threads / discuss / 40979

What's "wrong" with this fast-import?

Subject: What's "wrong" with this fast-import?

## tl;dr

3 messages between Dec 12, 2015 and Dec 14, 2015.

replies: 2people: 2as markdown or json

com.git-scm@io7m.com· Dec 12, 2015, 19:25 UTC · lore

Hello!

I'm trying to track down an issue with the Fossil SCM, specifically the export feature that can produce the fast-import files consumed by Git.

The symptom of the bug seems to be that if a branch B is created from branch A, files committed to B, and then B merged with A, the committed files are not present in the head of A.

As an example:

  http://waste.io7m.com/2015/12/12/fossilexport/

The given test.fossil repository was populated with the following steps:

  1. Create fossil repository.
  2. Add README.txt and commit in trunk.
  3. Create branch 'b0' and switch to it.
  4. Add README-b0.txt and commit in b0.
  5. Switch to trunk.
  6. Merge and commit 'b0'.

The HEAD of the fossil repository now contains README.txt and README-b0.txt.

Exporting the repository (see test.export) produces:

-- blob mark :4 data 7 Hello.

blob mark :10 data 10 Hello b0.

commit refs/heads/trunk mark :3 committer someone <someone> 1449930286 +0000 data 22 initial empty check-in deleteall

commit refs/heads/trunk mark :7 committer someone <someone> 1449930317 +0000 data 7 Initial from :3 M 100644 :4 README.txt

commit refs/heads/b0 mark :9 committer someone <someone> 1449930338 +0000 data 28 Create new branch named "b0" from :7

commit refs/heads/b0 mark :13 committer someone <someone> 1449930374 +0000 data 13 Add README-b0 from :9 M 100644 :10 README-b0.txt

commit refs/heads/trunk mark :15 committer someone <someone> 1449930396 +0000 data 8 Merge b0 from :7 merge :13 --

Importing that into git produces a trunk branch that only contains the file README.txt. Something is evidently being lost in the merge, but it's not clear how.

Does anyone have any idea what Fossil is doing wrong?

SZEDER Gábor· Dec 13, 2015, 00:53 UTC · re: com.git-scm@io7m.com · lore

Re: What's "wrong" with this fast-import?

> The symptom of the bug seems to be that if a branch B is created from
> branch A, files committed to B, and then B merged with A, the committed
> files are not present in the head of A.

fast-import's 'merge' command doesn't actually perform a merge, it merely records that the new commit has one more parent. All changes compared to the first parent (i.e. the addition of that new readme file on the side branch) have to be listed explicitly.

Show 66 quoted lines

> As an example:
> 
>   http://waste.io7m.com/2015/12/12/fossilexport/
> 
> The given test.fossil repository was populated with the following steps:
> 
>   1. Create fossil repository.
>   2. Add README.txt and commit in trunk.
>   3. Create branch 'b0' and switch to it.
>   4. Add README-b0.txt and commit in b0.
>   5. Switch to trunk.
>   6. Merge and commit 'b0'.
> 
> The HEAD of the fossil repository now contains README.txt and
> README-b0.txt.
> 
> Exporting the repository (see test.export) produces:
> 
> --
> blob
> mark :4
> data 7
> Hello.
> 
> blob
> mark :10
> data 10
> Hello b0.
> 
> commit refs/heads/trunk
> mark :3
> committer someone <someone> 1449930286 +0000
> data 22
> initial empty check-in
> deleteall
> 
> commit refs/heads/trunk
> mark :7
> committer someone <someone> 1449930317 +0000
> data 7
> Initial
> from :3
> M 100644 :4 README.txt
> 
> commit refs/heads/b0
> mark :9
> committer someone <someone> 1449930338 +0000
> data 28
> Create new branch named "b0"
> from :7
> 
> commit refs/heads/b0
> mark :13
> committer someone <someone> 1449930374 +0000
> data 13
> Add README-b0
> from :9
> M 100644 :10 README-b0.txt
> 
> commit refs/heads/trunk
> mark :15
> committer someone <someone> 1449930396 +0000
> data 8
> Merge b0
> from :7
> merge :13

I.e. this commit should also contain the following filemodify command to add that new readme file:

  M 100644 :10 README-b0.txt

com.git-scm@io7m.com· Dec 14, 2015, 16:20 UTC · re: SZEDER Gábor · lore

Re: What's "wrong" with this fast-import?

On 2015-12-13T01:53:39 +0100 SZEDER Gábor <szeder@ira.uka.de> wrote:

> All changes
> compared to the first parent (i.e. the addition of that new readme file
> on the side branch) have to be listed explicitly.
>

Apologies for the delay: Thanks for this!

It seems that this issue was actually unintentionally fixed in newer versions of Fossil, but the schema of repositories created with older versions had to be updated in order to actually get the benefits of the fix.