Adds a way to toggle font size without settings adjustments (#24857)

Closes https://github.com/zed-industries/zed/issues/23505

Now `zed::IncreaseBufferFontSize` (and all the same UI- and
Buffer-related settings) action is parameterized with `{ "persist": true
}` (default).
Using `"persist": false` brings back resizing behavior prior to
https://github.com/zed-industries/zed/pull/23265


Release Notes:

- Added a way to toggle font size without settings adjustments

crates/theme/src/settings.rs

@@ -6,7 +6,8 @@ use crate::{
 use anyhow::Result;
 use derive_more::{Deref, DerefMut};
 use gpui::{
-    px, App, Font, FontFallbacks, FontFeatures, FontStyle, FontWeight, Global, Pixels, Window,
+    px, App, Context, Font, FontFallbacks, FontFeatures, FontStyle, FontWeight, Global, Pixels,
+    Subscription, Window,
 };
 use refineable::Refineable;
 use schemars::{
@@ -234,6 +235,16 @@ impl SystemAppearance {
     }
 }
 
+#[derive(Default)]
+pub(crate) struct AdjustedBufferFontSize(Pixels);
+
+impl Global for AdjustedBufferFontSize {}
+
+#[derive(Default)]
+pub(crate) struct AdjustedUiFontSize(Pixels);
+
+impl Global for AdjustedUiFontSize {}
+
 /// Represents the selection of a theme, which can be either static or dynamic.
 #[derive(Clone, Debug, Serialize, Deserialize, JsonSchema, PartialEq, Eq)]
 #[serde(untagged)]
@@ -545,13 +556,10 @@ impl BufferLineHeight {
 
 impl ThemeSettings {
     /// Returns the buffer font size.
-    pub fn buffer_font_size(&self) -> Pixels {
-        Self::clamp_font_size(self.buffer_font_size)
-    }
-
-    /// Ensures that the font size is within the valid range.
-    pub fn clamp_font_size(size: Pixels) -> Pixels {
-        size.max(MIN_FONT_SIZE)
+    pub fn buffer_font_size(&self, cx: &App) -> Pixels {
+        cx.try_global::<AdjustedBufferFontSize>()
+            .map_or(self.buffer_font_size, |size| size.0)
+            .max(MIN_FONT_SIZE)
     }
 
     // TODO: Rename: `line_height` -> `buffer_line_height`
@@ -626,19 +634,105 @@ impl ThemeSettings {
     }
 }
 
+/// Observe changes to the adjusted buffer font size.
+pub fn observe_buffer_font_size_adjustment<V: 'static>(
+    cx: &mut Context<V>,
+    f: impl 'static + Fn(&mut V, &mut Context<V>),
+) -> Subscription {
+    cx.observe_global::<AdjustedBufferFontSize>(f)
+}
+
+/// Sets the adjusted buffer font size.
+pub fn adjusted_font_size(size: Pixels, cx: &App) -> Pixels {
+    if let Some(AdjustedBufferFontSize(adjusted_size)) = cx.try_global::<AdjustedBufferFontSize>() {
+        let buffer_font_size = ThemeSettings::get_global(cx).buffer_font_size;
+        let delta = *adjusted_size - buffer_font_size;
+        size + delta
+    } else {
+        size
+    }
+    .max(MIN_FONT_SIZE)
+}
+
+/// Returns the adjusted buffer font size.
+pub fn get_buffer_font_size(cx: &App) -> Pixels {
+    let buffer_font_size = ThemeSettings::get_global(cx).buffer_font_size;
+    cx.try_global::<AdjustedBufferFontSize>()
+        .map_or(buffer_font_size, |adjusted_size| adjusted_size.0)
+}
+
+/// Adjusts the buffer font size.
+pub fn adjust_buffer_font_size(cx: &mut App, mut f: impl FnMut(&mut Pixels)) {
+    let buffer_font_size = ThemeSettings::get_global(cx).buffer_font_size;
+    let mut adjusted_size = cx
+        .try_global::<AdjustedBufferFontSize>()
+        .map_or(buffer_font_size, |adjusted_size| adjusted_size.0);
+
+    f(&mut adjusted_size);
+    adjusted_size = adjusted_size.max(MIN_FONT_SIZE);
+    cx.set_global(AdjustedBufferFontSize(adjusted_size));
+    cx.refresh_windows();
+}
+
+/// Returns whether the buffer font size has been adjusted.
+pub fn has_adjusted_buffer_font_size(cx: &App) -> bool {
+    cx.has_global::<AdjustedBufferFontSize>()
+}
+
+/// Resets the buffer font size to the default value.
+pub fn reset_buffer_font_size(cx: &mut App) {
+    if cx.has_global::<AdjustedBufferFontSize>() {
+        cx.remove_global::<AdjustedBufferFontSize>();
+        cx.refresh_windows();
+    }
+}
+
 // TODO: Make private, change usages to use `get_ui_font_size` instead.
 #[allow(missing_docs)]
 pub fn setup_ui_font(window: &mut Window, cx: &mut App) -> gpui::Font {
     let (ui_font, ui_font_size) = {
         let theme_settings = ThemeSettings::get_global(cx);
         let font = theme_settings.ui_font.clone();
-        (font, theme_settings.ui_font_size)
+        (font, get_ui_font_size(cx))
     };
 
