time: invalid Weekday for old dates

[kovetskiy]

What version of Go are you using (go version)?

Go 1.9.2 linux/amd64

Does this issue reproduce with the latest release?

Yes

What operating system and processor architecture are you using (go env)?

GOARCH="amd64"
GOBIN=""
GOEXE=""
GOHOSTARCH="amd64"
GOHOSTOS="linux"
GOOS="linux"
GOPATH="/home/user/go"
GORACE=""
GOROOT="/usr/lib/go"
GOTOOLDIR="/usr/lib/go/pkg/tool/linux_amd64"
GCCGO="gccgo"
CC="gcc"
GOGCCFLAGS="-fPIC -m64 -pthread -fmessage-length=0 -fdebug-prefix-map=/tmp/go-build368226252=/tmp/go-build -gno-record-gcc-switches"
CXX="g++"
CGO_ENABLED="1"
CGO_CFLAGS="-g -O2"
CGO_CPPFLAGS=""
CGO_CXXFLAGS="-g -O2"
CGO_FFLAGS="-g -O2"
CGO_LDFLAGS="-g -O2"
PKG_CONFIG="pkg-config"

What did you do?

https://play.golang.org/p/Iv3m-4cuqUr

What did you expect to see?

I expect to see that the 3rd Januray of 1010 year is Tuesday.
http://henry.pha.jhu.edu/calendarDir/julianDir/julianHTML/1010.html

output from cal program is also showing Tuesday:

                               1010

       January               February                 March
Su Mo Tu We Th Fr Sa   Su Mo Tu We Th Fr Sa   Su Mo Tu We Th Fr Sa
 1  2  3  4  5  6  7             1  2  3  4             1  2  3  4

What did you see instead?

I see Wednesday.

[kovetskiy]

google: day of week 3rd january of 1010
result: Wednesday, December 28, 1009

[dominikh]

The time package uses the Gregorian calendar, not the Julian calendar. January 3rd, 1010 in the Gregorian calendar translates to (via extrapolation) December 28th, 1009 in the Julian calendar[1][2], which was indeed a Wednesday. That's also what your Google search is telling you.

Since the time package clearly states that it uses (only) the Gregorian calendar I don't think that there's anything to do here.

[1] https://en.wikipedia.org/wiki/Conversion_between_Julian_and_Gregorian_calendars
[2] https://www.wolframalpha.com/input/?i=January+3rd+1010+in+Gregorian+calendar