feat: add ability to mark field as optional with help of field tag

Author: xobotyi

go.mod

@@ -2,7 +2,10 @@ module github.com/GaijinEntertainment/go-exhaustruct/v2
 
 go 1.18
 
-require golang.org/x/tools v0.1.12
+require (
+	golang.org/x/exp v0.0.0-20220722155223-a9213eeb770e
+	golang.org/x/tools v0.1.12
+)
 
 require (
 	golang.org/x/mod v0.6.0-dev.0.20220419223038-86c51ed26bb4 // indirect

go.sum

@@ -1,3 +1,5 @@
+golang.org/x/exp v0.0.0-20220722155223-a9213eeb770e h1:+WEEuIdZHnUeJJmEUjyYC2gfUMj69yZXw17EnHg/otA=
+golang.org/x/exp v0.0.0-20220722155223-a9213eeb770e/go.mod h1:Kr81I6Kryrl9sr8s2FK3vxD90NdsKWRuOIl2O4CvYbA=
 golang.org/x/mod v0.6.0-dev.0.20220419223038-86c51ed26bb4 h1:6zppjxzCulZykYSLyVDYbneBfbaBIQPYMevg0bEwv2s=
 golang.org/x/mod v0.6.0-dev.0.20220419223038-86c51ed26bb4/go.mod h1:jJ57K6gSWd91VN4djpZkiMVwK6gcyfeH4XE8wZrZaV4=
 golang.org/x/sys v0.0.0-20220722155257-8c9f86f7a55f h1:v4INt8xihDGvnrfjMDVXGxw9wrfxYyCjk0KbXjhR55s=

pkg/analyzer/analyzer.go

@@ -183,20 +183,19 @@ func (a *analyzer) structMissingFields(lit *ast.CompositeLit, strct *types.Struc
 	keys, unnamed := literalKeys(lit)
 	fields := a.structFields(strct)
 
-	var fieldNames []string
+	if unnamed {
+		if private {
+			return fields.All[len(keys):]
+		}
 
-	if private {
-		// we're in same package and should match private fields
-		fieldNames = fields.All
-	} else {
-		fieldNames = fields.Public
+		return fields.Public[len(keys):]
 	}
 
-	if unnamed {
-		return fieldNames[len(keys):]
+	if private {
+		return difference(fields.AllRequired, keys)
 	}
 
-	return difference(fieldNames, keys)
+	return difference(fields.PublicRequired, keys)
 }
 
 func (a *analyzer) structFields(strct *types.Struct) *StructFields {

pkg/analyzer/struct-fields.go

@@ -2,28 +2,60 @@ package analyzer
 
 import (
 	"go/types"
+	"reflect"
+
+	"golang.org/x/exp/slices"
 )
 
 type StructFields struct {
-	All    []string
-	Public []string
+	All         []string
+	AllRequired []string
+
+	Public         []string
+	PublicRequired []string
 }
 
 func NewStructFields(strct *types.Struct) *StructFields {
 	sf := StructFields{
-		All:    make([]string, strct.NumFields()),
-		Public: []string{},
+		All:            make([]string, strct.NumFields()),
+		AllRequired:    make([]string, 0, strct.NumFields()),
+		Public:         make([]string, 0, strct.NumFields()),
+		PublicRequired: make([]string, 0, strct.NumFields()),
 	}
 
 	for i := 0; i < strct.NumFields(); i++ {
 		f := strct.Field(i)
+		isOptional := isFieldOptional(strct.Tag(i))
 
 		sf.All[i] = f.Name()
+		if !isOptional {
+			sf.AllRequired = append(sf.AllRequired, f.Name())
+		}
 
 		if f.Exported() {
 			sf.Public = append(sf.Public, f.Name())
+
+			if !isOptional {
+				sf.PublicRequired = append(sf.PublicRequired, f.Name())
+			}
 		}
 	}
 
+	sf.All = slices.Clip(sf.All)
+	sf.AllRequired = slices.Clip(sf.AllRequired)
+	sf.Public = slices.Clip(sf.Public)
+	sf.PublicRequired = slices.Clip(sf.PublicRequired)
+
 	return &sf
 }
+
+const (
+	TagName          = "exhaustruct"
+	OptionalTagValue = "optional"
+)
+
+// isFieldOptional checks if field tags has an optional tag, and therefore can
+// be omitted during structure initialization.
+func isFieldOptional(tags string) bool {
+	return reflect.StructTag(tags).Get(TagName) == OptionalTagValue
+}

testdata/src/s/s.go

@@ -18,6 +18,7 @@ type Test struct {
 	B int
 	C float32
 	D bool
+	E string `exhaustruct:"optional"`
 }
 
 type Test2 struct {
@@ -84,7 +85,7 @@ func shouldPass3() {
 }
 
 func shouldPassWithoutNames() Test {
-	return Test{"", 0, 0, false}
+	return Test{"", 0, 0, false, ""}
 }
 
 func shouldFailWithReturn() (Test, error) {