Exactly what is the change reported by `p4 -ztag sync ...#CLN`? - perforce

Question

If I run p4 -ztag sync, the first printed record looks like:
... depotFile //depot/foo/bar
... clientFile /src/foo/bar
... rev 8
... action updated
... fileSize 2928
... totalFileSize 9087
... totalFileCount 1
... change 1234
All subsequent records look like:
... depotFile //depot/foo/baz
... clientFile /src/foo/baz
... rev 2
... action updated
... fileSize 2422
The change field is listed only in the first record, and it looks like it's supposed to represent the change number that I'm syncing to. If I'm syncing from an earlier change to a later change, then that does appear to be the case.
However, if I sync backward to an earlier change by doing p4 sync ...#CLN, then the reported change sometimes is not CLN but is some slightly earlier change. (And yes, CLN is a valid, submitted change that affects files under .... If I sync even further back and then sync forward using the same p4 sync ...#CLN command, then the reported change is the change number I specified.)
Why is the reported value of change different for the same p4 sync ...#CLN command, apparently dependent on whether I'm syncing forward or backward? Is this a Perforce bug? (I am using P4/LINUX26X86_64/2015.1/1126382 with P4D/LINUX26X86_64/2015.1/1240625.)

Answer 1

The change reported is the highest changelist associated with any revision being synced.
In some cases this may happen to be the same as the changelist specified on the command line (if any), but it will frequently be lower (although I don't think there's any way it can ever be higher).
As an example:
c:\test\changes>p4 files -a ...
//stream/dev/changes/foo#3 - edit change 23 (text)
//stream/dev/changes/foo#2 - edit change 21 (text)
//stream/dev/changes/foo#1 - add change 19 (text)
c:\test\changes>p4 have ...
//stream/dev/changes/foo#2 - c:\test\changes\foo
c:\test\changes>p4 -Ztag sync -n ...#30
... depotFile //stream/dev/changes/foo
... clientFile c:\test\changes\foo
... rev 3
... action updated
... fileSize 26
... totalFileSize 26
... totalFileCount 1
... change 23
c:\test\changes>p4 -Ztag sync -n ...#20
... depotFile //stream/dev/changes/foo
... clientFile c:\test\changes\foo
... rev 1
... action updated
... fileSize 6
... totalFileSize 6
... totalFileCount 1
... change 19
c:\test\changes>p4 -Ztag sync -n ...#10
... depotFile //stream/dev/changes/foo
... clientFile c:\test\changes\foo
... rev 2
... action deleted
... totalFileSize 0
... totalFileCount 1
... change 0
Note that when syncing #30 change 23 is reported (because it's associated with foo#3), when syncing #20 change 19 is reported (because it's associated with foo#1), and when syncing #10 change 0 is reported (because now we're removing foo from the workspace, i.e. syncing to foo#none). If we were syncing multiple files, the change reported would be the highest from among the entire group of file revisions being synced to the workspace.