cmd/go: make go vet query cmd/vet for its flags

Add -flags flag to cmd/vet that causes it to describe its flags as JSON.

go vet's "-vettool" flag has been replaced with an environment
variable, GOVETTOOL, for two reasons:

  1) we need its value before flag processing,
     because we must run vet to discover its flags.

  2) users may change the env var to opt in/out of the new vet tool
     during the upcoming transition to vet based on the analysis API.

Change-Id: I5d8f90817623022f4170b88fab3c92c9b2fbdc37
Reviewed-on: https://go-review.googlesource.com/c/142617
Run-TryBot: Alan Donovan <adonovan@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Bryan C. Mills <bcmills@google.com>

1 files changed, 28 insertions, 2 deletions

diff --git a/src/cmd/vet/main.go b/src/cmd/vet/main.go
index 6e885121c8..cf91e4d596 100644
--- a/src/cmd/vet/main.go
+++ b/src/cmd/vet/main.go
@@ -22,6 +22,7 @@ import (
 	"go/types"
 	"io"
 	"io/ioutil"
+	"log"
 	"os"
 	"path/filepath"
 	"sort"
@@ -31,10 +32,9 @@ import (
 	"cmd/internal/objabi"
 )
 
-// Important! If you add flags here, make sure to update cmd/go/internal/vet/vetflag.go.
-
 var (
 	verbose = flag.Bool("v", false, "verbose")
+	flags   = flag.Bool("flags", false, "print flags in JSON")
 	source  = flag.Bool("source", false, "import from source instead of compiled object files")
 	tags    = flag.String("tags", "", "space-separated list of build tags to apply when parsing")
 	tagList = []string{} // exploded version of tags flag; set in main
@@ -259,6 +259,32 @@ func main() {
 	flag.Usage = Usage
 	flag.Parse()
 
+	// -flags: print flags as JSON. Used by go vet.
+	if *flags {
+		type jsonFlag struct {
+			Name  string
+			Bool  bool
+			Usage string
+		}
+		var jsonFlags []jsonFlag
+		flag.VisitAll(func(f *flag.Flag) {
+			isBool := false
+			switch v := f.Value.(type) {
+			case interface{ BoolFlag() bool }:
+				isBool = v.BoolFlag()
+			case *triState:
+				isBool = true // go vet should treat it as boolean
+			}
+			jsonFlags = append(jsonFlags, jsonFlag{f.Name, isBool, f.Usage})
+		})
+		data, err := json.MarshalIndent(jsonFlags, "", "\t")
+		if err != nil {
+			log.Fatal(err)
+		}
+		os.Stdout.Write(data)
+		os.Exit(0)
+	}
+
 	// If any flag is set, we run only those checks requested.
 	// If all flag is set true or if no flags are set true, set all the non-experimental ones
 	// not explicitly set (in effect, set the "-all" flag).