Style: forbid .zip and .chain (#8188)

The `zip(a, b)` variant produces clearer code imho.

Downside: added dependency on `itertools`

Cargo.lock

@@ -1257,6 +1257,7 @@ dependencies = [
  "document-features",
  "emath",
  "epaint",
+ "itertools 0.14.0",
  "log",
  "nohash-hasher",
  "profiling",
@@ -1363,6 +1364,7 @@ dependencies = [
  "ehttp",
  "enum-map",
  "image",
+ "itertools 0.14.0",
  "jiff",
  "log",
  "mime_guess2",

Cargo.toml

@@ -96,6 +96,7 @@ glutin-winit = { version = "0.5.0", default-features = false }
 harfrust = "0.7.0"
 home = "0.5.9"
 image = { version = "0.25.6", default-features = false }
+itertools = "0.14.0"
 jiff = { version = "0.2.23", default-features = false }
 js-sys = "0.3.77"
 kittest = { version = "0.4.0" }

crates/ecolor/src/color32.rs

@@ -489,7 +489,7 @@ mod test {
             } else {
                 // There will be small rounding errors whenever the alpha is not 0 or 255,
                 // because we multiply and then unmultiply the alpha.
-                for (&a, &b) in in_rgba.iter().zip(out_rgba.iter()) {
+                for (&a, &b) in std::iter::zip(&in_rgba, &out_rgba) {
                     assert!(a.abs_diff(b) <= 3, "{in_rgba:?} != {out_rgba:?}");
                 }
             }

crates/ecolor/src/rgba.rs

@@ -336,7 +336,7 @@ mod test {
             } else {
                 // There will be small rounding errors whenever the alpha is not 0 or 255,
                 // because we multiply and then unmultiply the alpha.
-                for (&a, &b) in in_rgba.iter().zip(out_rgba.iter()) {
+                for (&a, &b) in std::iter::zip(&in_rgba, &out_rgba) {
                     assert!(a.abs_diff(b) <= 3, "{in_rgba:?} != {out_rgba:?}");
                 }
             }

crates/eframe/src/web/input.rs

@@ -31,11 +31,12 @@ pub fn primary_touch_pos(
     runner: &mut AppRunner,
     event: &web_sys::TouchEvent,
 ) -> Option<(egui::Pos2, web_sys::Touch)> {
-    let all_touches: Vec<_> = (0..event.touches().length())
+    // On touchend we don't get anything in `touches`, but we still get `changed_touches`, so include those:
-        .filter_map(|i| event.touches().get(i))
+    let all_touches: Vec<_> = std::iter::chain(
-        // On touchend we don't get anything in `touches`, but we still get `changed_touches`, so include those:
+        (0..event.touches().length()).filter_map(|i| event.touches().get(i)),
-        .chain((0..event.changed_touches().length()).filter_map(|i| event.changed_touches().get(i)))
+        (0..event.changed_touches().length()).filter_map(|i| event.changed_touches().get(i)),
-        .collect();
+    )
+    .collect();
 
     if let Some(primary_touch) = runner.input.primary_touch {
         // Is the primary touch is gone?

crates/eframe/src/web/web_painter_wgpu.rs

@@ -365,7 +365,7 @@ impl WebPainter for WebPainterWgpu {
         // Submit the commands: both the main buffer and user-defined ones.
         render_state
             .queue
-            .submit(user_cmd_bufs.into_iter().chain([encoder.finish()]));
+            .submit(std::iter::chain(user_cmd_bufs, [encoder.finish()]));
 
         if let Some((frame, capture_buffer)) = frame_and_capture_buffer {
             if let Some(capture_buffer) = capture_buffer

crates/egui-wgpu/src/winit.rs

@@ -715,7 +715,7 @@ impl Painter {
             let start = web_time::Instant::now();
             render_state
                 .queue
-                .submit(user_cmd_bufs.into_iter().chain([encoded]));
+                .submit(std::iter::chain(user_cmd_bufs, [encoded]));
             vsync_sec += start.elapsed().as_secs_f32();
         };
 

crates/egui/Cargo.toml

@@ -74,6 +74,7 @@ epaint = { workspace = true, default-features = false }
 accesskit.workspace = true
 ahash.workspace = true
 bitflags.workspace = true
+itertools.workspace = true
 log.workspace = true
 nohash-hasher.workspace = true
 profiling.workspace = true

