fix(migrator): drop duplicate PRIMARY KEY clause in AlterColumn

[libvoid]

• Do only one thing
• Non breaking API changes
• Tested

What did this pull request do?

AlterColumn rewrites a column's definition using FullDataTypeOf, which inlines PRIMARY KEY AUTOINCREMENT for autoincrement fields.

If the table's DDL already declared that column's primary key as a separate PRIMARY KEY (`col`) table constraint, that clause was never removed producing a CREATE TABLE with two primary key definitions and failing with "table ... has more than one primary key".

We need to look for a matching standalone PRIMARY KEY clause referencing that column alone and drop it. Composite primary keys are left untouched, since they parse to more than one column.

This commit fixes a regression introduced since 139bd30 (v1.5.4)

User Case Description

I hit this bug in our project when trying to update the DB schema.

---

Here is a MCVE:

module repro

go 1.26

require (
	gorm.io/driver/sqlite v1.6.0
	gorm.io/gorm v1.31.2
)

package main

import (
	"fmt"
	"os"

	"gorm.io/driver/sqlite"
	"gorm.io/gorm"
)

type Host struct {
	ID       uint `gorm:"primaryKey"`
	SSHKeyID uint
	HopID    uint
}

func main() {
	os.Remove("repro.db")

	db, err := gorm.Open(sqlite.Open("repro.db"), &gorm.Config{})
	if err != nil {
		panic(err)
	}

	legacyDDL := "CREATE TABLE `hosts` (" +
		"`id` integer," +
		"`ssh_key_id` integer," +
		"`hop_id` integer," +
		"PRIMARY KEY (`id`)," +
		"CONSTRAINT `fk_hosts_hop` FOREIGN KEY (`hop_id`) REFERENCES `hosts`(`id`)" +
		")"

	if err := db.Exec(legacyDDL).Error; err != nil {
		panic(err)
	}

	// field forces GORM to rebuild the table, inlining "PRIMARY KEY AUTOINCREMENT" onto the id column.
	err = db.Migrator().AlterColumn(&Host{}, "ID")
	if err != nil {
		fmt.Println("BUG REPRODUCED:", err)
		os.Exit(1)
	}

	fmt.Println("OK")
}

go get gorm.io/driver/sqlite@master
go mod tidy
go run -v main.go

go mod edit -replace gorm.io/driver/sqlite=github.com/libvoid/sqlite@fix
go mod tidy
go run main.go