[Autofill Assistant] Simplify ElementFinder.

This CL is a pure refactoring that aims to simplify ElementFinder by
removing the current_match_arrays_ field.

Instead, ElementFinder now stores all current matches in
current_matches_. If a filter returns more than one match in a JS array,
then this array will be directly resolved and the elements it contains
will be added to current_matches_.

This should make it easier to make ElementFinder return multiple
elements matching a selector in the same order than they have in the
document. See [1] for more background on why we would need that.

[1] https://docs.google.com/document/d/167LaI_WQNr31wBuO3DNlCPD2sx3If2GOHpPsT4atXIk/

Change-Id: I859183d48e0ed85de111c6d7bf0a497363c4e230
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2510331
Commit-Queue: Jordan Demeulenaere <jdemeulenaere@chromium.org>
Reviewed-by: Sandro Maggi <sandromaggi@google.com>
Reviewed-by: Stephane Zermatten <szermatt@chromium.org>
Cr-Commit-Position: refs/heads/master@{#824046}

components/autofill_assistant/browser/web/element_finder.cc

@@ -443,18 +443,6 @@ void ElementFinder::ExecuteNextTask() {
 }
 
 bool ElementFinder::ConsumeOneMatchOrFail(std::string& object_id_out) {
-  // This logic relies on JsFilterBuilder::BuildFunction guaranteeing that
-  // arrays contain at least 2 elements to avoid having to fetch all matching
-  // elements in the common case where we just want to know whether there is at
-  // least one match.
-
-  if (!current_match_arrays_.empty()) {
-    VLOG(1) << __func__ << " Got " << current_match_arrays_.size()
-            << " arrays of 2 or more matches for " << selector_
-            << ", when only 1 match was expected.";
-    SendResult(ClientStatus(TOO_MANY_ELEMENTS));
-    return false;
-  }
   if (current_matches_.size() > 1) {
     VLOG(1) << __func__ << " Got " << current_matches_.size() << " matches for "
             << selector_ << ", when only 1 was expected.";
@@ -472,34 +460,18 @@ bool ElementFinder::ConsumeOneMatchOrFail(std::string& object_id_out) {
 }
 
 bool ElementFinder::ConsumeAnyMatchOrFail(std::string& object_id_out) {
-  // This logic relies on ApplyJsFilters guaranteeing that arrays contain at
-  // least 2 elements to avoid having to fetch all matching elements in the
-  // common case where we just want one match.
-
   if (current_matches_.size() > 0) {
     object_id_out = current_matches_[0];
     current_matches_.clear();
-    current_match_arrays_.clear();
     return true;
   }
-  if (!current_match_arrays_.empty()) {
-    std::string array_object_id = current_match_arrays_[0];
-    current_match_arrays_.clear();
-    ResolveMatchArrays({array_object_id}, /* max_count= */ 1);
-    return false;  // Caller should call again to check
-  }
+
   SendResult(ClientStatus(ELEMENT_RESOLUTION_FAILED));
   return false;
 }
 
 bool ElementFinder::ConsumeAllMatchesOrFail(
     std::vector<std::string>& matches_out) {
-  if (!current_match_arrays_.empty()) {
-    std::vector<std::string> array_object_ids =
-        std::move(current_match_arrays_);
-    ResolveMatchArrays(array_object_ids, /* max_count= */ -1);
-    return false;  // Caller should call again to check
-  }
   if (!current_matches_.empty()) {
     matches_out = std::move(current_matches_);
     current_matches_.clear();
@@ -510,68 +482,74 @@ bool ElementFinder::ConsumeAllMatchesOrFail(
 }
 
 bool ElementFinder::ConsumeMatchArrayOrFail(std::string& array_object_id) {
-  if (current_matches_.empty() && current_match_arrays_.empty()) {
+  if (!current_matches_js_array_.empty()) {
+    array_object_id = current_matches_js_array_;
+    current_matches_js_array_.clear();
+    return true;
+  }
+
+  if (current_matches_.empty()) {
     SendResult(ClientStatus(ELEMENT_RESOLUTION_FAILED));
     return false;
   }
 
-  if (current_matches_.empty() && current_match_arrays_.size() == 1) {
-    array_object_id = current_match_arrays_[0];
-    current_match_arrays_.clear();
-    return true;
+  MoveMatchesToJSArrayRecursive(/* index= */ 0);
+  return false;
+}
+
+void ElementFinder::MoveMatchesToJSArrayRecursive(size_t index) {
+  if (index >= current_matches_.size()) {
+    current_matches_.clear();
+    ExecuteNextTask();
+    return;
   }
 
