[Monotone-devel] fyi: format breakage on changeset branch

[graydon hoare]

hi,

I recently changed the changeset branch's revision and changeset 
formats. since these formats are hashed to produce revision IDs, any 
change to them will invalidate changeset-branch databases you're working 
on. I'm sorry for having done this, but I wanted to get it out of the 
way before a "release", and it was pretty clear the existing format was 
too ugly to ship. I think it was also pretty clear that the branch was 
still not-perfectly-stable, so I hope this doesn't come as too much of a 
surprise to anyone. it ought to be the last time fiddling with the 
format, or nearly so.

the old format, if you'll recall the discussion, was somewhat heavily 
structured: lots of whitespace, colons, braces, indentation, etc. to 
make it totally obvious (mostly to myself, while coding) what was going 
on. now that it more or less works, I've taken the time to rewrite the 
printer and parser in a way which is much more aesthetically pleasing. 
changesets which used to look like this:

---snip---
change_set:
{
  paths:
  {
     rename_file:
     {
       src: "usr/bin/sh"
       dst: "usr/bin/foo"
     }
     delete_dir: "usr/bin"
     add_file: "tmp/foo/bar.txt"
  }
  deltas:
  {
    delta:
    {
      path: "tmp/foo/bar.txt"
      src: []
      dst: [71e0274f16cd68bdf9a2bf5743b86fcc1e597cdc]
    }
  }
}
---snip---

now read more like this:

---snip---
rename_file: "usr/bin/sh"
         to: "usr/bin/foo"

delete_dir: "usr/bin"

add_file: "tmp/foo/bar.txt"

patch: "tmp/foo/bar.txt"
 from: []
   to: [71e0274f16cd68bdf9a2bf5743b86fcc1e597cdc]
---snip---

which has less chatter and takes up much less vertical room. indeed, 
changesets and revisions are now just a tightened-up version of the old 
status/diff/commit summary messages. key/value pairs are collected 
together into stanzas, and each stanza is indented so the values align 
vertically. it's a predictable normal form, and reads pretty well, I 
think; as best as I can do while keeping the printer and parser very simple.

-graydon