Using Meta to Specify time.Time Type Causes Code Generation Error

[Kahoulam]

Description

In my design file, I use the following code to specify a date-time format field as time.Time type:

Attribute(name, String, func() {
    Meta("struct:field:type", "time.Time", "time") // Specify struct field type metadata
    Description(desc)                              // Set description of the attribute
    Format(FormatDateTime)                         // Set format for date and time
    Example("2024-01-01T11:53:54Z")                // Provide example value
})

The reason for writing it this way is to avoid repeatedly converting between time.Time and string.

However, the generated code produces the following error:

cannot use *body.Timestamp (variable of type time.Time) as string value in argument to goa.ValidateFormat

Example

Below is the complete design file example:

package design

import (
    . "goa.design/goa/v3/dsl"
)

var _ = API("example", func() {
    Title("Example API")
    Server("example", func() {
        Host("localhost", func() {
            URI("http://localhost:8080")
        })
    })
})

var ExampleType = Type("ExampleType", func() {
    Attribute("timestamp", String, func() {
        Meta("struct:field:type", "time.Time", "time") // Specify struct field type metadata
        Description("Timestamp in RFC3339 format")
        Format(FormatDateTime)
        Example("2024-01-01T11:53:54Z")
    })
    Required("timestamp")
})

var _ = Service("example", func() {
    Method("show", func() {
        Payload(ExampleType)
        Result(ExampleType)
        HTTP(func() {
            GET("/example")
            Response(StatusOK)
        })
    })
})

Expected Solution

I hope to be able to specify a date-time format field as time.Time type in the design file using Meta, and have the generated code work without the above error.

Additional Information

goa version: v3.16.2
Golang version: go1.22.6
Operating System: linux/arm64

I would appreciate any solutions or guidance. Thank you!

[raphael]

Hello, the type specified with struct:field:type must be structurally compatible with the type defined in the design, here time.Time isn't compatible with String.

[Kahoulam]

Hello, the type specified with struct:field:type must be structurally compatible with the type defined in the design, here time.Time isn't compatible with String.

@raphael Thank you for your reply.

According to the documentation, the struct:field:type meta tag allows you to override the default Go struct field type specified in the design.

The error occurs because the validation code generated by Format(FormatDateTime) is not compatible.

My goal is to use time.Time directly in Go and to include format: date-time in the API specification.

[raphael]

The goal makes sense, it won't work out of the box though as Goa can't possibly know how to convert any type to any other type.

[tchssk]

I'm considering this feature.