From 2bbc791dacebfaea7ae0a610ff6ff790e8c7e341 Mon Sep 17 00:00:00 2001
From: Aaron Tinio <aptinio@gmail.com>
Date: Sat, 25 Jul 2026 07:43:42 +0800
Subject: [PATCH 1/5] Pass :sigils to mix format plugins invoked for a sigil

mix format passes the :sigils option to a plugin invoked for a file
extension, but not to a plugin invoked for a sigil, because the sigil
formatter closure captures the options before :sigils is put into them.
A plugin that formats embedded Elixir code therefore cannot dispatch a
sigil nested inside the sigil it is formatting by passing on the options
it received, so the same snippet formats differently in a .heex file and
in an ~H sigil.

The sigil formatters are part of the options they receive, so a private
function rebuilds the list whenever a sigil is formatted.
---
 lib/mix/lib/mix/tasks/format.ex        | 32 ++++++++------
 lib/mix/test/mix/tasks/format_test.exs | 60 ++++++++++++++++++++++++++
 2 files changed, 79 insertions(+), 13 deletions(-)

diff --git a/lib/mix/lib/mix/tasks/format.ex b/lib/mix/lib/mix/tasks/format.ex
index b19e82ed316..85dfc95bea9 100644
--- a/lib/mix/lib/mix/tasks/format.ex
+++ b/lib/mix/lib/mix/tasks/format.ex
@@ -354,19 +354,7 @@ defmodule Mix.Tasks.Format do
           sigil <- find_sigils_from_plugins(plugin, formatter_opts),
           do: {sigil, plugin}
 
-    sigils =
-      sigils
-      |> Enum.group_by(&elem(&1, 0), &elem(&1, 1))
-      |> Enum.map(fn {sigil, plugins} ->
-        {sigil,
-         fn input, opts ->
-           Enum.reduce(plugins, input, fn plugin, input ->
-             plugin.format(input, opts ++ formatter_opts)
-           end)
-         end}
-      end)
-
-    {Keyword.put(formatter_opts, :sigils, sigils),
+    {Keyword.put(formatter_opts, :sigils, sigil_formatters(sigils, formatter_opts)),
      Enum.map(subs, fn {path, formatter_opts_and_subs} ->
        {path, load_plugins(formatter_opts_and_subs, opts)}
      end)}
@@ -384,6 +372,24 @@ defmodule Mix.Tasks.Format do
     plugins
   end
 
+  # A sigil formatter must receive :sigils itself, so a plugin can format sigils
+  # nested inside the sigil it was given. The list is rebuilt on each invocation.
+  defp sigil_formatters(sigil_plugins, formatter_opts) do
+    sigil_plugins
+    |> Enum.group_by(&elem(&1, 0), &elem(&1, 1))
+    |> Enum.map(fn {sigil, plugins} ->
+      {sigil,
+       fn input, opts ->
+         formatter_opts =
+           Keyword.put(formatter_opts, :sigils, sigil_formatters(sigil_plugins, formatter_opts))
+
+         Enum.reduce(plugins, input, fn plugin, input ->
+           plugin.format(input, opts ++ formatter_opts)
+         end)
+       end}
+    end)
+  end
+
   @typedoc """
   Options for `formatter_for_file/2`.
   """
diff --git a/lib/mix/test/mix/tasks/format_test.exs b/lib/mix/test/mix/tasks/format_test.exs
index 1498d2a162f..f828e5c4790 100644
--- a/lib/mix/test/mix/tasks/format_test.exs
+++ b/lib/mix/test/mix/tasks/format_test.exs
@@ -572,6 +572,66 @@ defmodule Mix.Tasks.FormatTest do
     end)
   end
 
