Allow Args to be used in Variable Evaluation

If the Dockerfile has a `ARG CHOWN_VAL=6173:6173`, then
a `COPY --chown=${CHOWN_VAL} srcFile destFile` will fail.
However if the Dockerfile has a `ENV CHOWN_VAL=6173:6173`
then it succeeds.

The dispatchCopy() and add() functions were only going through the
list of Environment variables to resolve a Variable instead
of the list of Args and Environment variables.  If there's
a trailing equal `=` sign in the arg, assume that we'd a
variable that did not resolve and try to resolve from the
list of args.

At some point I'd like to look into converting the b.Env to
a Map from a slice like b.Args, but didn't want to run this
down now.

Fixes: containers/buildah#2192
       and probably containers/buildah#2345

Signed-off-by: TomSweeneyRedHat <[email protected]>

dispatchers.go

@@ -153,8 +153,9 @@ func add(b *Builder, args []string, attributes map[string]bool, flagArgs []strin
 	var chown string
 	last := len(args) - 1
 	dest := makeAbsolute(args[last], b.RunConfig.WorkingDir)
+	userArgs := makeUserArgs(b)
 	for _, a := range flagArgs {
-		arg, err := ProcessWord(a, b.Env)
+		arg, err := ProcessWord(a, userArgs)
 		if err != nil {
 			return err
 		}
@@ -181,8 +182,9 @@ func dispatchCopy(b *Builder, args []string, attributes map[string]bool, flagArg
 	dest := makeAbsolute(args[last], b.RunConfig.WorkingDir)
 	var chown string
 	var from string
+	userArgs := makeUserArgs(b)
 	for _, a := range flagArgs {
-		arg, err := ProcessWord(a, b.Env)
+		arg, err := ProcessWord(a, userArgs)
 		if err != nil {
 			return err
 		}
@@ -649,3 +651,16 @@ func errTooManyArguments(command string) error {
 func errNotJSON(command string) error {
 	return fmt.Errorf("%s requires the arguments to be in JSON form", command)
 }
+
+// makeUserArgs - Package the variables from the Dockerfile defined by
+// the ENV aand the ARG statements into one slice so the values
+// defined by both can later be evaluated when resolving variables
+// such as ${MY_USER}
+func makeUserArgs(b *Builder) (userArgs []string) {
+
+	userArgs = b.Env
+	for key, value := range b.Args {
+		userArgs = append(userArgs, key+"="+value)
+	}
+	return userArgs
+}

dispatchers_test.go

@@ -208,6 +208,39 @@ func TestDispatchCopyChownWithEnvironment(t *testing.T) {
 	}
 }
 
+func TestDispatchCopyChownWithArg(t *testing.T) {
+	argsMap := make(map[string]string)
+	argsMap["CHOWN_VAL"] = "6731:6731"
+	mybuilder := Builder{
+		RunConfig: docker.Config{
+			WorkingDir: "/root",
+			Cmd:        []string{"/bin/sh"},
+			Image:      "alpine",
+		},
+		Args: argsMap,
+	}
+
+	args := []string{"/go/src/github.com/kubernetes-incubator/service-catalog/controller-manager", "."}
+	flagArgs := []string{"--chown=${CHOWN_VAL}"}
+	original := "COPY --chown=${CHOWN_VAL} /go/src/github.com/kubernetes-incubator/service-catalog/controller-manager ."
+	if err := dispatchCopy(&mybuilder, args, nil, flagArgs, original); err != nil {
+		t.Errorf("dispatchCopy error: %v", err)
+	}
+
+	expectedPendingCopies := []Copy{
+		{
+			From:     "",
+			Src:      []string{"/go/src/github.com/kubernetes-incubator/service-catalog/controller-manager"},
+			Dest:     "/root/", // destination must contain a trailing slash
+			Download: false,
+			Chown:    "6731:6731",
+		},
+	}
+	if !reflect.DeepEqual(mybuilder.PendingCopies, expectedPendingCopies) {
+		t.Errorf("Expected %v, to match %v\n", expectedPendingCopies, mybuilder.PendingCopies)
+	}
+}
+
 func TestDispatchAddChown(t *testing.T) {
 	mybuilder := Builder{
 		RunConfig: docker.Config{