Jonathan Tan [off-list ref] writes:
The existing behavior of diff --color-moved=zebra does not define the
minimum size of a block at all, instead relying on a heuristic applied
later to filter out sets of adjacent moved lines that are shorter than 3
lines long. This can be confusing, because a block could thus be colored
as moved at the source but not at the destination (or vice versa),
depending on its neighbors.
Instead, teach diff that the minimum size of a block is 10
non-whitespace characters. This allows diff to still exclude
uninteresting lines appearing on their own (such as those solely
consisting of one or a few closing braces), as was the intention of the
adjacent-moved-line heuristic.
I recall that there is a logic backed by a similar rationale in
blame.c::blame_entry_score() but over there we count alnum, not
!isspace, to judge if a block has been split into too small a piece
to be significant. I do not know which one is better, but if there
is no strong reason, perhaps we want to unify the two, so that we
can improve both heuristics at the same time?
On Tue, Aug 15, 2017 at 12:54 PM, Junio C Hamano [off-list ref] wrote:
Jonathan Tan [off-list ref] writes:
quoted
The existing behavior of diff --color-moved=zebra does not define the
minimum size of a block at all, instead relying on a heuristic applied
later to filter out sets of adjacent moved lines that are shorter than 3
lines long. This can be confusing, because a block could thus be colored
as moved at the source but not at the destination (or vice versa),
depending on its neighbors.
Instead, teach diff that the minimum size of a block is 10
non-whitespace characters. This allows diff to still exclude
uninteresting lines appearing on their own (such as those solely
consisting of one or a few closing braces), as was the intention of the
adjacent-moved-line heuristic.
I recall that there is a logic backed by a similar rationale in
blame.c::blame_entry_score() but over there we count alnum, not
!isspace, to judge if a block has been split into too small a piece
to be significant. I do not know which one is better, but if there
is no strong reason, perhaps we want to unify the two, so that we
can improve both heuristics at the same time?
In an ideal world we would use entropy of the diffed characters as
that is a best approximation on how much "interesting" things are
going on in that particular diff.
Computing the entropy is cumbersome, but maybe ok for this
purpose (we're most likely IO bound anyway, specifically when
including the human understanding as the last part of IO).
Reasons that may influence the choice
* Non latin/ASCII characters should also work.
* Do we care about the whitespace esoteric
programming language?
The function blame_entry_score is documented to approach
this exact problem that we are trying to solve here, so I agree
we should have a common heuristic.
Stefan