[MM-18898] Stringify plugin.Log* parameters (#12700)

- Add stringutils with method that "stringify" object slices
  - "stringify" means convert each object to its string representation
- Move plugin.Log* implementations to client_rpc, use stringify method before calling server method
- Exclude Log* methods from generated RPC methods
- No signature change for plugin.Log* API
- Add test in plugin_api_test to use plugin.Log* methods with RPC

plugin/stringifier_test.go

@@ -0,0 +1,93 @@
+// Copyright (c) 2019-present Mattermost, Inc. All Rights Reserved.
+// See License.txt for license information.
+
+package plugin
+
+import (
+	"github.com/pkg/errors"
+	"github.com/stretchr/testify/assert"
+	"testing"
+)
+
+func TestStringify(t *testing.T) {
+	t.Run("NilShouldReturnEmpty", func(t *testing.T) {
+		strings := stringify(nil)
+		assert.Empty(t, strings)
+	})
+	t.Run("EmptyShouldReturnEmpty", func(t *testing.T) {
+		strings := stringify(make([]interface{}, 0, 0))
+		assert.Empty(t, strings)
+	})
+	t.Run("PrimitivesAndCompositesShouldReturnCorrectValues", func(t *testing.T) {
+		strings := stringify([]interface{}{
+			1234,
+			3.14159265358979323846264338327950288419716939937510,
+			true,
+			"foo",
+			nil,
+			[]string{"foo", "bar"},
+			map[string]int{"one": 1, "two": 2},
+			&WithString{},
+			&WithoutString{},
+			&WithStringAndError{},
+		})
+		assert.Equal(t, []string{
+			"1234",
+			"3.141592653589793",
+			"true",
+			"foo",
+			"<nil>",
+			"[foo bar]",
+			"map[one:1 two:2]",
+			"string",
+			"&{}",
+			"error",
+		}, strings)
+	})
+	t.Run("ErrorShouldReturnFormattedStack", func(t *testing.T) {
+		strings := stringify([]interface{}{
+			errors.New("error"),
+			errors.WithStack(errors.New("error")),
+		})
+		stackRegexp := "error\n.*plugin.TestStringify.func\\d+\n\t.*plugin/stringifier_test.go:\\d+\ntesting.tRunner\n\t.*testing.go:\\d+.*"
+		assert.Len(t, strings, 2)
+		assert.Regexp(t, stackRegexp, strings[0])
+		assert.Regexp(t, stackRegexp, strings[1])
+	})
+}
+
+type WithString struct {
+}
+
+func (*WithString) String() string {
+	return "string"
+}
+
+type WithoutString struct {
+}
+
+type WithStringAndError struct {
+}
+
+func (*WithStringAndError) String() string {
+	return "string"
+}
+
+func (*WithStringAndError) Error() string {
+	return "error"
+}
+
+func TestToObjects(t *testing.T) {
+	t.Run("NilShouldReturnNil", func(t *testing.T) {
+		objects := toObjects(nil)
+		assert.Nil(t, objects)
+	})
+	t.Run("EmptyShouldReturnEmpty", func(t *testing.T) {
+		objects := toObjects(make([]string, 0, 0))
+		assert.Empty(t, objects)
+	})
+	t.Run("ShouldReturnSliceOfObjects", func(t *testing.T) {
+		objects := toObjects([]string{"foo", "bar"})
+		assert.Equal(t, []interface{}{"foo", "bar"}, objects)
+	})
+}