From 0b98708a22941676bc1218e569a2709e1b610f57 Mon Sep 17 00:00:00 2001
From: Rodolfo Carvalho <rhcarvalho@gmail.com>
Date: Thu, 11 Dec 2025 17:31:36 +0100
Subject: [PATCH] Support filtering `mix deps` output

Makes it easier to report versions of specific dependencies by allowing
users (or tools) to pass dependency names as arguments to `mix deps`.

Warns when a dependency is not found, similar to `mix deps.unlock`.

Proposal: https://groups.google.com/g/elixir-lang-core/c/5tlLZ1yu4rQ/m/g7Z8fNWiBwAJ
---
 lib/mix/lib/mix/tasks/deps.ex        |  47 +++++++--
 lib/mix/test/mix/tasks/deps_test.exs | 144 +++++++++++++++++++++++++++
 2 files changed, 185 insertions(+), 6 deletions(-)

diff --git a/lib/mix/lib/mix/tasks/deps.ex b/lib/mix/lib/mix/tasks/deps.ex
index f17cd078cc2..82d4e42fc48 100644
--- a/lib/mix/lib/mix/tasks/deps.ex
+++ b/lib/mix/lib/mix/tasks/deps.ex
@@ -10,7 +10,7 @@ defmodule Mix.Tasks.Deps do
   @shortdoc "Lists dependencies and their status"
 
   @moduledoc ~S"""
-  Lists all dependencies and their status.
+  Lists dependencies and their status.
 
   Dependencies must be specified in the `mix.exs` file in one of
   the following formats:
@@ -171,7 +171,7 @@ defmodule Mix.Tasks.Deps do
 
   ## Deps task
 
-  `mix deps` task lists all dependencies in the following format:
+  The `mix deps` task lists dependencies in the following format:
 
       APP VERSION (SCM) (MANAGER)
       [locked at REF]
@@ -186,19 +186,40 @@ defmodule Mix.Tasks.Deps do
 
     * `--all` - lists all dependencies, regardless of specified environment
 
+  ### Listing specific dependencies (since v1.20.0)
+
+  Pass dependency names as arguments to filter the output:
+
+      $ mix deps phoenix phoenix_live_view
+
+  This is particularly useful when you need to quickly check versions for
+  bug reports or similar tasks.
   """
 
   @impl true
   def run(args) do
     Mix.Project.get!()
-    {opts, _, _} = OptionParser.parse(args, switches: [all: :boolean])
+    {opts, apps, _} = OptionParser.parse(args, switches: [all: :boolean])
     loaded_opts = if opts[:all], do: [], else: [env: Mix.env(), target: Mix.target()]
 
+    deps = Mix.Dep.Converger.converge(loaded_opts)
+
+    apps =
+      apps
+      |> Enum.map(&String.to_atom/1)
+      |> Enum.uniq()
+
+    # Sort deps when showing all or preserve input order when filtering
+    {deps, unknown} =
+      if apps == [] do
+        {Enum.sort_by(deps, & &1.app), []}
+      else
+        filter(deps, apps)
+      end
+
     shell = Mix.shell()
 
-    Mix.Dep.Converger.converge(loaded_opts)
-    |> Enum.sort_by(& &1.app)
-    |> Enum.each(fn dep ->
+    Enum.each(deps, fn dep ->
       %Mix.Dep{scm: scm, manager: manager} = dep
       dep = check_lock(dep)
       extra = if manager, do: " (#{manager})", else: ""
@@ -211,5 +232,19 @@ defmodule Mix.Tasks.Deps do
 
       shell.info("  #{format_status(dep)}")
     end)
+
+    # Warnings are displayed at the end for visibility
+    for app <- unknown do
+      shell.error("warning: unknown dependency #{app}")
+    end
+  end
+
+  defp filter(deps, apps) do
+    selected_deps =
+      Enum.flat_map(apps, fn app -> List.wrap(Enum.find(deps, &(&1.app == app))) end)
+
+    unknown_apps = apps -- Enum.map(selected_deps, & &1.app)
+
+    {selected_deps, unknown_apps}
   end
 end
diff --git a/lib/mix/test/mix/tasks/deps_test.exs b/lib/mix/test/mix/tasks/deps_test.exs
index 280e97dbf50..14a24f90d92 100644
--- a/lib/mix/test/mix/tasks/deps_test.exs
+++ b/lib/mix/test/mix/tasks/deps_test.exs
@@ -100,6 +100,79 @@ defmodule Mix.Tasks.DepsTest do
     end)
   end
 
