Support multiple VS installations

Currently, package_from_installed.py assumes only one version of VS is
installed. It takes the path of the first installation.

This could be incorrect in several ways:
- Maybe both 2017 and 2019 (the supported versions) are installed and
  although the user specified using 2019, the 2017 path comes first.
- Maybe 2019 and 2022 are installed, and the 2022 path is used even
  though it isn't supported.

This CL fixes that issue by parsing the vswhere.exe output to confirm
the VS version matches what the user specified, using its corresponding
path.

Change-Id: I2029a4f7126d0a45b5370ad58ab257df55571b3b
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/tools/depot_tools/+/3458722
Reviewed-by: Gavin Mak <gavinmak@google.com>
Reviewed-by: Chris Blume <cblume@chromium.org>
Commit-Queue: Chris Blume <cblume@chromium.org>
Auto-Submit: Chris Blume <cblume@chromium.org>

win_toolchain/package_from_installed.py

@@ -52,6 +52,7 @@ _vs_version = None
 _win_version = None
 _vc_tools = None
 SUPPORTED_VS_VERSIONS = ['2017', '2019']
+_allow_multiple_vs_installs = False
 
 
 def GetVSPath():
@@ -60,12 +61,34 @@ def GetVSPath():
   # version is installed.
   command = (r'C:\Program Files (x86)\Microsoft Visual Studio\Installer'
              r'\vswhere.exe -prerelease')
-  marker = 'installationPath: '
+  vs_version_marker = 'catalog_productLineVersion: '
+  vs_path_marker = 'installationPath: '
   output = subprocess.check_output(command, universal_newlines=True)
+  vs_path = None
+  vs_installs_count = 0
+  matching_vs_path = None
   for line in output.splitlines():
-    if line.startswith(marker):
-      return line[len(marker):]
-  raise Exception('VS %s path not found in vswhere output' % (_vs_version))
+    if line.startswith(vs_path_marker):
+      # The path information comes first
+      vs_path = line[len(vs_path_marker):]
+      vs_installs_count += 1
+    if line.startswith(vs_version_marker):
+      # The version for that path comes later
+      if line[len(vs_version_marker):] == VS_VERSION:
+        matching_vs_path = vs_path
+
+  if vs_installs_count == 0:
+    raise Exception('VS %s path not found in vswhere output' % (VS_VERSION))
+  if vs_installs_count > 1:
+    if not _allow_multiple_vs_installs:
+      raise Exception('Multiple VS installs detected. This is unsupported. '
+                      'It is recommended that packaging be done on a clean VM '
+                      'with just one version installed. To proceed anyway add '
+                      'the --allow_multiple_vs_installs flag to this script')
+    else:
+      print('Multiple VS installs were detected. This is unsupported. '
+            'Proceeding anyway')
+  return matching_vs_path
 
 
 def ExpandWildcards(root, sub_dir):
@@ -477,6 +500,9 @@ def main():
   parser.add_option('--repackage', action='store', type='string',
                     dest='repackage_dir', default=None,
                     help='Specify raw directory to be packaged, for hot fixes.')
+  parser.add_option('--allow_multiple_vs_installs', action='store_true',
+                    default=False, dest='allow_multiple_vs_installs',
+                    help='Specify if multiple VS installs are allowed.')
   (options, args) = parser.parse_args()
 
   if options.repackage_dir:
@@ -499,6 +525,8 @@ def main():
     global _win_version
     _win_version = options.winver
     global _vc_tools
+    global _allow_multiple_vs_installs
+    _allow_multiple_vs_installs = options.allow_multiple_vs_installs
     vs_path = GetVSPath()
     temp_tools_path = ExpandWildcards(vs_path, 'VC/Tools/MSVC/14.*.*')
     # Strip off the leading vs_path characters and switch back to / separators.