cmd/vet: change some warnings to errors for consistency.

Fixes #4980.

R=golang-dev, rsc, dsymonds
CC=golang-dev
https://golang.org/cl/7479044

src/cmd/vet/doc.go

@@ -9,6 +9,12 @@ calls whose arguments do not align with the format string. Vet uses heuristics
 that do not guarantee all reports are genuine problems, but it can find errors
 not caught by the compilers.
 
+Its exit code is 2 for erroneous invocation of the tool, 1 if a
+problem was reported, and 0 otherwise. Note that the tool does not
+check every possible problem and depends on unreliable heuristics
+so it should be used as guidance only, not as a firm indicator of
+program correctness.
+
 By default all checks are performed, but if explicit flags are provided, only
 those identified by the flags are performed.
 

src/cmd/vet/main.go

@@ -186,17 +186,21 @@ func doPackage(names []string) {
 	for _, name := range names {
 		f, err := os.Open(name)
 		if err != nil {
-			errorf("%s: %s", name, err)
+			// Warn but continue to next package.
+			warnf("%s: %s", name, err)
+			return
 		}
 		defer f.Close()
 		data, err := ioutil.ReadAll(f)
 		if err != nil {
-			errorf("%s: %s", name, err)
+			warnf("%s: %s", name, err)
+			return
 		}
 		checkBuildTag(name, data)
 		parsedFile, err := parser.ParseFile(fs, name, bytes.NewReader(data), 0)
 		if err != nil {
-			errorf("%s: %s", name, err)
+			warnf("%s: %s", name, err)
+			return
 		}
 		files = append(files, &File{fset: fs, name: name, file: parsedFile})
 		astFiles = append(astFiles, parsedFile)
@@ -229,7 +233,8 @@ func doPackage(names []string) {
 
 func visit(path string, f os.FileInfo, err error) error {
 	if err != nil {
-		errorf("walk error: %s", err)
+		warnf("walk error: %s", err)
+		return err
 	}
 	// One package per directory. Ignore the files themselves.
 	if !f.IsDir() {
@@ -239,7 +244,7 @@ func visit(path string, f os.FileInfo, err error) error {
 	return nil
 }
 
-// walkDir recursively walks the tree looking for .go files.
+// walkDir recursively walks the tree looking for Go packages.
 func walkDir(root string) {
 	filepath.Walk(root, visit)
 }

src/cmd/vet/method.go

@@ -93,7 +93,7 @@ func (f *File) checkCanonicalMethod(id *ast.Ident, t *ast.FuncType) {
 		actual = strings.TrimPrefix(actual, "func")
 		actual = id.Name + actual
 
-		f.Warnf(id.Pos(), "method %s should have signature %s", actual, expectFmt)
+		f.Badf(id.Pos(), "method %s should have signature %s", actual, expectFmt)
 	}
 }
 

src/cmd/vet/print.go

@@ -366,7 +366,7 @@ func (f *File) checkPrint(call *ast.CallExpr, name string, firstArg int) {
 		if sel, ok := args[0].(*ast.SelectorExpr); ok {
 			if x, ok := sel.X.(*ast.Ident); ok {
 				if x.Name == "os" && strings.HasPrefix(sel.Sel.Name, "Std") {
-					f.Warnf(call.Pos(), "first argument to %s is %s.%s", name, x.Name, sel.Sel.Name)
+					f.Badf(call.Pos(), "first argument to %s is %s.%s", name, x.Name, sel.Sel.Name)
 				}
 			}
 		}

src/cmd/vet/structtag.go

@@ -23,7 +23,7 @@ func (f *File) checkCanonicalFieldTag(field *ast.Field) {
 
 	tag, err := strconv.Unquote(field.Tag.Value)
 	if err != nil {
-		f.Warnf(field.Pos(), "unable to read struct tag %s", field.Tag.Value)
+		f.Badf(field.Pos(), "unable to read struct tag %s", field.Tag.Value)
 		return
 	}
 
@@ -31,7 +31,7 @@ func (f *File) checkCanonicalFieldTag(field *ast.Field) {
 	// new key:value to end and checking that
 	// the tag parsing code can find it.
 	if reflect.StructTag(tag+` _gofix:"_magic"`).Get("_gofix") != "_magic" {
-		f.Warnf(field.Pos(), "struct field tag %s not compatible with reflect.StructTag.Get", field.Tag.Value)
+		f.Badf(field.Pos(), "struct field tag %s not compatible with reflect.StructTag.Get", field.Tag.Value)
 		return
 	}
 }

src/cmd/vet/taglit.go

@@ -64,7 +64,7 @@ func (f *File) checkUntaggedLiteral(c *ast.CompositeLit) {
 	// Convert the package name to an import path, and compare to a whitelist.
 	path := pkgPath(f, pkg.Name)
 	if path == "" {
-		f.Warnf(c.Pos(), "unresolvable package for %s.%s literal", pkg.Name, s.Sel.Name)
+		f.Badf(c.Pos(), "unresolvable package for %s.%s literal", pkg.Name, s.Sel.Name)
 		return
 	}
 	typeName := path + "." + s.Sel.Name