add sizable trait

crates/theme/src/resolve.rs

@@ -1,7 +1,7 @@
 use crate::definition::ThemeDefinition;
 use crate::ramps::{AccentShades, Oklch, contrast_foreground, derive_shades, mix};
 use crate::system::SystemTheme;
-use crate::{ColorTokens, Radius, ThemeVariant};
+use crate::{ColorTokens, Radius, SizeTable, ThemeVariant};
 use gpui::px;
 
 /// Derived state shades for the colors that get pressed and hovered.
@@ -19,6 +19,9 @@ pub struct ResolvedTheme {
     pub colors: ColorTokens,
     pub ramps: Ramps,
     pub radius: Radius,
+    /// The platform's native root font size; the fallback theme uses 16.
+    pub root_font_size: gpui::Pixels,
+    pub sizes: SizeTable,
     pub accessibility: crate::system::AccessibilityPreferences,
 }
 
@@ -132,6 +135,17 @@ pub(crate) fn resolve(
         .to_hsla();
     }
 
+    // The platform's root font size scales every control metric:
+    // a medium control's label is exactly the root font size.
+    //
+    // Fallback: 16 (the web default gpui also uses for rems).
+    let root_font_size = system.root_font_size.unwrap_or(px(16.));
+
+    let mut sizes = SizeTable::with_root_font_size(root_font_size);
+    if let Some(input_height) = system.input_height {
+        sizes.set_input_height(input_height);
+    }
+
     let mut radius = Radius::default();
     if let Some(control) = preset
         .and_then(|def| def.control_radius)
@@ -158,6 +172,8 @@ pub(crate) fn resolve(
         },
         colors,
         radius,
+        root_font_size,
+        sizes,
         accessibility,
     }
 }
@@ -182,6 +198,8 @@ mod tests {
             accent,
             palette,
             control_radius: None,
+            input_height: None,
+            root_font_size: None,
             accessibility: AccessibilityPreferences::default(),
             source: SourceKind::Macos,
         }
@@ -218,9 +236,44 @@ mod tests {
             assert_eq!(resolved.ramps.secondary.base, base.secondary);
             assert_eq!(resolved.radius.sm, px(4.));
             assert_eq!(resolved.radius.control, px(6.));
+            assert_eq!(resolved.root_font_size, px(16.));
+            assert_eq!(resolved.sizes.medium.control_height, px(28.));
+            assert_eq!(resolved.sizes.medium.input_height, px(30.));
+            assert_eq!(resolved.sizes.medium.text_size, px(16.));
+            assert_eq!(resolved.sizes.large.avatar_size, px(48.));
         }
     }
 
+    #[test]
+    fn a_stated_root_font_size_scales_the_size_table() {
+        // macOS states 13pt; the medium control shrinks to native proportions.
+        let mut stated = system(ThemeVariant::Light, PartialPalette::default(), None);
+        stated.root_font_size = Some(px(13.));
+        let resolved = resolve(&stated, None, None);
+        assert_eq!(resolved.root_font_size, px(13.));
+        assert_eq!(resolved.sizes.medium.control_height, px(22.75));
+        assert_eq!(resolved.sizes.medium.text_size, px(13.));
+        assert_eq!(resolved.sizes.small.text_size, px(11.05));
+    }
+
+    #[test]
+    fn a_stated_input_height_overrides_the_derived_one_and_scales() {
+        let mut stated = system(ThemeVariant::Light, PartialPalette::default(), None);
+        stated.input_height = Some(px(24.));
+        let resolved = resolve(&stated, None, None);
+
+        // The medium class takes the stated height verbatim, and the other
+        // classes keep their derived ratio to the medium class.
+        assert_eq!(resolved.sizes.medium.input_height, px(24.));
+
+        // Derive what small would be without the statement, scale it by the
+        // stated-to-derived ratio, and compare.
+        let derived = SizeTable::with_root_font_size(px(16.));
+        let scale = px(24.) / derived.medium.input_height;
+        let expected_small = derived.small.input_height * scale;
+        assert!((resolved.sizes.small.input_height - expected_small).abs() < px(0.01));
+    }
+
     #[test]
     fn system_colors_override_the_base_but_leave_the_rest_intact() {
         let palette = PartialPalette {