Add feature flags handling to the client, rewrite staff mode to a trait extension style

crates/feature_flags/Cargo.toml

@@ -0,0 +1,12 @@
+[package]
+name = "feature_flags"
+version = "0.1.0"
+edition = "2021"
+publish = false
+
+[lib]
+path = "src/feature_flags.rs"
+
+[dependencies]
+gpui = { path = "../gpui" }
+anyhow.workspace = true

crates/feature_flags/src/feature_flags.rs

@@ -0,0 +1,79 @@
+use gpui::{AppContext, Subscription, ViewContext};
+
+#[derive(Default)]
+struct FeatureFlags {
+    flags: Vec<String>,
+    staff: bool,
+}
+
+impl FeatureFlags {
+    fn has_flag(&self, flag: &str) -> bool {
+        self.staff || self.flags.iter().find(|f| f.as_str() == flag).is_some()
+    }
+}
+
+pub trait FeatureFlag {
+    const NAME: &'static str;
+}
+
+pub enum ChannelsAlpha {}
+
+impl FeatureFlag for ChannelsAlpha {
+    const NAME: &'static str = "channels_alpha";
+}
+
+pub trait FeatureFlagViewExt<V: 'static> {
+    fn observe_flag<T: FeatureFlag, F>(&mut self, callback: F) -> Subscription
+    where
+        F: Fn(bool, &mut V, &mut ViewContext<V>) + 'static;
+}
+
+impl<V: 'static> FeatureFlagViewExt<V> for ViewContext<'_, '_, V> {
+    fn observe_flag<T: FeatureFlag, F>(&mut self, callback: F) -> Subscription
+    where
+        F: Fn(bool, &mut V, &mut ViewContext<V>) + 'static,
+    {
+        self.observe_global::<FeatureFlags, _>(move |v, cx| {
+            let feature_flags = cx.global::<FeatureFlags>();
+            callback(feature_flags.has_flag(<T as FeatureFlag>::NAME), v, cx);
+        })
+    }
+}
+
+pub trait FeatureFlagAppExt {
+    fn update_flags(&mut self, staff: bool, flags: Vec<String>);
+    fn set_staff(&mut self, staff: bool);
+    fn has_flag<T: FeatureFlag>(&self) -> bool;
+    fn is_staff(&self) -> bool;
+}
+
+impl FeatureFlagAppExt for AppContext {
+    fn update_flags(&mut self, staff: bool, flags: Vec<String>) {
+        self.update_default_global::<FeatureFlags, _, _>(|feature_flags, _| {
+            feature_flags.staff = staff;
+            feature_flags.flags = flags;
+        })
+    }
+
+    fn set_staff(&mut self, staff: bool) {
+        self.update_default_global::<FeatureFlags, _, _>(|feature_flags, _| {
+            feature_flags.staff = staff;
+        })
+    }
+
+    fn has_flag<T: FeatureFlag>(&self) -> bool {
+        if self.has_global::<FeatureFlags>() {
+            self.global::<FeatureFlags>().has_flag(T::NAME)
+        } else {
+            false
+        }
+    }
+
+    fn is_staff(&self) -> bool {
+        if self.has_global::<FeatureFlags>() {
+            return self.global::<FeatureFlags>().staff;
+        } else {
+            false
+        }
+    }
+}