RFR: 8282567: Improve source-date handling in build system

[Magnus Ihse Bursie]

On Wed, 2 Mar 2022 18:09:58 GMT, Severin Gehwolf <sgehwolf at openjdk.org> wrote:

>> To clarify, the end effect of these changes is that building OpenJDK will basically be compliant with the method of just setting SOURCE_DATE_EPOCH. (The caveat is that it must be set at configure time, not build time.) So
>> 
>> $ export SOURCE_DATE_EPOCH=123
>> $ bash configure
>> $ make
>> 
>> will cause the build to default to building in reproducible mode, with the date given by SOURCE_DATE_EPOCH.
>
>> To clarify, the end effect of these changes is that building OpenJDK will basically be compliant with the method of just setting SOURCE_DATE_EPOCH. (The caveat is that it must be set at configure time, not build time.) So
>> 
>> ```
>> $ export SOURCE_DATE_EPOCH=123
>> $ bash configure
>> $ make
>> ```
> 
> Do you have an example configure output when used like that post-patch?
> 
>> will cause the build to default to building in reproducible mode, with the date given by SOURCE_DATE_EPOCH.
> 
> Hmm, when building via RPM, `SOURCE_DATE_EPOCH` is usually set. If I understand this correctly, prior to this, the RPM build would be non-reproducible. After it it would be. That may be confusing to some. If post-patch this makes the build reproducible, does it mention that via a WARNING/INFO or anything like that after this patch? I don't see it. Am I missing it? It would be good to have something to that effect in the configure output.

@jerboaa 

The output in configure can look like this:

checking what source date to use... 946684800, from SOURCE_DATE_EPOCH
checking for --enable-reproducible-build... enabled, default


But your comment made me think. I believe this should be more prominently displayed. My latest update therefore adds a new line to the summary. So now it looks like this:


* Version string: 19-internal-adhoc (19-internal)
* Source date:    946684800 (2000-01-01T00:00:00Z)


If no fixed source date is set, this is shown instead:

* Version string: 19-internal-adhoc (19-internal)
* Source date:    Determined at build time


(This is still the default if --with-source-date is not given or SOURCE_DATE_EPOCH is not set.)

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PR: https://git.openjdk.java.net/jdk/pull/7660