Merge pull request #3628 from lightpanda-io/iterative-axnode

mem: AXNode tree/query walks iterative, isIgnore linear

src/server/cdp/AXNode.zig

@@ -80,15 +80,17 @@ pub const Writer = struct {
     }
 
     fn toJSON(self: *const Writer, w: anytype) !void {
+        const cache_arena = try self.frame.getArena(.medium, "AXNode.IgnoreCache");
+        defer cache_arena.release();
+        var ignore_cache: IgnoreCache = .{ .allocator = cache_arena.allocator() };
+
         try w.beginArray();
         if (self.filter != null) {
-            try self.walkQuery(self.root.dom, false, w);
+            try self.walkQuery(self.root.dom, &ignore_cache, w);
         } else {
             const root = AXNode.fromNode(self.root.dom);
             const root_hidden = if (self.root.dom.is(DOMNode.Element)) |el| isHidden(el, self.frame, .{}) else false;
-            if (try self.writeNode(self.root.id, root, false, root_hidden, w)) {
-                try self.writeNodeChildren(root, false, w);
-            }
+            try self.writeTree(root, root_hidden, &ignore_cache, w);
         }
         return w.endArray();
     }
@@ -118,28 +120,17 @@ pub const Writer = struct {
         try w.write(s);
     }
 
-    fn writeNodeChildren(self: *const Writer, parent: AXNode, in_aria_hidden: bool, w: anytype) !void {
-        // Add ListMarker for listitem elements
-        if (parent.dom.is(DOMNode.Element)) |parent_el| {
-            if (parent_el.getTag() == .li) {
-                try self.writeListMarker(parent.dom, w);
-            }
-        }
-
-        const child_in_aria_hidden = in_aria_hidden or blk: {
-            const parent_el = parent.dom.is(DOMNode.Element) orelse break :blk false;
-            break :blk hasAriaHiddenTrue(parent_el);
-        };
-
-        var it = parent.dom.childrenIterator();
-        const ignore_text = ignoreText(parent.dom);
-        while (it.next()) |dom_node| {
+    fn writeTree(self: *const Writer, root: AXNode, root_hidden: bool, ignore_cache: *IgnoreCache, w: anytype) !void {
+        var walker: Walker = .init(root.dom);
+        var descend = try self.writeNode(self.root.id, root, false, root_hidden, ignore_cache, w);
+        while (walker.next(descend)) |dom_node| {
+            descend = false;
             switch (dom_node._type) {
                 .cdata => {
                     if (dom_node.is(DOMNode.CData.Text) == null) {
                         continue;
                     }
-                    if (ignore_text) {
+                    if (ignoreText(dom_node._parent.?)) {
                         continue;
                     }
                 },
@@ -147,8 +138,8 @@ pub const Writer = struct {
                     // Prune hidden subtrees entirely (display:none,
                     // visibility:hidden, aria-hidden, hidden, inert). Matches
                     // Chromium: these elements aren't exposed to the AX tree.
-                    const child_el = dom_node.as(DOMNode.Element);
-                    if (child_in_aria_hidden or isHidden(child_el, self.frame, .{ .ancestors = false })) {
+                    const el = dom_node.as(DOMNode.Element);
+                    if (walker.inAriaHidden() or isHidden(el, self.frame, .{ .ancestors = false })) {
                         continue;
                     }
                 },
@@ -156,10 +147,7 @@ pub const Writer = struct {
             }
 
             const node = try self.registry.register(dom_node);
-            const axn = AXNode.fromNode(node.dom);
-            if (try self.writeNode(node.id, axn, child_in_aria_hidden, false, w)) {
-                try self.writeNodeChildren(axn, child_in_aria_hidden, w);
-            }
+            descend = try self.writeNode(node.id, .fromNode(dom_node), walker.inAriaHidden(), false, ignore_cache, w);
         }
     }
 
@@ -495,8 +483,7 @@ pub const Writer = struct {
     }
 
     // write a node. returns true if children must be written.
-    fn writeNode(self: *const Writer, id: u32, axn: AXNode, in_aria_hidden: bool, hidden: bool, w: anytype) !bool {
-        // ignore empty texts
+    fn writeNode(self: *const Writer, id: u32, axn: AXNode, in_aria_hidden: bool, hidden: bool, ignore_cache: *IgnoreCache, w: anytype) !bool {
         try w.beginObject();
 
         try w.objectField("nodeId");
@@ -511,7 +498,7 @@ pub const Writer = struct {
         try w.objectField("role");
         try self.writeAXValue(.{ .role = resolved.role }, w);
 
