Let the theme decide a button's minimum size

crates/egui/src/theme/default_style.rs

@@ -88,6 +88,9 @@ impl StyleProvider<ButtonStyle> for DefaultStyle {
                 ..Default::default()
             },
             text_style: ws.text,
+            // Historically only the height was floored, so that a button is at least as tall as
+            // any other interactive widget on the same row.
+            min_size: Vec2::new(0.0, spacing.interact_size.y),
         }
     }
 }

crates/egui/src/widget_style/mod.rs

@@ -10,6 +10,7 @@ pub use self::classes::{
 
 use core::fmt::Debug;
 
+use emath::Vec2;
 use epaint::{Color32, FontId, Stroke, text::TextWrapMode};
 
 use crate::{
@@ -51,6 +52,12 @@ impl WidgetStyle for BaseStyle {}
 pub struct ButtonStyle {
     pub frame: Frame,
     pub text_style: TextVisuals,
+
+    /// How small the button may get, before its contents are taken into account.
+    ///
+    /// Ignored by a [`crate::Button::small`] button, which sizes itself purely from its contents
+    /// and its own [`crate::Button::min_size`].
+    pub min_size: Vec2,
 }
 
 impl WidgetStyle for ButtonStyle {}

crates/egui/src/widgets/button.rs

@@ -2,8 +2,8 @@ use epaint::Margin;
 
 use crate::{
     Atom, AtomExt as _, AtomKind, AtomLayout, AtomLayoutResponse, Atoms, Color32, CornerRadius,
-    Frame, Image, IntoAtoms, NumExt as _, Response, Sense, Stroke, TextStyle, TextWrapMode, Ui,
+    Frame, Image, IntoAtoms, Response, Sense, Stroke, TextStyle, TextWrapMode, Ui, Vec2, Widget,
-    Vec2, Widget, WidgetInfo, WidgetText, WidgetType,
+    WidgetInfo, WidgetText, WidgetType,
     widget_style::{ButtonStyle, Classes, HasClasses, SELECTED_CLASS, WidgetState},
 };
 
@@ -303,11 +303,6 @@ impl<'a> Button<'a> {
             mut classes,
         } = self;
 
-        // Min size height always equal or greater than interact size if not small
-        if !small {
-            min_size.y = min_size.y.at_least(ui.spacing().interact_size.y);
-        }
-
         if limit_image_size {
             layout.map_atoms(|atom| {
                 if matches!(&atom.kind, AtomKind::Image(_)) {
@@ -328,7 +323,17 @@ impl<'a> Button<'a> {
 
         classes.add_class_if(SELECTED_CLASS, selected.unwrap_or(false));
 
-        let ButtonStyle { frame, text_style } = ui.widget_style(id, &classes);
+        let ButtonStyle {
+            frame,
+            text_style,
+            min_size: style_min_size,
+        } = ui.widget_style(id, &classes);
+
+        // The theme decides how small a button may get — unless it is a `small` one, which sizes
+        // itself purely from its contents.
+        if !small {
+            min_size = min_size.max(style_min_size);
+        }
 
         let mut button_padding = if has_frame_margin {
             frame.inner_margin