diff tests/test-help.t @ 27263:4efb36ecaaec

commands: add debugdeltachain command

We have debug commands for displaying overall revlog statistics
(debugrevlog) and for dumping a revlog index (debugindex). As part
of investigating various aspects of revlog behavior and performance,
I found it important to have an understanding of how revlog
delta chains behave in practice.

This patch implements a "debugdeltachain" command. For each revision
in a revlog, it dumps information about the delta chain. Which delta
chain it is part of, length of the delta chain, distance since base
revision, info about base revision, size of the delta chain, etc. The
generic formatting facility is used, which means we can templatize
output and get machine readable output like JSON.

This command has already uncovered some weird history in
mozilla-central I didn't know about. So I think it's valuable.

--- a/tests/test-help.t	Sat Oct 24 19:56:39 2015 +0100
+++ b/tests/test-help.t	Sat Dec 05 23:37:46 2015 -0800
@@ -812,6 +812,8 @@
                  description
    debugdata     dump the contents of a data file revision
    debugdate     parse and display a date
+   debugdeltachain
+                 dump information about delta chains in a revlog
    debugdirstate
                  show the contents of the current dirstate
    debugdiscovery