Expose --quiet option in assay mix task

CHANGELOG.md

@@ -4,6 +4,14 @@ All notable changes to this project will be documented in this file.
 
 This project adheres to [Semantic Versioning](https://semver.org/).
 
+## [Unreleased]
+
+### Added
+
+- `--quiet` flag for `mix assay` to suppress informational output (header,
+  ignore logs, summary, and the warnings exit message). Formatted warning
+  output and exit codes are unchanged.
+
 ## [0.6.1] - 2026-06-05
 
 ### Fixed

README.md

@@ -140,6 +140,7 @@ mix assay
 mix assay --print-config
 mix assay --format github --format sarif
 mix assay --no-compile          # skip compilation (project must already be compiled)
+mix assay --quiet               # suppress header, ignore logs, summary, and exit message
 ```
 
 Exit codes: `0` (clean), `1` (warnings), `2` (error).

lib/mix/tasks/assay.ex

@@ -13,6 +13,7 @@ defmodule Mix.Tasks.Assay do
   * `--dialyzer-flag FLAG` - Pass additional Dialyzer flags
   * `--ignore-file PATH` - Override ignore file path (default: `dialyzer_ignore.exs`)
   * `--explain-ignores` - Show detailed information about which warnings were ignored and which rules matched them
+  * `--quiet` - Suppress informational output (header, ignore logs, summary, and warnings exit message)
 
   ## Exit Codes
 
@@ -29,6 +30,7 @@ defmodule Mix.Tasks.Assay do
       mix assay --dialyzer-flag="--statistics"
       mix assay --ignore-file="custom_ignore.exs"
       mix assay --explain-ignores
+      mix assay --quiet --format json
   """
   use Mix.Task
 
@@ -43,7 +45,10 @@ defmodule Mix.Tasks.Assay do
         :ok
 
       :warnings ->
-        Mix.shell().info("Dialyzer reported warnings")
+        if !Keyword.get(opts, :quiet, false) do
+          Mix.shell().info("Dialyzer reported warnings")
+        end
+
         exit({:shutdown, 1})
     end
   end
@@ -60,7 +65,8 @@ defmodule Mix.Tasks.Assay do
           apps: :string,
           warning_apps: :string,
           ignore_file: :string,
-          explain_ignores: :boolean
+          explain_ignores: :boolean,
+          quiet: :boolean
         ],
         aliases: [f: :format]
       )
@@ -92,6 +98,7 @@ defmodule Mix.Tasks.Assay do
       |> Keyword.put(:formats, normalized_formats)
       |> Keyword.put(:no_compile, Keyword.get(opts, :no_compile, false))
       |> Keyword.put(:explain_ignores, Keyword.get(opts, :explain_ignores, false))
+      |> Keyword.put(:quiet, Keyword.get(opts, :quiet, false))
       |> maybe_put(:apps, apps_override)
       |> maybe_put(:warning_apps, warning_override)
       |> maybe_put(:dialyzer_flags, flag_overrides)

test/mix_tasks_assay_test.exs

@@ -166,6 +166,39 @@ defmodule Mix.Tasks.AssayTest do
     assert Keyword.get(runner_opts, :no_compile) == false
   end
 
+  test "run forwards --quiet flag" do
+    Process.put(:runner_stub_status, :ok)
+
+    ExUnit.CaptureIO.capture_io(fn ->
+      Assay.run(["--quiet"])
+    end)
+
+    assert_received {:runner_called, _config, runner_opts}
+    assert Keyword.get(runner_opts, :quiet) == true
+  end
+
+  test "run defaults quiet to false when flag is omitted" do
+    Process.put(:runner_stub_status, :ok)
+
+    ExUnit.CaptureIO.capture_io(fn ->
+      Assay.run([])
+    end)
+
+    assert_received {:runner_called, _config, runner_opts}
+    assert Keyword.get(runner_opts, :quiet) == false
+  end
+
+  test "run suppresses warnings exit message when --quiet is set" do
+    Process.put(:runner_stub_status, :warnings)
+
+    output =
+      capture_io(fn ->
+        assert catch_exit(Assay.run(["--quiet"])) == {:shutdown, 1}
+      end)
+
+    refute output =~ "Dialyzer reported warnings"
+  end
+
   test "assay.daemon task boots the daemon" do
     Application.put_env(:assay, :daemon_module, DaemonStub)
 

test/test_helper.exs

@@ -203,7 +203,7 @@ defmodule Assay.TestSupport.IOProxy do
     case :binary.match(buffer, "\n") do
       {pos, _len} ->
         len = pos + 1
-        <<line::binary-size(len), rest::binary>> = buffer
+        <<line::binary-size(^len), rest::binary>> = buffer
         {:reply, line, rest}
 
       :nomatch ->
@@ -215,7 +215,7 @@ defmodule Assay.TestSupport.IOProxy do
 
   defp fetch_chars(buffer, true, len) do
     if byte_size(buffer) >= len do
-      <<chunk::binary-size(len), rest::binary>> = buffer
+      <<chunk::binary-size(^len), rest::binary>> = buffer
       {:reply, chunk, rest}
     else
       {:reply, buffer, <<>>}
@@ -224,7 +224,7 @@ defmodule Assay.TestSupport.IOProxy do
 
   defp fetch_chars(buffer, false, len) do
     if byte_size(buffer) >= len do
-      <<chunk::binary-size(len), rest::binary>> = buffer
+      <<chunk::binary-size(^len), rest::binary>> = buffer
       {:reply, chunk, rest}
     else
       :pending