I will add a test to prevent regression from #2229 and look at failing tests tomorrow.

@jackc Looking at the following examples, I believe that the current scanning behavior is in inconsistent.

type Foo struct{}

var dst *Foo
err = conn.QueryRow(context.Background(), `select 'null'::jsonb`).Scan(&dst)
// err == nil
// dst == nil

var dst *Foo
err = conn.QueryRow(context.Background(), `select null::jsonb`).Scan(&dst)
// err == nil
// dst == nil

var dst Foo
err = conn.QueryRow(context.Background(), `select 'null'::jsonb`).Scan(&dst)
// err == nil
// dst == Foo{}

var dst Foo
err = conn.QueryRow(context.Background(), `select null::jsonb`).Scan(&dst)
// err == can't scan into dest[0] (col: jsonb): cannot scan NULL into *pgx_test.Foo
// dst == Foo{}

I believe either both cases of scanning Foo should error or none (or change scanning of *Foo). What is your opinion?

I decided to revert #2151 partially. This is because this should never be necessary, as such cases would be handled by the PointerPointerScanPlan. JSON requires special care to handle the scanning of 'null'::jsonb.

Thanks! sql.Scanner especially plus json has been such a pain. Hopefully, this finally resolves it.

@jackc Can we add this to the next patch version v5.7.3 please as v5.7.2 has the regression when scanning null jsonb columns into a pointer?

@emreisikligil Just released v5.7.3.

@jackc Thanks a lot 🙏

Just as a FYI, this did change the behavior of scanning a constant null into a json.RawMessage. If I pass in a jSON value null, then I don't get back what I put into it, but a NULL/nil. I don't know the whole history of this change, and I'm sure it's needed somehow, so I put this comment here as a warning/gotcha, maybe it helps someone:

    ["CREATE TABLE pgx (jsoncol JSONB NOT NULL DEFAULT 'null')"]
    ["INSERT INTO pgx (jsoncol) VALUES ('null')"]
    var j json.RawMessage
    require.NoError(t, db.QueryRow(ctx, `SELECT jsoncol FROM pgx`).Scan(&j))
    require.Equal(t, json.RawMessage([]byte("null")), j)

this now fails in 5.7.3 with:

        	Error:      	Not equal: 
        	            	expected: json.RawMessage{0x6e, 0x75, 0x6c, 0x6c}
        	            	actual  : json.RawMessage(nil)

The test passes on 5.7.2.