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 moves sent while a button is held now include the active `button` value, allowing Chrome to start drag sessions
+  and emit `Input.dragIntercepted` [#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

@@ -156,12 +156,14 @@ def move(x:, y:, steps: 1)
       steps.times do |i|
         new_x = from_x + ((@x - from_x) * ((i + 1) / steps.to_f))
         new_y = from_y + ((@y - from_y) * ((i + 1) / steps.to_f))
+        button = BUTTON_MASKS.find { |_name, mask| mask.positive? && @buttons.anybits?(mask) }&.first || "none"
 
         @page.command("Input.dispatchMouseEvent",
                       slowmoable: true,
                       type: "mouseMoved",
                       x: new_x,
                       y: new_y,
+                      button: button,
                       buttons: @buttons)
       end
 

spec/mouse_spec.rb

@@ -57,6 +57,29 @@
   end
 
   describe "#move" do
+    it "preserves the pressed button for drag interception" do
+      browser.go_to("/simple")
+      browser.execute(<<~JS)
+        const source = document.createElement("div");
+        source.draggable = true;
+        source.style.cssText = "position:fixed;left:0;top:0;width:100px;height:100px";
+        document.body.appendChild(source);
+      JS
+
+      intercepted = Queue.new
+      browser.page.on("Input.dragIntercepted") { |params| intercepted << params }
+      browser.page.command("Input.setInterceptDrags", enabled: true)
+
+      browser.mouse.move(x: 10, y: 10)
+             .down(button: :left)
+             .move(x: 80, y: 80, steps: 5)
+
+      expect(intercepted.pop(timeout: 1)).not_to be_nil
+    ensure
+      browser&.mouse&.up(button: :left)
+      browser&.page&.command("Input.setInterceptDrags", enabled: false)
+    end
+
     it "splits into steps" do
       browser.go_to("/simple")
       browser.mouse.move(x: 100, y: 100)