cmd/go: make package list order predicable

also add a cleanup phase to cmd/go/test.bash.

R=golang-dev, bradfitz
CC=golang-dev
https://golang.org/cl/6741050

src/cmd/go/pkg.go

@@ -674,12 +674,11 @@ func packagesAndErrors(args []string) []*Package {
 	var set = make(map[string]bool)
 
 	for _, arg := range args {
-		set[arg] = true
-	}
-	for arg := range set {
-		pkgs = append(pkgs, loadPackage(arg, &stk))
+		if !set[arg] {
+			pkgs = append(pkgs, loadPackage(arg, &stk))
+			set[arg] = true
+		}
 	}
-
 	computeStale(pkgs...)
 
 	return pkgs

src/cmd/go/test.bash

@@ -142,6 +142,18 @@ if [ $(./testgo test fmt fmt fmt fmt fmt | wc -l) -ne 1 ] ; then
     ok=false
 fi
 
+# ensure that output of 'go list' is consistent between runs
+./testgo list std > test_std.list
+if ! ./testgo list std | cmp -s test_std.list - ; then
+	echo "go list std ordering is inconsistent"
+	ok=false
+fi
+rm -f test_std.list
+
+# clean up
+rm -rf testdata/bin testdata/bin1
+rm -f testgo
+
 if $ok; then
 	echo PASS
 else