Theme · Editing: a theme laid open, and an owner's palette per mode

settings::ThemeEditor lays a theme open: density, corners, text size,
high contrast and reduced motion, then twelve colors of the mode shown,
each a swatch that opens a picker beside its hex; each change hands the
owner a whole draft. Theme::set_palette takes an owner's palette per
mode, the colors fading to it when the mode shows; Theme::palette names
the palette the shown mode fades to; Palette::token_mut and
Syntax::token_mut reach a color by its field's name. The gallery's
theme page applies the editor to the whole gallery live, with a way
back to Ely's theme.

src/settings/tests/theme.rs

@@ -0,0 +1,64 @@
+use gpui::{AnyElement, App, Entity, IntoElement, TestAppContext, Window};
+
+use super::{Desk, desk, said, say, tab, tap};
+use crate::{
+    settings::{ThemeDraft, ThemeEditor},
+    theme::ActiveTheme,
+};
+
+fn editor(_: &mut Window, cx: &mut App, owner: Entity<Desk>) -> AnyElement {
+    ThemeEditor::new("editor", ThemeDraft::of(cx.theme()))
+        .on_change(move |draft, _, cx| {
+            say(
+                &owner,
+                format!(
+                    "{:?} contrast {} still {}",
+                    draft.density, draft.high_contrast, draft.reduced_motion
+                ),
+                cx,
+            )
+        })
+        .into_any_element()
+}
+
+/// Stops: the three densities, corners, text size, high contrast, reduced motion, then the colors. A switch hands on a draft with its own flag turned and the rest as it stood.
+#[gpui::test]
+fn a_switch_turns_its_own_flag(cx: &mut TestAppContext) {
+    let (host, cx) = desk(editor, cx);
+    tab(6, cx);
+    tap("space", cx);
+    tab(7, cx);
+    tap("space", cx);
+    assert_eq!(
+        said(&host, cx),
+        [
+            "Standard contrast true still true",
+            "Standard contrast false still false"
+        ],
+        "the desk runs with reduced motion on, so its switch turns it off"
+    );
+}
+
+fn colors(_: &mut Window, cx: &mut App, owner: Entity<Desk>) -> AnyElement {
+    ThemeEditor::new("editor", ThemeDraft::of(cx.theme()))
+        .on_change(move |draft, _, cx| {
+            let background = gpui::Rgba::from(draft.colors.bg);
+            say(&owner, crate::forms::hex(background), cx)
+        })
+        .into_any_element()
+}
+
+/// The first color is the eighth stop; Enter opens its picker, where the third stop is the hex field, which takes a new background.
+#[gpui::test]
+fn a_color_well_sets_its_own_color(cx: &mut TestAppContext) {
+    let (host, cx) = desk(colors, cx);
+    tab(8, cx);
+    tap("enter", cx);
+    for _ in 0..3 {
+        tap("tab", cx);
+    }
+    tap("cmd-a", cx);
+    cx.simulate_input("#224466");
+    tap("enter", cx);
+    assert_eq!(said(&host, cx), ["#224466"]);
+}