Make the "tab-as-character" behaviour opt-in.

Added `tab_moves_focus()` to `TextEdit` so we can opt-in to the
"tab-as-character" behaviour.

Also because we decided to lock the tab size to 4 spaces, we gave
up on the `tab_size` property, but we kept the opt-in for the
"tab-as-spaces" behaviour.

An updated example of how to use `TextEdit` with those two opt-in
behaviours can be found in the "Misc Demos" demo.

egui/src/memory.rs

@@ -190,6 +190,7 @@ impl Focus {
                 }
             ) {
                 self.id = None;
+                self.is_focus_locked = false;
                 break;
             }
 
@@ -293,9 +294,17 @@ impl Memory {
         self.interaction.focus.id == Some(id)
     }
 
-    pub(crate) fn lock_focus(&mut self, id: Id) {
+    pub(crate) fn lock_focus(&mut self, id: Id, b: bool) {
         if self.had_focus_last_frame(id) && self.has_focus(id) {
-            self.interaction.focus.is_focus_locked = true;
+            self.interaction.focus.is_focus_locked = b;
+        }
+    }
+
+    pub(crate) fn has_lock_focus(&mut self, id: Id) -> bool {
+        if self.had_focus_last_frame(id) && self.has_focus(id) {
+            self.interaction.focus.is_focus_locked
+        } else {
+            false
         }
     }
 

egui/src/widgets/text_edit.rs

@@ -136,7 +136,7 @@ pub struct TextEdit<'t> {
     desired_width: Option<f32>,
     desired_height_rows: usize,
     tab_as_spaces: bool,
-    tab_size: usize,
+    tab_moves_focus: bool,
 }
 impl<'t> TextEdit<'t> {
     pub fn cursor(ui: &Ui, id: Id) -> Option<CursorPair> {
@@ -167,8 +167,8 @@ impl<'t> TextEdit<'t> {
             enabled: true,
             desired_width: None,
             desired_height_rows: 1,
-            tab_as_spaces: true,
-            tab_size: 4,
+            tab_as_spaces: false,
+            tab_moves_focus: true,
         }
     }
 
@@ -186,8 +186,8 @@ impl<'t> TextEdit<'t> {
             enabled: true,
             desired_width: None,
             desired_height_rows: 4,
-            tab_as_spaces: true,
-            tab_size: 4,
+            tab_as_spaces: false,
+            tab_moves_focus: true,
         }
     }
 
@@ -202,14 +202,18 @@ impl<'t> TextEdit<'t> {
         self
     }
 
-    /// Registers if this widget will insert spaces instead of tab char
+    /// When this is true, then pass focus to the next
+    /// widget.
+    ///
+    /// When this is false, then insert identation based on the value of
+    /// `tab_as_spaces` property.
     ///
     /// ```rust, ignore
     /// ui.add(egui::TextEdit::multiline(&mut self.multiline_text_input)
-    ///     .tab_size(4));
+    ///     .tab_moves_focus(true));
     /// ```
-    pub fn tab_size(mut self, size: usize) -> Self {
-        self.tab_size = size;
+    pub fn tab_moves_focus(mut self, b: bool) -> Self {
+        self.tab_moves_focus = b;
         self
     }
 
@@ -326,7 +330,7 @@ impl<'t> TextEdit<'t> {
             desired_width,
             desired_height_rows,
             tab_as_spaces,
-            tab_size,
+            tab_moves_focus,
         } = self;
 
         let text_style = text_style.unwrap_or_else(|| ui.style().body_text_style);
@@ -413,9 +417,7 @@ impl<'t> TextEdit<'t> {
         }
 
         if ui.memory().has_focus(id) && enabled {
-            if multiline {
-                ui.memory().lock_focus(id);
-            }
+            ui.memory().lock_focus(id, !tab_moves_focus);
 
             let mut cursorp = state
                 .cursorp
@@ -481,16 +483,12 @@ impl<'t> TextEdit<'t> {
                         if multiline {
                             let mut ccursor = delete_selected(text, &cursorp);
 
-                            if tab_as_spaces {
-                                let mut spaces = String::with_capacity(tab_size);
-
-                                for _ in 0..tab_size {
-                                    spaces.push(' ');
+                            if ui.memory().has_lock_focus(id) {
+                                if tab_as_spaces {
+                                    insert_text(&mut ccursor, text, "    ");
+                                } else {
+                                    insert_text(&mut ccursor, text, "\t");
                                 }
-
-                                insert_text(&mut ccursor, text, &spaces);
-                            } else {
-                                insert_text(&mut ccursor, text, "\t");
                             }
 
                             Some(CCursorPair::one(ccursor))

egui_demo_lib/src/apps/demo/widgets.rs

@@ -25,6 +25,7 @@ pub struct Widgets {
     single_line_text_input: String,
     tab_size: usize,
     tab_as_spaces: bool,
+    tab_moves_focus: bool,
     multiline_text_input: String,
 }
 
@@ -40,6 +41,7 @@ impl Default for Widgets {
 
             tab_size: 4,
             tab_as_spaces: true,
+            tab_moves_focus: false,
             multiline_text_input: r#"Text can both be so wide that it needs a line break, but you can also add manual line break by pressing enter, creating new paragraphs.
 This is the start of the next paragraph.
 
@@ -149,17 +151,14 @@ impl Widgets {
 
             ui.separator();
 
-            ui.add(egui::Slider::usize(&mut self.tab_size, 2..=8).text("Tab size"));
-
-            ui.separator();
-
             ui.checkbox(&mut self.tab_as_spaces, "Tabs as spaces");
+            ui.checkbox(&mut self.tab_moves_focus, "Tabs moves focus");
         });
 
         ui.add(
             egui::TextEdit::multiline(&mut self.multiline_text_input)
-                .tab_as_spaces(self.tab_as_spaces)
-                .tab_size(self.tab_size),
+                .tab_moves_focus(self.tab_moves_focus)
+                .tab_as_spaces(self.tab_as_spaces),
         );
     }
 }