+  test "filters dependencies by name" do
+    in_fixture("deps_status", fn ->
+      Mix.Project.push(DepsApp)
+
+      Mix.Tasks.Deps.run(["ok"])
+
+      assert_received {:mix_shell, :info, ["* ok (https://github.com/elixir-lang/ok.git) (mix)"]}
+      refute_received {:mix_shell, :info, ["* invalidvsn" <> _]}
+      refute_received {:mix_shell, :info, ["* invalidapp" <> _]}
+      refute_received {:mix_shell, :info, ["* noappfile" <> _]}
+      refute_received {:mix_shell, :info, ["* nosemver" <> _]}
+    end)
+  end
+
+  test "warns when filtering for unknown dependencies" do
+    in_fixture("deps_status", fn ->
+      Mix.Project.push(DepsApp)
+
+      Mix.Tasks.Deps.run(["ok", "unknowndep"])
+
+      assert_received {:mix_shell, :info, ["* ok (https://github.com/elixir-lang/ok.git) (mix)"]}
+      assert_received {:mix_shell, :error, ["warning: unknown dependency unknowndep"]}
+    end)
+  end
+
+  test "filters dependencies preserving argument order" do
+    in_fixture("deps_status", fn ->
+      Mix.Project.push(DepsApp)
+
+      Mix.Tasks.Deps.run(["nosemver", "unknowndep2", "ok", "unknowndep1", "invalidapp"])
+
+      assert_output_order([
+        {:info, "nosemver"},
+        {:info, "ok"},
+        {:info, "invalidapp"},
+        {:error, "unknowndep2"},
+        {:error, "unknowndep1"}
+      ])
+    end)
+  end
+
+  test "deduplicates arguments preserving first occurrence order" do
+    in_fixture("deps_status", fn ->
+      Mix.Project.push(DepsApp)
+
+      Mix.Tasks.Deps.run(["ok", "ok", "nosemver", "unknowndep", "ok", "unknowndep"])
+
+      messages = receive_shell_messages()
+
+      assert_output_once(messages, "ok")
+      assert_output_once(messages, "nosemver")
+      assert_output_once(messages, "unknowndep")
+
+      assert_output_order(messages, [{:info, "ok"}, {:info, "nosemver"}, {:error, "unknowndep"}])
+    end)
+  end
+
+  test "lists all dependencies in alphabetical order when no filter is given" do
+    in_fixture("deps_status", fn ->
+      Mix.Project.push(DepsApp)
+
+      Mix.Tasks.Deps.run([])
+
+      assert_output_order([
+        {:info, "invalidapp"},
+        {:info, "invalidvsn"},
+        {:info, "noappfile"},
+        {:info, "nosemver"},
+        {:info, "ok"}
+      ])
+    end)
+  end
+
   test "prints list of dependencies and their status, including req mismatches and custom apps" do
     in_fixture("deps_status", fn ->
       Mix.Project.push(ReqDepsApp)
@@ -977,4 +1050,75 @@ defmodule Mix.Tasks.DepsTest do
       assert File.exists?("deps/ok")
     end)
   end
+
+  ## Helpers
+
+  defp assert_output_once(messages, dep) do
+    matches = Enum.count(messages, &(info_message?(&1, dep) or warning_message?(&1, dep)))
+
+    if matches != 1 do
+      flunk("""
+      Expected output for #{dep} to appear only once!
+
+      Output:
+      #{inspect(messages)}
+      """)
+    end
+  end
+
+  defp assert_output_order(expected) do
+    assert_output_order(receive_shell_messages(), expected)
+  end
+
+  defp assert_output_order(output, expected) do
+    # Find the index of each expected output line
+    indices =
+      Enum.map(expected, fn
+        {:info, dep} -> Enum.find_index(output, &info_message?(&1, dep))
+        {:error, dep} -> Enum.find_index(output, &warning_message?(&1, dep))
+      end)
+
+    if not Enum.all?(indices) do
+      flunk("""
+      Expected output not found!
+
+      Expected:
+      #{inspect(expected)}
+
+      Output:
+      #{inspect(output)}
+      """)
+    end
+
+    if not strictly_increasing?(indices) do
+      flunk("""
+      Output not in expected order!
+
+      Expected:
+      #{inspect(expected)}
+
+      Output:
+      #{inspect(output)}
+      """)
+    end
+  end
+
+  defp receive_shell_messages(acc \\ []) do
+    receive do
+      {:mix_shell, level, [line]} when level in [:info, :error] ->
+        receive_shell_messages([{level, line} | acc])
+    after
+      0 -> Enum.reverse(acc)
+    end
+  end
+
+  defp info_message?({:info, line}, dep), do: line =~ ~r/^\* #{dep} /
+  defp info_message?(_message, _dep), do: false
+
+  defp warning_message?({:error, line}, dep), do: line =~ ~r/^warning: .* #{dep}/
+  defp warning_message?(_message, _dep), do: false
+
+  defp strictly_increasing?([]), do: true
+  defp strictly_increasing?([_]), do: true
+  defp strictly_increasing?([a, b | rest]), do: a < b and strictly_increasing?([b | rest])
 end