bug: context.Background.WithCancel can't assignable to context.Backgroud

[islishude]

package main

import (
	"context"
	"fmt"

	"github.com/golang/mock/gomock"
)

func main() {
	ctx, cancel := context.WithCancel(context.Background())
	defer cancel()

	res := gomock.AssignableToTypeOf(context.Background()).Matches(ctx)
	fmt.Println(res) // fasle
}

[poy]

Yup, this looks like a bug. Thanks for filing it!

[poy]

After further review, it looks like what's going on is, Context.Background() is a *context.emptyCtx where as ctx is a *context.cancelCtx. So in fact, it should print false.

[islishude]

According to the documentation,

AssignableToTypeOf is a Matcher that matches if the parameter to the mock function is assignable to the type of the parameter to this function.

Context.Background is context.Context and context.cancelCtx is also context.Context.so AssignableToTypeOf(context.Background()) should match context.cancelCtx.

package main

import (
	"context"
	"fmt"
)

func main() {
	ctx := context.Background()
	ctxWithCancel, cancel := context.WithCancel(context.Background())
	defer cancel()
	ctx = ctxWithCancel // no error here
	fmt.Println(ctx.Err())
}

[islishude]

relates to #365