Sergey Ponomarev created MJAR-314:
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Summary: Use a predefined constant for
project.build.outputTimestamp
Key: MJAR-314
URL: https://issues.apache.org/jira/browse/MJAR-314
Project: Maven JAR Plugin
Issue Type: Improvement
Reporter: Sergey Ponomarev
The "Configuring for Reproducible Builds" guide shows and example how to
specify a static outputTimestamp:
<project.build.outputTimestamp>2023-01-01T00:00:00Z</project.build.outputTimestamp>
The date inside is really doesn't matter and I used the property as is but was
afraid of being asked on a review why the 2023 year was used so used the
current year.
But still during a review I was asked:
bq. these changes are likely going to confuse future developers ("This date
shouldn't be static! Lets make it a variable!").
The Gradle has an option preserveFileTimestamps = false that will just put 1
Feb 1980 as a date. The 1 Jan 1980 is a minimal date in Zip archive but the 1
Jan has some special treatment by Java that's why the Gradle team used the 1
Feb.
See more detailed description in CONSTANT_TIME_FOR_ZIP_ENTRIES
https://github.com/gradle/gradle/blob/master/platforms/core-runtime/files/src/main/java/org/gradle/api/internal/file/archive/ZipEntryConstants.java#L39
I don't think it worth to declare some new property e.g.
<preserveFileTimestamps>true</preserveFileTimestamps>
But we can simply make a special constant value like:
<project.build.outputTimestamp>REPRODUCIBLE_BUILD_STATIC_DATE</project.build.outputTimestamp>
Then the constant will be replaced with the same 1 Feb 1980 to be similar with
Gradle produced artifacts.
This constant should make it more clear intention of the outputTimestamp but
also easier to find an explanation for this.
The outputTimestamp parsing is performed in the maven-archiver but the
maven-compiler-plugin and maven-jar-plugin would need to update a JavaDoc for
the outputTimestamp config option
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