File rpm-4.20-sde-mtime.patch of Package rpm

commit b91aec866c4be289c451fc4abeb29d3079f90703
Author: Bernhard M. Wiedemann <bwiedemann@suse.de>
Date:   Mon Apr 21 17:01:01 2025 +0200

    Add an option to use a different mtime
    
    File mtimes are required to increase with new versions and releases
    of an rpm with the same name, as rsync without --checksum and similar
    tools would get confused if the content changes without newer mtime.
    
    If SOURCE_DATE_EPOCH_MTIME is set, use it instead for file modification time
    stamps. It is supposed to be newer. This can be used if we might want to
    compare if the file content remains the same when a build dependency
    changes while a build script embeds SOURCE_DATE_EPOCH in the file
    content.
    
    This can be used to support automatic rebuilds. Normally automatic
    rebuilds work, but together with reproducible builds an undesirable
    situation may occur. If a build embeds SOURCE_DATE_EPOCH in the
    output, then the output changes every time such a rebuild happens, which
    can be very often. This is to be avoided as updating packages without
    necessity is too expensive.
    
    Co-Authored-By: Jan Zerebecki <jan.suse@zerebecki.de>

diff --git a/build/files.cc b/build/files.cc
index 4e8960488..4427e2b8e 100644
--- build/files.c
+++ build/files.c
@@ -1022,8 +1022,20 @@ static void genCpioListAndHeader(FileList fl, rpmSpec spec, Package pkg, int isS
     int override_date = 0;
     time_t mtime_clamp = 0;
     char *srcdate = getenv("SOURCE_DATE_EPOCH");
+    char *msrcdate = getenv("SOURCE_DATE_EPOCH_MTIME");
     char *mtime_policy_str = rpmExpand("%{?build_mtime_policy}", NULL);
 
+    /* If SOURCE_DATE_EPOCH_MTIME is set, use it for file modification time
+     * stamps, it is supposed to be newer. This can be used if we might want to
+     * compare if the file content remains the same when a build dependency
+     * changes while a build script embeds SOURCE_DATE_EPOCH in the file
+     * content. mtimes are required to increase with new versions and releases
+     * of an rpm with the same name, as rsync without --checksum and similar
+     * tools would get confused if the content changes without newer mtime. */
+    if (msrcdate != NULL) {
+       srcdate = msrcdate;
+    }
+
     /* backward compatibility */
     if (!*mtime_policy_str) {
         if (srcdate && rpmExpandNumeric("%{?clamp_mtime_to_source_date_epoch}")) {