status: add validateFlags()

cmd/dep/status.go

@@ -211,6 +211,10 @@ func (out *templateOutput) MissingLine(ms *MissingStatus) {
 }
 
 func (cmd *statusCommand) Run(ctx *dep.Ctx, args []string) error {
+	if err := cmd.validateFlags(); err != nil {
+		return err
+	}
+
 	p, err := ctx.LoadProject()
 	if err != nil {
 		return err
@@ -301,6 +305,54 @@ func (cmd *statusCommand) Run(ctx *dep.Ctx, args []string) error {
 	return nil
 }
 
+func (cmd *statusCommand) validateFlags() error {
+	// Operating mode flags.
+	opModes := []string{}
+
+	if cmd.detailed {
+		opModes = append(opModes, "-detailed")
+	}
+
+	if cmd.old {
+		opModes = append(opModes, "-old")
+	}
+
+	if cmd.missing {
+		opModes = append(opModes, "-missing")
+	}
+
+	if cmd.unused {
+		opModes = append(opModes, "-unused")
+	}
+
+	if cmd.modified {
+		opModes = append(opModes, "-modified")
+	}
+
+	// Check if any other flags are passed with -dot.
+	if cmd.dot {
+		if cmd.template != "" {
+			return errors.New("cannot pass template string with -dot")
+		}
+
+		if cmd.json {
+			return errors.New("cannot pass multiple output format flags")
+		}
+
+		if len(opModes) > 0 {
+			return errors.New("-dot generates dependency graph; cannot pass other flags")
+		}
+	}
+
+	if len(opModes) > 1 {
+		// List the flags because which flags are for operation mode might not
+		// be apparent to the users.
+		return errors.Wrapf(errors.New("cannot pass multiple operating mode flags"), "%v", opModes)
+	}
+
+	return nil
+}
+
 type rawStatus struct {
 	ProjectRoot  string
 	Constraint   string

cmd/dep/status_test.go

@@ -17,6 +17,7 @@ import (
 	"github.com/golang/dep"
 	"github.com/golang/dep/gps"
 	"github.com/golang/dep/internal/test"
+	"github.com/pkg/errors"
 )
 
 func TestStatusFormatVersion(t *testing.T) {
@@ -406,3 +407,61 @@ func TestCollectConstraints(t *testing.T) {
 		})
 	}
 }
+
+func TestValidateFlags(t *testing.T) {
+	testCases := []struct {
+		name    string
+		cmd     statusCommand
+		wantErr error
+	}{
+		{
+			name:    "no flags",
+			cmd:     statusCommand{},
+			wantErr: nil,
+		},
+		{
+			name:    "-dot only",
+			cmd:     statusCommand{dot: true},
+			wantErr: nil,
+		},
+		{
+			name:    "-dot with template",
+			cmd:     statusCommand{dot: true, template: "foo"},
+			wantErr: errors.New("cannot pass template string with -dot"),
+		},
+		{
+			name:    "-dot with -json",
+			cmd:     statusCommand{dot: true, json: true},
+			wantErr: errors.New("cannot pass multiple output format flags"),
+		},
+		{
+			name:    "-dot with operating mode",
+			cmd:     statusCommand{dot: true, old: true},
+			wantErr: errors.New("-dot generates dependency graph; cannot pass other flags"),
+		},
+		{
+			name:    "single operating mode",
+			cmd:     statusCommand{unused: true},
+			wantErr: nil,
+		},
+		{
+			name:    "multiple operating modes",
+			cmd:     statusCommand{missing: true, old: true},
+			wantErr: errors.Wrapf(errors.New("cannot pass multiple operating mode flags"), "[-old -missing]"),
+		},
+	}
+
+	for _, tc := range testCases {
+		t.Run(tc.name, func(t *testing.T) {
+			err := tc.cmd.validateFlags()
+
+			if err == nil {
+				if tc.wantErr != nil {
+					t.Errorf("unexpected error: \n\t(GOT): %v\n\t(WNT): %v", err, tc.wantErr)
+				}
+			} else if err.Error() != tc.wantErr.Error() {
+				t.Errorf("unexpected error: \n\t(GOT): %v\n\t(WNT): %v", err, tc.wantErr)
+			}
+		})
+	}
+}