[Monotone-devel] Manifest Comments

[Markus Schiltknecht]

Hi,

I've been thinking about how to store additional information for a 
revision which got imported from another VCS (i.e. as cvs_import does). 
As certs are not stored and transmitted efficiently enough, it has been 
proposed to store such information in attributes.

However, that has various drawbacks. IMO, the most annoying one is that 
such attributes are inherited by child revisions. So let's say I have a 
manifest from an imported revision, which might look something like that:

manifest_of 0acef6004d07589fa5d7ae502bc78d2d4f8990e7
format_version "1"

dir ""

   file "fileA"
content [56ac1c08fa5479fd57c4a5c65861c4ed3ed93ff8]
   attr "RCS-REVISION" "1.2.1.6"

Whenever I commit a new revision, maybe into another branch, that 
revision inherits the RCS-REVISION attribute for fileA. Which is 
obviously wrong if fileA has changed. Also, this information should be 
used to allow subsequent cvs_import commands to continue from the last 
revision they imported and just add new revisions since the last import.

Thus, one would have to remove these attributes. I've been looking 
around about how to implement "vanishing attributes", which would 
disappear on a subsequent commit. But should they appear in a 'mtn 
diff'? Then a checked out revision would show lots of changes just after 
the checkout. Maybe they could silently be ignored? Anyway, implementing 
these special attributes seems quite a lot of work, after studying some 
of the code in rosters.cc.

Another point is, that these comments don't necessarily apply to files, 
but often to revisions (say, a svn_import could just list the svn 
revision number there). Of course we could also add an attribute to the 
root directory, but that seems like a hack.

Thus I've thought about another way: adding a 'comment' field to the 
Manifest. (I've been thinking about adding it to the Revision, but the 
revision merely shows changes, and a change set, while the manifest 
seems to list contents). Such a comment would have to be provided 
*before* committing and could not be changed afterwards. It would not be 
inherited by subsequent commits and would not show up in diffs.

I've added a trivial patch which adds the field with bogus content. I'm 
not sure how to continue from there, as I'd have to fiddle with 
roster->nodes and mappings...

Thus I'm asking for comment and thoughts, first.

Regards

Markus

P.S.: a manifest could look like:

manifest_of 0acef6004d07589fa5d7ae502bc78d2d4f8990e7
format_version "1"
       comment "imported from CVS on 12/03/2006

fileA: 1.2.1.6
"

dir ""

   file "fileA"
content [56ac1c08fa5479fd57c4a5c65861c4ed3ed93ff8]

# 
# old_revision [6a2036cae0ca461c169ae66696a84951a9233783]
# 
# patch "basic_io.hh"
#  from [d8c0da1addf5ce3ebda40f4508db86375620343a]
#    to [684298aa542d429853e5eccb88769025c88ff720]
# 
# patch "roster.cc"
#  from [3e46ae0e6698e47779091ef0b39f66cd31b1f2e2]
#    to [1332c1654a31cb0a9c40c64b0e97f37e89d91aea]
# 
============================================================
--- basic_io.hh d8c0da1addf5ce3ebda40f4508db86375620343a
+++ basic_io.hh 684298aa542d429853e5eccb88769025c88ff720
@@ -40,6 +40,7 @@ namespace basic_io
           symbol const file("file");
           symbol const content("content");
           symbol const attr("attr");
+          symbol const comment("comment");
       
           // 'local' roster and marking symbols
           // FIXME: should these be listed as "general" symbols here as well?
============================================================
--- roster.cc   3e46ae0e6698e47779091ef0b39f66cd31b1f2e2
+++ roster.cc   1332c1654a31cb0a9c40c64b0e97f37e89d91aea
@@ -2366,6 +2366,7 @@ roster_t::print_to(basic_io::printer & p
   {
     basic_io::stanza st;
     st.push_str_pair(basic_io::syms::format_version, "1");
+    st.push_str_pair(basic_io::syms::comment, "some comment here....");
     pr.print_stanza(st);
   }
   for (dfs_iter i(root_dir); !i.finished(); ++i)
@@ -2495,6 +2496,15 @@ roster_t::parse_from(basic_io::parser & 
           pa.str(ident);
           n = dir_t(new dir_node(read_num(ident)));
         }
+      else if (pa.symp(basic_io::syms::comment))
+        {
+          // TODO
+          L(FL("a comment..."));
+          pa.sym();
+          pa.str(pth);
+          L(FL("   the comment is: %s") % pth);
+          continue;
+        }
       else
         break;