Unexpected highlight

[walles]

The Problem

black is highlighted even though I think it shouldn't. Either explain this or fix it!

The diff

--- /tmp/pirate/pirate-ipsum-before.txt	2020-12-31 00:11:15.000000000 +0100
+++ /tmp/pirate/pirate-ipsum-after.txt	2020-12-31 00:11:46.000000000 +0100
@@ -1,6 +1,7 @@
-Hornswaggle knave coffer rum Nelsons folly bilge water lugger. Fire in the hole black
-spot knave come about jury mast coxswain rutters. Keelhaul hail-shot Jack Ketch no prey,
-no pay gunwalls gaff haul wind. Ho fire in the hole Sail ho booty rum trysail hail-shot.
-Knave Letter of Marque barkadeer league mizzen strike colors spike. Jack Ketch spirits
-hail-shot long clothes walk the plank gabion warp. Poop deck holystone black spot tackle
-long boat loot run a shot across the bow.
+Hornswaggle knave coffer rum Nelsons folly bilge water lugger. Fire in the hole
+black spot knave come about jury mast coxswain rutters. Keelhaul hail-shot Jack
+Ketch no prey, no pay gunwalls gaff haul wind. Ho fire in the hole Sail ho booty
+rum trysail hail-shot. Knave Letter of Marque barkadeer league mizzen strike
+colors spike. Jack Ketch spirits hail-shot long clothes walk the plank gabion
+warp. Poop deck holystone black spot tackle long boat loot run a shot across the
+bow.

[walles]

git bisect blames 6243516:

6243516b7de4ba19157cb8a5ed4988539b0d339d is the first bad commit
commit 6243516b7de4ba19157cb8a5ed4988539b0d339d
Author: Johan Walles <[email protected]>
Date:   Wed Nov 11 23:46:04 2020 +0100

    Refine by word rather than by character

    Hello #7.

 README.md      | 10 ++++++----
 src/refiner.rs | 36 +++++++++++++++++++++---------------
 2 files changed, 27 insertions(+), 19 deletions(-)

[walles]

Smaller test case:

--- /tmp/pirate/pirate-ipsum-before.txt	2020-12-31 00:11:15.000000000 +0100
+++ /tmp/pirate/pirate-ipsum-after.txt	2020-12-31 00:11:46.000000000 +0100
@@ -1,6 +1,7 @@
-the hole black
-spot
+the hole
+black spot

[walles]

Explanation

  old: the _ hole  _ black \n spot \n
johan:             ^       ^^
 riff:             ^ ^^^^^

  new: the _ hole \n black  _ spot \n
johan:            ^^        ^
 riff:               ^^^^^  ^

So I see this as a space and a newline switched places.

And riff thinks that in this case, black (note leading space) has been removed from the first line, and black (note trailing space) has been added to the second line.

Given that riff works with words rather than characters (see #7), riff's solution contains just as many changes as mine, and both are valid.

I still don't like it though.

[walles]

I think the correct solution to this would be to say that highlighting words is more expensive than highlighting non-words.

But that would require support in https://github.com/distil/diffus which is not there right now.