-  std::vector<std::unique_ptr<runtime::CallArgument>> arguments;
-  std::string object_id;  // Will be "this" in Javascript.
+  // Push the value at |current_matches_[index]| to |current_matches_js_array_|.
   std::string function;
-  if (current_match_arrays_.size() > 1) {
-    object_id = current_match_arrays_.back();
-    current_match_arrays_.pop_back();
-    // Merge both arrays into current_match_arrays_[0]
-    function = "function(dest) { dest.push(...this); }";
-    AddRuntimeCallArgumentObjectId(current_match_arrays_[0], &arguments);
-  } else if (!current_matches_.empty()) {
-    object_id = current_matches_.back();
-    current_matches_.pop_back();
-    if (current_match_arrays_.empty()) {
+  std::vector<std::unique_ptr<runtime::CallArgument>> arguments;
+  if (index == 0) {
     // Create an array containing a single element.
     function = "function() { return [this]; }";
   } else {
     // Add an element to an existing array.
     function = "function(dest) { dest.push(this); }";
-      AddRuntimeCallArgumentObjectId(current_match_arrays_[0], &arguments);
-    }
+    AddRuntimeCallArgumentObjectId(current_matches_js_array_, &arguments);
   }
+
   devtools_client_->GetRuntime()->CallFunctionOn(
       runtime::CallFunctionOnParams::Builder()
-          .SetObjectId(object_id)
+          .SetObjectId(current_matches_[index])
           .SetArguments(std::move(arguments))
           .SetFunctionDeclaration(function)
           .Build(),
       current_frame_id_,
-      base::BindOnce(&ElementFinder::OnConsumeMatchArray,
-                     weak_ptr_factory_.GetWeakPtr()));
-  return false;
+      base::BindOnce(&ElementFinder::OnMoveMatchesToJSArrayRecursive,
+                     weak_ptr_factory_.GetWeakPtr(), index));
 }
 
-void ElementFinder::OnConsumeMatchArray(
+void ElementFinder::OnMoveMatchesToJSArrayRecursive(
+    size_t index,
     const DevtoolsClient::ReplyStatus& reply_status,
     std::unique_ptr<runtime::CallFunctionOnResult> result) {
   ClientStatus status =
       CheckJavaScriptResult(reply_status, result.get(), __FILE__, __LINE__);
   if (!status.ok()) {
-    VLOG(1) << __func__ << ": Failed to get element from array for "
-            << selector_;
+    VLOG(1) << __func__ << ": Failed to push value to JS array.";
     SendResult(status);
     return;
   }
-  if (current_match_arrays_.empty()) {
-    std::string returned_object_id;
-    if (SafeGetObjectId(result->GetResult(), &returned_object_id)) {
-      current_match_arrays_.push_back(returned_object_id);
-    }
+
+  // We just created an array which contains the first element. We store its ID
+  // in |current_matches_js_array_|.
+  if (index == 0 &&
+      !SafeGetObjectId(result->GetResult(), &current_matches_js_array_)) {
+    VLOG(1) << __func__ << " Failed to get array ID.";
+    SendResult(ClientStatus(ELEMENT_RESOLUTION_FAILED));
+    return;
   }
-  ExecuteNextTask();
+
+  // Continue the recursion to push the other values into the array.
+  MoveMatchesToJSArrayRecursive(index + 1);
 }
 
 void ElementFinder::GetDocumentElement() {
@@ -645,14 +623,18 @@ void ElementFinder::OnApplyJsFilters(
     return;
   }
 
-  // The result can be empty (nothing found), a an array (multiple matches
+  // The result can be empty (nothing found), an array (multiple matches
   // found) or a single node.
   std::string object_id;
   if (SafeGetObjectId(result->GetResult(), &object_id)) {
     if (result->GetResult()->HasSubtype() &&
         result->GetResult()->GetSubtype() ==
             runtime::RemoteObjectSubtype::ARRAY) {
-      current_match_arrays_.emplace_back(object_id);
+      // Return early because ResolveMatchArrayRecursive will call
+      // DecrementResponseCountAndContinue() once it has finished processing the
+      // array.
+      ResolveMatchArrayRecursive(object_id, /* index= */ 0);
+      return;
     } else {
       current_matches_.emplace_back(object_id);
     }
@@ -978,24 +960,9 @@ void ElementFinder::OnProximityFilterJs(
   ExecuteNextTask();
 }
 
-void ElementFinder::ResolveMatchArrays(
-    const std::vector<std::string>& array_object_ids,
-    int max_count) {
-  if (array_object_ids.empty()) {
-    // Nothing to do
-    ExecuteNextTask();
-    return;
-  }
-  pending_response_count_ = array_object_ids.size();
-  for (const std::string& array_object_id : array_object_ids) {
-    ResolveMatchArrayRecursive(array_object_id, 0, max_count);
-  }
-}
-
 void ElementFinder::ResolveMatchArrayRecursive(
     const std::string& array_object_id,
-    int index,
-    int max_count) {
+    int index) {
   std::vector<std::unique_ptr<runtime::CallArgument>> arguments;
   AddRuntimeCallArgument(index, &arguments);
   devtools_client_->GetRuntime()->CallFunctionOn(
@@ -1006,14 +973,12 @@ void ElementFinder::ResolveMatchArrayRecursive(
           .Build(),
       current_frame_id_,
       base::BindOnce(&ElementFinder::OnResolveMatchArray,
-                     weak_ptr_factory_.GetWeakPtr(), array_object_id, index,
-                     max_count));
+                     weak_ptr_factory_.GetWeakPtr(), array_object_id, index));
 }
 
