Make sure class={@value} in HEEx is escaped

lib/phoenix_html/tag.ex

@@ -127,6 +127,15 @@ defmodule Phoenix.HTML.Tag do
     {:safe, attrs |> Enum.to_list() |> build_attrs()}
   end
 
+  defp build_attrs([{k, true} | t]),
+    do: [?\s, key_escape(k) | build_attrs(t)]
+
+  defp build_attrs([{_, false} | t]),
+    do: build_attrs(t)
+
+  defp build_attrs([{_, nil} | t]),
+    do: build_attrs(t)
+
   defp build_attrs([{"data", v} | t]) when is_list(v),
     do: nested_attrs(v, " data", t)
 
@@ -145,15 +154,6 @@ defmodule Phoenix.HTML.Tag do
   defp build_attrs([{:class, v} | t]) when is_list(v),
     do: [" class=\"", class_value(v), ?" | build_attrs(t)]
 
-  defp build_attrs([{k, true} | t]),
-    do: [?\s, key_escape(k) | build_attrs(t)]
-
-  defp build_attrs([{_, false} | t]),
-    do: build_attrs(t)
-
-  defp build_attrs([{_, nil} | t]),
-    do: build_attrs(t)
-
   defp build_attrs([{k, v} | t]),
     do: [?\s, key_escape(k), ?=, ?", attr_escape(v), ?" | build_attrs(t)]
 
@@ -172,10 +172,11 @@ defmodule Phoenix.HTML.Tag do
     value
     |> Enum.filter(& &1)
     |> Enum.join(" ")
+    |> attr_escape()
   end
 
   defp class_value(value) do
-    value
+    attr_escape(value)
   end
 
   defp key_escape(value) when is_atom(value), do: String.replace(Atom.to_string(value), "_", "-")

test/phoenix_html/tag_test.exs

@@ -39,11 +39,18 @@ defmodule Phoenix.HTML.TagTest do
 
     test "handle class value as string" do
       assert attributes_escape([{:class, "btn"}]) |> safe_to_string() == ~s( class="btn")
+      assert attributes_escape([{:class, "<active>"}]) |> safe_to_string() == ~s( class="&lt;active&gt;")
     end
 
     test "handle class value as list" do
-      assert attributes_escape([{:class, ["btn", nil, false, "active"]}]) |> safe_to_string() ==
-               ~s( class="btn active")
+      assert attributes_escape([{:class, ["btn", nil, false, "<active>"]}]) |> safe_to_string() ==
+               ~s( class="btn &lt;active&gt;")
+    end
+
+    test "handle class value as false/nil/true" do
+      assert attributes_escape([{:class, false}]) |> safe_to_string() == ~s()
+      assert attributes_escape([{:class, nil}]) |> safe_to_string() == ~s()
+      assert attributes_escape([{:class, true}]) |> safe_to_string() == ~s( class)
     end
 
     test "handle class key as string" do