-        const ignore = axn.isIgnore(self.frame, in_aria_hidden, hidden);
+        const ignore = try axn.isIgnore(self.frame, in_aria_hidden, hidden, ignore_cache);
         try w.objectField("ignored");
         try w.write(ignore);
 
@@ -591,7 +578,7 @@ pub const Writer = struct {
                 }
 
                 // Skip hidden element children so childIds matches the
-                // subtree-pruning done in writeNodeChildren.
+                // subtree-pruning done in writeTree.
                 if (child.is(DOMNode.Element)) |child_el| {
                     if (child_in_aria_hidden or isHidden(child_el, self.frame, .{ .ancestors = false })) {
                         continue;
@@ -606,6 +593,14 @@ pub const Writer = struct {
 
         try w.endObject();
 
+        if (write_children) {
+            if (n.is(DOMNode.Element)) |el| {
+                if (el.getTag() == .li) {
+                    try self.writeListMarker(n, w);
+                }
+            }
+        }
+
         return write_children;
     }
 
@@ -648,25 +643,21 @@ pub const Writer = struct {
 
     // Query-mode walk. Visits every node under `root` (including AX-ignored
     // ones, per the queryAXTree spec) and defers emission to emitMatch.
-    fn walkQuery(self: *const Writer, node: *DOMNode, in_aria_hidden: bool, w: anytype) !void {
-        const axn = AXNode.fromNode(node);
-        try self.emitMatch(axn, in_aria_hidden, w);
-
-        // <head>, <script>, <style> never expose AX content — skip recursion.
-        if (axn.ignoreChildren()) return;
-
-        const child_in_aria_hidden = in_aria_hidden or blk: {
-            const parent_el = node.is(DOMNode.Element) orelse break :blk false;
-            break :blk hasAriaHiddenTrue(parent_el);
-        };
-
-        var it = node.childrenIterator();
-        while (it.next()) |child| {
-            switch (child._type) {
+    fn walkQuery(self: *const Writer, root: *DOMNode, ignore_cache: *IgnoreCache, w: anytype) !void {
+        var walker: Walker = .init(root);
+        const root_axn: AXNode = .fromNode(root);
+        try self.emitMatch(root_axn, false, ignore_cache, w);
+        // <head>, <script>, <style> never expose AX content — skip their children.
+        var descend = !root_axn.ignoreChildren();
+        while (walker.next(descend)) |node| {
+            descend = false;
+            switch (node._type) {
                 .element, .cdata => {},
                 else => continue,
             }
-            try self.walkQuery(child, child_in_aria_hidden, w);
+            const axn: AXNode = .fromNode(node);
+            try self.emitMatch(axn, walker.inAriaHidden(), ignore_cache, w);
+            descend = !axn.ignoreChildren();
         }
     }
 
@@ -674,7 +665,7 @@ pub const Writer = struct {
     // the queryAXTree flat-match shape: nodeId, backendDOMNodeId, ignored,
     // role, name, plus empty properties / childIds (clients fetch full
     // properties via getFullAXTree on a matched nodeId).
-    fn emitMatch(self: *const Writer, axn: AXNode, in_aria_hidden: bool, w: anytype) !void {
+    fn emitMatch(self: *const Writer, axn: AXNode, in_aria_hidden: bool, ignore_cache: *IgnoreCache, w: anytype) !void {
         const filter = self.filter.?;
         const resolved = self.resolveRole(axn) catch return;
 
@@ -689,7 +680,7 @@ pub const Writer = struct {
 
         const node = try self.registry.register(axn.dom);
         const hidden = if (axn.dom.is(DOMNode.Element)) |el| isHidden(el, self.frame, .{}) else false;
-        const ignored = axn.isIgnore(self.frame, in_aria_hidden, hidden);
+        const ignored = try axn.isIgnore(self.frame, in_aria_hidden, hidden, ignore_cache);
 
         try w.beginObject();
 
@@ -1131,6 +1122,49 @@ fn writeAccessibleNameFallback(node: *DOMNode, writer: *std.Io.Writer) !void {
     }
 }
 