+  defmodule Elixir.SigilOuterPlugin do
+    @behaviour Mix.Tasks.Format
+
+    def features(opts) do
+      assert opts[:from_formatter_exs] == :yes
+      [sigils: [:O]]
+    end
+
+    def format(contents, opts) do
+      assert opts[:from_formatter_exs] == :yes
+      assert opts[:sigil] == :O
+      [Code.format_string!(contents, opts), ?\n]
+    end
+  end
+
+  defmodule Elixir.SigilInnerPlugin do
+    @behaviour Mix.Tasks.Format
+
+    def features(opts) do
+      assert opts[:from_formatter_exs] == :yes
+      [sigils: [:I]]
+    end
+
+    def format(contents, opts) do
+      assert opts[:from_formatter_exs] == :yes
+      assert opts[:sigil] == :I
+      String.upcase(contents)
+    end
+  end
+
+  test "uses sigil plugins for sigils nested inside sigils", context do
+    in_tmp(context.test, fn ->
+      File.write!(".formatter.exs", """
+      [
+        inputs: ["a.ex"],
+        plugins: [SigilOuterPlugin, SigilInnerPlugin],
+        from_formatter_exs: :yes
+      ]
+      """)
+
+      File.write!("a.ex", """
+      def nested_sigil_test do
+        ~O'''
+        inner(~I"foo bar")
+        '''
+      end
+      """)
+
+      Mix.Tasks.Format.run([])
+
+      assert File.read!("a.ex") == """
+             def nested_sigil_test do
+               ~O'''
+               inner(~I"FOO BAR")
+               '''
+             end
+             """
+    end)
+  end
+
   test "customizes plugin loading", context do
     in_tmp(context.test, fn ->
       File.write!(".formatter.exs", """

From ca1da9f442fbe619ca1f2f01bbe2ba85a3ed5f2a Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Jos=C3=A9=20Valim?= <jose.valim@gmail.com>
Date: Sat, 25 Jul 2026 09:36:44 +0200
Subject: [PATCH 2/5] Reduce recursive sigil logic

---
 lib/mix/lib/mix/tasks/format.ex | 37 +++++++++++++++++++--------------
 1 file changed, 21 insertions(+), 16 deletions(-)

diff --git a/lib/mix/lib/mix/tasks/format.ex b/lib/mix/lib/mix/tasks/format.ex
index 85dfc95bea9..8bbdcb1ffe1 100644
--- a/lib/mix/lib/mix/tasks/format.ex
+++ b/lib/mix/lib/mix/tasks/format.ex
@@ -349,12 +349,17 @@ defmodule Mix.Tasks.Format do
       end
     end
 
-    sigils =
+    flatten_sigils =
       for plugin <- plugins,
           sigil <- find_sigils_from_plugins(plugin, formatter_opts),
           do: {sigil, plugin}
 
-    {Keyword.put(formatter_opts, :sigils, sigil_formatters(sigils, formatter_opts)),
+    formatter_opts =
+      flatten_sigils
+      |> Enum.group_by(&elem(&1, 0), &elem(&1, 1))
+      |> prepend_sigils(Keyword.delete(formatter_opts, :sigils))
+
+    {formatter_opts,
      Enum.map(subs, fn {path, formatter_opts_and_subs} ->
        {path, load_plugins(formatter_opts_and_subs, opts)}
      end)}
@@ -374,20 +379,20 @@ defmodule Mix.Tasks.Format do
 
   # A sigil formatter must receive :sigils itself, so a plugin can format sigils
   # nested inside the sigil it was given. The list is rebuilt on each invocation.
-  defp sigil_formatters(sigil_plugins, formatter_opts) do
-    sigil_plugins
-    |> Enum.group_by(&elem(&1, 0), &elem(&1, 1))
-    |> Enum.map(fn {sigil, plugins} ->
-      {sigil,
-       fn input, opts ->
-         formatter_opts =
-           Keyword.put(formatter_opts, :sigils, sigil_formatters(sigil_plugins, formatter_opts))
-
-         Enum.reduce(plugins, input, fn plugin, input ->
-           plugin.format(input, opts ++ formatter_opts)
-         end)
-       end}
-    end)
+  defp prepend_sigils(grouped_sigils, formatter_opts_without_sigils) do
+    sigils =
+      Enum.map(sigil_groups, fn {sigil, plugins} ->
+        {sigil,
+         fn input, opts ->
+           formatter_opts = prepend_sigils(grouped_sigils, formatter_opts_without_sigils)
+  
+           Enum.reduce(plugins, input, fn plugin, input ->
+             plugin.format(input, opts ++ formatter_opts)
+           end)
+         end}
+      end)
+
+    [sigils: sigils] ++ formatter_opts_without_sigils
   end
 
