From 7983fc626923b7f0e80755499b9d2aed212d550e Mon Sep 17 00:00:00 2001
From: Nikola Kovacs <nikola.kovacs@gmail.com>
Date: Sun, 22 May 2016 09:58:37 +0200
Subject: [PATCH] fix panic in AddForeignKey on mysql dialect

---
 association_test.go | 24 ++++++++++++++++--------
 dialect_mysql.go    | 10 +++++++---
 migration_test.go   | 12 +++++++++++-
 3 files changed, 34 insertions(+), 12 deletions(-)

diff --git a/association_test.go b/association_test.go
index 2b2d3bac..ad56d84e 100644
--- a/association_test.go
+++ b/association_test.go
@@ -842,25 +842,33 @@ func TestForeignKey(t *testing.T) {
 	}
 }
 
-func TestLongForeignKey(t *testing.T) {
+func testForeignKey(t *testing.T, source interface{}, sourceFieldName string, target interface{}, targetFieldName string) {
 	if dialect := os.Getenv("GORM_DIALECT"); dialect == "" || dialect == "sqlite" {
 		// sqlite does not support ADD CONSTRAINT in ALTER TABLE
 		return
 	}
-	targetScope := DB.NewScope(&ReallyLongTableNameToTestMySQLNameLengthLimit{})
+	targetScope := DB.NewScope(target)
 	targetTableName := targetScope.TableName()
-	modelScope := DB.NewScope(&NotSoLongTableName{})
-	modelField, ok := modelScope.FieldByName("ReallyLongThingID")
+	modelScope := DB.NewScope(source)
+	modelField, ok := modelScope.FieldByName(sourceFieldName)
 	if !ok {
-		t.Fatalf("Failed to get field by name: ReallyLongThingID")
+		t.Fatalf(fmt.Sprintf("Failed to get field by name: %v", sourceFieldName))
 	}
-	targetField, ok := targetScope.FieldByName("ID")
+	targetField, ok := targetScope.FieldByName(targetFieldName)
 	if !ok {
-		t.Fatalf("Failed to get field by name: ID")
+		t.Fatalf(fmt.Sprintf("Failed to get field by name: %v", targetFieldName))
 	}
 	dest := fmt.Sprintf("%v(%v)", targetTableName, targetField.DBName)
-	err := DB.Model(&NotSoLongTableName{}).AddForeignKey(modelField.DBName, dest, "CASCADE", "CASCADE").Error
+	err := DB.Model(source).AddForeignKey(modelField.DBName, dest, "CASCADE", "CASCADE").Error
 	if err != nil {
 		t.Fatalf(fmt.Sprintf("Failed to create foreign key: %v", err))
 	}
 }
+
+func TestLongForeignKey(t *testing.T) {
+	testForeignKey(t, &NotSoLongTableName{}, "ReallyLongThingID", &ReallyLongTableNameToTestMySQLNameLengthLimit{}, "ID")
+}
+
+func TestLongForeignKeyWithShortDest(t *testing.T) {
+	testForeignKey(t, &ReallyLongThingThatReferencesShort{}, "ShortID", &Short{}, "ID")
+}
diff --git a/dialect_mysql.go b/dialect_mysql.go
index d848de35..bc4828de 100644
--- a/dialect_mysql.go
+++ b/dialect_mysql.go
@@ -7,6 +7,7 @@ import (
 	"regexp"
 	"strings"
 	"time"
+	"unicode/utf8"
 )
 
 type mysql struct {
@@ -120,7 +121,7 @@ func (mysql) SelectFromDummyTable() string {
 
 func (s mysql) BuildForeignKeyName(tableName, field, dest string) string {
 	keyName := s.commonDialect.BuildForeignKeyName(tableName, field, dest)
-	if len(keyName) <= 64 {
+	if utf8.RuneCountInString(keyName) <= 64 {
 		return keyName
 	}
 	h := sha1.New()
@@ -128,7 +129,10 @@ func (s mysql) BuildForeignKeyName(tableName, field, dest string) string {
 	bs := h.Sum(nil)
 
 	// sha1 is 40 digits, keep first 24 characters of destination
-	keyName = regexp.MustCompile("(_*[^a-zA-Z]+_*|_+)").ReplaceAllString(dest, "_")
+	destRunes := []rune(regexp.MustCompile("(_*[^a-zA-Z]+_*|_+)").ReplaceAllString(dest, "_"))
+	if len(destRunes) > 24 {
+		destRunes = destRunes[:24]
+	}
 
-	return fmt.Sprintf("%s%x", keyName[:24], bs)
+	return fmt.Sprintf("%s%x", string(destRunes), bs)
 }
diff --git a/migration_test.go b/migration_test.go
index 4d15917c..3e385466 100644
--- a/migration_test.go
+++ b/migration_test.go
@@ -49,6 +49,16 @@ type ReallyLongTableNameToTestMySQLNameLengthLimit struct {
 	Id int64
 }
 
+type ReallyLongThingThatReferencesShort struct {
+	Id      int64
+	ShortID int64
+	Short   Short
+}
+
+type Short struct {
+	Id int64
+}
+
 type CreditCard struct {
 	ID        int8
 	Number    string
@@ -241,7 +251,7 @@ func runMigration() {
 		DB.Exec(fmt.Sprintf("drop table %v;", table))
 	}
 
-	values := []interface{}{&ReallyLongTableNameToTestMySQLNameLengthLimit{}, &NotSoLongTableName{}, &Product{}, &Email{}, &Address{}, &CreditCard{}, &Company{}, &Role{}, &Language{}, &HNPost{}, &EngadgetPost{}, &Animal{}, &User{}, &JoinTable{}, &Post{}, &Category{}, &Comment{}, &Cat{}, &Dog{}, &Toy{}}
+	values := []interface{}{&Short{}, &ReallyLongThingThatReferencesShort{}, &ReallyLongTableNameToTestMySQLNameLengthLimit{}, &NotSoLongTableName{}, &Product{}, &Email{}, &Address{}, &CreditCard{}, &Company{}, &Role{}, &Language{}, &HNPost{}, &EngadgetPost{}, &Animal{}, &User{}, &JoinTable{}, &Post{}, &Category{}, &Comment{}, &Cat{}, &Dog{}, &Toy{}}
 	for _, value := range values {
 		DB.DropTable(value)
 	}