vet: add -W flag and detailed help (#9331)

cmd/tools/vvet/vvet.v

@@ -32,6 +32,8 @@ const vet_options = cmdline.options_after(os.args, ['vet'])
 
 const is_force = '-force' in vet_options
 
+const is_werror = '-W' in vet_options
+
 const is_verbose = '-verbose' in vet_options || '-v' in vet_options
 
 const show_warnings = '-hide-warnings' !in vet_options
@@ -104,7 +106,7 @@ fn main() {
 	if errors_vfmt.len > 0 {
 		eprintln('NB: You can run `v fmt -w file.v` to fix these automatically')
 	}
-	if errors.len > 0 {
+	if errors.len > 0 || (is_werror && warnings.len > 0) {
 		exit(1)
 	}
 }

cmd/v/help/default.txt

@@ -49,4 +49,4 @@ Use "v help <command>" for more information about a command, example: `v help bu
 Use "v help other" to see less frequently used commands.
 
 Note: Help is required to write more help topics.
-Only build, new, init, doc, fmt, run, test, search, install, remove, update, bin2v, check-md are properly documented currently.
+Only build, new, init, doc, fmt, vet, run, test, search, install, remove, update, bin2v, check-md are properly documented currently.

cmd/v/help/vet.txt

@@ -0,0 +1,11 @@
+Usage:
+  v vet [options] path_to_source.v [path_to_other_source.v]
+  v vet [options] path/to/dir [path/to/other_dir]
+
+Reports suspicious code constructs.
+
+Options:
+  -W               Exit with code 1, even if vet only reported warnings. Useful for checks in CI.
+  -hide-warnings   Do not print warnings to stderr.
+  -v, -verbose     Enable verbose logging.
+  -force           (NB: vet development only!) Do not skip the vet regression tests.