cmd/go: invoke godoc with import path when possible

Also add -n -x flags to doc, fmt, vet.
Also shorten unknown command error.

Fixes #3612.
Fixes #3613.

R=golang-dev, bradfitz, r
CC=golang-dev
https://golang.org/cl/6211053

src/cmd/go/build.go

@@ -152,6 +152,11 @@ func addBuildFlags(cmd *Command) {
 	cmd.Flag.Var(buildCompiler{}, "compiler", "")
 }
 
+func addBuildFlagsNX(cmd *Command) {
+	cmd.Flag.BoolVar(&buildN, "n", false, "")
+	cmd.Flag.BoolVar(&buildX, "x", false, "")
+}
+
 type stringsFlag []string
 
 func (v *stringsFlag) Set(s string) error {

src/cmd/go/doc.go

@@ -145,7 +145,7 @@ Run godoc on package sources
 
 Usage:
 
-	go doc [packages]
+	go doc [-n] [-x] [packages]
 
 Doc runs the godoc command on the packages named by the
 import paths.
@@ -153,6 +153,9 @@ import paths.
 For more about godoc, see 'godoc godoc'.
 For more about specifying packages, see 'go help packages'.
 
+The -n flag prints commands that would be executed.
+The -x flag prints commands as they are executed.
+
 To run godoc with specific options, run godoc itself.
 
 See also: go fix, go fmt, go vet.
@@ -192,7 +195,7 @@ Run gofmt on package sources
 
 Usage:
 
-	go fmt [packages]
+	go fmt [-n] [-x] [packages]
 
 Fmt runs the command 'gofmt -l -w' on the packages named
 by the import paths.  It prints the names of the files that are modified.
@@ -200,6 +203,9 @@ by the import paths.  It prints the names of the files that are modified.
 For more about gofmt, see 'godoc gofmt'.
 For more about specifying packages, see 'go help packages'.
 
+The -n flag prints commands that would be executed.
+The -x flag prints commands as they are executed.
+
 To run gofmt with specific options, run gofmt itself.
 
 See also: go doc, go fix, go vet.
@@ -414,7 +420,7 @@ Run go tool vet on packages
 
 Usage:
 
-	go vet [packages]
+	go vet [-n] [-x] [packages]
 
 Vet runs the Go vet command on the packages named by the import paths.
 
@@ -423,6 +429,9 @@ For more about specifying packages, see 'go help packages'.
 
 To run the vet tool with specific options, run 'go tool vet'.
 
+The -n flag prints commands that would be executed.
+The -x flag prints commands as they are executed.
+
 See also: go fmt, go fix.
 
 

src/cmd/go/fmt.go

@@ -4,9 +4,14 @@
 
 package main
 
+func init() {
+	addBuildFlagsNX(cmdFmt)
+	addBuildFlagsNX(cmdDoc)
+}
+
 var cmdFmt = &Command{
 	Run:       runFmt,
-	UsageLine: "fmt [packages]",
+	UsageLine: "fmt [-n] [-x] [packages]",
 	Short:     "run gofmt on package sources",
 	Long: `
 Fmt runs the command 'gofmt -l -w' on the packages named
@@ -15,6 +20,9 @@ by the import paths.  It prints the names of the files that are modified.
 For more about gofmt, see 'godoc gofmt'.
 For more about specifying packages, see 'go help packages'.
 
+The -n flag prints commands that would be executed.
+The -x flag prints commands as they are executed.
+
 To run gofmt with specific options, run gofmt itself.
 
 See also: go doc, go fix, go vet.
@@ -32,7 +40,7 @@ func runFmt(cmd *Command, args []string) {
 
 var cmdDoc = &Command{
 	Run:       runDoc,
-	UsageLine: "doc [packages]",
+	UsageLine: "doc [-n] [-x] [packages]",
 	Short:     "run godoc on package sources",
 	Long: `
 Doc runs the godoc command on the packages named by the
@@ -41,6 +49,9 @@ import paths.
 For more about godoc, see 'godoc godoc'.
 For more about specifying packages, see 'go help packages'.
 
+The -n flag prints commands that would be executed.
+The -x flag prints commands as they are executed.
+
 To run godoc with specific options, run godoc itself.
 
 See also: go fix, go fmt, go vet.
@@ -53,6 +64,10 @@ func runDoc(cmd *Command, args []string) {
 			errorf("go doc: cannot use package file list")
 			continue
 		}
-		run("godoc", pkg.Dir)
+		if pkg.local {
+			run("godoc", pkg.Dir)
+		} else {
+			run("godoc", pkg.ImportPath)
+		}
 	}
 }

src/cmd/go/main.go

@@ -144,8 +144,9 @@ func main() {
 		}
 	}
 
-	fmt.Fprintf(os.Stderr, "Unknown command %#q\n\n", args[0])
+	fmt.Fprintf(os.Stderr, "go: unknown subcommand %#q\nRun 'go help' for usage.\n", args[0])
-	usage()
+	setExitStatus(2)
+	exit()
 }
 
 var usageTemplate = `Go is a tool for managing Go source code.
@@ -339,6 +340,13 @@ func exitIfErrors() {
 
 func run(cmdargs ...interface{}) {
 	cmdline := stringList(cmdargs...)
+	if buildN || buildV {
+		fmt.Printf("%s\n", strings.Join(cmdline, " "))
+		if buildN {
+			return
+		}
+	}
+
 	cmd := exec.Command(cmdline[0], cmdline[1:]...)
 	cmd.Stdout = os.Stdout
 	cmd.Stderr = os.Stderr

src/cmd/go/vet.go

@@ -4,9 +4,13 @@
 
 package main
 
+func init() {
+	addBuildFlagsNX(cmdVet)
+}
+
 var cmdVet = &Command{
 	Run:       runVet,
-	UsageLine: "vet [packages]",
+	UsageLine: "vet [-n] [-x] [packages]",
 	Short:     "run go tool vet on packages",
 	Long: `
 Vet runs the Go vet command on the packages named by the import paths.
@@ -16,6 +20,9 @@ For more about specifying packages, see 'go help packages'.
 
 To run the vet tool with specific options, run 'go tool vet'.
 
+The -n flag prints commands that would be executed.
+The -x flag prints commands as they are executed.
+
 See also: go fmt, go fix.
 	`,
 }