Auto merge of #121182 - majaha:mingw_ci_new, r=Mark-Simulacrum

Improvements to building and CI for mingw/msys

I was getting error messages when trying to follow the build instructions the mingw build for Rust, and managed to track the issue down to an incomparability of Rust's bootstrap program with MSYS2's version of git. Essentially, the problem is that MSYS2's git works in emulated unix-y paths, but bootstrap expects a Windows path. I found a workaround for this by using relative paths instead of absolute paths.

Along with that fix, this PR also updates the build instructions for MinGW to be compatible with modern versions of MSYS2, and some changes to CI to make sure that MSYS2's version of git is tested. In particular, I'm suggesting using the [MSYS2 github action](https://github.com/marketplace/actions/setup-msys2) specially made for this purpose, which is much less hacky than the old approach and gives us more control of what packages are installed. I also cleaned up as many alternate versions of key tools as I could find from PATH, to avoid accidental usage, and cleaned up some abuses of the `CUSTOM_MINGW` environment variable.

This fixes https://github.com/rust-lang/rust/issues/105696 and fixes https://github.com/rust-lang/rust/issues/117567

3 files changed, 37 insertions, 14 deletions

diff --git a/src/ci/scripts/install-clang.sh b/src/ci/scripts/install-clang.sh
index 77164ed4117..aa7ff813f51 100755
--- a/src/ci/scripts/install-clang.sh
+++ b/src/ci/scripts/install-clang.sh
@@ -37,8 +37,7 @@ if isMacOS; then
     # Configure `AR` specifically so rustbuild doesn't try to infer it as
     # `clang-ar` by accident.
     ciCommandSetEnv AR "ar"
-elif isWindows && [[ ${CUSTOM_MINGW-0} -ne 1 ]]; then
-
+elif isWindows && ! isKnownToBeMingwBuild; then
     # If we're compiling for MSVC then we, like most other distribution builders,
     # switch to clang as the compiler. This'll allow us eventually to enable LTO
     # amongst LLVM and rustc. Note that we only do this on MSVC as I don't think
diff --git a/src/ci/scripts/install-mingw.sh b/src/ci/scripts/install-mingw.sh
index 7eccb9b8650..87b835b63db 100755
--- a/src/ci/scripts/install-mingw.sh
+++ b/src/ci/scripts/install-mingw.sh
@@ -38,11 +38,11 @@ if isWindows; then
             ;;
     esac
 
-    if [[ "${CUSTOM_MINGW-0}" -ne 1 ]]; then
-        pacman -S --noconfirm --needed mingw-w64-$arch-toolchain mingw-w64-$arch-cmake \
-            mingw-w64-$arch-gcc \
-            mingw-w64-$arch-python # the python package is actually for python3
-        ciCommandAddPath "$(ciCheckoutPath)/msys2/mingw${bits}/bin"
+    if [[ "${CUSTOM_MINGW:-0}" == 0 ]]; then
+        pacboy -S --noconfirm toolchain:p
+        # According to the comment in the Windows part of install-clang.sh, in the future we might
+        # want to do this instead:
+        # pacboy -S --noconfirm clang:p ...
     else
         mingw_dir="mingw${bits}"
 
diff --git a/src/ci/scripts/install-msys2.sh b/src/ci/scripts/install-msys2.sh
index 0aa4b42a6a8..905edf38a09 100755
--- a/src/ci/scripts/install-msys2.sh
+++ b/src/ci/scripts/install-msys2.sh
@@ -1,17 +1,12 @@
 #!/bin/bash
-# Download and install MSYS2, needed primarily for the test suite (run-make) but
-# also used by the MinGW toolchain for assembling things.
+# Clean up and prepare the MSYS2 installation. MSYS2 is needed primarily for
+# the test suite (run-make), but is also used by the MinGW toolchain for assembling things.
 
 set -euo pipefail
 IFS=$'\n\t'
 
 source "$(cd "$(dirname "$0")" && pwd)/../shared.sh"
-
 if isWindows; then
-    msys2Path="c:/msys64"
-    mkdir -p "${msys2Path}/home/${USERNAME}"
-    ciCommandAddPath "${msys2Path}/usr/bin"
-
     # Detect the native Python version installed on the agent. On GitHub
     # Actions, the C:\hostedtoolcache\windows\Python directory contains a
     # subdirectory for each installed Python version.
@@ -29,4 +24,33 @@ if isWindows; then
     fi
     ciCommandAddPath "C:\\hostedtoolcache\\windows\\Python\\${native_python_version}\\x64"
     ciCommandAddPath "C:\\hostedtoolcache\\windows\\Python\\${native_python_version}\\x64\\Scripts"
+
+    # Install pacboy for easily installing packages
+    pacman -S --noconfirm pactoys
+
+    # Delete these pre-installed tools so we can't accidentally use them, because we are using the
+    # MSYS2 setup action versions instead.
+    # Delete pre-installed version of MSYS2
+    rm -r "/c/msys64/"
+    # Delete Strawberry Perl, which contains a version of mingw
+    rm -r "/c/Strawberry/"
+    # Delete these other copies of mingw, I don't even know where they come from.
+    rm -r "/c/mingw64/"
+    rm -r "/c/mingw32/"
+
+    if isKnownToBeMingwBuild; then
+        # Use the mingw version of CMake for mingw builds.
+        # However, the MSVC build needs native CMake, as it fails with the mingw one.
+        # Delete native CMake
+        rm -r "/c/Program Files/CMake/"
+        # Install mingw-w64-$arch-cmake
+        pacboy -S --noconfirm cmake:p
+
+        # We use Git-for-Windows for MSVC builds, and MSYS2 Git for mingw builds,
+        # so that both are tested.
+        # Delete Windows-Git
+        rm -r "/c/Program Files/Git/"
+        # Install MSYS2 git
+        pacman -S --noconfirm git
+    fi
 fi