From: Andres Freund <andres@anarazel.de>
Date: Fri, 12 Jun 2026 08:46:00 -0400
Subject: [PATCH v13a 4/9] ci: Make our own msys2 install from scratch, instead
 of moving

Previously we relocated the existing install, for performance reasons. However
that has two disadvantages:

1) moving the install and then installing the packages we need is slower than
   just creating a new install
2) It hardcodes that D: is the fast drive, but that turns out to depend on the
   type of runner used
3) We were not using any caching and therefore downloaded the same files over
   and over. We could have added caching in the previous approach too, but
   it'd have been extra work.

I previously prototyped handrolling the install, instead of using
msys2/setup-msys2@v2, and that does turn out to be a bit faster, but it
doesn't include caching. By the time we add that, the overall complexity seems
like it'd be too big.

The other alternative would be to generate a downloadable release in the
pg-vm-images repo. That'd likely be even faster.

Discussion: https://postgr.es/m/a2ejn7lfqolutzz7kozalbhy3bixdrujb4buc3pgbtlk4am2ba@wbv6v7riia33
---
 .github/workflows/pg-ci.yml | 64 +++++++++++++++++--------------------
 1 file changed, 29 insertions(+), 35 deletions(-)

diff --git a/.github/workflows/pg-ci.yml b/.github/workflows/pg-ci.yml
index 442052b72e1..794a2600a23 100644
--- a/.github/workflows/pg-ci.yml
+++ b/.github/workflows/pg-ci.yml
@@ -1063,48 +1063,42 @@ jobs:
 
     defaults:
       run:
-        shell: 'D:\msys64\usr\bin\bash.exe --login -eo pipefail "{0}"'
+        shell: msys2 {0}
 
     steps:
       - *windows_disable_defender_step
       - *window_setup_hosts_step
       - *checkout_step
 
-      # Relocate the preinstalled MSYS2 tree from C:\ (slow system disk) to
-      # D:\ (faster ephemeral data disk). Every subsequent MSYS2 step uses
-      # D:\msys64\usr\bin\bash.exe via the job's `defaults.run.shell`.
+      # The pre-existing msys install is on C:\, often a rather slow system
+      # disk, whereas the workspace is often on a faster, ephemeral disk.
+      # Using the pre-existing msys would often increase the total runtime of
+      # this task by ~15 minutes.
       #
-      # This reduces the total runtime of this task by ~15 minutes.
-      #
-      # robocopy returns 0-7 on success (with various "files copied" bits
-      # set) and 8+ on real failure, so we have to translate its exit code.
-      - name: Relocate MSYS2 to D
-        shell: pwsh
-        run: |
-          robocopy C:\msys64 D:\msys64 /E /NJS /NJH /NFL /NDL /NP
-          if ($LASTEXITCODE -ge 8) { exit $LASTEXITCODE }
-          exit 0
-
-      - name: Setup MSYS2
-        run: |
-          # ${MINGW_PACKAGE_PREFIX} is an environment variable used in the
-          # MSYS2. It dynamically expands to the correct prefix for the active
-          # shell environment.
-          pacman -S --noconfirm --needed  --asdeps \
-            bison flex \
-            ${MINGW_PACKAGE_PREFIX}-ccache \
-            ${MINGW_PACKAGE_PREFIX}-gcc \
-            ${MINGW_PACKAGE_PREFIX}-icu \
-            ${MINGW_PACKAGE_PREFIX}-libxml2 \
-            ${MINGW_PACKAGE_PREFIX}-libxslt \
-            ${MINGW_PACKAGE_PREFIX}-lz4 \
-            ${MINGW_PACKAGE_PREFIX}-make \
-            ${MINGW_PACKAGE_PREFIX}-meson \
-            ${MINGW_PACKAGE_PREFIX}-perl \
-            ${MINGW_PACKAGE_PREFIX}-pkgconf \
-            ${MINGW_PACKAGE_PREFIX}-readline \
-            ${MINGW_PACKAGE_PREFIX}-zlib \
-            ${MINGW_PACKAGE_PREFIX}-zstd
+      # Instead we use msys2/setup-msys2 to set up our own install. That's
+      # faster than moving the install from C:\, and also works when the
+      # workspace is not on a separate disk.
+      - name: Install MSYS2
+        uses: msys2/setup-msys2@66cd2cce69caa17b53920067426061ca1de3a884 # v2.31.1
+        with:
+          msystem: ${{env.MSYSTEM}}
+          update: true
+          location: ${{github.workspace}}
+          install: >-
+            bison flex
+            mingw-w64-ucrt-x86_64-ccache
+            mingw-w64-ucrt-x86_64-gcc
+            mingw-w64-ucrt-x86_64-icu
+            mingw-w64-ucrt-x86_64-libxml2
+            mingw-w64-ucrt-x86_64-libxslt
+            mingw-w64-ucrt-x86_64-lz4
+            mingw-w64-ucrt-x86_64-make
+            mingw-w64-ucrt-x86_64-meson
+            mingw-w64-ucrt-x86_64-perl
+            mingw-w64-ucrt-x86_64-pkgconf
+            mingw-w64-ucrt-x86_64-readline
+            mingw-w64-ucrt-x86_64-zlib
+            mingw-w64-ucrt-x86_64-zstd
 
       - *nix_sysinfo_step
 
-- 
2.54.0.450.g9ac3f193c0


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