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In at least Apple's version of ranlib, the output file is updated to have a mod time equal to the max of the timestamps of its components, and that data only has seconds precision. On a filesystem with sub-second file timestamp precision --- say, APFS --- this can result in the finished static library appearing older than its input files, which causes useless rebuilds and possible outright failures in parallel makes. We've only seen this reported in the field from people using Apple's ranlib with a non-Apple make, because Apple's make doesn't know about sub-second timestamps either so it doesn't decide rebuilds are needed. But Apple's ranlib presumably shares code with at least some BSDen, so it's not that unlikely that the same problem could arise elsewhere. To fix, just "touch" the output file after ranlib finishes. We seem to need this in only one place. There are other calls of ranlib in our makefiles, but they are working on intermediate files whose timestamps are not actually important, or else on an installed static library for which sub-second timestamp precision is unlikely to matter either. (Also, so far as I can tell, Apple's ranlib doesn't mess up the file timestamp in the latter usage anyhow.) In passing, change "ranlib" to "$(RANLIB)" in one place that was bypassing the make macro for no good reason. Per bug #15525 from Jack Kelly (via Alyssa Ross). Back-patch to all supported branches. Discussion: https://postgr.es/m/15525-a30da084f17a1faa@postgresql.org
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