Seek lib deps via CMake FetchContent

`FetchContent` respects existing installs, and downloads and compiles the libs
if they aren't found.
This is admittedly a little finicky, since this ignores the usual `Find*`
modules provided by CMake, requiring a bit of glue on our side.

But, one upside is that this moves that logic from our CI into the build system,
which can thus benefit other downstream users.
This also opens the door to some improvements in upcoming commits.

Doing this with Bison turned out to be much more painful, however, due to
`FindBISON` providing the specific `bison_target` command; thus, it remains
installed externally, so that it can be picked up by `FindBISON`.

This also bumps our CMake version requirement slightly, though it's
possible that older versions keep working, or could be supported with small patches;
however, our CI doesn't provide anything below 3.31, so we can't check.

.github/scripts/get_win_deps.ps1

@@ -15,9 +15,4 @@ function getlibrary ([string] $URI, [string] $filename, [string] $hash, [string]
 	Expand-Archive -DestinationPath $destdir $filename
 }
 
-getlibrary 'https://www.zlib.net/zlib132.zip' 'zlib.zip' 'e8bf55f3017aa181690990cb58a994e77885da140609fc8f94abe9b65d2cae28' .
-getlibrary 'https://github.com/pnggroup/libpng/archive/refs/tags/v1.6.53.zip' 'libpng.zip' '9fb99118ec4523d9a9dab652ce7c2472ec76f6ccd69d1aba3ab873bb8cf84b98' .
-getlibrary 'https://github.com/lexxmark/winflexbison/releases/download/v2.5.25/win_flex_bison-2.5.25.zip' 'winflexbison.zip' '8d324b62be33604b2c45ad1dd34ab93d722534448f55a16ca7292de32b6ac135' install_dir
-
-Move-Item zlib-1.3.2 zlib
-Move-Item libpng-1.6.53 libpng
+getlibrary 'https://github.com/lexxmark/winflexbison/releases/download/v2.5.25/win_flex_bison-2.5.25.zip' 'winflexbison.zip' '8d324b62be33604b2c45ad1dd34ab93d722534448f55a16ca7292de32b6ac135' bison

.github/workflows/create-release-artifacts.yml

@@ -28,27 +28,14 @@ jobs:
         uses: actions/checkout@v4
       - name: Install deps
         run: .github/scripts/get_win_deps.ps1
-      - name: Build zlib
-        run: | # BUILD_SHARED_LIBS causes the output DLL to be called `z.dll` as of zlib 1.3.2 (formerly `zlib1.dll`)
-          cmake -S zlib -B zbuild -A ${{ matrix.platform }} -Wno-dev -DCMAKE_INSTALL_PREFIX=install_dir -DBUILD_SHARED_LIBS=ON
-          cmake --build zbuild --config Release -j
-      - name: Install zlib
-        run: |
-          cmake --install zbuild --config Release
-      - name: Build libpng
-        shell: bash
-        run: |
-          cmake -S libpng -B pngbuild -A ${{ matrix.platform }} -Wno-dev -DCMAKE_INSTALL_PREFIX=install_dir -DPNG_SHARED=ON -DPNG_STATIC=OFF -DPNG_TESTS=OFF
-          cmake --build pngbuild --config Release -j
-      - name: Install libpng
-        run: |
-          cmake --install pngbuild --config Release
       - name: Build Windows binaries
         shell: bash
+        # We instruct CMake to download and build third-party projects outside of our source tree,
+        # otherwise they can trigger `-Werror=dev` (from the `develop` preset).
         run: |
-          cmake -S . -B build -A ${{ matrix.platform }} -DCMAKE_INSTALL_PREFIX=install_dir -DCMAKE_BUILD_TYPE=Release
-          cmake --build build --config Release -j --verbose
-          cmake --install build --config Release --strip
+          cmake -S . -B build -A ${{ matrix.platform }} -DCMAKE_BUILD_TYPE=Release -DFETCHCONTENT_BASE_DIR="$TEMP/cmake-deps" -DBISON_EXECUTABLE=bison/win_bison.exe
+          cmake --build build --config Release -j
+          cmake --install build --config Release --prefix install_dir --verbose
       - name: Package binaries
         run: |
           Compress-Archive -LiteralPath @("install_dir/bin/rgbasm.exe", "install_dir/bin/rgblink.exe", "install_dir/bin/rgbfix.exe", "install_dir/bin/rgbgfx.exe", "install_dir/bin/z.dll", "install_dir/bin/libpng16.dll") "rgbds-win${{ matrix.bits }}.zip"