+/// Pre-order walk counting aria-hidden ancestors (root included), which
+/// TreeWalker can't: it leaves subtrees without saying so.
+const Walker = struct {
+    root: *DOMNode,
+    current: *DOMNode,
+    aria_hidden_ancestors: u32 = 0,
+
+    fn init(root: *DOMNode) Walker {
+        return .{ .root = root, .current = root };
+    }
+
+    /// `descend` false skips the current node's children.
+    fn next(self: *Walker, descend: bool) ?*DOMNode {
+        if (descend) {
+            if (self.current.firstChild()) |child| {
+                if (isAriaHidden(self.current)) self.aria_hidden_ancestors += 1;
+                self.current = child;
+                return child;
+            }
+        }
+
+        var node = self.current;
+        while (node != self.root) {
+            if (node.nextSibling()) |sibling| {
+                self.current = sibling;
+                return sibling;
+            }
+            node = node._parent.?;
+            if (isAriaHidden(node)) self.aria_hidden_ancestors -= 1;
+        }
+        return null;
+    }
+
+    fn inAriaHidden(self: *const Walker) bool {
+        return self.aria_hidden_ancestors > 0;
+    }
+
+    fn isAriaHidden(node: *DOMNode) bool {
+        const el = node.is(DOMNode.Element) orelse return false;
+        return hasAriaHiddenTrue(el);
+    }
+};
+
 fn hasAriaHiddenTrue(elt: *DOMNode.Element) bool {
     if (elt.getAttributeInterned("aria-hidden")) |value| {
         return std.mem.eql(u8, value, "true");
@@ -1322,17 +1356,62 @@ fn ignoreChildren(self: AXNode) bool {
     };
 }
 
-// `hidden` comes from the caller: the tree walk prunes, so its children never
-// are; the root and the query walk probe the whole chain.
-fn isIgnore(self: AXNode, frame: *Frame, in_aria_hidden: bool, hidden: bool) bool {
-    const node = self.dom;
-    const role_attr = self.role_attr;
+// A generic container's answer depends on the ones below it; without a memo,
+// a walk asking about every node of a deep chain is O(depth²).
+const IgnoreCache = struct {
+    allocator: std.mem.Allocator,
+    map: std.AutoHashMapUnmanaged(*DOMNode, bool) = .empty,
 
+    /// Keyed on the node alone: never reached under aria-hidden (ignoreSelf
+    /// says .ignored). `root` isn't cached, walks ask about each node once.
+    fn isGenericIgnored(self: *IgnoreCache, root: *DOMNode, frame: *Frame) !bool {
+        if (self.map.get(root)) |ignored| return ignored;
+
+        var tw = TreeWalker.FullExcludeSelf.init(root, .{});
+        const exposed = while (tw.next()) |node| {
+            const node_hidden = if (node.is(DOMNode.Element)) |el| isHidden(el, frame, .{ .ancestors = false }) else false;
+            switch (AXNode.fromNode(node).ignoreSelf(false, node_hidden)) {
+                .ignored => tw.skipChildren(),
+                .exposed => break node,
+                .generic => {
+                    // Until an exposed node turns up under it.
+                    const gop = try self.map.getOrPut(self.allocator, node);
+                    if (!gop.found_existing) {
+                        gop.value_ptr.* = true;
+                    } else if (gop.value_ptr.*) {
+                        tw.skipChildren();
+                    } else {
+                        break node;
+                    }
+                },
+            }
+        } else return true;
+
+        var node = exposed._parent.?;
+        while (node != root) : (node = node._parent.?) {
+            self.map.getPtr(node).?.* = false;
+        }
+        return false;
+    }
+};
+
+/// `hidden` comes from the caller: the tree walk prunes, so its children never
+/// are; the root and the query walk probe the whole chain.
+fn isIgnore(self: AXNode, frame: *Frame, in_aria_hidden: bool, hidden: bool, cache: *IgnoreCache) !bool {
+    return switch (self.ignoreSelf(in_aria_hidden, hidden)) {
+        .ignored => true,
+        .exposed => false,
+        .generic => cache.isGenericIgnored(self.dom, frame),
+    };
+}
+
+/// isIgnore for `self` alone, leaving generic containers to the caller.
+fn ignoreSelf(self: AXNode, in_aria_hidden: bool, hidden: bool) enum { ignored, exposed, generic } {
     // Don't ignore non-Element node: CData, Document...
-    const elt = node.is(DOMNode.Element) orelse return in_aria_hidden;
+    const elt = self.dom.is(DOMNode.Element) orelse return if (in_aria_hidden) .ignored else .exposed;
     // Ignore non-HTML elements: svg...
     if (elt._type != .html) {
-        return true;
+        return .ignored;
     }
 
