From e3c5bd6fae4e6d7b169a027fea4d5f301d6b3784 Mon Sep 17 00:00:00 2001
From: Steffen Deusch <steffen@deusch.me>
Date: Fri, 20 Feb 2026 12:46:52 +0000
Subject: [PATCH] Strip EEx comments in parser when compiling templates

Fixes #4144.

When we simplified root tracking in #4125, we did not account for
EEx comments (<%!-- ... --%>). Since those are just ignored in the
compiler, we can already omit them at the tokenizer level.
---
 lib/phoenix_live_view/tag_engine.ex          |  2 +-
 lib/phoenix_live_view/tag_engine/compiler.ex |  5 -----
 lib/phoenix_live_view/tag_engine/parser.ex   | 16 +++++++++++++---
 test/phoenix_live_view/html_engine_test.exs  |  1 +
 4 files changed, 15 insertions(+), 9 deletions(-)

diff --git a/lib/phoenix_live_view/tag_engine.ex b/lib/phoenix_live_view/tag_engine.ex
index 78f1443a27..d336438fc2 100644
--- a/lib/phoenix_live_view/tag_engine.ex
+++ b/lib/phoenix_live_view/tag_engine.ex
@@ -44,7 +44,7 @@ defmodule Phoenix.LiveView.TagEngine do
         file: "nofile",
         engine: Phoenix.LiveView.Engine
       ])
-      |> Keyword.merge(source: source, trim_eex: false)
+      |> Keyword.merge(source: source, trim_eex: false, strip_eex_comments: true)
 
     source
     |> TagEngine.Parser.parse!(options)
diff --git a/lib/phoenix_live_view/tag_engine/compiler.ex b/lib/phoenix_live_view/tag_engine/compiler.ex
index 9047cb839b..de30255caf 100644
--- a/lib/phoenix_live_view/tag_engine/compiler.ex
+++ b/lib/phoenix_live_view/tag_engine/compiler.ex
@@ -94,11 +94,6 @@ defmodule Phoenix.LiveView.TagEngine.Compiler do
     {state, substate}
   end
 
-  ## Skip EEx comments (<%!-- ... --%>)
-  defp handle_node({:eex_comment, _text}, substate, state) do
-    {state, substate}
-  end
-
   ## HEEx interpolation {...}
   defp handle_node({:body_expr, expr, %{line: line, column: column}}, substate, state) do
     ast = Code.string_to_quoted!(expr, line: line, column: column, file: state.file)
diff --git a/lib/phoenix_live_view/tag_engine/parser.ex b/lib/phoenix_live_view/tag_engine/parser.ex
index 3c1b85d24d..7da8bd97eb 100644
--- a/lib/phoenix_live_view/tag_engine/parser.ex
+++ b/lib/phoenix_live_view/tag_engine/parser.ex
@@ -112,13 +112,19 @@ defmodule Phoenix.LiveView.TagEngine.Parser do
     file = Keyword.get(opts, :file, "nofile")
     indentation = Keyword.get(opts, :indentation, 0)
     trim_eex = Keyword.get(opts, :trim_eex, true)
+    strip_eex_comments = Keyword.get(opts, :strip_eex_comments, false)
     {:ok, eex_nodes} = EEx.tokenize(source, opts)
 
     {tokens, cont} =
       Enum.reduce(
         eex_nodes,
         {[], {:text, :enabled}},
-        &do_tokenize(&1, &2, source, %{file: file, indentation: indentation, trim_eex: trim_eex})
+        &do_tokenize(&1, &2, source, %{
+          file: file,
+          indentation: indentation,
+          trim_eex: trim_eex,
+          strip_eex_comments: strip_eex_comments
+        })
       )
 
     Tokenizer.finalize(tokens, file, cont, source)
@@ -134,8 +140,12 @@ defmodule Phoenix.LiveView.TagEngine.Parser do
     Tokenizer.tokenize(text, meta, tokens, cont, state)
   end
 
-  defp do_tokenize({:comment, text, meta}, {tokens, cont}, _contents, _opts) do
-    {[{:eex_comment, List.to_string(text), meta} | tokens], cont}
+  defp do_tokenize({:comment, text, meta}, {tokens, cont}, _contents, opts) do
+    if opts.strip_eex_comments do
+      {tokens, cont}
+    else
+      {[{:eex_comment, List.to_string(text), meta} | tokens], cont}
+    end
   end
 
   defp do_tokenize(
diff --git a/test/phoenix_live_view/html_engine_test.exs b/test/phoenix_live_view/html_engine_test.exs
index 73e17e9c45..bf95d172de 100644
--- a/test/phoenix_live_view/html_engine_test.exs
+++ b/test/phoenix_live_view/html_engine_test.exs
@@ -1432,6 +1432,7 @@ defmodule Phoenix.LiveView.HTMLEngineTest do
 
       assert eval("  <foo></foo>  ").root == true
       assert eval("\n\n<foo></foo>\n").root == true
+      assert eval("<%!-- comment --%>\n\n<foo></foo>\n").root == true
     end
 
     test "invalid cases" do