Remove FetchContent from compiler build.

Author: alexreinking

CMakeLists.txt

@@ -1,20 +1,4 @@
 cmake_minimum_required(VERSION 3.28)
-
-# TODO: remove this after updating build bots.
-if (CMAKE_TOOLCHAIN_FILE MATCHES "vcpkg")
-    if (NOT DEFINED VCPKG_MANIFEST_FEATURES)
-        set(VCPKG_MANIFEST_FEATURES developer)
-    endif ()
-
-    # vcpkg and FetchContent are incompatible
-    set(Halide_USE_FETCHCONTENT OFF)
-endif ()
-
-option(Halide_USE_FETCHCONTENT "When Halide is top-level, use FetchContent for build-time dependencies." ON)
-if (Halide_USE_FETCHCONTENT)
-    list(APPEND CMAKE_PROJECT_TOP_LEVEL_INCLUDES "${CMAKE_CURRENT_LIST_DIR}/cmake/dependencies.cmake")
-endif ()
-
 project(Halide
         VERSION 22.0.0
         DESCRIPTION "Halide compiler and libraries"

CMakePresets.json

@@ -30,7 +30,7 @@
       "toolchainFile": "$env{VCPKG_ROOT}/scripts/buildsystems/vcpkg.cmake",
       "cacheVariables": {
         "VCPKG_MANIFEST_FEATURES": "developer",
-        "Halide_USE_FETCHCONTENT": false
+        "FETCHCONTENT_FULLY_DISCONNECTED": "ON"
       }
     },
     {

cmake/dependencies.cmake

@@ -230,7 +230,7 @@ necessary, it is convenient to install Python system-wide on Windows (i.e.
 `C:\Program Files`) because CMake looks at standard paths and registry keys.
 This removes the need to manually set the `PATH`.
 
-Once Python is installed, you can install the Python module dependencies in 
+Once Python is installed, you can install the Python module dependencies in
 a [virtual environment][venv] by running
 
 ```shell
@@ -444,12 +444,12 @@ The following options are _advanced_ and should not be required in typical
 workflows. Generally, these are used by Halide's own CI infrastructure, or as
 escape hatches for third-party packagers.
 
-| Option                      | Default                                                            | Description                                                                              |
-|-----------------------------|--------------------------------------------------------------------|------------------------------------------------------------------------------------------|
-| `Halide_CCACHE_BUILD`       | `OFF`                                                              | Use ccache with Halide-recommended settings to accelerate rebuilds.                      |
-| `Halide_CCACHE_PARAMS`      | `CCACHE_CPP2=yes CCACHE_HASHDIR=yes CCACHE_SLOPPINESS=pch_defines` | Options to pass to `ccache` when using `Halide_CCACHE_BUILD`.                            |
-| `Halide_VERSION_OVERRIDE`   | `${Halide_VERSION}`                                                | Override the VERSION for libHalide.                                                      |
-| `Halide_SOVERSION_OVERRIDE` | `${Halide_VERSION_MAJOR}`                                          | Override the SOVERSION for libHalide. Expects a positive integer (i.e. not a version).   |
+| Option                      | Default                                                            | Description                                                                            |
+|-----------------------------|--------------------------------------------------------------------|----------------------------------------------------------------------------------------|
+| `Halide_CCACHE_BUILD`       | `OFF`                                                              | Use ccache with Halide-recommended settings to accelerate rebuilds.                    |
+| `Halide_CCACHE_PARAMS`      | `CCACHE_CPP2=yes CCACHE_HASHDIR=yes CCACHE_SLOPPINESS=pch_defines` | Options to pass to `ccache` when using `Halide_CCACHE_BUILD`.                          |
+| `Halide_VERSION_OVERRIDE`   | `${Halide_VERSION}`                                                | Override the VERSION for libHalide.                                                    |
+| `Halide_SOVERSION_OVERRIDE` | `${Halide_VERSION_MAJOR}`                                          | Override the SOVERSION for libHalide. Expects a positive integer (i.e. not a version). |
 
 The following options control whether to build certain test subsets. They only
 apply when `WITH_TESTS=ON`:
@@ -501,10 +501,9 @@ install it into the currently active Python environment.
 
 However, this comes with a few caveats:
 
-1. `Halide_USE_FETCHCONTENT` is disabled, so the environment must be prepared
-   for CMake to find its dependencies. This is easiest to do by setting either
-   `CMAKE_PREFIX_PATH` to pre-built dependencies or by setting
-   `CMAKE_TOOLCHAIN_FILE` to vcpkg.
+1. The environment must be prepared for CMake to find its dependencies. This is
+   easiest to do by setting either `CMAKE_PREFIX_PATH` to pre-built dependencies
+   or by setting `CMAKE_TOOLCHAIN_FILE` to vcpkg.
 2. The build settings are fixed, meaning that `wabt` is required on non-Windows
    systems, `flatbuffers` is always required, and the Python bindings must be
    built.
@@ -577,8 +576,8 @@ Local storage:
   Misses:             0 / 1079 ( 0.00%)
 ```
 
-On this test system (an M3 MacBook Pro), the build is three times faster,
-with a 100% cache hit rate!
+On this test system (an M3 MacBook Pro), the build is three times faster, with a
+100% cache hit rate!
 
