Normalize UTC dates in pgxtypes v5

[jalandis]

Is your feature request related to a problem? Please describe.

When decoding timestamptz fields, UTC values have an unexpected location set instead of the GO standard nil value.

Test code comparing structs with reflect.DeepEqual fails on time.Time fields.

Describe the solution you'd like
This appears to have been solved already in the separate pgtypes project but didn't make it to v5.

jackc/pgtype@7544603

Changing the logic to match how GO std time works with UTC seems like a safe choice. I would be happy to create a PR with the code already in pgtypes v4.

Describe alternatives you've considered

• Creating a separate custom type
• Using pgx v4

Converting all assertions in the project is a large lift. It would not be feasible for our code base.

Additional context
I am using the sql/database interfaces and not the pgx interfaces.

From GO time

        // loc specifies the Location that should be used to
	// determine the minute, hour, month, day, and year
	// that correspond to this Time.
	// The nil location means UTC.
	// All UTC times are represented with loc==nil, never loc==&utcLoc.
	loc *Location

[jalandis]

I found that there was a PR in testify.Equal to use time.Equal in comparisons. This was determined to be a bug as 2 times with different representations were not considered equal.

The PR's fix/bug was reverted by 1.9.0 :-(

stretchr/testify#1536

stretchr/testify#1537

[jackc]

I think that jackc/pgtype@7544603 only affects parsing a text formatted timestamptz because the time zone will be part of the string. Binary formatted values do not contain any time zone information. The time zone is somewhat arbitrary. This led to #1195.

Hmm... thinking about this issue and reviewing #1195 gives me an idea...

...
...
...

Try PR #1948. I think that this issue could be resolved by the following code in an after connect hook.

		conn.TypeMap().RegisterType(&pgtype.Type{
			Name:  "timestamptz",
			OID:   pgtype.TimestamptzOID,
			Codec: &pgtype.TimestamptzCodec{ScanLocation: time.UTC},
		})

[jalandis]

That worked beautifully! All my tests are now passing.

[jackc]

Merged #1948.