Set default terminal fg/bg from Emacs theme colors

The terminal hardcoded default colors to rgb(204,204,204) on black,
ignoring the active Emacs theme.  Add ghostel--set-default-colors
(Zig) to set the terminal's default fg/bg from hex strings, and call
it from ghostel--apply-palette using the Emacs default face.  This
makes terminals respect the current theme at creation and on theme
change.

Author: dakra

ghostel.el

@@ -312,6 +312,7 @@ Bump this only when the Elisp code requires a newer native module
 (declare-function ghostel--scroll "ghostel-module")
 (declare-function ghostel--scroll-bottom "ghostel-module")
 (declare-function ghostel--scroll-top "ghostel-module")
+(declare-function ghostel--set-default-colors "ghostel-module")
 (declare-function ghostel--set-palette "ghostel-module")
 (declare-function ghostel--set-size "ghostel-module")
 (declare-function ghostel--write-input "ghostel-module")
@@ -1502,15 +1503,20 @@ Falls back to \"#000000\" if the color cannot be resolved."
       "#000000"))
 
 (defun ghostel--apply-palette (term)
-  "Apply colors from `ghostel-color-palette' faces to TERM."
-  (when (and term ghostel-color-palette)
-    (let ((colors
-           (mapconcat
-            (lambda (face)
-              (ghostel--face-hex-color face :foreground))
-            ghostel-color-palette
-            "")))
-      (ghostel--set-palette term colors))))
+  "Apply colors from `ghostel-color-palette' faces and default fg/bg to TERM."
+  (when term
+    (ghostel--set-default-colors
+     term
+     (ghostel--face-hex-color 'default :foreground)
+     (ghostel--face-hex-color 'default :background))
+    (when ghostel-color-palette
+      (let ((colors
+             (mapconcat
+              (lambda (face)
+                (ghostel--face-hex-color face :foreground))
+              ghostel-color-palette
+              "")))
+        (ghostel--set-palette term colors)))))
 
 
 ;;; Theme synchronization

src/module.zig

@@ -42,6 +42,7 @@ export fn emacs_module_init(runtime: *c.struct_emacs_runtime) callconv(.c) c_int
     env.bindFunction("ghostel--mouse-event", 6, 6, &fnMouseEvent, "Send a mouse event to the terminal.\n\n(ghostel--mouse-event TERM ACTION BUTTON ROW COL MODS)");
     env.bindFunction("ghostel--focus-event", 2, 2, &fnFocusEvent, "Send a focus event to the terminal.\n\n(ghostel--focus-event TERM GAINED)");
     env.bindFunction("ghostel--set-palette", 2, 2, &fnSetPalette, "Set the ANSI color palette.\n\n(ghostel--set-palette TERM COLORS-STRING)");
+    env.bindFunction("ghostel--set-default-colors", 3, 3, &fnSetDefaultColors, "Set default foreground and background colors.\n\n(ghostel--set-default-colors TERM FG-HEX BG-HEX)");
     env.bindFunction("ghostel--mode-enabled", 2, 2, &fnModeEnabled, "Return t if terminal DEC private MODE is enabled.\n\n(ghostel--mode-enabled TERM MODE)");
     env.bindFunction("ghostel--debug-state", 1, 1, &fnDebugState, "Return debug info about terminal/render state.\n\n(ghostel--debug-state TERM)");
     env.bindFunction("ghostel--debug-feed", 2, 2, &fnDebugFeed, "Feed STR to terminal and return first row + cursor.\n\n(ghostel--debug-feed TERM STR)");
@@ -559,6 +560,55 @@ fn hexDigit(ch: u8) ?u8 {
     return null;
 }
 
