Adds iterators and a check to avoid segfault when removing node in LinkedList.

Bug: dawn:628
Change-Id: I1250ffe303155004572c2476ec357daa78b7bb3b
Reviewed-on: https://dawn-review.googlesource.com/c/dawn/+/65860
Commit-Queue: Loko Kung <lokokung@google.com>
Reviewed-by: Austin Eng <enga@chromium.org>

src/common/LinkedList.h

diff --git a/src/common/LinkedList.h b/src/common/LinkedList.h
index 47ca1eb..9b89ad5 100644
--- a/src/common/LinkedList.h
+++ b/src/common/LinkedList.h
@@ -2,7 +2,10 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-// This file is a copy of Chromium's /src/base/containers/linked_list.h
+// This file is a copy of Chromium's /src/base/containers/linked_list.h with the following
+// modifications:
+//   - Added iterators for ranged based iterations
+//   - Added in list check before removing node to prevent segfault, now returns true iff removed
 
 #ifndef COMMON_LINKED_LIST_H
 #define COMMON_LINKED_LIST_H
@@ -43,6 +46,11 @@
 //     ...
 //   }
 //
+//   for (LinkNode<MyNodeType*> node : list) {
+//     MyNodeType* value = node->value();
+//     ...
+//   }
+//
 // Or to iterate the linked list backwards:
 //
 //   for (LinkNode<MyNodeType>* node = list.tail();
@@ -125,14 +133,18 @@
         return this->next_ != nullptr;
     }
 
-    // Remove |this| from the linked list.
-    void RemoveFromList() {
+    // Remove |this| from the linked list. Returns true iff removed from a list.
+    bool RemoveFromList() {
+        if (!IsInList()) {
+            return false;
+        }
+
         this->previous_->next_ = this->next_;
         this->next_->previous_ = this->previous_;
-        // next() and previous() return non-null if and only this node is not in any
-        // list.
+        // next() and previous() return non-null if and only this node is not in any list.
         this->next_ = nullptr;
         this->previous_ = nullptr;
+        return true;
     }
 
     LinkNode<T>* previous() const {
@@ -197,4 +209,44 @@
   private:
     LinkNode<T> root_;
 };
+
+template <typename T>
+class LinkedListIterator {
+  public:
+    LinkedListIterator(LinkNode<T>* node) : current_(node), next_(node->next()) {
+    }
+
+    // We keep an early reference to the next node in the list so that even if the current element
+    // is modified or removed from the list, we have a valid next node.
+    LinkedListIterator<T> const& operator++() {
+        current_ = next_;
+        next_ = current_->next();
+        return *this;
+    }
+
+    bool operator!=(const LinkedListIterator<T>& other) const {
+        return current_ != other.current_;
+    }
+
+    LinkNode<T>* operator*() const {
+        return current_;
+    }
+
+  private:
+    LinkNode<T>* current_;
+    LinkNode<T>* next_;
+};
+
+template <typename T>
+LinkedListIterator<T> begin(LinkedList<T>& l) {
+    return LinkedListIterator<T>(l.head());
+}
+
+// Free end function does't use LinkedList<T>::end because of it's const nature. Instead we wrap
+// around from tail.
+template <typename T>
+LinkedListIterator<T> end(LinkedList<T>& l) {
+    return LinkedListIterator<T>(l.tail()->next());
+}
+
 #endif  // COMMON_LINKED_LIST_H

src/tests/unittests/LinkedListTests.cpp

diff --git a/src/tests/unittests/LinkedListTests.cpp b/src/tests/unittests/LinkedListTests.cpp
index 7dcb37f..1a06d8c 100644
--- a/src/tests/unittests/LinkedListTests.cpp
+++ b/src/tests/unittests/LinkedListTests.cpp
@@ -19,6 +19,10 @@
         return id_;
     }
 
+    void set_id(int id) {
+        id_ = id;
+    }
+
   private:
     int id_;
 };
@@ -360,6 +364,27 @@
     EXPECT_FALSE(n.IsInList());
     list.Append(&n);
     EXPECT_TRUE(n.IsInList());
-    n.RemoveFromList();
+    EXPECT_TRUE(n.RemoveFromList());
     EXPECT_FALSE(n.IsInList());
+    EXPECT_FALSE(n.RemoveFromList());
+}
+
+TEST(LinkedList, RangeBasedModify) {
+    LinkedList<Node> list;
+
+    Node n1(1);
+    Node n2(2);
+    list.Append(&n1);
+    list.Append(&n2);
+
+    for (LinkNode<Node>* node : list) {
+        node->value()->set_id(node->value()->id() + 1);
+    }
+    const int expected[] = {2, 3};
+    ExpectListContents(list, 2, expected);
+}
+
+TEST(LinkedList, RangeBasedEndIsEnd) {
+    LinkedList<Node> list;
+    EXPECT_EQ(list.end(), *end(list));
 }