Reuse cached fixed-size widget boxes when descendant layout changes

evidence/fixed-box-source-20261007/README.md

@@ -0,0 +1,45 @@
+# Fixed native box source
+
+The native fixed/fill box resolver reads its own styles and supplied size,
+viewport and fractions. It does not measure descendants. Previously its cache
+generation still included descendant layout changes. The existing local style
+dependency owner now supplies this distinction; the existing box cache binds
+these results to the actual RenderStyles object and generation. It retains that
+object so replacement and object lifetime cannot alias an unrelated source.
+
+Intrinsic sizing, fractional width with greedy=False, custom style getters and
+custom scalar resolvers retain full layout invalidation. Native spacing and
+border inputs are required for the narrower source. Parent auto-size and parent
+lifetime remain inputs. Held mutation-box admission remains first. Width,
+viewport and fraction variants remain separate. Original extrema are restored
+on cache hits. Repeated generation fields were removed from individual keys:
+the owning cache already retires its previous generation.
+
+The complete consumers are Widget._get_box_model and
+box_depends_on_available_height; presentation release already retires the style
+dependency and box sources. Related tests now check stale results and actual
+cache lifetime instead of duplicating internal key shape. Existing Package
+analysis parsed 250 production modules without omissions.
+
+Final related controls: 34 passed in 2.63s, using this native source. Coverage
+includes descendant changes, style-source replacement, intrinsic versus fixed
+sizing, fractional greedy modes, custom Scalar/RenderStyles behavior, extrema
+restoration and held geometry. An attempted Spacing-subclass control failed at
+declaration because the actual accelerated Spacing is not subclassable; that
+invalid control was removed. Its original failure log is preserved.
+
+One original raw-driver resize App used source 623e07dd with the existing
+installed Toad/Core runtime, without changing packages. It reached width 60,
+released capture, exited zero and produced empty stderr. Final width appeared
+at 993.66ms; matching earlier installed observation was 1057.70ms. Layout counts
+were 69 versus 61. Different work and profiling overhead mean this does not
+establish a reliable latency gain. Width frames still take roughly 100ms.
+The subsequent source changes only decline non-native spacing/border inputs and
+name the already-used tuple fields; the App's native-input path is unchanged.
+
+Full App output and profiles remain at
+/home/ts/.cache/agent-scratch/native-box-source-20261007. The original fixture
+owns joined teardown; exact individual child births were not recorded. This is
+source/App acceptance, not an installed or physical speed claim. There were no
+provider calls, public inputs or package writes. Parent owns integration and
+durable delivery. Required width-dependent rewrapping and arrangement remain.

