Kevin Bracey <ke...@bracey.fi> writes:

> @@ -342,13 +342,13 @@ In the following, we will always refer to the same 
> example history to
>  illustrate the differences between simplification settings.  We assume
>  that you are filtering for a file `foo` in this commit graph:
>  -----------------------------------------------------------------------
> +       .-A---M---N---O---P---Q
> +      /     /   /   /   /   /
> +     I     B   C   D   E   Y
> +      \   /   /   /   /   /
> +       `-------------'   X
>  -----------------------------------------------------------------------
> -The horizontal line of history A---P is taken to be the first parent of
> +The horizontal line of history A---Q is taken to be the first parent of
>  each merge.  The commits are:
>  
>  * `I` is the initial commit, in which `foo` exists with contents
> @@ -369,6 +369,10 @@ each merge.  The commits are:
>  * `E` changes `quux` to "xyzzy", and its merge `P` combines the
>    strings to "quux xyzzy".  `P` is TREESAME to `O`, but not to `E`.
>  
> +* `X` is an indpendent root commit that added a new file `side`, and `Y`
> +  modified it. `Y` is TREESAME to `X`. Its merge `Q` added `side` to `P`, and
> +  `Q` is TREESAME to `P`, but not to `Y`.
> +

OK, we say "filtering for a file `foo`" in the very beginning, so
there is an implied "with respect to `foo`" in all of these "A is
TREESAME to B", and the description in the new bullet point looks
correct.

> diff --git a/revision.c b/revision.c
> index 7535757..20c7058 100644
> --- a/revision.c
> +++ b/revision.c
> @@ -2119,6 +2119,22 @@ static int mark_redundant_parents(struct rev_info 
> *revs, struct commit *commit)
>       return marked;
>  }
>  
> +static int mark_treesame_root_parents(struct rev_info *revs, struct commit 
> *commit)
> +{
> +     struct commit_list *p;
> +     int marked = 0;
> +
> +     for (p = commit->parents; p; p = p->next) {
> +             struct commit *parent = p->item;
> +             if (!parent->parents && (parent->object.flags & TREESAME)) {
> +                     parent->object.flags |= TMP_MARK;
> +                     marked++;
> +             }
> +     }
> +
> +     return marked;
> +}
> +
>  /*
>   * Awkward naming - this means one parent we are TREESAME to.
>   * cf mark_treesame_root_parents: root parents that are TREESAME (to an
> @@ -2284,10 +2300,18 @@ static struct commit_list **simplify_one(struct 
> rev_info *revs, struct commit *c
>        *     /    /           o: a commit that touches the paths;
>        * ---o----'
>        *
> -      * Detect and simplify this case.
> +      * Further, a merge of an independent branch that doesn't
> +      * touch the path will reduce to a treesame root parent:
> +      *
> +      *  ----o----X          X: the commit we are looking at;
> +      *          /           o: a commit that touches the paths;
> +      *         r            r: a root commit not touching the paths
> +      *
> +      * Detect and simplify both cases.
>        */
>       if (1 < cnt) {
>               int marked = mark_redundant_parents(revs, commit);
> +             marked += mark_treesame_root_parents(revs, commit);
>               if (marked)
>                       marked -= leave_one_treesame_to_parent(revs, commit);
>               if (marked)

The solution looks surprisingly simple ;-)

Thanks.

> diff --git a/t/t6012-rev-list-simplify.sh b/t/t6012-rev-list-simplify.sh
> index 4e55872..57ce239 100755
> --- a/t/t6012-rev-list-simplify.sh
> +++ b/t/t6012-rev-list-simplify.sh
> @@ -110,7 +110,7 @@ check_result 'L K J I H G F E D C B A' --full-history
>  check_result 'K I H E C B A' --full-history -- file
>  check_result 'K I H E C B A' --full-history --topo-order -- file
>  check_result 'K I H E C B A' --full-history --date-order -- file
> -check_outcome failure 'I E C B A' --simplify-merges -- file
> +check_result 'I E C B A' --simplify-merges -- file
>  check_result 'I B A' -- file
>  check_result 'I B A' --topo-order -- file
>  check_result 'H' --first-parent -- another-file
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