cmd/vet: make vetx output deterministic

The vetx output file is a build output, and as such should be
deterministic. This CL changes it to not depend on map iteration order.

This avoids a pointless GODEBUG=gocacheverify=1 failure.

Updates #25666

Change-Id: Ic132bad134cb10938275f883c2c68432cb7c4409
Reviewed-on: https://go-review.googlesource.com/121941
Run-TryBot: Ian Lance Taylor <[email protected]>
TryBot-Result: Gobot Gobot <[email protected]>
Reviewed-by: Rob Pike <[email protected]>

Author: ianlancetaylor

src/cmd/vet/main.go

@@ -24,6 +24,7 @@ import (
 	"io/ioutil"
 	"os"
 	"path/filepath"
+	"sort"
 	"strconv"
 	"strings"
 
@@ -163,6 +164,12 @@ var (
 	exporters   = make(map[string]func() interface{})
 )
 
+// The exporters data as written to the vetx output file.
+type vetxExport struct {
+	Name string
+	Data interface{}
+}
+
 // Vet can provide its own "export information"
 // about package A to future invocations of vet
 // on packages importing A. If B imports A,
@@ -399,10 +406,17 @@ func doPackageCfg(cfgFile string) {
 	mustTypecheck = true
 	doPackage(vcfg.GoFiles, nil)
 	if vcfg.VetxOutput != "" {
-		out := make(map[string]interface{})
+		out := make([]vetxExport, 0, len(exporters))
 		for name, fn := range exporters {
-			out[name] = fn()
+			out = append(out, vetxExport{
+				Name: name,
+				Data: fn(),
+			})
 		}
+		// Sort the data so that it is consistent across builds.
+		sort.Slice(out, func(i, j int) bool {
+			return out[i].Name < out[j].Name
+		})
 		var buf bytes.Buffer
 		if err := gob.NewEncoder(&buf).Encode(out); err != nil {
 			errorf("encoding vet output: %v", err)
@@ -721,11 +735,15 @@ func readVetx(path, key string) interface{} {
 		if err != nil {
 			return nil
 		}
-		m = make(map[string]interface{})
-		err = gob.NewDecoder(bytes.NewReader(data)).Decode(&m)
+		var out []vetxExport
+		err = gob.NewDecoder(bytes.NewReader(data)).Decode(&out)
 		if err != nil {
 			return nil
 		}
+		m = make(map[string]interface{})
+		for _, x := range out {
+			m[x.Name] = x.Data
+		}
 		imported[path] = m
 	}
 	return m[key]

src/cmd/vet/print.go

@@ -16,6 +16,7 @@ import (
 	"go/token"
 	"go/types"
 	"regexp"
+	"sort"
 	"strconv"
 	"strings"
 	"unicode/utf8"
@@ -30,7 +31,7 @@ func init() {
 		funcDecl, callExpr)
 	registerPkgCheck("printf", findPrintfLike)
 	registerExport("printf", exportPrintfLike)
-	gob.Register(map[string]int(nil))
+	gob.Register([]printfExport(nil))
 }
 
 func initPrintFlags() {
@@ -57,6 +58,15 @@ func initPrintFlags() {
 
 var localPrintfLike = make(map[string]int)
 
+type printfExport struct {
+	Name string
+	Kind int
+}
+
+// printfImported maps from package name to the printf vet data
+// exported by that package.
+var printfImported = make(map[string]map[string]int)
+
 type printfWrapper struct {
 	name       string
 	fn         *ast.FuncDecl
@@ -241,7 +251,17 @@ func checkPrintfFwd(pkg *Package, w *printfWrapper, call *ast.CallExpr, kind int
 }
 
 func exportPrintfLike() interface{} {
-	return localPrintfLike
+	out := make([]printfExport, 0, len(localPrintfLike))
+	for name, kind := range localPrintfLike {
+		out = append(out, printfExport{
+			Name: name,
+			Kind: kind,
+		})
+	}
+	sort.Slice(out, func(i, j int) bool {
+		return out[i].Name < out[j].Name
+	})
+	return out
 }
 
 // isPrint records the print functions.
@@ -438,9 +458,18 @@ func printfNameAndKind(pkg *Package, called ast.Expr) (pkgpath, name string, kin
 
 	if pkgpath == "" {
 		kind = localPrintfLike[name]
+	} else if m, ok := printfImported[pkgpath]; ok {
+		kind = m[name]
 	} else {
-		printfLike, _ := readVetx(pkgpath, "printf").(map[string]int)
-		kind = printfLike[name]
+		var m map[string]int
+		if out, ok := readVetx(pkgpath, "printf").([]printfExport); ok {
+			m = make(map[string]int)
+			for _, x := range out {
+				m[x.Name] = x.Kind
+			}
+		}
+		printfImported[pkgpath] = m
+		kind = m[name]
 	}
 
 	if kind == 0 {