cmd/go: nicer error diagnosis in go test

Before,
        go test -bench .
would just dump the long generic "go help" message. Confusing and
unhelpful. Now the message is short and on point and also reminds the
user about the oft-forgotten "go help testflag".

        % go test -bench
        go test: missing argument for flag bench
        run "go help test" or "go help testflag" for more information
        %

R=rsc
CC=golang-dev
https://golang.org/cl/12662046

diff --git a/src/cmd/go/testflag.go b/src/cmd/go/testflag.go
index 0509fcdfdf5cfa91cc93ecc83067825ab1c54483..1e0724a993b752b15f74b28b365932e208402a37 100644 (file)
--- a/src/cmd/go/testflag.go
+++ b/src/cmd/go/testflag.go
@@ -256,13 +256,13 @@ func testFlag(args []string, i int) (f *testFlagSpec, value string, extra bool)
                                extra = equals < 0
                                if extra {
                                        if i+1 >= len(args) {
-                                               usage()
+                                               testSyntaxError("missing argument for flag " + f.name)
                                        }
                                        value = args[i+1]
                                }
                        }
                        if f.present && !f.multiOK {
-                               usage()
+                               testSyntaxError(f.name + " flag may be set only once")
                        }
                        f.present = true
                        return
@@ -276,8 +276,7 @@ func testFlag(args []string, i int) (f *testFlagSpec, value string, extra bool)
 func setBoolFlag(flag *bool, value string) {
        x, err := strconv.ParseBool(value)
        if err != nil {
-               fmt.Fprintf(os.Stderr, "go test: illegal bool flag value %s\n", value)
-               usage()
+               testSyntaxError("illegal bool flag value " + value)
        }
        *flag = x
 }
@@ -286,8 +285,13 @@ func setBoolFlag(flag *bool, value string) {
 func setIntFlag(flag *int, value string) {
        x, err := strconv.Atoi(value)
        if err != nil {
-               fmt.Fprintf(os.Stderr, "go test: illegal int flag value %s\n", value)
-               usage()
+               testSyntaxError("illegal int flag value " + value)
        }
        *flag = x
 }
+
+func testSyntaxError(msg string) {
+       fmt.Fprintf(os.Stderr, "go test: %s\n", msg)
+       fmt.Fprintf(os.Stderr, `run "go help test" or "go help testflag" for more information`+"\n")
+       os.Exit(2)
+}