libghostty: add selection adjustment api

include/ghostty/vt/selection.h

@@ -77,6 +77,61 @@ typedef struct {
   bool rectangle;
 } GhosttySelection;
 
+/**
+ * Operation used to adjust a selection endpoint.
+ *
+ * Adjustment mutates the selection's logical end endpoint, not whichever
+ * endpoint is visually bottom/right. This preserves keyboard and drag
+ * behavior for both forward and reversed selections.
+ *
+ * @ingroup selection
+ */
+typedef enum GHOSTTY_ENUM_TYPED {
+  /** Move left to the previous non-empty cell, wrapping upward. */
+  GHOSTTY_SELECTION_ADJUST_LEFT = 0,
+
+  /** Move right to the next non-empty cell, wrapping downward. */
+  GHOSTTY_SELECTION_ADJUST_RIGHT = 1,
+
+  /**
+   * Move up one row at the current column, or to the beginning of the
+   * line if already at the top.
+   */
+  GHOSTTY_SELECTION_ADJUST_UP = 2,
+
+  /**
+   * Move down to the next non-blank row at the current column, or to the
+   * end of the line if none exists.
+   */
+  GHOSTTY_SELECTION_ADJUST_DOWN = 3,
+
+  /** Move to the top-left cell of the screen. */
+  GHOSTTY_SELECTION_ADJUST_HOME = 4,
+
+  /** Move to the right edge of the last non-blank row on the screen. */
+  GHOSTTY_SELECTION_ADJUST_END = 5,
+
+  /**
+   * Move up by one terminal page height, or to home if that would move
+   * past the top.
+   */
+  GHOSTTY_SELECTION_ADJUST_PAGE_UP = 6,
+
+  /**
+   * Move down by one terminal page height, or to end if that would move
+   * past the bottom.
+   */
+  GHOSTTY_SELECTION_ADJUST_PAGE_DOWN = 7,
+
+  /** Move to the left edge of the current line. */
+  GHOSTTY_SELECTION_ADJUST_BEGINNING_OF_LINE = 8,
+
+  /** Move to the right edge of the current line. */
+  GHOSTTY_SELECTION_ADJUST_END_OF_LINE = 9,
+
+  GHOSTTY_SELECTION_ADJUST_MAX_VALUE = GHOSTTY_ENUM_MAX_VALUE,
+} GhosttySelectionAdjust;
+
 /** @} */
 
 #ifdef __cplusplus

include/ghostty/vt/terminal.h

@@ -1123,6 +1123,35 @@ GHOSTTY_API GhosttyResult ghostty_terminal_get_multi(GhosttyTerminal terminal,
                                     void** values,
                                     size_t* out_written);
 
+/**
+ * Adjust a selection snapshot using terminal selection semantics.
+ *
+ * This mutates the caller-provided GhosttySelection in place. The logical end
+ * endpoint is always moved, regardless of whether the selection is forward or
+ * reversed visually. The input selection remains a snapshot: after adjustment,
+ * call ghostty_terminal_set() with GHOSTTY_TERMINAL_OPT_SELECTION to install it
+ * as the terminal-owned selection if desired.
+ *
+ * The selection's start and end grid refs must both be valid untracked
+ * snapshots for the given terminal's currently active screen. In practice,
+ * they must come from that terminal and screen, and no mutating terminal call
+ * may have occurred since the refs were produced or reconstructed from
+ * tracked refs. Passing refs from another terminal, another screen, or stale
+ * refs violates this precondition.
+ *
+ * @param terminal The terminal handle (NULL returns GHOSTTY_INVALID_VALUE)
+ * @param selection Selection snapshot to adjust in place
+ * @param adjustment The adjustment operation to apply
+ * @return GHOSTTY_SUCCESS on success, GHOSTTY_INVALID_VALUE if the terminal,
+ *         selection, selection references, or adjustment are invalid
+ *
+ * @ingroup terminal
+ */
+GHOSTTY_API GhosttyResult ghostty_terminal_selection_adjust(
+                                    GhosttyTerminal terminal,
+                                    GhosttySelection* selection,
+                                    GhosttySelectionAdjust adjustment);
+
 /**
  * Resolve a point in the terminal grid to a grid reference.
  *

src/lib_vt.zig

@@ -239,6 +239,7 @@ comptime {
         @export(&c.terminal_mode_set, .{ .name = "ghostty_terminal_mode_set" });
         @export(&c.terminal_get, .{ .name = "ghostty_terminal_get" });
         @export(&c.terminal_get_multi, .{ .name = "ghostty_terminal_get_multi" });
+        @export(&c.terminal_selection_adjust, .{ .name = "ghostty_terminal_selection_adjust" });
         @export(&c.terminal_grid_ref, .{ .name = "ghostty_terminal_grid_ref" });
         @export(&c.terminal_grid_ref_track, .{ .name = "ghostty_terminal_grid_ref_track" });
         @export(&c.terminal_point_from_grid_ref, .{ .name = "ghostty_terminal_point_from_grid_ref" });

src/terminal/Selection.zig

@@ -4,6 +4,7 @@ const Selection = @This();
 const std = @import("std");
 const assert = @import("../quirks.zig").inlineAssert;
 const Allocator = std.mem.Allocator;
+const lib = @import("lib.zig");
 const page = @import("page.zig");
 const point = @import("point.zig");
 const PageList = @import("PageList.zig");
@@ -389,18 +390,18 @@ pub fn containedRowCached(
 }
 
