Bug 751984 - Use UTC timezone when displaying QDateTimes parsed from SOURCE_DATE_EPOCH

[infinity0]

According to the SOURCE_DATE_EPOCH spec [1], "Formatting MUST be deferred until runtime if an end user should observe the value in their own locale or timezone."

However setTime_t uses localtime, so the output is in the timezone of the build machine running doxygen, and not the timezone of the reader consuming the final output.

To adhere to the spec, the easiest option is to add a setTimeUtc_t function that is the same as setTime_t, but only uses gmtime instead of first trying localtime.

[1] https://reproducible-builds.org/specs/source-date-epoch/

[doxygen]

I don't understand the change. When doxygen produces output, it should use local time right? i.e. the time is put into the generated output, so how else can users ever observe the time in their own locale?

[infinity0]

If the user-doing-the-building sets SOURCE_DATE_EPOCH it means they want reproducible builds, so the build-user can't (and doesn't even want to) output this time in their locale. (Reproducible builds by definition means that the build should be independent of the build-user.)

A more complex alternative (to this PR, that still preserves locale) is to allow reader-users to observe SOURCE_DATE_EPOCH in their own locale, which means adding some javascript to parse this timestamp into the reader's locale. This would allow builders to produce the same reproducible output.

[doxygen]

Thanks for the clarification. Indeed I agree that viewing the timestamp in the user's local could better be facilitated by javascript.

[infinity0]

Great, thanks!