.github/workflows/testing.yml

@@ -30,8 +30,13 @@ jobs:
           sudo make install -j Q=
       - name: Build & install using CMake
         if: matrix.buildsys == 'cmake'
+        # Since GitHub's runners are basically kitchen sinks,
+        # the Mono framework exposes a libpng 1.4.x header, breaking everything.
+        # Searching frameworks last makes Homebrew's libpng be discovered first, which works.
+        # Note that since this is specific to our CI environment, the workaround is
+        # better applied here than in our CMakeLists, where it could affect and break someone else.
         run: |
-          cmake -S . -B build --preset develop -DCMAKE_CXX_COMPILER=${{ matrix.cxx }} -DTESTS_OS_NAME=${{ matrix.os }}
+          cmake -S . -B build --preset develop -DCMAKE_FIND_FRAMEWORK=LAST -DCMAKE_CXX_COMPILER=${{ matrix.cxx }} -DTESTS_OS_NAME=${{ matrix.os }}
           cmake --build build -j --verbose
           sudo cmake --install build --verbose
       - name: Package binaries
@@ -147,38 +152,14 @@ jobs:
         uses: actions/checkout@v4
       - name: Install deps
         run: .github/scripts/get_win_deps.ps1
-      - name: Check libraries cache
-        id: cache
-        uses: actions/cache@v4
-        with:
-          path: |
-            zbuild
-            pngbuild
-          key: ${{ matrix.os }}-${{ matrix.arch }}-${{ hashFiles('zlib/**', 'libpng/**') }}
-      - name: Build zlib
-        if: steps.cache.outputs.cache-hit != 'true'
-        shell: bash
-        run: | # BUILD_SHARED_LIBS causes the output DLL to be called `z.dll` as of zlib 1.3.2 (formerly `zlib1.dll`)
-          cmake -S zlib -B zbuild -A ${{ matrix.platform }} -Wno-dev -DCMAKE_INSTALL_PREFIX=install_dir -DBUILD_SHARED_LIBS=ON
-          cmake --build zbuild --config Debug -j
-      - name: Install zlib
-        run: |
-          cmake --install zbuild --config Debug
-      - name: Build libpng
-        if: steps.cache.outputs.cache-hit != 'true'
-        shell: bash
-        run: |
-          cmake -S libpng -B pngbuild -A ${{ matrix.platform }} -Wno-dev -DCMAKE_INSTALL_PREFIX=install_dir -DCMAKE_BUILD_TYPE=Debug -DPNG_SHARED=ON -DPNG_STATIC=OFF -DPNG_TESTS=OFF
-          cmake --build pngbuild --config Debug -j
-      - name: Install libpng
-        run: |
-          cmake --install pngbuild --config Debug
       - name: Build Windows binaries
         shell: bash
-        run: | # ASan seems to be broken on Windows.
-          cmake -S . -B build -A ${{ matrix.platform }} --preset develop -DCMAKE_INSTALL_PREFIX=install_dir -DSANITIZERS=OFF
-          cmake --build build --config Debug -j --verbose
-          cmake --install build --verbose
+        # We instruct CMake to download and build third-party projects outside of our source tree,
+        # otherwise they can trigger `-Werror=dev` (from the `develop` preset).
+        run: | # ASan seems to be broken on Windows, so we disable it.
+          cmake -S . -B build -A ${{ matrix.platform }} --preset develop -DFETCHCONTENT_BASE_DIR="$TEMP/cmake-deps" -DBISON_EXECUTABLE=bison/win_bison.exe -DSANITIZERS=OFF
+          cmake --build build --config Debug -j
+          cmake --install build --config Debug --prefix install_dir --verbose
       - name: Package binaries
         shell: bash
         run: |