evidence/fixed-box-source-20261007/app-result.json

@@ -0,0 +1,212 @@
+{
+  "posted_ms": 706.3528039725497,
+  "frames": [
+    {
+      "ms": 111.03438097052276,
+      "width": 49,
+      "latest_requested_delta": 7
+    },
+    {
+      "ms": 230.6039429968223,
+      "width": 55,
+      "latest_requested_delta": 10
+    },
+    {
+      "ms": 345.3719209646806,
+      "width": 56,
+      "latest_requested_delta": 3
+    },
+    {
+      "ms": 463.6130550643429,
+      "width": 57,
+      "latest_requested_delta": 4
+    },
+    {
+      "ms": 578.8633780321106,
+      "width": 50,
+      "latest_requested_delta": 11
+    },
+    {
+      "ms": 689.6544770570472,
+      "width": 52,
+      "latest_requested_delta": 12
+    },
+    {
+      "ms": 877.9696580022573,
+      "width": 58,
+      "latest_requested_delta": 12
+    },
+    {
+      "ms": 993.6596649931744,
+      "width": 60,
+      "latest_requested_delta": 12
+    }
+  ],
+  "requests": [
+    [
+      0.2652329858392477,
+      1
+    ],
+    [
+      18.897947040386498,
+      2
+    ],
+    [
+      37.19545598141849,
+      3
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+    [
+      53.384628030471504,
+      4
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+    [
+      66.79921899922192,
+      5
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+    [
+      85.08271095342934,
+      6
+    ],
+    [
+      103.35164598654956,
+      7
+    ],
+    [
+      121.61416804883629,
+      8
+    ],
+    [
+      136.9925830513239,
+      9
+    ],
+    [
+      150.25750105269253,
+      10
+    ],
+    [
+      168.59511495567858,
+      11
+    ],
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+      186.9223100366071,
+      12
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+      11
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+      9
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+      8
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+    [
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+      7
+    ],
+    [
+      278.1075610546395,
+      6
+    ],
+    [
+      296.5192859992385,
+      5
+    ],
+    [
+      314.88417205400765,
+      4
+    ],
+    [
+      333.2842959789559,
+      3
+    ],
+    [
+      351.663860026747,
+      2
+    ],
+    [
+      369.79632498696446,
+      1
+    ],
+    [
+      383.2449109759182,
+      0
+    ],
+    [
+      401.6143069602549,
+      1
+    ],
+    [
+      420.00607401132584,
+      2
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+    [
+      438.38870397303253,
+      3
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+    [
+      456.77275699563324,
+      4
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+    [
+      475.2445960184559,
+      5
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+    [
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+    [
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+    [
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+      11
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+      598.4561620280147,
+      12
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+  ],
+  "messages": {
+    "MouseMove": 16,
+    "CoreEventMessage": 40,
+    "Update": 465,
+    "Layout": 69,
+    "Resize": 80,
+    "InvokeLater": 42,
+    "Callback": 96,
+    "MouseUp": 2,
+    "TextSelected": 2,
+    "MouseRelease": 1,
+    "Click": 5,
+    "Compose": 153,
+    "Mount": 140,
+    "StateChanged": 66,
+    "TableOfContentsUpdated": 53
+  },
+  "widgets": 778,
+  "error": null,
+  "final_width": 60,
+  "boundary": "completed headless display; raw Driver ingress; not terminal pixels"
+}

src/textual/_measurement.py

@@ -6,6 +6,8 @@
 from typing import TYPE_CHECKING, Callable, TypeVar
 
 from textual.css.scalar import Scalar, Unit
+from textual.css.styles import RenderStyles
+from textual.geometry import Spacing
 
 if TYPE_CHECKING:
     from textual.widget import Widget
@@ -229,10 +231,13 @@ def decorate(function: Function) -> Function:
     return decorate
 
 
-def _local_box_inputs(widget: Widget) -> tuple[bool, bool, bool]:
+def _local_box_inputs(widget: Widget) -> tuple[bool, bool, bool, bool]:
     """Resolve local scalar dependencies once per owning style generation."""
     styles = widget.styles
-    revision = styles._cache_key
+    if type(styles) is not RenderStyles:
+        return True, False, False, False
+    # Retain the actual source so replacement cannot reuse an unrelated epoch.
+    revision = id(styles), styles, styles._cache_key
     cached = widget.__dict__.get("_height_style_dependency_cache")
     if cached is not None and cached[0] == revision:
         return cached[1]
@@ -244,11 +249,11 @@ def _local_box_inputs(widget: Widget) -> tuple[bool, bool, bool]:
             # Compile this check at the style-plan boundary, not each cache hit.
             # A custom scalar resolver need not obey its nominal unit's inputs.
             if type(scalar).resolve is not Scalar.resolve:
-                result = (True, False, False)
+                result = (True, False, False, False)
                 break
             unit = scalar.percent_unit if scalar.unit is Unit.PERCENT else scalar.unit
             if unit is Unit.HEIGHT:
-                result = (True, False, False)
+                result = (True, False, False, False)
                 break
     else:
         result = (
@@ -258,6 +263,16 @@ def _local_box_inputs(widget: Widget) -> tuple[bool, bool, bool]:
             or (max_height is not None and not max_height.is_cells),
             width is not None and (width.is_auto or width.is_fraction),
             height is not None and height.is_auto,
+            all(scalar is None or type(scalar) is Scalar for scalar in (
+                width, height, min_width, max_width, min_height, max_height,
+            ))
+            and (width is None or not width.is_auto)
+            and (height is None or not height.is_auto)
+            and all(type(spacing) is Spacing and all(
+                type(cell) in (int, bool) for cell in spacing
+            ) for spacing in (styles.margin, styles.padding))
+            and all(type(edge) is tuple and type(edge[0]) is str
+                    for edge in styles.border),
         )
     widget._height_style_dependency_cache = revision, result
     return result
@@ -267,7 +282,7 @@ def box_depends_on_available_height(widget: Widget) -> bool:
     """Conservative proof for the native box resolver, including its extrema."""
     if not widget._native_box_measurement:
         return True
-    depends, content_width, content_height = _local_box_inputs(widget)
+    depends, content_width, content_height, _ = _local_box_inputs(widget)
     if depends:
         return True
     if content_width and widget._content_width_dependency.depends(widget):

