Meta+Tests: Allow running FLAC spec tests

The FLAC "spec tests", or rather the test suite by xiph that exercises
weird FLAC features and edge cases, can be found at
https://github.com/ietf-wg-cellar/flac-test-files and is a good
challenge for our FLAC decoder to become more spec compliant. Running
these tests is similar to LibWasm spec tests, you need to pass
INCLUDE_FLAC_SPEC_TESTS to CMake.

As of integrating these tests, 23 out of 63 fail. :yakplus:

8 files changed, 108 insertions, 0 deletions

diff --git a/CMakeLists.txt b/CMakeLists.txt
index 3ce94fa769..977403de9e 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -206,6 +206,7 @@ option(BUILD_EVERYTHING "Build all optional components" ON)
 
 include(utils)
 include(wasm_spec_tests)
+include(flac_spec_tests)
 
 serenity_component(
     Tests
diff --git a/Documentation/AdvancedBuildInstructions.md b/Documentation/AdvancedBuildInstructions.md
index 94c7199429..c35513dbd3 100644
--- a/Documentation/AdvancedBuildInstructions.md
+++ b/Documentation/AdvancedBuildInstructions.md
@@ -62,6 +62,7 @@ There are some optional features that can be enabled during compilation that are
 - `ENABLE_JAKT`: builds the `jakt` compiler as a Lagom host tool and enables building applications and libraries that are written in the jakt language.
 - `JAKT_SOURCE_DIR`: `jakt` developer's local checkout of the jakt programming language for rapid testing. To use a local checkout, set to an absolute path when changing the CMake cache of Lagom. e.g. ``cmake -S Meta/Lagom -B Build/lagom -DENABLE_JAKT=ON -DJAKT_SOURCE_DIR=/home/me/jakt``
 - `INCLUDE_WASM_SPEC_TESTS`: downloads and includes the WebAssembly spec testsuite tests. In order to use this option, you will need to install `prettier` and `wabt`. wabt version 1.0.23 or higher is required to pre-process the WebAssembly spec testsuite.
+- `INCLUDE_FLAC_SPEC_TESTS`: downloads and includes the xiph.org FLAC test suite.
 - `SERENITY_TOOLCHAIN`: Specifies whether to use the established GNU toolchain, or the experimental Clang-based toolchain for building SerenityOS. See the [Clang-based toolchain](#clang-based-toolchain) section below.
 - `SERENITY_ARCH`: Specifies which architecture to build for. Currently supported options are `i686` and `x86_64`. `x86_64` requires a separate toolchain build from `i686`.
 - `BUILD_<component>`: builds the specified component, e.g. `BUILD_HEARTS` (note: must be all caps). Check the components.ini file in your build directory for a list of available components. Make sure to run `ninja clean` and `rm -rf Build/i686/Root` after disabling components. These options can be easily configured by using the `ConfigureComponents` utility. See the [Component Configuration](#component-configuration) section below.
diff --git a/Meta/CMake/common_options.cmake b/Meta/CMake/common_options.cmake
index da879ffaed..8ca08c1a76 100644
--- a/Meta/CMake/common_options.cmake
+++ b/Meta/CMake/common_options.cmake
@@ -12,6 +12,7 @@ serenity_option(ENABLE_COMPILETIME_HEADER_CHECK OFF CACHE BOOL "Enable compileti
 serenity_option(ENABLE_TIME_ZONE_DATABASE_DOWNLOAD ON CACHE BOOL "Enable download of the IANA Time Zone Database at build time")
 serenity_option(ENABLE_UNICODE_DATABASE_DOWNLOAD ON CACHE BOOL "Enable download of Unicode UCD and CLDR files at build time")
 serenity_option(INCLUDE_WASM_SPEC_TESTS OFF CACHE BOOL "Download and include the WebAssembly spec testsuite")
+serenity_option(INCLUDE_FLAC_SPEC_TESTS OFF CACHE BOOL "Download and include the FLAC spec testsuite")
 
