Use runtime knowledge of OS for OS-specific text editing (#3840)

How text editing behaves depends on what OS we are running on.

`target_os` is a compile-time check, but `ctx.os()` is a runtime check,
that works also on web.

crates/egui/src/widgets/label.rs

@@ -377,7 +377,7 @@ fn process_selection_key_events(
                 }
 
                 event => {
-                    cursor_range.on_event(event, galley, widget_id);
+                    cursor_range.on_event(ui.ctx().os(), event, galley, widget_id);
                 }
             }
         }

crates/egui/src/widgets/text_edit/builder.rs

@@ -2,7 +2,9 @@ use std::sync::Arc;
 
 use epaint::text::{cursor::*, Galley, LayoutJob};
 
-use crate::{output::OutputEvent, text_edit::cursor_interaction::cursor_rect, *};
+use crate::{
+    os::OperatingSystem, output::OutputEvent, text_edit::cursor_interaction::cursor_rect, *,
+};
 
 use super::{
     cursor_interaction::{ccursor_next_word, ccursor_previous_word, find_line_start},
@@ -773,6 +775,8 @@ fn events(
     char_limit: usize,
     event_filter: EventFilter,
 ) -> (bool, CursorRange) {
+    let os = ui.ctx().os();
+
     let mut cursor_range = state.cursor.range(galley).unwrap_or(default_cursor_range);
 
     // We feed state to the undoer both before and after handling input
@@ -794,7 +798,7 @@ fn events(
     for event in &events {
         let did_mutate_text = match event {
             // First handle events that only changes the selection cursor, not the text:
-            event if cursor_range.on_event(event, galley, id) => None,
+            event if cursor_range.on_event(os, event, galley, id) => None,
 
             Event::Copy => {
                 if cursor_range.is_empty() {
@@ -909,7 +913,7 @@ fn events(
                 key,
                 pressed: true,
                 ..
-            } => check_for_mutating_key_press(&mut cursor_range, text, galley, modifiers, *key),
+            } => check_for_mutating_key_press(os, &mut cursor_range, text, galley, modifiers, *key),
 
             Event::CompositionStart => {
                 state.has_ime = true;
@@ -1143,6 +1147,7 @@ fn delete_paragraph_after_cursor(
 
 /// Returns `Some(new_cursor)` if we did mutate `text`.
 fn check_for_mutating_key_press(
+    os: OperatingSystem,
     cursor_range: &mut CursorRange,
     text: &mut dyn TextBuffer,
     galley: &Galley,
@@ -1166,7 +1171,7 @@ fn check_for_mutating_key_press(
             Some(CCursorRange::one(ccursor))
         }
 
-        Key::Delete if !modifiers.shift || !cfg!(target_os = "windows") => {
+        Key::Delete if !modifiers.shift || os != OperatingSystem::Windows => {
             let ccursor = if modifiers.mac_cmd {
                 delete_paragraph_after_cursor(text, galley, cursor_range)
             } else if let Some(cursor) = cursor_range.single() {

crates/egui/src/widgets/text_edit/cursor_range.rs

@@ -1,6 +1,6 @@
 use epaint::{text::cursor::*, Galley};
 
-use crate::{Event, Id, Key, Modifiers};
+use crate::{os::OperatingSystem, Event, Id, Key, Modifiers};
 
 use super::cursor_interaction::{ccursor_next_word, ccursor_previous_word, slice_char_range};
 
@@ -115,7 +115,13 @@ impl CursorRange {
     /// Check for key presses that are moving the cursor.
     ///
     /// Returns `true` if we did mutate `self`.
-    pub fn on_key_press(&mut self, galley: &Galley, modifiers: &Modifiers, key: Key) -> bool {
+    pub fn on_key_press(
+        &mut self,
+        os: OperatingSystem,
+        galley: &Galley,
+        modifiers: &Modifiers,
+        key: Key,
+    ) -> bool {
         match key {
             Key::A if modifiers.command => {
                 *self = Self::select_all(galley);
@@ -137,17 +143,17 @@ impl CursorRange {
             | Key::ArrowDown
             | Key::Home
             | Key::End => {
-                move_single_cursor(&mut self.primary, galley, key, modifiers);
+                move_single_cursor(os, &mut self.primary, galley, key, modifiers);
                 if !modifiers.shift {
                     self.secondary = self.primary;
                 }
                 true
             }
 
             Key::P | Key::N | Key::B | Key::F | Key::A | Key::E
-                if cfg!(target_os = "macos") && modifiers.ctrl && !modifiers.shift =>
+                if os == OperatingSystem::Mac && modifiers.ctrl && !modifiers.shift =>
             {
-                move_single_cursor(&mut self.primary, galley, key, modifiers);
+                move_single_cursor(os, &mut self.primary, galley, key, modifiers);
                 self.secondary = self.primary;
                 true
             }
@@ -159,14 +165,20 @@ impl CursorRange {
     /// Check for events that modify the cursor range.
     ///
     /// Returns `true` if such an event was found and handled.
-    pub fn on_event(&mut self, event: &Event, galley: &Galley, _widget_id: Id) -> bool {
+    pub fn on_event(
+        &mut self,
+        os: OperatingSystem,
+        event: &Event,
+        galley: &Galley,
+        _widget_id: Id,
+    ) -> bool {
         match event {
             Event::Key {
                 modifiers,
                 key,
                 pressed: true,
                 ..
-            } => self.on_key_press(galley, modifiers, *key),
+            } => self.on_key_press(os, galley, modifiers, *key),
 
             #[cfg(feature = "accesskit")]
             Event::AccessKitActionRequest(accesskit::ActionRequest {
@@ -287,8 +299,14 @@ fn ccursor_from_accesskit_text_position(
 // ----------------------------------------------------------------------------
 
 /// Move a text cursor based on keyboard
-fn move_single_cursor(cursor: &mut Cursor, galley: &Galley, key: Key, modifiers: &Modifiers) {
-    if cfg!(target_os = "macos") && modifiers.ctrl && !modifiers.shift {
+fn move_single_cursor(
+    os: OperatingSystem,
+    cursor: &mut Cursor,
+    galley: &Galley,
+    key: Key,
+    modifiers: &Modifiers,
+) {
+    if os == OperatingSystem::Mac && modifiers.ctrl && !modifiers.shift {
         match key {
             Key::A => *cursor = galley.cursor_begin_of_row(cursor),
             Key::E => *cursor = galley.cursor_end_of_row(cursor),

scripts/lint.py

@@ -66,6 +66,15 @@ def lint_lines(filepath, lines_in):
                 )
                 lines_out.append("#[inline]")
 
+        if (
+            "(target_os" in line
+            and filepath.startswith("./crates/egui/")
+            and filepath != "./crates/egui/src/os.rs"
+        ):
+            errors.append(
+                f"{filepath}:{line_nr}: Don't use `target_os` - use ctx.os() instead."
+            )
+
         lines_out.append(line)
 
         prev_line = line