Allow building Mozc with Visual Studio 2026 (#1495)

This makes Mozc build on machines where only Visual Studio 2026 is
installed, while keeping Visual Studio 2022 as the default toolchain
on machines where VS 2022 is available. GitHub Actions runners stay on
VS 2022 for the time being; explicit opt-in to VS 2026 when both
versions are present can be added in a subsequent commit.

Three coordinated changes make this work:

1. Have vs_util.py call vswhere twice when the first call returns
   nothing: '[17,18)' first to find VS 2022, then '[18,19)' to find
   VS 2026. Combined with -latest, the resulting matrix is:

   * Only VS 2022 installed -> picks VS 2022 (no behavior change).
   * Only VS 2026 installed -> picks VS 2026.
   * Both installed         -> picks VS 2022 (no behavior change).

2. Pass BAZEL_VC into the installer genrule's command line as
   --vs_install_dir, derive vcvarsall.bat from it inside
   build_installer.py, and feed it to vs_util as the path hint. Add
   --action_env=BAZEL_VC under config:windows_env so Bazel propagates
   the value into action environments. Without this, build_installer.py
   would run its own vswhere lookup and could pick a different VS than
   Bazel did, especially on machines with multiple installs.

3. Pick the CRT redist subfolder dynamically. The subfolder is named
   after the platform toolset, not the MSVC compiler version: VS 2022
   stayed on toolset v143 even after MSVC ticked into the 14.4x range
   (to avoid breaking existing project files / CI pipelines), so its
   redist lives under 'Microsoft.VC143.CRT'. VS 2026 jumped the toolset
   to v145 (matching MSVC 14.50), skipping v144 entirely; its redist
   lives under 'Microsoft.VC145.CRT'. Read VCTOOLSVERSION (which
   vcvarsall.bat exports next to VCTOOLSREDISTDIR) and pick the v145
   subfolder when the minor component is >=50, otherwise v143.

Closes #1487.

PiperOrigin-RevId: 913010498

Author: yukawa

docs/build_mozc_in_windows.md

@@ -45,7 +45,12 @@ Building Mozc on Windows requires the following software.
 *   `.NET 6` or later (for `dotnet` command).
 *   [Bazelisk](https://github.com/bazelbuild/bazelisk)
 
-> [!NOTE] Bazelisk is a wrapper of [Bazel](https://bazel.build) that allows you
+> [!TIP]
+> Visual Studio 2026 Community Edition is also supported to build Mozc. When
+> both VS 2022 and 2026 are installed, VS 2022 will be used.
+
+> [!NOTE]
+> Bazelisk is a wrapper of [Bazel](https://bazel.build) that allows you
 > to use a specific version of Bazel.
 
 ### Download the repository from GitHub

src/.bazelrc

@@ -39,6 +39,7 @@ build:windows_env --extra_toolchains=@local_config_cc//:cc-toolchain-x64_windows
 build:windows_env --extra_toolchains=@local_config_cc//:cc-toolchain-x64_x86_windows-clang-cl
 build:windows_env --host_platform=//:host-windows-clang-cl
 build:windows_env --repo_env=BAZEL_WIN32_WINNT=/D_WIN32_WINNT=0x0A00
+build:windows_env --action_env=BAZEL_VC
 
 ## Compiler options
 common:linux_env   --config=compiler_gcc_like

src/build_tools/vs_util.py

@@ -77,7 +77,7 @@ def get_vcvarsall(
         r' --vcvarsall_path=C:\VS\VC\Auxiliary\Build\vcvarsall.bat'
     )
 