 serenity_option(HACKSTUDIO_BUILD OFF CACHE BOOL "Automatically enabled when building from HackStudio")
 
diff --git a/Meta/CMake/flac_spec_tests.cmake b/Meta/CMake/flac_spec_tests.cmake
new file mode 100644
index 0000000000..2f37b75595
--- /dev/null
+++ b/Meta/CMake/flac_spec_tests.cmake
@@ -0,0 +1,29 @@
+include(utils)
+
+if(INCLUDE_FLAC_SPEC_TESTS)
+    if (CMAKE_PROJECT_NAME STREQUAL "SerenityOS")
+        set(SOURCE_DIR "${SerenityOS_SOURCE_DIR}")
+    else()
+        set(SOURCE_DIR "${SERENITY_PROJECT_ROOT}")
+    endif()
+    set(FLAC_SPEC_TEST_GZ_URL https://github.com/ietf-wg-cellar/flac-test-files/archive/refs/heads/main.tar.gz)
+
+    set(FLAC_TEST_PATH ${CMAKE_BINARY_DIR}/Tests/LibAudio/FLAC CACHE PATH "Location of FLAC tests")
+    set(FLAC_SPEC_TEST_GZ_PATH ${FLAC_TEST_PATH}/flac-spec-testsuite.tar.gz)
+    set(FLAC_SPEC_TEST_PATH ${FLAC_TEST_PATH}/SpecTests)
+
+    if(NOT EXISTS ${FLAC_SPEC_TEST_GZ_PATH})
+        message(STATUS "Downloading the IETF CELLAR FLAC testsuite from ${FLAC_SPEC_TEST_GZ_URL}...")
+        download_file(${FLAC_SPEC_TEST_GZ_URL} ${FLAC_SPEC_TEST_GZ_PATH})
+    endif()
+
+    if(EXISTS ${FLAC_SPEC_TEST_GZ_PATH} AND NOT EXISTS ${FLAC_SPEC_TEST_PATH})
+        file(MAKE_DIRECTORY ${FLAC_SPEC_TEST_PATH})
+        message(STATUS "Extracting the FLAC testsuite from ${FLAC_SPEC_TEST_GZ_PATH}...")
+        execute_process(COMMAND "${TAR_TOOL}" -xzf ${FLAC_SPEC_TEST_GZ_PATH} -C ${FLAC_TEST_PATH} RESULT_VARIABLE tar_result)
+        if (NOT tar_result EQUAL 0)
+            message(FATAL_ERROR "Failed to unzip ${FLAC_TEST_PATH} from ${FLAC_SPEC_TEST_GZ_PATH} with status ${tar_result}")
+        endif()
+        file(RENAME "${FLAC_TEST_PATH}/flac-test-files-main/subset" ${FLAC_SPEC_TEST_PATH})
+    endif()
+endif()
diff --git a/Meta/Lagom/CMakeLists.txt b/Meta/Lagom/CMakeLists.txt
index 9e23947e61..d759939a64 100644
--- a/Meta/Lagom/CMakeLists.txt
+++ b/Meta/Lagom/CMakeLists.txt
@@ -61,6 +61,7 @@ if (ENABLE_FUZZERS_LIBFUZZER OR ENABLE_FUZZERS_OSSFUZZ)
 endif()
 
 include(wasm_spec_tests)
+include(flac_spec_tests)
 include(lagom_compile_options)
 
 include(GNUInstallDirs) # make sure to include before we mess w/RPATH
@@ -643,6 +644,12 @@ if (BUILD_LAGOM)
             lagom_test(${source} WORKING_DIRECTORY ${CMAKE_CURRENT_SOURCE_DIR}/../../Tests/AK)
         endforeach()
 