   @typedoc """

From f336eb7ee5b096dc8e82f81b6fffe9c1d90792da Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Jos=C3=A9=20Valim?= <jose.valim@gmail.com>
Date: Sat, 25 Jul 2026 09:39:28 +0200
Subject: [PATCH 3/5] Apply suggestion from @josevalim

---
 lib/mix/lib/mix/tasks/format.ex | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/lib/mix/lib/mix/tasks/format.ex b/lib/mix/lib/mix/tasks/format.ex
index 8bbdcb1ffe1..7b0f72068b7 100644
--- a/lib/mix/lib/mix/tasks/format.ex
+++ b/lib/mix/lib/mix/tasks/format.ex
@@ -381,7 +381,7 @@ defmodule Mix.Tasks.Format do
   # nested inside the sigil it was given. The list is rebuilt on each invocation.
   defp prepend_sigils(grouped_sigils, formatter_opts_without_sigils) do
     sigils =
-      Enum.map(sigil_groups, fn {sigil, plugins} ->
+      Enum.map(grouped_sigils, fn {sigil, plugins} ->
         {sigil,
          fn input, opts ->
            formatter_opts = prepend_sigils(grouped_sigils, formatter_opts_without_sigils)

From 3eac352c82662961d4fd8c794ee60ce6070ded8e Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Jos=C3=A9=20Valim?= <jose.valim@gmail.com>
Date: Sat, 25 Jul 2026 09:45:11 +0200
Subject: [PATCH 4/5] Apply suggestion from @josevalim

---
 lib/mix/lib/mix/tasks/format.ex | 1 -
 1 file changed, 1 deletion(-)

diff --git a/lib/mix/lib/mix/tasks/format.ex b/lib/mix/lib/mix/tasks/format.ex
index 7b0f72068b7..fceb0004b65 100644
--- a/lib/mix/lib/mix/tasks/format.ex
+++ b/lib/mix/lib/mix/tasks/format.ex
@@ -385,7 +385,6 @@ defmodule Mix.Tasks.Format do
         {sigil,
          fn input, opts ->
            formatter_opts = prepend_sigils(grouped_sigils, formatter_opts_without_sigils)
-  
            Enum.reduce(plugins, input, fn plugin, input ->
              plugin.format(input, opts ++ formatter_opts)
            end)

From 8195bcc20f16fb163e3db7121a5f964e9743c4d6 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Jos=C3=A9=20Valim?= <jose.valim@gmail.com>
Date: Sat, 25 Jul 2026 09:50:01 +0200
Subject: [PATCH 5/5] Apply suggestion from @josevalim

---
 lib/mix/lib/mix/tasks/format.ex | 1 +
 1 file changed, 1 insertion(+)

diff --git a/lib/mix/lib/mix/tasks/format.ex b/lib/mix/lib/mix/tasks/format.ex
index fceb0004b65..2951ceac1ac 100644
--- a/lib/mix/lib/mix/tasks/format.ex
+++ b/lib/mix/lib/mix/tasks/format.ex
@@ -385,6 +385,7 @@ defmodule Mix.Tasks.Format do
         {sigil,
          fn input, opts ->
            formatter_opts = prepend_sigils(grouped_sigils, formatter_opts_without_sigils)
+
            Enum.reduce(plugins, input, fn plugin, input ->
              plugin.format(input, opts ++ formatter_opts)
            end)