 void ElementFinder::OnResolveMatchArray(
     const std::string& array_object_id,
     int index,
-    int max_count,
     const DevtoolsClient::ReplyStatus& reply_status,
     std::unique_ptr<runtime::CallFunctionOnResult> result) {
   ClientStatus status =
@@ -1024,22 +989,18 @@ void ElementFinder::OnResolveMatchArray(
     SendResult(status);
     return;
   }
+
   std::string object_id;
   if (!SafeGetObjectId(result->GetResult(), &object_id)) {
-    // We've reached the end of the array
+    // We've reached the end of the array.
     DecrementResponseCountAndContinue();
     return;
   }
 
   current_matches_.emplace_back(object_id);
-  int next_index = index + 1;
-  if (max_count != -1 && next_index >= max_count) {
-    DecrementResponseCountAndContinue();
-    return;
-  }
 
   // Fetch the next element.
-  ResolveMatchArrayRecursive(array_object_id, next_index, max_count);
+  ResolveMatchArrayRecursive(array_object_id, index + 1);
 }
 
 void ElementFinder::DecrementResponseCountAndContinue() {

components/autofill_assistant/browser/web/element_finder.h

@@ -200,10 +200,12 @@ class ElementFinder : public WebControllerWorker {
 
   // Make sure there's at least one match and move them all into a single array.
   //
-  // If there are no matches, call SendResult() return false. If there are
-  // matches, but they're not in a single array, move the element into the array
-  // in the background and return false. ExecuteNextTask() is called again once
-  // the background tasks have executed.
+  // If there are no matches, call SendResult() and return false.
+  //
+  // If there are matches, return false directly and move the matches into
+  // an JS array in the background. ExecuteNextTask() is called again
+  // once the background tasks have executed, and calling this will return true
+  // and write the JS array id to |array_object_id_out|.
   bool ConsumeMatchArrayOrFail(std::string& array_object_id_out);
 
   void OnConsumeMatchArray(
@@ -254,27 +256,14 @@ class ElementFinder : public WebControllerWorker {
       const DevtoolsClient::ReplyStatus& reply_status,
       std::unique_ptr<runtime::CallFunctionOnResult> result);
 
-  // Get elements from |array_object_ids|, and put the result into
-  // |element_matches_|.
-  //
-  // This calls ExecuteNextTask() once all the elements of all the arrays are in
-  // |element_matches_|. If |max_count| is -1, fetch until the end of the array,
-  // otherwise fetch |max_count| elements at most in each array.
-  void ResolveMatchArrays(const std::vector<std::string>& array_object_ids,
-                          int max_count);
-
-  // ResolveMatchArrayRecursive calls itself recursively, incrementing |index|,
-  // as long as there are elements. The chain of calls end with
-  // DecrementResponseCountAndContinue() as there can be more than one such
-  // chains executing at a time.
-  void ResolveMatchArrayRecursive(const std::string& array_object_ids,
-                                  int index,
-                                  int max_count);
+  // Get all elements from |array_object_id| starting from |index| and put them
+  // into |current_matches_|, then call DecrementResponseCountAndContinue().
+  void ResolveMatchArrayRecursive(const std::string& array_object_id,
+                                  int index);
 
   void OnResolveMatchArray(
       const std::string& array_object_id,
       int index,
-      int max_count,
       const DevtoolsClient::ReplyStatus& reply_status,
       std::unique_ptr<runtime::CallFunctionOnResult> result);
 
@@ -282,6 +271,16 @@ class ElementFinder : public WebControllerWorker {
   // has reached 0.
   void DecrementResponseCountAndContinue();
 
+  // Fill |current_matches_js_array_| with the values in |current_matches_|
+  // starting from |index|, then clear |current_matches_| and call
+  // ExecuteNextTask().
+  void MoveMatchesToJSArrayRecursive(size_t index);
+
+  void OnMoveMatchesToJSArrayRecursive(
+      size_t index,
+      const DevtoolsClient::ReplyStatus& reply_status,
+      std::unique_ptr<runtime::CallFunctionOnResult> result);
+
   content::WebContents* const web_contents_;
   DevtoolsClient* const devtools_client_;
   const Selector selector_;
@@ -304,16 +303,12 @@ class ElementFinder : public WebControllerWorker {
 
   // Object IDs of the current set matching elements. Cleared once it's used to
   // query or filter.
-  //
-  // More matches can be found in |current_match_arrays_|. Use one of the
-  // Consume*Match() function to current matches.
   std::vector<std::string> current_matches_;
 
-  // Object ID of arrays of at least 2 matching elements.
-  //
-  // More matches can be found in |current_matches_|. Use one of the
-  // Consume*Match() function to current matches.
-  std::vector<std::string> current_match_arrays_;
+  // Object ID of the JavaScript array of the currently matching elements. In
+  // practice, this is used by ConsumeMatchArrayOrFail() to convert
+  // |current_matches_| to a JavaScript array.
+  std::string current_matches_js_array_;
 
   // True if current_matches are pseudo-elements.
   bool matching_pseudo_elements_ = false;