Code Generation Fails When Binding Types: "Unable to Bind to Interface

[islamaliev]

Hello gqlgen community,

I'm facing a perplexing issue with gqlgen's code generation in my Go project. I have a GraphQL schema and a Go interface, and I'm trying to bind a GraphQL type CourseProduct to a Go struct. However, I'm encountering an error during the code generation process that I can't seem to resolve.

GraphQL Schema:

interface Product @goModel(
    model: "project.com/internal/service/product/model.Product"
) {
  id: Int!
}

type CourseProduct implements Product @goModel(
    model: "project.com/internal/service.CourseWrapper2"
) {
  id: Int!
  title: String!
}

I have a Go interface defined in internal/service/product/model/product.go:

package model

import (
    "time"
)

type Product interface {
    GetID() int
    GetTitle() string
    GetCreatedAt() time.Time
}

I also have wrapper structs in different packages:

CourseWrapper1 in internal/service/product
CourseWrapper2 in internal/service
Both wrappers embed *model.Course.

When I run go generate ./..., the code generation fails with the following error:

merging type systems failed: unable to bind to interface: project.com/internal/service.CourseWrapper2 does not satisfy the interface project.com/internal/service/product/model.Product
exit status 3
resolver.go:17: running "go": exit status 1
generate: open /path/to/project/api/graphql/generated/generated.go: no such file or directory

Interestingly, if I bind CourseProduct to project.com/internal/service/product.CourseWrapper1 (which is essentially the same struct but one package closer to model.Product), the error disappears.

Additional Observation:
If I comment out the GetCreatedAt() time.Time method in the model.Product interface, the code generates successfully even when binding to project.com/internal/service.CourseWrapper2.

I've tried debugging this issue, but it goes deep into go/types, golang.org/x/tools/go/packages/packages.go, and other internals of how Go loads and resolves packages and types.

I've also posted this question on Stack Overflow for additional visibility.

Any insights or suggestions would be greatly appreciated!

[pwaterz]

You need to implement the interface methods.

Example I had this interface

interface Node {
    id: ID!
}

I had to add this to my object

func (ObjectNmae) IsNode() {}