+/// Parse a "#RRGGBB" hex color string into a ColorRgb.
+fn parseHexColor(s: []const u8) ?gt.ColorRgb {
+    if (s.len < 7 or s[0] != '#') return null;
+    const r = parseHexByte(s[1], s[2]) orelse return null;
+    const g = parseHexByte(s[3], s[4]) orelse return null;
+    const b = parseHexByte(s[5], s[6]) orelse return null;
+    return .{ .r = r, .g = g, .b = b };
+}
+
+/// (ghostel--set-default-colors TERM FG-HEX BG-HEX)
+/// Set the terminal's default foreground and background colors from "#RRGGBB" strings.
+fn fnSetDefaultColors(raw_env: ?*c.emacs_env, _: isize, args: [*c]c.emacs_value, _: ?*anyopaque) callconv(.c) c.emacs_value {
+    const env = emacs.Env.init(raw_env.?);
+    const term = env.getUserPtr(Terminal, args[0]) orelse {
+        env.signalError("ghostel: invalid terminal handle");
+        return env.nil();
+    };
+
+    var fg_buf: [16]u8 = undefined;
+    var bg_buf: [16]u8 = undefined;
+    const fg_str = env.extractString(args[1], &fg_buf) orelse {
+        env.signalError("ghostel: invalid foreground color");
+        return env.nil();
+    };
+    const bg_str = env.extractString(args[2], &bg_buf) orelse {
+        env.signalError("ghostel: invalid background color");
+        return env.nil();
+    };
+
+    const fg = parseHexColor(fg_str) orelse {
+        env.signalError("ghostel: cannot parse foreground color");
+        return env.nil();
+    };
+    const bg = parseHexColor(bg_str) orelse {
+        env.signalError("ghostel: cannot parse background color");
+        return env.nil();
+    };
+
+    term.setColorForeground(&fg) catch {
+        env.signalError("ghostel: failed to set foreground color");
+        return env.nil();
+    };
+    term.setColorBackground(&bg) catch {
+        env.signalError("ghostel: failed to set background color");
+        return env.nil();
+    };
+    return env.t();
+}
+
 /// (ghostel--debug-state TERM)
 /// Returns a string with render state debug info.
 fn fnDebugState(raw_env: ?*c.emacs_env, _: isize, args: [*c]c.emacs_value, _: ?*anyopaque) callconv(.c) c.emacs_value {

test/ghostel-test.el

@@ -923,6 +923,36 @@ cell, so the visual line width must equal the terminal column count."
           (kill-buffer buf)
           (kill-buffer other))))))
 
+;; -----------------------------------------------------------------------
+;; Test: apply-palette sets default fg/bg from Emacs default face
+;; -----------------------------------------------------------------------
+
+(ert-deftest ghostel-test-apply-palette-default-colors ()
+  "Test that ghostel--apply-palette sets default fg/bg from the Emacs default face."
+  (let ((default-colors-calls nil)
+        (palette-calls nil))
+    (cl-letf (((symbol-function 'ghostel--set-default-colors)
+               (lambda (term fg bg)
+                 (push (list term fg bg) default-colors-calls)))
+              ((symbol-function 'ghostel--set-palette)
+               (lambda (term colors) (push (list term colors) palette-calls))))
+      ;; With a fake terminal, apply-palette should call set-default-colors
+      (ghostel--apply-palette 'fake-term)
+      (should (= 1 (length default-colors-calls)))
+      (should (eq 'fake-term (car (car default-colors-calls))))
+      ;; fg and bg should be hex color strings from the default face
+      (let ((fg (nth 1 (car default-colors-calls)))
+            (bg (nth 2 (car default-colors-calls))))
+        (should (string-prefix-p "#" fg))
+        (should (string-prefix-p "#" bg)))
+      ;; Palette should also be set
+      (should (= 1 (length palette-calls)))
+      ;; With nil term, nothing should be called
+      (setq default-colors-calls nil palette-calls nil)
+      (ghostel--apply-palette nil)
+      (should-not default-colors-calls)
+      (should-not palette-calls))))
+
 ;; -----------------------------------------------------------------------
 ;; OSC 51 elisp eval
 ;; -----------------------------------------------------------------------
@@ -1066,6 +1096,7 @@ cell, so the visual line width must equal the terminal column count."
     ghostel-test-filter-soft-wraps
     ghostel-test-prompt-navigation
     ghostel-test-sync-theme
+    ghostel-test-apply-palette-default-colors
     ghostel-test-osc51-eval
     ghostel-test-osc51-eval-unknown
     ghostel-test-copy-mode-cursor