Use the recommended ghactions action to set up msys2

.github/build.sh

@@ -76,6 +76,7 @@ if [[ -z ${BSH_NO_PACKAGES-} ]]; then
 			else
 				pacman -S --noconfirm --needed mingw-w64-ucrt-x86_64-{pkgconf,bzip2,luajit,jsoncpp,curl,SDL2,libpng,meson,fftw}
 			fi
+			export PKG_CONFIG=$(which pkg-config.exe)
 		fi
 		;;
 	linux)

.github/force-msys2-bash.sh

@@ -1,10 +0,0 @@
-set -euo pipefail
-IFS=$'\t\n'
-
-echo 'C:\msys64\ucrt64\bin' >> tmp
-echo 'C:\msys64\usr\bin' >> tmp
-cat $GITHUB_PATH >> tmp
-mv tmp $GITHUB_PATH
-
-echo "MSYSTEM=UCRT64" >> $GITHUB_ENV
-echo "PKG_CONFIG="'C:\msys64\ucrt64\bin\pkg-config.exe' >> $GITHUB_ENV

.github/prepare.py

@@ -173,6 +173,10 @@ for        arch,     platform,         libc,   statdyn, bplatform,         runso
 		debug_asset_path = f'{app_name_slug}-{arch}.AppImage.dbg'
 		debug_asset_name = f'{app_name_slug}-{arch}.AppImage.dbg'
 	starcatcher_name = f'powder-{release_name}-{starcatcher}{suffix}'
+	msys2_bash = (bplatform == 'windows' and libc == 'mingw')
+	shell = 'bash'
+	if msys2_bash:
+		shell = 'msys2 {0}'
 	build_matrix.append({
 		'bsh_build_platform': bplatform, # part of the unique portion of the matrix
 		'bsh_host_arch': arch, # part of the unique portion of the matrix
@@ -181,7 +185,7 @@ for        arch,     platform,         libc,   statdyn, bplatform,         runso
 		'bsh_static_dynamic': statdyn, # part of the unique portion of the matrix
 		'bsh_debug_release': dbgrel, # part of the unique portion of the matrix
 		'runs_on': runson,
-		'force_msys2_bash': (bplatform == 'windows' and libc == 'mingw') and 'yes' or 'no',
+		'force_msys2_bash': msys2_bash and 'yes' or 'no',
 		'package_suffix': suffix,
 		'package_mode': mode,
 		'publish': publish and 'yes' or 'no',
@@ -192,6 +196,7 @@ for        arch,     platform,         libc,   statdyn, bplatform,         runso
 		'debug_asset_path': debug_asset_path,
 		'debug_asset_name': debug_asset_name,
 		'job_name': job_name,
+		'shell': shell,
 	})
 	if publish:
 		publish_matrix.append({

.github/workflows/build.yaml

@@ -54,17 +54,45 @@ jobs:
     strategy:
       fail-fast: false
       matrix: ${{ fromJSON(needs.prepare.outputs.build_matrix) }}
+    defaults:
+      run:
+        shell: ${{ matrix.shell }}
     steps:
+      - if: matrix.force_msys2_bash == 'yes'
+        uses: msys2/setup-msys2@v2
+        with:
+          msystem: UCRT64
+          update: true
+          path-type: strict
+          cache: true
+          # this list doesn't have to mirror the one in build.sh perfectly
+          # but the packages listed here get cached properly and take less time to install
+          install: >-
+            git
+            curl
+            mingw-w64-ucrt-x86_64-gcc
+            mingw-w64-ucrt-x86_64-pkgconf
+            mingw-w64-ucrt-x86_64-bzip2
+            mingw-w64-ucrt-x86_64-luajit
+            mingw-w64-ucrt-x86_64-jsoncpp
+            mingw-w64-ucrt-x86_64-curl
+            mingw-w64-ucrt-x86_64-SDL2
+            mingw-w64-ucrt-x86_64-libpng
+            mingw-w64-ucrt-x86_64-meson
+            mingw-w64-ucrt-x86_64-python
+            mingw-w64-ucrt-x86_64-python-pip
+            mingw-w64-ucrt-x86_64-fftw
+            mingw-w64-ucrt-x86_64-cmake
+            mingw-w64-ucrt-x86_64-7zip
+            patch
       - run: git config --global core.autocrlf false
       - uses: actions/checkout@v4
-      - if: matrix.force_msys2_bash == 'yes'
-        run: bash -c './.github/force-msys2-bash.sh'
-      - if: matrix.force_msys2_bash == 'yes'
-        run: bash -c 'pacman -Syu --noconfirm'
-      - uses: actions/setup-python@v5
+      - if: matrix.force_msys2_bash != 'yes'
+        uses: actions/setup-python@v5
         with:
           python-version: '3.10'
-      - run: python -m pip install meson==1.2.3 ninja # TODO: go back to using latest meson once https://github.com/mesonbuild/meson/pull/12544 is live
+      - if: matrix.force_msys2_bash != 'yes'
+        run: python -m pip install meson==1.2.3 ninja # TODO: go back to using latest meson once https://github.com/mesonbuild/meson/pull/12544 is live
       - if: matrix.bsh_build_platform == 'darwin'
         run: brew install bash coreutils
       - run: bash -c './.github/build.sh'