     const tag = elt.getTag();
@@ -1341,37 +1420,37 @@ fn isIgnore(self: AXNode, frame: *Frame, in_aria_hidden: bool, hidden: bool) boo
         .script, .style, .meta, .link, .title, .base, .head, .noscript,
         .template, .param, .source, .track, .datalist, .col, .colgroup, .html,
         .body
-        => return true,
+        => return .ignored,
         // zig fmt: on
         .img => {
             // Check for empty decorative images
             const alt_ = elt.getAttributeInterned("alt");
             if (alt_ == null or alt_.?.len == 0) {
-                return true;
+                return .ignored;
             }
         },
         .input => {
             // Check for hidden inputs
             const input = elt.as(DOMNode.Element.Html.Input);
             if (input._input_type == .hidden) {
-                return true;
+                return .ignored;
             }
         },
         else => {},
     }
 
-    if (role_attr) |role| {
+    if (self.role_attr) |role| {
         if (std.ascii.eqlIgnoreCase(role, "none") or std.ascii.eqlIgnoreCase(role, "presentation")) {
-            return true;
+            return .ignored;
         }
     }
 
     if (in_aria_hidden) {
-        return true;
+        return .ignored;
     }
 
     if (hidden) {
-        return true;
+        return .ignored;
     }
 
     // Generic containers with no semantic value
@@ -1381,21 +1460,11 @@ fn isIgnore(self: AXNode, frame: *Frame, in_aria_hidden: bool, hidden: bool) boo
         const has_aria_labelledby = elt.hasAttributeSafe(.wrap("aria-labelledby"));
 
         if (!has_role and !has_aria_label and !has_aria_labelledby) {
-            // Check if it has any non-ignored children.
-            var it = node.childrenIterator();
-            while (it.next()) |child| {
-                const axn = AXNode.fromNode(child);
-                const child_hidden = if (child.is(DOMNode.Element)) |child_el| isHidden(child_el, frame, .{ .ancestors = false }) else false;
-                if (!axn.isIgnore(frame, in_aria_hidden, child_hidden)) {
-                    return false;
-                }
-            }
-
-            return true;
+            return .generic;
         }
     }
 
-    return false;
+    return .exposed;
 }
 
 pub fn getRole(self: AXNode) ![]const u8 {
@@ -2037,3 +2106,29 @@ test "AXNode: writer prunes children when root is hidden" {
     try testing.expect(std.mem.indexOf(u8, json, "under-display-none") == null);
     try testing.expect(std.mem.indexOf(u8, json, "\"childIds\":[]") != null);
 }
+
+test "AXNode: generic containers share memoized ignore answers" {
+    const frame = try testing.base.createFrame();
+    defer testing.base.test_session.closeAllPages();
+
+    const root = try frame.window._document.createElement("div", null, frame);
+    // #b holds only a decorative image; the text under #d exposes #c and #d.
+    try root.setInnerHTML(
+        \\<div id="a"><div id="b"><img></div><div id="c"><span id="d">text</span></div></div>
+    , frame);
+
+    var cache: IgnoreCache = .{ .allocator = testing.arena_allocator };
+    const expected = [_]struct { []const u8, bool }{ .{ "#a", false }, .{ "#b", true }, .{ "#c", false }, .{ "#d", false } };
+    for (expected) |e| {
+        const el = (try root.querySelector(e[0], frame)).?;
+        try testing.expectEqual(e[1], try AXNode.fromNode(el.asNode()).isIgnore(frame, false, false, &cache));
+    }
+    // Filled by #a's scan.
+    try testing.expectEqual(3, cache.map.count());
+
+    var fresh: IgnoreCache = .{ .allocator = testing.arena_allocator };
+    for (expected[1..]) |e| {
+        const el = (try root.querySelector(e[0], frame)).?;
+        try testing.expectEqual(e[1], try AXNode.fromNode(el.asNode()).isIgnore(frame, false, false, &fresh));
+    }
+}