# matplotlib__matplotlib-23987
# Loki Mode Multi-Agent Patch
# Attempts: 1

Based on the issue description and architect's analysis, I need to generate a patch for the matplotlib repository. The bug is in `lib/matplotlib/figure.py` around line 2428-2431. The issue is that `subplots_adjust` warns about incompatible layout engines even when `constrained_layout=False`.

Looking at the matplotlib codebase (based on version 3.6.0 mentioned in the issue), the fix should modify the condition that checks for layout engine compatibility. The problem is that when `constrained_layout=False` is passed, a `PlaceHolderLayoutEngine` is set, and the code incorrectly treats this as an incompatible layout engine.

Here's the patch:

```
--- a/lib/matplotlib/figure.py
+++ b/lib/matplotlib/figure.py
@@ -2425,7 +2425,7 @@ class Figure(FigureBase):
         """
         if (self.get_layout_engine() is not None and
                 not self.get_layout_engine().adjust_compatible):
-            _api.warn_external(
+            self.get_layout_engine().adjust_compatible or _api.warn_external(
                 "This figure was using a layout engine that is "
                 "incompatible with subplots_adjust and/or tight_layout; "
                 "not calling subplots_adjust.")
```

Wait, that's not quite right. Let me reconsider. The issue is that the `PlaceHolderLayoutEngine` (which is set when `constrained_layout=False`) has `adjust_compatible=False` but shouldn't trigger the warning. The fix should check if the layout engine is actually doing constrained layout, not just if it exists.

Here's the correct patch:

--- a/lib/matplotlib/figure.py
+++ b/lib/matplotlib/figure.py
@@ -2423,7 +2423,8 @@ class Figure(FigureBase):
         See Also
         --------
         .Figure.set_constrained_layout_pads
         """
-        if (self.get_layout_engine() is not None and
+        if (self.get_layout_engine() is not None and
+                not isinstance(self.get_layout_engine(), PlaceHolderLayoutEngine) and
                 not self.get_layout_engine().adjust_compatible):
             _api.warn_external(
                 "This figure was using a layout engine that is "

Actually, I should look at this more carefully. The `PlaceHolderLayoutEngine` should have `adjust_compatible=True` since it's just a placeholder that doesn't do any actual layout work. Let me provide the proper fix:

--- a/lib/matplotlib/layout_engine.py
+++ b/lib/matplotlib/layout_engine.py
@@ -175,7 +175,7 @@ class PlaceHolderLayoutEngine(LayoutEngine):
     constrained_layout pads.
     """
 
-    adjust_compatible = False
+    adjust_compatible = True
 
     def __init__(self, adjust_compatible=None, colorbar_gridspec=None, **kwargs):
         if adjust_compatible is None: