Add gob mode to support custom package loading techniques in place of --exec_only

Change uber-go#207 replaced reflect mode with package mode.
In doing so, we no longer had to create separate reflect programs
that would encode the resulting package into a gob
for the rest of mockgen to read from.
Because of that, we removed the `--exec_only` flag.

However, this flag was actually used to pass in programs that created gob encodings
in other ways, allowing customization of the package loading and encoding portion of mockgen.
As an alternative, this adds a new flag to mockgen `--model_gob`,
which allows mockgen users to pass a path to a gob encoding of a `model.Package`,
so that custom ways of loading package information can still be supported.

Author: JacobOaks

mockgen/gob.go

@@ -0,0 +1,21 @@
+package main
+
+import (
+	"encoding/gob"
+	"os"
+
+	"go.uber.org/mock/mockgen/model"
+)
+
+func gobMode(path string) (*model.Package, error) {
+	in, err := os.Open(path)
+	if err != nil {
+		return nil, err
+	}
+	defer in.Close()
+	var pkg model.Package
+	if err := gob.NewDecoder(in).Decode(&pkg); err != nil {
+		return nil, err
+	}
+	return &pkg, nil
+}

mockgen/gob_test.go

@@ -0,0 +1,31 @@
+package main
+
+import (
+	"encoding/gob"
+	"os"
+	"path/filepath"
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+)
+
+func TestGobMode(t *testing.T) {
+
+	// Encode a package to a temporary gob.
+	parser := packageModeParser{}
+	want, err := parser.parsePackage(
+		"go.uber.org/mock/mockgen/internal/tests/package_mode" /* package name */,
+		[]string{ "Human", "Earth" } /* ifaces */,
+	)
+	path := filepath.Join(t.TempDir(), "model.gob")
+	outfile, err := os.Create(path)
+	require.NoError(t, err)
+	require.NoError(t, gob.NewEncoder(outfile).Encode(want))
+	outfile.Close()
+
+	// Ensure gobMode loads it correctly.
+	got, err := gobMode(path)
+	require.NoError(t, err)
+	assert.Equal(t, want, got)
+}

mockgen/mockgen.go

@@ -69,6 +69,7 @@ var (
 	imports                = flag.String("imports", "", "(source mode) Comma-separated name=path pairs of explicit imports to use.")
 	auxFiles               = flag.String("aux_files", "", "(source mode) Comma-separated pkg=path pairs of auxiliary Go source files.")
 	excludeInterfaces      = flag.String("exclude_interfaces", "", "(source mode) Comma-separated names of interfaces to be excluded")
+	modelGob               = flag.String("model_gob", "", "Skip package/source loading entirely and use the gob encoded model.Package at the given path")
 
 	debugParser = flag.Bool("debug_parser", false, "Print out parser results only.")
 	showVersion = flag.Bool("version", false, "Print version.")
@@ -88,7 +89,9 @@ func main() {
 	var pkg *model.Package
 	var err error
 	var packageName string
-	if *source != "" {
+	if *modelGob != "" {
+		pkg, err = gobMode(*modelGob)
+	} else if *source != "" {
 		pkg, err = sourceMode(*source)
 	} else {
 		if flag.NArg() != 2 {