From c5849929105209bcdaba2f86ab65cb8b21d6190d Mon Sep 17 00:00:00 2001
From: Cody Ley-Han <codyleyhan@gmail.com>
Date: Thu, 23 Aug 2018 18:16:58 -0700
Subject: [PATCH] adds binding by passed tag

---
 codegen/config.go       |  1 +
 codegen/input_build.go  |  2 +-
 codegen/object_build.go |  2 +-
 codegen/util.go         | 61 +++++++++++++++++++++++++++++++----------
 4 files changed, 50 insertions(+), 16 deletions(-)

diff --git a/codegen/config.go b/codegen/config.go
index 0ba1f65dabc..f5fc8abd348 100644
--- a/codegen/config.go
+++ b/codegen/config.go
@@ -64,6 +64,7 @@ type Config struct {
 	Model          PackageConfig `yaml:"model"`
 	Resolver       PackageConfig `yaml:"resolver,omitempty"`
 	Models         TypeMap       `yaml:"models,omitempty"`
+	StructTag      string        `yaml:"struct_tag,omitempty"`
 
 	FilePath string `yaml:"-"`
 
diff --git a/codegen/input_build.go b/codegen/input_build.go
index c333201522d..1059601a3c5 100644
--- a/codegen/input_build.go
+++ b/codegen/input_build.go
@@ -27,7 +27,7 @@ func (cfg *Config) buildInputs(namedTypes NamedTypes, prog *loader.Program, impo
 			}
 			if def != nil {
 				input.Marshaler = buildInputMarshaler(typ, def)
-				bindErrs := bindObject(def.Type(), input, imports)
+				bindErrs := bindObject(def.Type(), input, imports, cfg.StructTag)
 				if len(bindErrs) > 0 {
 					return nil, bindErrs
 				}
diff --git a/codegen/object_build.go b/codegen/object_build.go
index 95602a9138d..686b2bfe2a4 100644
--- a/codegen/object_build.go
+++ b/codegen/object_build.go
@@ -28,7 +28,7 @@ func (cfg *Config) buildObjects(types NamedTypes, prog *loader.Program, imports
 			return nil, err
 		}
 		if def != nil {
-			for _, bindErr := range bindObject(def.Type(), obj, imports) {
+			for _, bindErr := range bindObject(def.Type(), obj, imports, cfg.StructTag) {
 				log.Println(bindErr.Error())
 				log.Println("  Adding resolver method")
 			}
diff --git a/codegen/util.go b/codegen/util.go
index fae94adeadd..0e880ec6601 100644
--- a/codegen/util.go
+++ b/codegen/util.go
@@ -3,6 +3,7 @@ package codegen
 import (
 	"fmt"
 	"go/types"
+	"reflect"
 	"regexp"
 	"strings"
 
@@ -104,19 +105,46 @@ func findMethod(typ *types.Named, name string) *types.Func {
 	return nil
 }
 
-func findField(typ *types.Struct, name string) *types.Var {
+// findField attempts to match the name to a struct field with the following
+// priorites:
+// 1. If struct tag is passed then struct tag has highest priority
+// 2. Field in an embedded struct
+// 3. Actual Field name
+func findField(typ *types.Struct, name, structTag string) (*types.Var, error) {
+	var foundField *types.Var
+
 	for i := 0; i < typ.NumFields(); i++ {
 		field := typ.Field(i)
+
+		if structTag != "" {
+			tags := reflect.StructTag(typ.Tag(i))
+			if val, ok := tags.Lookup(structTag); ok {
+				if strings.EqualFold(val, name) {
+					if foundField != nil {
+						return nil, errors.Errorf("tag %s is ambigious; multiple fields have the same tag value of %s", structTag, val)
+					}
+				}
+			}
+		}
+
 		if field.Anonymous() {
 			if named, ok := field.Type().(*types.Struct); ok {
-				if f := findField(named, name); f != nil {
-					return f
+				f, err := findField(named, name, structTag)
+				if err != nil {
+					return nil, err
+				}
+				if f != nil && foundField == nil {
+					foundField = f
 				}
 			}
 
 			if named, ok := field.Type().Underlying().(*types.Struct); ok {
-				if f := findField(named, name); f != nil {
-					return f
+				f, err := findField(named, name, structTag)
+				if err != nil {
+					return nil, err
+				}
+				if f != nil && foundField == nil {
+					foundField = f
 				}
 			}
 		}
@@ -125,11 +153,16 @@ func findField(typ *types.Struct, name string) *types.Var {
 			continue
 		}
 
-		if strings.EqualFold(field.Name(), name) {
-			return field
+		if strings.EqualFold(field.Name(), name) && foundField == nil {
+			foundField = field
 		}
 	}
-	return nil
+
+	if foundField == nil {
+		return nil, fmt.Errorf("no field named %s", name)
+	}
+
+	return foundField, nil
 }
 
 type BindError struct {
@@ -161,7 +194,7 @@ func (b BindErrors) Error() string {
 	return strings.Join(errs, "\n\n")
 }
 
-func bindObject(t types.Type, object *Object, imports *Imports) BindErrors {
+func bindObject(t types.Type, object *Object, imports *Imports, structTag string) BindErrors {
 	var errs BindErrors
 	for i := range object.Fields {
 		field := &object.Fields[i]
@@ -177,7 +210,7 @@ func bindObject(t types.Type, object *Object, imports *Imports) BindErrors {
 		}
 
 		// otherwise try binding to a var
-		varErr := bindVar(imports, t, field)
+		varErr := bindVar(imports, t, field, structTag)
 
 		if varErr != nil {
 			errs = append(errs, BindError{
@@ -231,7 +264,7 @@ func bindMethod(imports *Imports, t types.Type, field *Field) error {
 	return nil
 }
 
-func bindVar(imports *Imports, t types.Type, field *Field) error {
+func bindVar(imports *Imports, t types.Type, field *Field, structTag string) error {
 	underlying, ok := t.Underlying().(*types.Struct)
 	if !ok {
 		return fmt.Errorf("not a struct")
@@ -241,9 +274,9 @@ func bindVar(imports *Imports, t types.Type, field *Field) error {
 	if field.GoFieldName != "" {
 		goName = field.GoFieldName
 	}
-	structField := findField(underlying, goName)
-	if structField == nil {
-		return fmt.Errorf("no field named %s", field.GQLName)
+	structField, err := findField(underlying, goName, structTag)
+	if err != nil {
+		return err
 	}
 
 	if err := validateTypeBinding(imports, field, structField.Type()); err != nil {