v.builder: try finding msvc from env variables, when not found from registry (#10072)

vlib/v/builder/msvc.v

@@ -80,15 +80,28 @@ struct WindowsKit {
 
 // Try and find the root key for installed windows kits
 fn find_windows_kit_root(target_arch string) ?WindowsKit {
+	$if windows {
+		wkroot := find_windows_kit_root_by_reg(target_arch) or {
+			if wkroot := find_windows_kit_root_by_env(target_arch) {
+				return wkroot
+			}
+			return err
+		}
+
+		return wkroot
+	} $else {
+		return error('Host OS does not support finding a windows kit')
+	}
+}
+
+// Try to find the root key for installed windows kits from registry
+fn find_windows_kit_root_by_reg(target_arch string) ?WindowsKit {
 	$if windows {
 		root_key := RegKey(0)
 		path := 'SOFTWARE\\Microsoft\\Windows Kits\\Installed Roots'
 		rc := C.RegOpenKeyEx(builder.hkey_local_machine, path.to_wide(), 0, builder.key_query_value | builder.key_wow64_32key | builder.key_enumerate_sub_keys,
 			&root_key)
-		// TODO: Fix defer inside ifs
-		// defer {
-		// C.RegCloseKey(root_key)
-		// }
+
 		if rc != 0 {
 			return error('Unable to open root key')
 		}
@@ -97,6 +110,14 @@ fn find_windows_kit_root(target_arch string) ?WindowsKit {
 			C.RegCloseKey(root_key)
 			return error('Unable to find a windows kit')
 		}
+		C.RegCloseKey(root_key)
+		return new_windows_kit(kit_root, target_arch)
+	} $else {
+		return error('Host OS does not support finding a windows kit')
+	}
+}
+
+fn new_windows_kit(kit_root string, target_arch string) ?WindowsKit {
 	kit_lib := kit_root + 'Lib'
 	files := os.ls(kit_lib) ?
 	mut highest_path := ''
@@ -111,7 +132,6 @@ fn find_windows_kit_root(target_arch string) ?WindowsKit {
 	}
 	kit_lib_highest := kit_lib + '\\$highest_path'
 	kit_include_highest := kit_lib_highest.replace('Lib', 'Include')
-		C.RegCloseKey(root_key)
 	return WindowsKit{
 		um_lib_path: kit_lib_highest + '\\um\\$target_arch'
 		ucrt_lib_path: kit_lib_highest + '\\ucrt\\$target_arch'
@@ -120,7 +140,14 @@ fn find_windows_kit_root(target_arch string) ?WindowsKit {
 		shared_include_path: kit_include_highest + '\\shared'
 	}
 }
-	return error('Host OS does not support finding a windows kit')
+
+fn find_windows_kit_root_by_env(target_arch string) ?WindowsKit {
+	kit_root := os.getenv('WindowsSdkDir')
+	if kit_root == '' {
+		return none
+	}
+
+	return new_windows_kit(kit_root, target_arch)
 }
 
 struct VsInstallation {
@@ -130,9 +157,21 @@ struct VsInstallation {
 }
 
 fn find_vs(vswhere_dir string, host_arch string, target_arch string) ?VsInstallation {
-	$if !windows {
+	$if windows {
+		vsinst := find_vs_by_reg(vswhere_dir, host_arch, target_arch) or {
+			if vsinst := find_vs_by_env(host_arch, target_arch) {
+				return vsinst
+			}
+			return err
+		}
+		return vsinst
+	} $else {
 		return error('Host OS does not support finding a Visual Studio installation')
 	}
+}
+
+fn find_vs_by_reg(vswhere_dir string, host_arch string, target_arch string) ?VsInstallation {
+	$if windows {
 		// Emily:
 		// VSWhere is guaranteed to be installed at this location now
 		// If its not there then end user needs to update their visual studio
@@ -163,6 +202,31 @@ fn find_vs(vswhere_dir string, host_arch string, target_arch string) ?VsInstalla
 		}
 		println('Unable to find vs installation (attempted to use lib path "$lib_path")')
 		return error('Unable to find vs exe folder')
+	} $else {
+		return error('Host OS does not support finding a Visual Studio installation')
+	}
+}
+
+fn find_vs_by_env(host_arch string, target_arch string) ?VsInstallation {
+	vs_dir := os.getenv('VSINSTALLDIR')
+	if vs_dir == '' {
+		return none
+	}
+
+	vc_tools_dir := os.getenv('VCToolsInstallDir')
+	if vc_tools_dir == '' {
+		return none
+	}
+
+	bin_dir := '${vc_tools_dir}bin\\Host$host_arch\\$target_arch'
+	lib_path := '${vc_tools_dir}lib\\$target_arch'
+	include_path := '${vc_tools_dir}include'
+
+	return VsInstallation{
+		exe_path: bin_dir
+		lib_path: lib_path
+		include_path: include_path
+	}
 }
 
 fn find_msvc(m64_target bool) ?MsvcResult {