From c40182ebd79456df1f40f6d0adf22c5c5a17c8dc Mon Sep 17 00:00:00 2001
From: Daniel Kukula <daniel.kuku@gmail.com>
Date: Thu, 31 Jul 2025 00:33:28 +0200
Subject: [PATCH 1/2] Print intermediate results of dbg for pipes

---
 lib/elixir/lib/macro.ex               | 56 +++++++++++++--------------
 lib/elixir/test/elixir/macro_test.exs | 22 +++++++++++
 2 files changed, 48 insertions(+), 30 deletions(-)

diff --git a/lib/elixir/lib/macro.ex b/lib/elixir/lib/macro.ex
index b09a418f7e1..2cadcf63148 100644
--- a/lib/elixir/lib/macro.ex
+++ b/lib/elixir/lib/macro.ex
@@ -2639,34 +2639,29 @@ defmodule Macro do
   # Pipelines.
   defp dbg_ast_to_debuggable({:|>, _meta, _args} = pipe_ast, _env) do
     value_var = unique_var(:value, __MODULE__)
-    values_acc_var = unique_var(:values, __MODULE__)
 
-    [start_ast | rest_asts] = asts = for {ast, 0} <- unpipe(pipe_ast), do: ast
-    rest_asts = Enum.map(rest_asts, &pipe(value_var, &1, 0))
+    [start_ast | rest_asts] = for {ast, 0} <- unpipe(pipe_ast), do: ast
+    piped_rest_asts = Enum.map(rest_asts, &{&1, pipe(value_var, &1, 0)})
 
-    initial_acc =
+    first_entry =
       quote do
         unquote(value_var) = unquote(start_ast)
-        unquote(values_acc_var) = [unquote(value_var)]
+        {:multi_value, unquote(escape(start_ast)), unquote(value_var)}
       end
 
-    values_ast =
-      for step_ast <- rest_asts, reduce: initial_acc do
-        ast_acc ->
-          quote do
-            unquote(ast_acc)
-            unquote(value_var) = unquote(step_ast)
-            unquote(values_acc_var) = [unquote(value_var) | unquote(values_acc_var)]
-          end
-      end
+    len = length(piped_rest_asts)
 
-    [
-      quote do
-        unquote(values_ast)
+    pipe_entries =
+      Enum.with_index(piped_rest_asts, fn {original_ast, step_ast}, i ->
+        tag = if i + 1 == len, do: :pipe_end, else: :pipe
 
-        {:pipe, unquote(escape(asts)), Enum.reverse(unquote(values_acc_var))}
-      end
-    ]
+        quote do
+          unquote(value_var) = unquote(step_ast)
+          {unquote(tag), unquote(escape(original_ast)), unquote(value_var)}
+        end
+      end)
+
+    [first_entry | pipe_entries]
   end
 
   dbg_decomposed_binary_operators = [:&&, :||, :and, :or]
@@ -2886,18 +2881,19 @@ defmodule Macro do
     result
   end
 
-  defp dbg_format_ast_to_debug({:pipe, code_asts, values}, options) do
-    result = List.last(values)
-    code_strings = Enum.map(code_asts, &to_string_with_colors(&1, options))
-    [{first_ast, first_value} | asts_with_values] = Enum.zip(code_strings, values)
-    first_formatted = [dbg_format_ast(first_ast), " ", inspect(first_value, options), ?\n]
+  defp dbg_format_ast_to_debug({:pipe, code_ast, value}, options) do
+    formatted = [
+      [:faint, "|> ", :reset],
+      dbg_format_ast_with_value_no_newline(code_ast, value, options)
+    ]
+
+    {formatted, value}
+  end
 
-    rest_formatted =
-      Enum.map(asts_with_values, fn {code_ast, value} ->
-        [:faint, "|> ", :reset, dbg_format_ast(code_ast), " ", inspect(value, options), ?\n]
-      end)
+  defp dbg_format_ast_to_debug({:pipe_end, code_ast, value}, options) do
+    {formatted, value} = dbg_format_ast_to_debug({:pipe, code_ast, value}, options)
 
-    {[first_formatted | rest_formatted], result}
+    {[formatted | ?\n], value}
   end
 
   defp dbg_format_ast_to_debug({:case_argument, expr_ast, expr_value}, options) do
diff --git a/lib/elixir/test/elixir/macro_test.exs b/lib/elixir/test/elixir/macro_test.exs
index c3f752eea40..78c5a12610c 100644
--- a/lib/elixir/test/elixir/macro_test.exs
+++ b/lib/elixir/test/elixir/macro_test.exs
@@ -444,6 +444,28 @@ defmodule MacroTest do
       assert formatted =~ ~r/[^\n]\n\n$/
     end
 
+    test "pipeline on multiple lines that raises" do
+      {result, formatted} =
+        dbg_format_no_newline(
+          abc()
+          |> tl()
+          |> tl()
+          |> tl()
+          |> tl()
+        )
+
+      assert %ArgumentError{} = result
+
+      assert formatted =~ "macro_test.exs"
+
+      assert formatted =~ """
+             abc() #=> [:a, :b, :c]
+             |> tl() #=> [:b, :c]
+             |> tl() #=> [:c]
+             |> tl() #=> []
+             """
+    end
+
     test "simple boolean expressions" do
       {result, formatted} = dbg_format(:rand.uniform() < 0.0 and length([]) == 0)
       assert result == false

From c1aec54fb20925391ed8335d15fda2c1ba9d2bf7 Mon Sep 17 00:00:00 2001
From: Daniel Kukula <daniel.kuku@gmail.com>
Date: Thu, 31 Jul 2025 06:06:16 +0200
Subject: [PATCH 2/2] use proper list

---
 lib/elixir/lib/macro.ex | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/lib/elixir/lib/macro.ex b/lib/elixir/lib/macro.ex
index 2cadcf63148..cbc58958e2c 100644
--- a/lib/elixir/lib/macro.ex
+++ b/lib/elixir/lib/macro.ex
@@ -2893,7 +2893,7 @@ defmodule Macro do
   defp dbg_format_ast_to_debug({:pipe_end, code_ast, value}, options) do
     {formatted, value} = dbg_format_ast_to_debug({:pipe, code_ast, value}, options)
 
-    {[formatted | ?\n], value}
+    {[formatted, ?\n], value}
   end
 
   defp dbg_format_ast_to_debug({:case_argument, expr_ast, expr_value}, options) do