crates/egui/src/containers/popup.rs

@@ -472,17 +472,15 @@ impl<'a> Popup<'a> {
         RectAlign::find_best_align(
             #[expect(clippy::iter_on_empty_collections)]
             #[expect(clippy::or_fun_call)]
-            once(self.rect_align).chain(
+            std::iter::chain(
+                once(self.rect_align),
                 self.alternative_aligns
                     // Need the empty slice so the iters have the same type so we can unwrap_or
-                    .map(|a| a.iter().copied().chain([].iter().copied()))
+                    .map(|a| std::iter::chain(a.iter().copied(), [].iter().copied()))
-                    .unwrap_or(
+                    .unwrap_or(std::iter::chain(
-                        self.rect_align
+                        self.rect_align.symmetries().iter().copied(),
-                            .symmetries()
+                        RectAlign::MENU_ALIGNS.iter().copied(),
-                            .iter()
+                    )),
-                            .copied()
-                            .chain(RectAlign::MENU_ALIGNS.iter().copied()),
-                    ),
             ),
             self.ctx.content_rect(),
             anchor_rect,

crates/egui/src/context.rs

@@ -641,11 +641,7 @@ impl ContextImpl {
     }
 
     fn all_viewport_ids(&self) -> ViewportIdSet {
-        self.viewports
+        std::iter::chain(self.viewports.keys().copied(), [ViewportId::ROOT]).collect()
-            .keys()
-            .copied()
-            .chain([ViewportId::ROOT])
-            .collect()
     }
 
     /// The current active viewport

crates/egui/src/interaction.rs

@@ -232,20 +232,14 @@ pub(crate) fn interact(
     //     );
     // }
 
-    let contains_pointer: IdSet = hits
+    let contains_pointer: IdSet =
-        .contains_pointer
+        itertools::chain!(&hits.contains_pointer, &hits.click, &hits.drag)
-        .iter()
+            .map(|w| w.id)
-        .chain(&hits.click)
+            .collect();
-        .chain(&hits.drag)
-        .map(|w| w.id)
-        .collect();
 
     let hovered = if clicked.is_some() || dragged.is_some() || long_touched.is_some() {
         // If currently clicking or dragging, only that and nothing else is hovered.
-        clicked
+        itertools::chain!(&clicked, &dragged, &long_touched)
-            .iter()
-            .chain(&dragged)
-            .chain(&long_touched)
             .copied()
             .collect()
     } else {
@@ -268,7 +262,9 @@ pub(crate) fn interact(
         let drag_order = hits.drag.and_then(|w| order(w.id)).unwrap_or(0);
         let top_interactive_order = click_order.max(drag_order);
 
-        let mut hovered: IdSet = hits.click.iter().chain(&hits.drag).map(|w| w.id).collect();
+        let mut hovered: IdSet = std::iter::chain(&hits.click, &hits.drag)
+            .map(|w| w.id)
+            .collect();
 
         for w in &hits.contains_pointer {
             let is_interactive = w.sense.senses_click() || w.sense.senses_drag();

crates/egui/src/memory/mod.rs

@@ -1232,11 +1232,12 @@ impl Areas {
     }
 
     pub fn visible_layer_ids(&self) -> ahash::HashSet<LayerId> {
-        self.visible_areas_last_frame
+        std::iter::chain(
-            .iter()
+            &self.visible_areas_last_frame,
-            .copied()
+            &self.visible_areas_current_frame,
-            .chain(self.visible_areas_current_frame.iter().copied())
+        )
-            .collect()
+        .copied()
+        .collect()
     }
 
     pub(crate) fn visible_windows(&self) -> impl Iterator<Item = (LayerId, &area::AreaState)> {

crates/egui_extras/Cargo.toml

@@ -74,6 +74,7 @@ egui = { workspace = true, default-features = false }
 
 ahash.workspace = true
 enum-map.workspace = true
+itertools.workspace = true
 log.workspace = true
 profiling.workspace = true
 

crates/egui_extras/src/table.rs

@@ -619,11 +619,8 @@ impl TableState {
             // to take up the remainder of the current available width.
             // Also handles changing item spacing.
             let mut sizing = crate::sizing::Sizing::default();
-            for ((prev_width, max_used), column) in state
+            for (prev_width, max_used, column) in
-                .column_widths
+                itertools::izip!(&state.column_widths, &state.max_used_widths, columns)
-                .iter()
-                .zip(&state.max_used_widths)
-                .zip(columns)
             {
                 use crate::Size;
 

crates/egui_kittest/src/wgpu.rs

@@ -222,7 +222,7 @@ impl crate::TestRenderer for WgpuTestRenderer {
 
         self.render_state
             .queue
-            .submit(user_buffers.into_iter().chain(once(encoder.finish())));
+            .submit(std::iter::chain(user_buffers, once(encoder.finish())));
 
         self.render_state
             .device

crates/epaint/src/text/font.rs

@@ -508,12 +508,7 @@ impl FontFace {
         let axes = font_data.skrifa.axes();
         // Override the default coordinates with ones specified via FontTweak, then the ones specified directly via the
         // argument (probably from TextFormat).
-        let settings = self
+        let settings = std::iter::chain(self.tweak.coords.as_ref(), coords.as_ref());
-            .tweak
-            .coords
-            .as_ref()
-            .iter()
-            .chain(coords.as_ref().iter());
         let location = axes.location(settings);
 