 /// Possible adjustments to the selection.
-pub const Adjustment = enum {
+pub const Adjustment = lib.Enum(lib.target, &.{
-    left,
+    "left",
-    right,
+    "right",
-    up,
+    "up",
-    down,
+    "down",
-    home,
+    "home",
-    end,
+    "end",
-    page_up,
+    "page_up",
-    page_down,
+    "page_down",
-    beginning_of_line,
+    "beginning_of_line",
-    end_of_line,
+    "end_of_line",
-};
+});
 
 /// Adjust the selection by some given adjustment. An adjustment allows
 /// a selection to be expanded slightly left, right, up, down, etc.

src/terminal/c/main.zig

@@ -170,6 +170,7 @@ pub const terminal_mode_get = terminal.mode_get;
 pub const terminal_mode_set = terminal.mode_set;
 pub const terminal_get = terminal.get;
 pub const terminal_get_multi = terminal.get_multi;
+pub const terminal_selection_adjust = terminal.selection_adjust;
 pub const terminal_grid_ref = terminal.grid_ref;
 pub const terminal_grid_ref_track = terminal.grid_ref_track;
 pub const terminal_point_from_grid_ref = terminal.point_from_grid_ref;

src/terminal/c/terminal.zig

@@ -7,6 +7,7 @@ const ZigTerminal = @import("../Terminal.zig");
 const Stream = @import("../stream_terminal.zig").Stream;
 const ScreenSet = @import("../ScreenSet.zig");
 const PageList = @import("../PageList.zig");
+const Selection = @import("../Selection.zig");
 const apc = @import("../apc.zig");
 const kitty = @import("../kitty/key.zig");
 const kitty_gfx_c = @import("kitty_graphics.zig");
@@ -664,6 +665,26 @@ pub fn get_multi(
     return .success;
 }
 
+pub fn selection_adjust(
+    terminal_: Terminal,
+    selection: ?*selection_c.CSelection,
+    adjustment: Selection.Adjustment,
+) callconv(lib.calling_conv) Result {
+    if (comptime std.debug.runtime_safety) {
+        _ = std.meta.intToEnum(Selection.Adjustment, @intFromEnum(adjustment)) catch {
+            log.warn("terminal_selection_adjust invalid adjustment value={d}", .{@intFromEnum(adjustment)});
+            return .invalid_value;
+        };
+    }
+
+    const t: *ZigTerminal = (terminal_ orelse return .invalid_value).terminal;
+    const sel_ptr = selection orelse return .invalid_value;
+    var sel = sel_ptr.toZig() orelse return .invalid_value;
+    sel.adjust(t.screens.active, adjustment);
+    sel_ptr.* = .fromZig(sel);
+    return .success;
+}
+
 fn getTyped(
     terminal_: Terminal,
     comptime data: TerminalData,
@@ -1389,6 +1410,54 @@ test "set and get selection" {
     try testing.expectEqual(Result.no_value, get(t, .selection, @ptrCast(&out)));
 }
 
+test "selection_adjust mutates snapshot end" {
+    var t: Terminal = null;
+    try testing.expectEqual(Result.success, new(
+        &lib.alloc.test_allocator,
+        &t,
+        .{
+            .cols = 80,
+            .rows = 24,
+            .max_scrollback = 0,
+        },
+    ));
+    defer free(t);
+
+    vt_write(t, "Hello", 5);
+
+    var start_ref: grid_ref_c.CGridRef = .{};
+    try testing.expectEqual(Result.success, grid_ref(t, .{
+        .tag = .active,
+        .value = .{ .active = .{ .x = 0, .y = 0 } },
+    }, &start_ref));
+
+    var end_ref: grid_ref_c.CGridRef = .{};
+    try testing.expectEqual(Result.success, grid_ref(t, .{
+        .tag = .active,
+        .value = .{ .active = .{ .x = 1, .y = 0 } },
+    }, &end_ref));
+
+    var sel: selection_c.CSelection = .{
+        .start = start_ref,
+        .end = end_ref,
+    };
+    try testing.expectEqual(Result.success, selection_adjust(t, &sel, .right));
+    try testing.expectEqual(@as(u16, 0), sel.start.toPin().?.x);
+    try testing.expectEqual(@as(u16, 2), sel.end.toPin().?.x);
+
+    try testing.expectEqual(Result.success, selection_adjust(t, &sel, .left));
+    try testing.expectEqual(@as(u16, 0), sel.start.toPin().?.x);
+    try testing.expectEqual(@as(u16, 1), sel.end.toPin().?.x);
+
+    sel = .{
+        .start = end_ref,
+        .end = start_ref,
+    };
+    try testing.expectEqual(Result.success, selection_adjust(t, &sel, .right));
+    try testing.expectEqual(@as(u16, 1), sel.start.toPin().?.x);
+    try testing.expectEqual(@as(u16, 1), sel.end.toPin().?.x);
+}
+
 test "grid_ref" {
     var t: Terminal = null;
     try testing.expectEqual(Result.success, new(