Improve solution by using vswhere.exe (I'm sure this works for MSVC 2022 too)

Author: jmarrec

build.py

@@ -115,18 +115,62 @@ def Exit( self ):
   'See the YCM docs for details on how to use a custom Clangd.' )
 
 
-def FindLatestMSVC():
-    import winreg
-    handle = winreg.ConnectRegistry(None, winreg.HKEY_LOCAL_MACHINE)
-    msvc = None
-    for i in [17, 16, 15]:
-        try:
-            winreg.OpenKey(handle, rf'SOFTWARE\Microsoft\VisualStudio\{i}.0')
-            msvc = i
-            break
-        except FileNotFoundError:
-            pass
-    return msvc
+def FindLatestMSVC(quiet):
+  ACCEPTABLE_VERSIONS = [17, 16, 15]
+
+  VSWHERE_EXE = os.path.join(os.environ['ProgramFiles(x86)'],
+                             'Microsoft Visual Studio',
+                             'Installer', 'vswhere.exe')
+
+  if os.path.exists(VSWHERE_EXE):
+    if not quiet:
+      print("Calling vswhere -latest -installationVersion")
+    latest_full_v = subprocess.check_output(
+      [VSWHERE_EXE, '-latest', '-property', 'installationVersion']
+    ).strip().decode()
+    if '.' in latest_full_v:
+      try:
+        latest_v = int(latest_full_v.split('.')[0])
+      except ValueError:
+        raise ValueError("{latest_full_v=} is not a version number.")
+
+      if not quiet:
+        print(f'vswhere -latest returned version {latest_full_v=}')
+
+      if latest_v not in ACCEPTABLE_VERSIONS:
+        if latest_v > 17:
+          if not quiet:
+            print(f'MSVC Version {latest_full_v=} is newer than expected.')
+        else:
+          raise ValueError(
+            f'vswhere returned {latest_full_v=} which is unexpected.'
+            'Pass --msvc <version> argument.')
+      return latest_v
+    else:
+      if not quiet:
+        print(f'vswhere returned nothing usable, {latest_full_v=}')
+
+  # Fall back to registry parsing, which works at least until MSVC 2019 (16)
+  # but is likely failing on MSVC 2022 (17)
+  if not quiet:
+    print("vswhere method failed, falling back to searching the registry")
+
+  import winreg
+  handle = winreg.ConnectRegistry(None, winreg.HKEY_LOCAL_MACHINE)
+  msvc = None
+  for i in ACCEPTABLE_VERSIONS:
+    if not quiet:
+      print('Trying to find '
+            rf'HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\VisualStudio\{i}.0')
+      try:
+        winreg.OpenKey(handle, rf'SOFTWARE\Microsoft\VisualStudio\{i}.0')
+        if not quiet:
+          print(f"Found MSVC version {i}")
+          msvc = i
+          break
+      except FileNotFoundError:
+        pass
+  return msvc
 
 
 def RemoveDirectory( directory ):
@@ -507,9 +551,9 @@ def ParseArguments():
     args.enable_debug = True
 
   if OnWindows() and args.msvc is None:
-    args.msvc = FindLatestMSVC()
+    args.msvc = FindLatestMSVC(args.quiet)
     if args.msvc is None:
-      raise FileNotFoundError("Could not find a valid MSVC version")
+      raise FileNotFoundError("Could not find a valid MSVC version.")
 
   if args.core_tests:
     os.environ[ 'YCM_TESTRUN' ] = '1'