src/textual/widget.py

@@ -57,7 +57,7 @@
 from textual._extrema import Extrema
 from textual._measurement import (
     CONTEXT_HEIGHT, INDEPENDENT_HEIGHT, NATIVE_WIDGET_HEIGHT, NATIVE_WIDGET_WIDTH,
-    HeightDependency, _arrangement_wrapper_uses_height,
+    HeightDependency, _arrangement_wrapper_uses_height, _local_box_inputs,
     box_depends_on_available_height, height_dependency,
 )
 from textual.message_pump import MessagePump
@@ -531,7 +531,7 @@ def __init__(
         self._repaint_regions: set[Region] = set()
 
         self._box_model_cache: LRUCache[object, tuple[BoxModel, Extrema]] = LRUCache(16)
-        self._box_model_revision: tuple[int | None, ...] | None = None
+        self._box_model_revision: tuple[object, ...] | None = None
 
         # Cache the auto content dimensions
         self._content_width_cache: tuple[object, int] = (None, 0)
@@ -1958,10 +1958,21 @@ def _get_box_model(
             # never descend through an actively changing child to size siblings.
             return box
         nodes = self.__dict__.get("_nodes")
-        revision = (self._layout_updates,
+        revision: tuple[object, ...] = (self._layout_updates,
                     nodes._updates if nodes is not None else 0)
+        if self._native_box_measurement:
+            _, content_width, _, styles_only = _local_box_inputs(self)
+            local_styles = styles_only and (greedy or not content_width)
+        else:
+            local_styles = False
+        if local_styles:
+            # Fixed/fill native boxes never query child content. Their source
+            # is the original local style owner, not descendant layout epochs.
+            styles = self.styles
+            revision = (id(styles), styles, styles._cache_key)
         cache_container, cache_height_fraction = container, height_fraction
-        if not self._box_depends_on_available_height():
+        independent_height = not self._box_depends_on_available_height()
+        if local_styles or independent_height:
             # The class/method/layout declarations proved these two inputs unused.
             # Include the immediate parent's actual auto-size inputs before idle,
             # and retire prior epochs rather than accumulating stale aliases.
@@ -1971,6 +1982,7 @@ def _get_box_model(
                 parent is not None and parent.styles.is_auto_width,
                 parent is not None and parent.styles.is_auto_height,
             )
+        if independent_height:
             cache_container = container.with_height(0)
             cache_height_fraction = Fraction(0)
         if revision != self._box_model_revision:
@@ -1989,7 +2001,6 @@ def _get_box_model(
             cache_height_fraction,
             constrain_width,
             greedy,
-            *revision,
         )
         if cached_measurement := self._box_model_cache.get(cache_key):
             # Alignment consumes the same original constraints that produced