 [ATLAS]: http://math-atlas.sourceforge.net/
 

doc/BuildingHalideWithCMake.md

@@ -137,14 +137,14 @@ There are also several functions that are disallowed for other reasons:
 | `include_external_msproject`    | Halide must remain portable                                                       | Write a CMake package config file or find module.                              |
 | `include_guard`                 | Use of recursive inclusion is not allowed                                         | Write (recursive) functions.                                                   |
 | `include_regular_expression`    | Changes default dependency checking behavior                                      | None                                                                           |
-| `load_cache`                    | Superseded by [`FetchContent`][FetchContent]/[`ExternalProject`][ExternalProject] | Use aforementioned modules                                                     |
+| `load_cache`                    | Superseded by [`FetchContent`][FetchContent]/[`ExternalProject`][ExternalProject] | Write a vcpkg port or present a case for an exception.                         |
 | `macro`                         | CMake macros are not hygienic and are therefore error-prone                       | Use functions instead.                                                         |
 | `site_name`                     | Privacy: do not want leak host name information                                   | Provide a cache variable, generate a unique name.                              |
 | `variable_watch`                | Debugging helper                                                                  | None. Not needed in production.                                                |
 
 Do not introduce any dependencies via [`find_package`][find_package]
-without broader approval. Importantly, never introduce a new use of
-`FetchContent`; prefer to add dependencies to `vcpkg.json`.
+without broader approval. Importantly, never introduce a use of `FetchContent`.
+Add dependencies to `vcpkg.json` or create a custom port.
 
 ## Prohibited variables list
 

doc/CodeStyleCMake.md

@@ -109,10 +109,10 @@ metadata.version.provider = "scikit_build_core.metadata.setuptools_scm"
 [tool.scikit-build.cmake.define]
 CMAKE_DISABLE_FIND_PACKAGE_JPEG = true
 CMAKE_DISABLE_FIND_PACKAGE_PNG = true
+FETCHCONTENT_FULLY_DISCONNECTED = true
 Halide_ENABLE_EXCEPTIONS = true
 Halide_ENABLE_RTTI = true
 Halide_INSTALL_PYTHONDIR = "."
-Halide_USE_FETCHCONTENT = false
 Halide_WASM_BACKEND = "wabt"
 WITH_PYTHON_BINDINGS = true
 WITH_TESTS = false

pyproject.toml

@@ -530,12 +530,7 @@ if (WITH_SERIALIZATION)
     )
     _Halide_pkgdep(flatbuffers)
 
-    if (Halide_USE_FETCHCONTENT AND NOT BUILD_SHARED_LIBS)
-        target_sources(Halide PRIVATE "$<TARGET_OBJECTS:flatbuffers::flatbuffers>")
-        target_link_libraries(Halide PRIVATE "$<BUILD_LOCAL_INTERFACE:$<COMPILE_ONLY:flatbuffers::flatbuffers>>")
-    else ()
-        target_link_libraries(Halide PRIVATE flatbuffers::flatbuffers)
-    endif ()
+    target_link_libraries(Halide PRIVATE flatbuffers::flatbuffers)
 
     set(fb_def "${CMAKE_CURRENT_SOURCE_DIR}/halide_ir.fbs")
     set(fb_dir "${Halide_BINARY_DIR}/include/flatc")
@@ -591,13 +586,7 @@ if (Halide_WASM_BACKEND STREQUAL "wabt")
     find_package(wabt 1.0.39 REQUIRED)
     _Halide_pkgdep(wabt)
 
-    if (Halide_USE_FETCHCONTENT AND NOT BUILD_SHARED_LIBS)
-        target_sources(Halide PRIVATE "$<TARGET_OBJECTS:wabt::wabt>")
-        target_link_libraries(Halide PRIVATE "$<BUILD_LOCAL_INTERFACE:$<COMPILE_ONLY:wabt::wabt>>")
-    else ()
-        target_link_libraries(Halide PRIVATE wabt::wabt)
-    endif ()
-
+    target_link_libraries(Halide PRIVATE wabt::wabt)
     target_compile_definitions(Halide PRIVATE WITH_WABT)
 elseif (Halide_WASM_BACKEND STREQUAL "V8")
     find_package(V8 REQUIRED)