         StyledMetrics {

crates/epaint/src/text/text_layout.rs

@@ -1,7 +1,7 @@
 #![expect(clippy::unwrap_used)] // TODO(emilk): remove unwraps
 
-use std::ops::Range;
 use std::sync::Arc;
+use std::{iter, ops::Range};
 
 use emath::{Align, GuiRounding as _, NumExt as _, Pos2, Rect, Vec2, pos2, vec2};
 
@@ -244,11 +244,7 @@ fn layout_shaped_run(
     let mut cluster_start_byte: usize = 0;
     let mut cluster_glyph_count: usize = 0;
 
-    for (info, pos) in glyph_buffer
+    for (info, pos) in iter::zip(glyph_buffer.glyph_infos(), glyph_buffer.glyph_positions()) {
-        .glyph_infos()
-        .iter()
-        .zip(glyph_buffer.glyph_positions())
-    {
         let glyph_id = skrifa::GlyphId::new(info.glyph_id);
         let cluster = info.cluster;
         let mut advance_width_px = pos.x_advance as f32 * px_scale;
@@ -525,7 +521,7 @@ fn layout_section(
 /// Avoids `Box<dyn Iterator>` and `Vec<&str>` allocation.
 enum SplitOrWhole<'a> {
     Split(std::str::Split<'a, char>),
-    Whole(std::iter::Once<&'a str>),
+    Whole(iter::Once<&'a str>),
 }
 
 impl<'a> SplitOrWhole<'a> {
@@ -533,7 +529,7 @@ impl<'a> SplitOrWhole<'a> {
         if split {
             Self::Split(text.split('\n'))
         } else {
-            Self::Whole(std::iter::once(text))
+            Self::Whole(iter::once(text))
         }
     }
 }
@@ -1406,11 +1402,7 @@ fn shape_text(
     let tweak = font_face.tweak();
 
     // Build shaper with variable font instance if variation coordinates are set.
-    let variations: Vec<harfrust::Variation> = tweak
+    let variations: Vec<harfrust::Variation> = iter::chain(tweak.coords.as_ref(), coords.as_ref())
-        .coords
-        .as_ref()
-        .iter()
-        .chain(coords.as_ref().iter())
         .map(|&(tag, value)| harfrust::Variation { tag, value })
         .collect();
 
@@ -1439,6 +1431,7 @@ fn shape_text(
 
 #[cfg(test)]
 mod tests {
+    use std::iter;
 
     use super::{super::*, *};
     use crate::text::cursor::CCursor;
@@ -1575,10 +1568,11 @@ mod tests {
                     &mut fonts,
                     pixels_per_point,
                     Arc::new(LayoutJob::single_section(
-                        (0..elided_galley.rows[0].char_count_excluding_newline())
+                        iter::chain(
-                            .map(|_| ch)
+                            (0..elided_galley.rows[0].char_count_excluding_newline()).map(|_| ch),
-                            .chain(std::iter::once('…'))
+                            iter::once('…'),
-                            .collect::<String>(),
+                        )
+                        .collect::<String>(),
                         TextFormat::default(),
                     )),
                 );

scripts/lint.py

@@ -72,6 +72,16 @@ def lint_lines(filepath, lines_in):
                 f"{filepath}:{line_nr}: write 'TODO(username):' instead"
             )
 
+        if re.search(r"\.zip\(", line):
+            errors.append(
+                f"{filepath}:{line_nr}: use `std::iter::zip` or `itertools::izip!` instead of `.zip(`"
+            )
+
+        if re.search(r"\.chain\(", line):
+            errors.append(
+                f"{filepath}:{line_nr}: use `std::iter::chain` or `itertools::chain!` instead of `.chain(`"
+            )
+
         if (
             "(target_os" in line
             and filepath.startswith("./crates/egui/")
@@ -105,6 +115,10 @@ def test_lint():
             self
         }
         """,
+        "for (a, b) in std::iter::zip(xs, ys) {}",
+        "for (a, b, c) in itertools::izip!(xs, ys, zs) {}",
+        "for x in std::iter::chain(xs, ys) {}",
+        "for x in itertools::chain!(xs, ys, zs) {}",
     ]
 
     should_fail = [
@@ -121,6 +135,8 @@ def test_lint():
             self
         }
         """,
+        "for (a, b) in xs.iter().zip(ys) {}",
+        "for x in xs.iter().chain(ys) {}",
     ]
 
     for code in should_pass: