fix(mouse): preserve held button during movement

CHANGELOG.md

@@ -25,6 +25,8 @@
   the browser; a failed `IO.close` is raised to the caller.
 
 ### Fixed
+- `Mouse#move` with a button held didn't send which button, so Chrome never started a drag. Native HTML5 drag and drop
+  now works with `down`, `move` and `up`, and `Input.dragIntercepted` fires when drags are intercepted [#635]
 - An out-of-process iframe, e.g. Chrome's PDF viewer for an embedded PDF, appearing while a web worker was connected
   raised `'Page.enable' wasn't found` in the event thread. Only pages and iframes are now searched for its parent [#640]
 - A browser that stopped reading its websocket froze the whole client: a large command blocked in a socket write

lib/ferrum/mouse.rb

@@ -152,6 +152,7 @@ def move(x:, y:, steps: 1)
       from_y = @y
       @x = x
       @y = y
+      button = pressed_button
 
       steps.times do |i|
         new_x = from_x + ((@x - from_x) * ((i + 1) / steps.to_f))
@@ -162,6 +163,7 @@ def move(x:, y:, steps: 1)
                       type: "mouseMoved",
                       x: new_x,
                       y: new_y,
+                      button: button,
                       buttons: @buttons)
       end
 
@@ -185,6 +187,10 @@ def validate_button(button)
       button
     end
 
+    def pressed_button
+      BUTTON_MASKS.find { |_name, mask| mask.positive? && @buttons.anybits?(mask) }&.first || "none"
+    end
+
     def register_event_button(type, button)
       case type
       when "mousePressed"

sig/ferrum/mouse.rbs

@@ -29,6 +29,8 @@ module Ferrum
 
     def validate_button: (Symbol button) -> String
 
+    def pressed_button: () -> String
+
     def register_event_button: (String type, String button) -> ::Integer
   end
 end

spec/mouse_spec.rb

@@ -57,6 +57,14 @@
   end
 
   describe "#move" do
+    it "drags and drops with a button held" do
+      browser.go_to("/html5_drag")
+
+      browser.mouse.move(x: 10, y: 10).down.move(x: 250, y: 50, steps: 10).up
+
+      expect(browser.evaluate("window.events")).to eq(%w[dragstart dragover drop dragend])
+    end
+
     it "splits into steps" do
       browser.go_to("/simple")
       browser.mouse.move(x: 100, y: 100)

spec/support/views/html5_drag.erb

@@ -0,0 +1,33 @@
+<!DOCTYPE html>
+<html>
+  <head>
+    <meta http-equiv="Content-type" content="text/html; charset=utf-8"/>
+    <title>ferrum html5 drag and drop</title>
+    <link rel="icon" href="data:,">
+    <style>
+      #source, #target { position: fixed; top: 0; width: 100px; height: 100px; }
+      #source { left: 0; background: red; }
+      #target { left: 200px; background: blue; }
+    </style>
+    <script>
+      window.events = [];
+      document.addEventListener("DOMContentLoaded", () => {
+        const source = document.getElementById("source");
+        const target = document.getElementById("target");
+        for (const type of ["dragstart", "dragend"]) {
+          source.addEventListener(type, () => window.events.push(type));
+        }
+        for (const type of ["dragover", "drop"]) {
+          target.addEventListener(type, event => {
+            event.preventDefault();
+            if (!window.events.includes(type)) window.events.push(type);
+          });
+        }
+      });
+    </script>
+  </head>
+  <body>
+    <div id="source" draggable="true"></div>
+    <div id="target"></div>
+  </body>
+</html>