+        # LibAudio
+        file(GLOB LIBAUDIO_TEST_SOURCES CONFIGURE_DEPENDS "../../Tests/LibAudio/*.cpp")
+        foreach(source ${LIBAUDIO_TEST_SOURCES})
+            lagom_test(${source} LIBS LibAudio WORKING_DIRECTORY ${FLAC_TEST_PATH})
+        endforeach()
+
         # LibCore
         lagom_test(../../Tests/LibCore/TestLibCoreIODevice.cpp WORKING_DIRECTORY ${CMAKE_CURRENT_SOURCE_DIR}/../../Tests/LibCore)
 
diff --git a/Tests/CMakeLists.txt b/Tests/CMakeLists.txt
index 1023b38265..92d6ea160f 100644
--- a/Tests/CMakeLists.txt
+++ b/Tests/CMakeLists.txt
@@ -1,5 +1,6 @@
 add_subdirectory(AK)
 add_subdirectory(Kernel)
+add_subdirectory(LibAudio)
 add_subdirectory(LibC)
 add_subdirectory(LibCompress)
 add_subdirectory(LibCore)
diff --git a/Tests/LibAudio/CMakeLists.txt b/Tests/LibAudio/CMakeLists.txt
new file mode 100644
index 0000000000..5e70e6c524
--- /dev/null
+++ b/Tests/LibAudio/CMakeLists.txt
@@ -0,0 +1,9 @@
+set(TEST_SOURCES
+    TestFLACSpec.cpp
+)
+
+foreach(source IN LISTS TEST_SOURCES)
+    serenity_test("${source}" LibAudio LIBS LibAudio)
+endforeach()
+
+install(DIRECTORY ${FLAC_SPEC_TEST_PATH} DESTINATION usr/Tests/LibAudio)
diff --git a/Tests/LibAudio/TestFLACSpec.cpp b/Tests/LibAudio/TestFLACSpec.cpp
new file mode 100644
index 0000000000..23a040d1e1
--- /dev/null
+++ b/Tests/LibAudio/TestFLACSpec.cpp
@@ -0,0 +1,59 @@
+/*
+ * Copyright (c) 2022, kleines Filmröllchen <filmroellchen@serenityos.org>
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#include <AK/LexicalPath.h>
+#include <AK/Types.h>
+#include <LibAudio/FlacLoader.h>
+#include <LibCore/DirIterator.h>
+#include <LibCore/Stream.h>
+#include <LibTest/TestCase.h>
+
+struct FlacTest : Test::TestCase {
+    FlacTest(LexicalPath path)
+        : Test::TestCase(
+            String::formatted("flac_spec_test_{}", path.basename()), [this]() { run(); }, false)
+        , m_path(std::move(path))
+    {
+    }
+
+    void run() const
+    {
+        auto loader = Audio::FlacLoaderPlugin { m_path.string() };
+        if (auto result = loader.initialize(); result.is_error()) {
+            FAIL(String::formatted("{} (at {})", result.error().description, result.error().index));
+            return;
+        }
+
+        while (true) {
+            auto maybe_samples = loader.get_more_samples(2 * MiB);
+            if (maybe_samples.is_error()) {
+                FAIL(String::formatted("{} (at {})", maybe_samples.error().description, maybe_samples.error().index));
+                return;
+            }
+            if (maybe_samples.value().is_empty())
+                return;
+        }
+    }
+
+    LexicalPath m_path;
+};
+
+struct DiscoverFLACTestsHack {
+    DiscoverFLACTestsHack()
+    {
+        // FIXME: Also run (our own) tests in this directory.
+        auto test_iterator = Core::DirIterator { "./SpecTests", Core::DirIterator::Flags::SkipParentAndBaseDir };
+
+        while (test_iterator.has_next()) {
+            auto file = LexicalPath { test_iterator.next_full_path() };
+            if (file.extension() == "flac"sv) {
+                Test::add_test_case_to_suite(make_ref_counted<FlacTest>(move(file)));
+            }
+        }
+    }
+};
+// Hack taken from TEST_CASE; the above constructor will run as part of global initialization before the tests are actually executed
+static struct DiscoverFLACTestsHack hack;