes.py
@@ -4,7 +4,7 @@
 
 import bpy
 from bpy_extras.node_utils import connect_sockets
-from math import hypot
+from math import hypot, inf
 
 
 def force_update(context):
@@ -200,23 +200,85 @@ def get_output_location(tree):
     return loc_x, loc_y
 
 
-def nw_check(context):
+def nw_check(cls, context):
     space = context.space_data
+    if space.type != 'NODE_EDITOR':
+        cls.poll_message_set("Current editor is not a node editor.")
+        return False
+    if space.node_tree is None:
+        cls.poll_message_set("No node tree was found in the current node editor.")
+        return False
+    if space.node_tree.library is not None:
+        cls.poll_message_set("Current node tree is linked from another .blend file.")
+        return False
+    return True
+
+
+def nw_check_not_empty(cls, context):
+    if not context.space_data.node_tree.nodes:
+        cls.poll_message_set("Current node tree does not contain any nodes.")
+        return False
+    return True
+
 
-    return (space.type == 'NODE_EDITOR'
-            and space.node_tree is not None
-            and space.node_tree.library is None)
+def nw_check_active(cls, context):
+    if context.active_node is None or not context.active_node.select:
+        cls.poll_message_set("No active node.")
+        return False
+    return True
+
+
+def nw_check_selected(cls, context, min=1, max=inf):
+    num_selected = len(context.selected_nodes)
+    if num_selected < min:
+        if min > 1:
+            cls.poll_message_set(f"At least {min} nodes must be selected.")
+        else:
+            cls.poll_message_set(f"At least {min} node must be selected.")
+        return False
+    if num_selected > max:
+        cls.poll_message_set(f"{num_selected} nodes are selected, but this operator can only work on {max}.")
+        return False
+    return True
 
 
-def nw_check_space_type(cls, context, *args):
-    if context.space_data.tree_type not in args:
-        tree_types_str = ", ".join(t.split('NodeTree')[0].lower() for t in sorted(args))
+def nw_check_space_type(cls, context, types):
+    if context.space_data.tree_type not in types:
+        tree_types_str = ", ".join(t.split('NodeTree')[0].lower() for t in sorted(types))
         cls.poll_message_set("Current node tree type not supported.\n"
                              "Should be one of " + tree_types_str + ".")
         return False
     return True
 
 
+def nw_check_node_type(cls, context, type, invert=False):
+    if invert and context.active_node.type == type:
+        cls.poll_message_set(f"Active node should be not of type {type}.")
+        return False
+    elif not invert and context.active_node.type != type:
+        cls.poll_message_set(f"Active node should be of type {type}.")
+        return False
+    return True
+
+
+def nw_check_visible_outputs(cls, context):
+    if not any(is_visible_socket(out) for out in context.active_node.outputs):
+        cls.poll_message_set("Current node has no visible outputs.")
+        return False
+    return True
+
+
+def nw_check_viewer_node(cls):
+    for img in bpy.data.images:
+        # False if not connected or connected but no image
+        if (img.source == 'VIEWER'
+                and len(img.render_slots) == 0
+                and sum(img.size) > 0):
+            return True
+    cls.poll_message_set("Viewer image not found.")
+    return False
+
+
 def get_first_enabled_output(node):
     for output in node.outputs:
         if output.enabled:
@@ -232,4 +294,13 @@ def is_visible_socket(socket):
 class NWBase:
     @classmethod
     def poll(cls, context):
-        return nw_check(context)
+        return nw_check(cls, context)
+
+
+class NWBaseMenu:
+    @classmethod
+    def poll(cls, context):
+        space = context.space_data
+        return (space.type == 'NODE_EDITOR'
+                and space.node_tree is not None
+                and space.node_tree.library is None)
-- 
2.11.4.GIT