Reland "Support multiple VS installations" (with fix)

This reverts commit 9ce8be33.

Reason for revert: To apply fix

Original change's description:
> Revert "Support multiple VS installations"
>
> This reverts commit 36d41cef.
>
> Reason for revert: Script references VS_VERSION variable that was
> renamed in the prior change, so it doesn't work.
>
> Original change's description:
> > 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>
>
> Change-Id: I3d9147a7786f7f54f861087d16967b75d4afe2c5
> Reviewed-on: https://chromium-review.googlesource.com/c/chromium/tools/depot_tools/+/3504193
> Bot-Commit: Rubber Stamper <rubber-stamper@appspot.gserviceaccount.com>
> Commit-Queue: Bruce Dawson <brucedawson@chromium.org>

Change-Id: Ica90cb8d5ce08b8b127da64969401cb40d4aee63
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/tools/depot_tools/+/3497899Reviewed-by: Bruce Dawson <brucedawson@chromium.org>
Commit-Queue: 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 = ""
   for line in output.splitlines():
-    if line.startswith(marker):
-      return line[len(marker):]
+    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):
@@ -475,6 +498,9 @@ 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:
@@ -497,6 +523,8 @@ 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.