-  cmd = [
+  base_cmd = [
       str(vswhere_path),
       '-products',
       'Microsoft.VisualStudio.Product.Enterprise',
@@ -86,41 +86,43 @@ def get_vcvarsall(
       'Microsoft.VisualStudio.Product.BuildTools',
       '-find',
       'VC/Auxiliary/Build/vcvarsall.bat',
-      '-version',
-      '[17,18)',  # See https://github.com/microsoft/vswhere/wiki/Versions
       '-latest',
       '-utf8',
-  ]
-  cmd += [
       '-requires',
       'Microsoft.VisualStudio.Component.VC.Redist.14.Latest',
   ]
   if arch.endswith('arm64'):
-    cmd += ['Microsoft.VisualStudio.Component.VC.Tools.ARM64']
-
-  process = subprocess.Popen(
-      cmd,
-      stdout=subprocess.PIPE,
-      stderr=subprocess.PIPE,
-      shell=False,
-      text=True,
-      encoding='utf-8',
-  )
-  stdout, stderr = process.communicate()
-  exitcode = process.wait()
-  if exitcode != 0:
-    msgs = ['Failed to execute vswhere.exe']
-    if stdout:
-      msgs += ['-----stdout-----', stdout]
-    if stderr:
-      msgs += ['-----stderr-----', stderr]
-    raise ChildProcessError('\n'.join(msgs))
-
-  lines = stdout.splitlines()
-  if len(lines) > 0:
-    vcvarsall = pathlib.Path(lines[0])
-    if vcvarsall.exists():
-      return vcvarsall
+    base_cmd += ['Microsoft.VisualStudio.Component.VC.Tools.ARM64']
+
+  # Try Visual Studio 2022 first, then fall back to Visual Studio 2026 when
+  # VS 2022 is not installed. This keeps VS 2022 as the default on machines
+  # that have both versions installed.
+  # See https://github.com/microsoft/vswhere/wiki/Versions
+  for version_filter in ('[17,18)', '[18,19)'):
+    cmd = base_cmd + ['-version', version_filter]
+    process = subprocess.Popen(
+        cmd,
+        stdout=subprocess.PIPE,
+        stderr=subprocess.PIPE,
+        shell=False,
+        text=True,
+        encoding='utf-8',
+    )
+    stdout, stderr = process.communicate()
+    exitcode = process.wait()
+    if exitcode != 0:
+      msgs = ['Failed to execute vswhere.exe']
+      if stdout:
+        msgs += ['-----stdout-----', stdout]
+      if stderr:
+        msgs += ['-----stderr-----', stderr]
+      raise ChildProcessError('\n'.join(msgs))
+
+    lines = stdout.splitlines()
+    if len(lines) > 0:
+      vcvarsall = pathlib.Path(lines[0])
+      if vcvarsall.exists():
+        return vcvarsall
 
   msg = 'Could not find vcvarsall.bat.'
   if arch.endswith('arm64'):

src/win32/installer/BUILD.bazel

@@ -117,6 +117,7 @@ genrule(
         "--wxs_path=$(location " + _WXS_FILE + ")",
         "--wix_path=$(location @wix//:wix.exe)",
         "--branding=" + BRANDING,
+        "--vs_install_dir=\"$$BAZEL_VC\"",
     ]) + select({
         ":build_arm64_binaries": " " + " ".join([
             "--mozc_tip64arm=$(location //win32/tip:mozc_tip64arm)",

src/win32/installer/build_installer.py

@@ -78,13 +78,30 @@ def run_wix4(args) -> None:
   """
   arch = args.arch
 
+  vcvarsall_hint = None
+  if args.vs_install_dir:
+    vcvarsall_hint = str(
+        pathlib.Path(args.vs_install_dir).joinpath(
+            'Auxiliary', 'Build', 'vcvarsall.bat'
+        )
+    )
+
   # 'VCTOOLSREDISTDIR' environment variable is the same among x86, x64 and arm64
   # architectures, so just using 'x64' should be fine here.
-  redist_root = pathlib.Path(
-      vs_util.get_vs_env_vars('x64')['VCTOOLSREDISTDIR']
-  ).resolve()
-
-  redist_64bit = redist_root.joinpath(arch).joinpath('Microsoft.VC143.CRT')
+  vs_env = vs_util.get_vs_env_vars('x64', vcvarsall_hint)
+  redist_root = pathlib.Path(vs_env['VCTOOLSREDISTDIR']).resolve()
+
+  # The CRT redist subfolder is named after the platform toolset, not the
+  # MSVC compiler version: VS 2022 ships 'Microsoft.VC143.CRT' (toolset v143,
+  # MSVC 14.3x/14.4x) while VS 2026 ships 'Microsoft.VC145.CRT' (toolset
+  # v145, MSVC 14.50+). v144 was skipped. Pick the subfolder by reading the
+  # MSVC compiler minor version that vcvarsall.bat exports as
+  # 'VCTOOLSVERSION'.
+  vc_tools_minor = int(vs_env['VCTOOLSVERSION'].split('.')[1])
+  crt_subdir = (
+      'Microsoft.VC145.CRT' if vc_tools_minor >= 50 else 'Microsoft.VC143.CRT'
+  )
+  redist_64bit = redist_root.joinpath(arch).joinpath(crt_subdir)
   version_file = pathlib.Path(args.version_file).resolve()
   version = mozc_version.MozcVersion(version_file)
   credit_file = pathlib.Path(args.credit_file).resolve()
@@ -194,6 +211,12 @@ def main():
       default=False,
       action='store_true',
   )
+  parser.add_argument(
+      '--vs_install_dir',
+      type=str,
+      default='',
+      help='Path to the Visual Studio VC directory (same as BAZEL_VC).',
+  )
 
   args = parser.parse_args()