make the NullTime type an alias of sql.NullTime

[shogo82148]

Description

updates #960

currently, the following code will fails because of type miss match.

func doSomething() mysql.NullTime

var nt sql.NullTime
nt = doSomething() // compile error

It may prevent migrating from mysql.NullTime to sql.NullTime.
From Go 1.9, Go supports type aliases. https://golang.org/doc/go1.9#language
It helps migrating.

Checklist

• Code compiles correctly
• Created tests which fail without the change (if possible)
• All tests passing
• Extended the README / documentation, if necessary
• Added myself / the copyright holder to the AUTHORS file

[julienschmidt]

Something seems to be broken with Go13+ (see Travis):

--- FAIL: TestRowsColumnTypes (0.04s)

    driver_test.go:2910: failed to scan values in sql: Scan error on column index 38, name "datetime": unsupported Scan, storing driver.Value type []uint8 into type *time.Time

--- FAIL: TestScanNullTime (0.00s)

    nulltime_test.go:53: 2012-06-14: expected error status false, got true

    nulltime_test.go:53: [50 48 49 50 45 48 54 45 49 52]: expected error status false, got true

    nulltime_test.go:53: 2011-11-20 21:27:37: expected error status false, got true

    nulltime_test.go:53: [50 48 49 49 45 49 49 45 50 48 32 50 49 58 50 55 58 51 55]: expected error status false, got true

    nulltime_test.go:53: 0000-00-00: expected error status false, got true

    nulltime_test.go:53: [48 48 48 48 45 48 48 45 48 48]: expected error status false, got true

    nulltime_test.go:53: 0000-00-00 00:00:00: expected error status false, got true

    nulltime_test.go:53: [48 48 48 48 45 48 48 45 48 48 32 48 48 58 48 48 58 48 48]: expected error status false, got true

    nulltime_test.go:56: : expected valid status false, got true

    nulltime_test.go:56: 1234: expected valid status false, got true

    nulltime_test.go:56: 0: expected valid status false, got true

[julienschmidt]

parseDateTime for []byte and string are still required, even with sql.NullTime in Go 1.3+.

[shogo82148]

I think it is misuse of mysqlNullTime, users should add the parseTime=true option.
because parseDateTime does not consider timezones.
TestLegacyNullTime and TestNullTime are working examples.

but, you know, it may break existing codes. I'm thinking about it now... 🤔

[julienschmidt]

We should at least not push it right before a release. Let's reconsider this later.

[shogo82148]

Agree

[dolmen]

You probably don't need that much this change for your migration path. Here is a simple workaround: a type cast, because the representations are now the same.

nt = sql.NullTime(doSomething())

See this code on the Go playground.

[shogo82148]

close this because this pull request breaks the compatibility, and it is enough to add a deprecated message into mysql.NullTime.