time: == on time.Time values compiles but doesn't work

[robpike]

When we permitted == on structs in an earlier release of Go, we accidentally made
time.Time values comparable this way. However, because time.Time values contain a
*Location pointer, it's possible (and easy) to have two time.Times represent the same
instant, even in the same time zone, yet compare unequal. This is a serious bug, as it
enables subtle bugs if a time.Time is used as a key in a map or database.

We need to find a way either to to break == statically or make it work dynamically.

Too late for 1.4, as the issue is subtle. Marking for 1.5.

[robpike]

Comment 1:

Labels changed: added repo-main.

[dsymonds]

Comment 2:

I don't this can be changed. With sufficient care one can construct time.Time values
that *are* sensibly comparable with ==, and use them as map keys or whatever. We'd be
breaking such code.

[robpike]

Closing; the comment is all we can reasonably without significantly breaking code.