Re: Assertion in git log graphing [regression in v2.25]

From: Jeff King <peff@peff.net>
Date: Jan 7, 2020, 11:48 UTC
Message-ID: <20200107114812.GE1073219@coredump.intra.peff.net>
In-Reply-To: <CAHt=fUXTHc4JPsapvHKnw5vHhp2cBOYRNfdaSDWBUnKt8fWfeA@mail.gmail.com>

On Tue, Jan 07, 2020 at 11:24:50AM +0000, Bradley Smith wrote:

Show 7 quoted lines

> The following git repository (https://github.com/brads55/git-testcase)
> causes an assertion when running:
> 
>   $ git log --oneline --graph --all
> 
>   git-log: graph.c:1228: graph_output_collapsing_line: Assertion
> `graph->mapping[i - 3] == target' failed.

Thanks for the report, and especially for providing a reproduction case!

The problem is new in the v2.25 release candidates, so we should try to deal with it before the release.

> The assertion seems to be caused by commit
> 0f0f389f12029b1c3745f8ed7aacfe6b2fc7a6cc. The graph structure of the
> above repository is as follows (as produced by v2.24.1):

Yeah, I can confirm that this introduces the problem. I admit to not following the recent graph changes too closely, so I'll add James to the cc for attention.

The assertion itself is quite old, so I wondered if it was even still relevant. Removing it does produce a reasonable-looking graph:

  *   a0a130c Merge commit '8f076d8' into HEAD
  |\  
  | | *   f0f3be5 Merge commit '1b4b8d0' into HEAD
  | | |\  
  | | | * 1b4b8d0 6
  | | * | 2c44f1b 2
  | | | | * dd068b4 Merge commit '8f076d8' into HEAD
  | |_|_|/| 
  |/| | |/  
  | | |/|   
  | |/| |   
  | * | | 8f076d8 5
  | | |/  
  | |/|   
  * | | a261135 4
  | |/  
  |/|   
  * | a267dd6 1
  |/  
  * 68f4772 0

but the colors aren't quite right. In particular, in this segment:

    | | | | * dd068b4 Merge commit '8f076d8' into HEAD
    | |_|_|/| 
    |/| | |/

the first-parent line coming from dd068b4 is red in the slashes, but uncolored in the underscores.

So much for naive fix. :)

-Peff