Meta: Promote SERENITY_CACHE_DIR to a real option

We've had it as a secret option for long enough, let's make it more
visible.

Documentation/AdvancedBuildInstructions.md

@@ -67,6 +67,7 @@ There are some optional features that can be enabled during compilation that are
 - `SERENITY_ARCH`: Specifies which architecture to build for. Currently supported options are `x86_64`.
 - `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/x86_64/Root` after disabling components. These options can be easily configured by using the `ConfigureComponents` utility. See the [Component Configuration](#component-configuration) section below.
 - `BUILD_EVERYTHING`: builds all optional components, overrides other `BUILD_<component>` flags when enabled
+- `SERENITY_CACHE_DIR`: sets the location of a shared cache of downloaded files. Should not need to be set unless managing a distribution package.
 
 Many parts of the SerenityOS codebase have debug functionality, mostly consisting of additional messages printed to the debug console. This is done via the `<component_name>_DEBUG` macros, which can be enabled individually at build time. They are listed in [this file](../Meta/CMake/all_the_debug_macros.cmake).
 

Meta/Azure/Lagom.yml

@@ -51,7 +51,7 @@ jobs:
         os: '${{ parameters.os }}'
         arch: 'Lagom'
         toolchain: '$(toolchain)'
-        download_cache_path: 'Meta/Lagom/Build'
+        download_cache_path: 'Meta/Lagom/caches'
         serenity_ccache_path: '$(SERENITY_CCACHE_DIR)'
         with_remote_data_caches: true
         ${{ if eq(parameters.os, 'macOS') }}:

Meta/CMake/Superbuild/CMakeLists.txt

@@ -44,9 +44,6 @@ if(NOT SERENITY_TOOLCHAIN STREQUAL "GNU")
 endif()
 set(SERENITY_BUILD_DIR "${PROJECT_BINARY_DIR}/../${SERENITY_ARCH}${SERENITY_BUILD_DIR_SUFFIX}")
 
-# Location to cache artifacts downloaded during the build.
-file(REAL_PATH "${PROJECT_BINARY_DIR}/../caches" SERENITY_CACHE_DIR)
-
 # Pkgconf incorrectly discards a sysroot if it doesn't match the start of the path to the
 # library file. To avoid that, resolve our sysroot into an absolute and canonical path
 # that matches pkgconf's result for resolving the library file.

Meta/CMake/common_options.cmake

@@ -24,3 +24,5 @@ serenity_option(HACKSTUDIO_BUILD OFF CACHE BOOL "Automatically enabled when buil
 
 serenity_option(ENABLE_JAKT OFF CACHE BOOL "Enable building jakt files")
 serenity_option(JAKT_SOURCE_DIR "" CACHE STRING "Pre-existing jakt language source directory")
+
+serenity_option(SERENITY_CACHE_DIR "${PROJECT_BINARY_DIR}/../caches" CACHE PATH "Location of shared cache of downloaded files")

Meta/Lagom/CMakeLists.txt

@@ -25,8 +25,6 @@ get_filename_component(
 )
 set(SerenityOS_SOURCE_DIR "${SERENITY_PROJECT_ROOT}" CACHE STRING "")
 
-set(SERENITY_CACHE_DIR "${PROJECT_BINARY_DIR}" CACHE STRING "")
-
 list(APPEND CMAKE_MODULE_PATH "${SERENITY_PROJECT_ROOT}/Meta/CMake")
 
 if(NOT COMMAND serenity_option)