CMakeLists.txt

@@ -1,7 +1,10 @@
 # SPDX-License-Identifier: MIT
 
-# 3.17 required for LTO checks messages
-cmake_minimum_required(VERSION 3.17...4.2 FATAL_ERROR)
+# - 3.24 is required for `FetchContent`'s `find_package` integration.
+#   Older versions *may* work, but we can't test them; compat patches are welcome.
+# - 3.17 is required for `CHECK_*` messages to display properly, but is not essential.
+# - 3.9 is required for LTO checks.
+cmake_minimum_required(VERSION 3.24...4.2 FATAL_ERROR)
 
 # Read the project version from the header (the canonical source of truth).
 file(STRINGS "include/version.hpp" version_defines REGEX "^[ \t]*#define[ \t]+PACKAGE_VERSION_")
@@ -136,15 +139,34 @@ endif()
 
 ## Dependencies.
 
-find_package(PkgConfig)
-if(MSVC OR NOT PKG_CONFIG_FOUND)
-  # fallback to find_package
-  # cmake's FindPNG is very fragile; it breaks when multiple versions are installed
-  # this is most evident on macOS but can occur on Linux too
-  find_package(PNG REQUIRED)
-else()
-  pkg_check_modules(LIBPNG REQUIRED IMPORTED_TARGET libpng)
-  add_library(PNG::PNG ALIAS PkgConfig::LIBPNG)
+include(FetchContent)
+FetchContent_Declare(PNG
+                     URL https://download.sourceforge.net/libpng/libpng-1.6.55.tar.xz
+                     URL_HASH SHA256=d925722864837ad5ae2a82070d4b2e0603dc72af44bd457c3962298258b8e82d
+                     FIND_PACKAGE_ARGS 1.5.4)
+FetchContent_Declare(ZLIB
+                     URL https://www.zlib.net/zlib-1.3.2.tar.xz
+                     URL_HASH SHA256=d7a0654783a4da529d1bb793b7ad9c3318020af77667bcae35f95d0e42a792f3
+# libpng documents requiring "zlib 1.0.4 or later (1.2.13 or later recommended for performance and security reasons)".
+# We thus enforce 1.0.4, but note that the libpng source code mentions that "it may work with versions as old as zlib 0.95".
+                     FIND_PACKAGE_ARGS 1.0.4)
+set(ZLIB_BUILD_SHARED ON CACHE INTERNAL "")
+set(ZLIB_BUILD_STATIC OFF CACHE INTERNAL "")
+FetchContent_MakeAvailable(ZLIB)
+if(NOT DEFINED ZLIB_INCLUDE_DIRS)
+  set(ZLIB_INCLUDE_DIRS "${zlib_BINARY_DIR};${zlib_SOURCE_DIR}") # libpng's `genout` script relies on this variable to be set.
+endif()
+set(PNG_TESTS OFF CACHE INTERNAL "") # We do not care for these two (and they can even cause compile errors!)
+set(PNG_TOOLS OFF CACHE INTERNAL "")
+set(PNG_SHARED ON CACHE INTERNAL "") # Upstream seems to favour the dynamic lib over the static one?
+set(PNG_STATIC OFF CACHE INTERNAL "")
+FetchContent_MakeAvailable(PNG)
+if(NOT TARGET PNG::PNG)
+  if(PNG_SHARED)
+    add_library(PNG::PNG ALIAS png_shared)
+  else()
+    add_library(PNG::PNG ALIAS png_static)
+  endif()
 endif()
 
 ## The actual stuff.

src/CMakeLists.txt

@@ -13,7 +13,7 @@ target_compile_definitions(common PRIVATE "BUILD_VERSION_STRING=\"${GIT_REV}\"")
 
 find_package(BISON 3.0.0 REQUIRED)
 set(BISON_FLAGS "-Wall -Dlr.type=ielr")
-# Set some flags on versions that support them
+# Set some flags on versions that support them.
 if(BISON_VERSION VERSION_GREATER_EQUAL "3.5")
   set(BISON_FLAGS "${BISON_FLAGS} -Dparse.lac=full -Dapi.token.raw=true -Wdangling-alias")
 endif()