threads / patch / 16455

patchAvoid breaking the walk prematurely

Subject: [EGIT PATCH] Avoid breaking the walk prematurely

## tl;dr

2 messages between Nov 24, 2008 and Nov 25, 2008. Diffs are folded; open one to read it.

replies: 1people: 2as markdown or json

Robin Rosenberg· Nov 24, 2008, 23:45 UTC · lore

The optimization broke the walk when all changes we adds, assuming the parent was an empty tree. This assumption was wrong. The tree does not have to bee empty, it can contain other trees and blobs.

http://code.google.com/p/egit/issues/detail?id=46

Signed-off-by: Robin Rosenberg <robin.rosenberg@dewire.com>
---
 .../spearce/jgit/revwalk/RewriteTreeFilter.java    |    7 -------
 1 files changed, 0 insertions(+), 7 deletions(-)

We could introduce a fixed version later on if we supply an option to select whether to optimize the walk this way. The problem with doing it without an option is that imports from legacy SCMs do not necessarily record file moves as add/removes in direct sucession, but other events may happen in beteens for various reasons.

-- robin

Show changes to org.spearce.jgit/src/org/spearce/jgit/revwalk/RewriteTreeFilter.java +0 −7

diff --git a/org.spearce.jgit/src/org/spearce/jgit/revwalk/RewriteTreeFilter.java b/org.spearce.jgit/src/org/spearce/jgit/revwalk/RewriteTreeFilter.java
index 587d6d2..a5edbf0 100644
--- a/org.spearce.jgit/src/org/spearce/jgit/revwalk/RewriteTreeFilter.java
+++ b/org.spearce.jgit/src/org/spearce/jgit/revwalk/RewriteTreeFilter.java
@@ -118,13 +118,6 @@ public boolean include(final RevWalk walker, final RevCommit c)
 				//
 				c.flags |= REWRITE;
 				return false;
-			} else if (chgs == adds) {
-				// We added everything, so the parent may as well just
-				// be an empty tree. Kill our parent, we can assume
-				// it did not supply interesting changes.
-				//
-				c.parents = RevCommit.NO_PARENTS;
-				return true;
 			} else {
 				// We have interesting items, but neither of the special
 				// cases denoted above.

-- 
1.6.0.3.640.g6331a

Shawn O. Pearce· Nov 25, 2008, 00:12 UTC · re: Robin Rosenberg · lore

Re: [EGIT PATCH] Avoid breaking the walk prematurely

Robin Rosenberg <robin.rosenberg@dewire.com> wrote:

Show 16 quoted lines

> The optimization broke the walk when all changes we adds, assuming
> the parent was an empty tree. This assumption was wrong. The tree does
> not have to bee empty, it can contain other trees and blobs.
> 
> http://code.google.com/p/egit/issues/detail?id=46
> 
> Signed-off-by: Robin Rosenberg <robin.rosenberg@dewire.com>
> ---
>  .../spearce/jgit/revwalk/RewriteTreeFilter.java    |    7 -------
>  1 files changed, 0 insertions(+), 7 deletions(-)
> 
> We could introduce a fixed version later on if we supply an option to select
> whether to optimize the walk this way. The problem with doing it without an
> option is that imports from legacy SCMs do not necessarily record file moves
> as add/removes in direct sucession, but other events may happen in beteens
> for various reasons.

This is a fairly useful optimization in git. Most people use it, because most people don't pass "--full-history" when they run "git log -- path". So I think we really want to do it by default in jgit.

Enabling this optimization again probably requires adding a new method to TreeFilter which allows the filter graph to return only nodes which select paths by name, and then do something like:

  else if (chgs == adds && isPathSetEmpty(c.getTree())) {
    c.parents = RevCommit.NO_PARENTS;
    return true;
  }

where isPathSetEmpty runs a second TreeWalk iteration but uses the new (smaller) filter graph that only matches on paths.

I'm not going to write that out today.  But I thought I'd at least
write an email while the idea was fresh in my head.

-- 
Shawn.