Add hook system.

src/View.zig

@@ -20,6 +20,7 @@ const View = @This();
 
 pub const Side = Layout.Side;
 pub const Kind = Pane.Kind;
+pub const Status = Pane.Status;
 
 /// Where a dragged pane would land.
 pub const Target = struct {
@@ -72,11 +73,13 @@ closing: bool = false,
 
 on_empty: *const fn (ctx: ?*anyopaque) void,
 on_title: *const fn (ctx: ?*anyopaque) void,
+on_status: *const fn (ctx: ?*anyopaque) void,
 ctx: ?*anyopaque = null,
 
 pub const Callbacks = struct {
     on_empty: *const fn (ctx: ?*anyopaque) void,
     on_title: *const fn (ctx: ?*anyopaque) void,
+    on_status: *const fn (ctx: ?*anyopaque) void,
     ctx: ?*anyopaque,
 };
 
@@ -90,6 +93,7 @@ pub fn create(alloc: std.mem.Allocator, cbs: Callbacks) !*View {
         .layout = .{ .alloc = alloc },
         .on_empty = cbs.on_empty,
         .on_title = cbs.on_title,
+        .on_status = cbs.on_status,
         .ctx = cbs.ctx,
     };
 
@@ -215,6 +219,10 @@ pub fn closePane(self: *View, pane: *Pane) void {
     self.setFocused(self.panes.items[next]);
     self.panes.items[next].grabFocus();
     self.on_title(self.ctx);
+
+    // Closing a busy pane changes what the tab as a whole is reporting, so
+    // the row has to be recomputed even though no pane changed its own state.
+    self.on_status(self.ctx);
 }
 
 pub fn setFocused(self: *View, pane: *Pane) void {
@@ -229,6 +237,34 @@ pub fn paneTitleChanged(self: *View, pane: *Pane) void {
     if (self.focused == pane or self.panes.items.len == 1) self.on_title(self.ctx);
 }
 
+pub fn paneStatusChanged(self: *View, pane: *Pane) void {
+    _ = pane;
+    if (self.closing) return;
+    self.on_status(self.ctx);
+}
+
+/// The view's status: the most urgent thing any of its panes is reporting.
+///
+/// A tab is one row however many panes it holds, so the row has to say
+/// something about all of them at once. Urgency wins rather than, say, the
+/// focused pane's status, because the whole point of the indicator is to be
+/// read from another tab — a pane blocked on a permission prompt matters
+/// even if it isn't the one you left focused.
+pub fn status(self: *View) Status {
+    var worst: Status = .idle;
+    for (self.panes.items) |pane| {
+        worst = switch (pane.status) {
+            // Nothing outranks a pane waiting on the user, so this can
+            // return the moment one is found.
+            .needs_input => return .needs_input,
+            .failed => .failed,
+            .busy => if (worst == .failed) worst else .busy,
+            .idle => worst,
+        };
+    }
+    return worst;
+}
+
 // -------------------------------------------------------------------------
 // Layouts