build: catch API changes during build

Adds new file api/go1.txt, locking down the current API.
Any changes to the API will need to update that file.

run.bash (but not make.bash, or Windows) will check for
accidental API changes.

R=golang-dev, dsymonds, rsc
CC=golang-dev
https://golang.org/cl/5820070

src/cmd/api/goapi.go

@@ -131,7 +131,7 @@ func main() {
 		if err != nil {
 			log.Fatalf("Error reading file %s: %v", *checkFile, err)
 		}
-		v1 := strings.Split(string(bs), "\n")
+		v1 := strings.Split(strings.TrimSpace(string(bs)), "\n")
 		sort.Strings(v1)
 		v2 := features
 		take := func(sl *[]string) string {
@@ -139,17 +139,24 @@ func main() {
 			*sl = (*sl)[1:]
 			return s
 		}
+		changes := false
 		for len(v1) > 0 || len(v2) > 0 {
 			switch {
 			case len(v2) == 0 || v1[0] < v2[0]:
 				fmt.Fprintf(bw, "-%s\n", take(&v1))
+				changes = true
 			case len(v1) == 0 || v1[0] > v2[0]:
 				fmt.Fprintf(bw, "+%s\n", take(&v2))
+				changes = true
 			default:
 				take(&v1)
 				take(&v2)
 			}
 		}
+		if changes {
+			bw.Flush()
+			os.Exit(1)
+		}
 	} else {
 		for _, f := range features {
 			fmt.Fprintf(bw, "%s\n", f)
@@ -284,7 +291,9 @@ func (w *Walker) WalkPackage(name string) {
 		}
 	}
 
+	if *verbose {
 		log.Printf("package %s", name)
+	}
 	pop := w.pushScope("pkg " + name)
 	defer pop()
 

src/run.bash

@@ -74,7 +74,7 @@ make clean
 
 echo
 echo '#' ../misc/dashboard/builder ../misc/goplay
-go build ../misc/dashboard/builder ../misc/goplay || exit $?
+go build ../misc/dashboard/builder ../misc/goplay
 
 [ "$GOARCH" == arm ] ||
 (xcd ../test/bench/shootout
@@ -83,11 +83,15 @@ go build ../misc/dashboard/builder ../misc/goplay || exit $?
 
 echo
 echo '#' ../test/bench/go1
-go test ../test/bench/go1 || exit $?
+go test ../test/bench/go1
 
 (xcd ../test
 time go run run.go
 ) || exit $?
 
+echo
+echo '# Checking API compatibility.'
+go tool api -c $GOROOT/api/go1.txt
+
 echo
 echo ALL TESTS PASSED