     window.set_rem_size(ui_font_size);
     ui_font
 }
 
+/// Gets the adjusted UI font size.
+pub fn get_ui_font_size(cx: &App) -> Pixels {
+    let ui_font_size = ThemeSettings::get_global(cx).ui_font_size;
+    cx.try_global::<AdjustedUiFontSize>()
+        .map_or(ui_font_size, |adjusted_size| adjusted_size.0)
+}
+
+/// Sets the adjusted UI font size.
+pub fn adjust_ui_font_size(cx: &mut App, mut f: impl FnMut(&mut Pixels)) {
+    let ui_font_size = ThemeSettings::get_global(cx).ui_font_size;
+    let mut adjusted_size = cx
+        .try_global::<AdjustedUiFontSize>()
+        .map_or(ui_font_size, |adjusted_size| adjusted_size.0);
+
+    f(&mut adjusted_size);
+    adjusted_size = adjusted_size.max(MIN_FONT_SIZE);
+    cx.set_global(AdjustedUiFontSize(adjusted_size));
+    cx.refresh_windows();
+}
+
+/// Returns whether the UI font size has been adjusted.
+pub fn has_adjusted_ui_font_size(cx: &App) -> bool {
+    cx.has_global::<AdjustedUiFontSize>()
+}
+
+/// Resets the UI font size to the default value.
+pub fn reset_ui_font_size(cx: &mut App) {
+    if cx.has_global::<AdjustedUiFontSize>() {
+        cx.remove_global::<AdjustedUiFontSize>();
+        cx.refresh_windows();
+    }
+}
+
 fn clamp_font_weight(weight: f32) -> FontWeight {
     FontWeight(weight.clamp(100., 950.))
 }

crates/theme/src/theme.rs

@@ -23,6 +23,7 @@ use std::path::Path;
 use std::sync::Arc;
 
 use ::settings::Settings;
+use ::settings::SettingsStore;
 use anyhow::Result;
 use fallback_themes::apply_status_color_defaults;
 use fs::Fs;
@@ -101,6 +102,16 @@ pub fn init(themes_to_load: LoadThemes, cx: &mut App) {
 
     ThemeSettings::register(cx);
     FontFamilyCache::init_global(cx);
+
+    let mut prev_buffer_font_size = ThemeSettings::get_global(cx).buffer_font_size;
+    cx.observe_global::<SettingsStore>(move |cx| {
+        let buffer_font_size = ThemeSettings::get_global(cx).buffer_font_size;
+        if buffer_font_size != prev_buffer_font_size {
+            prev_buffer_font_size = buffer_font_size;
+            reset_buffer_font_size(cx);
+        }
+    })
+    .detach();
 }
 
 /// Implementing this trait allows accessing the active theme.