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Original file line number | Diff line number | Diff line change |
---|---|---|
@@ -0,0 +1,193 @@ | ||
diff-highlight | ||
============== | ||
|
||
Line oriented diffs are great for reviewing code, because for most | ||
hunks, you want to see the old and the new segments of code next to each | ||
other. Sometimes, though, when an old line and a new line are very | ||
similar, it's hard to immediately see the difference. | ||
|
||
You can use "--color-words" to highlight only the changed portions of | ||
lines. However, this can often be hard to read for code, as it loses | ||
the line structure, and you end up with oddly formatted bits. | ||
|
||
Instead, this script post-processes the line-oriented diff, finds pairs | ||
of lines, and highlights the differing segments. It's currently very | ||
simple and stupid about doing these tasks. In particular: | ||
|
||
1. It will only highlight hunks in which the number of removed and | ||
added lines is the same, and it will pair lines within the hunk by | ||
position (so the first removed line is compared to the first added | ||
line, and so forth). This is simple and tends to work well in | ||
practice. More complex changes don't highlight well, so we tend to | ||
exclude them due to the "same number of removed and added lines" | ||
restriction. Or even if we do try to highlight them, they end up | ||
not highlighting because of our "don't highlight if the whole line | ||
would be highlighted" rule. | ||
|
||
2. It will find the common prefix and suffix of two lines, and | ||
consider everything in the middle to be "different". It could | ||
instead do a real diff of the characters between the two lines and | ||
find common subsequences. However, the point of the highlight is to | ||
call attention to a certain area. Even if some small subset of the | ||
highlighted area actually didn't change, that's OK. In practice it | ||
ends up being more readable to just have a single blob on the line | ||
showing the interesting bit. | ||
|
||
The goal of the script is therefore not to be exact about highlighting | ||
changes, but to call attention to areas of interest without being | ||
visually distracting. Non-diff lines and existing diff coloration is | ||
preserved; the intent is that the output should look exactly the same as | ||
the input, except for the occasional highlight. | ||
|
||
Use | ||
--- | ||
|
||
You can try out the diff-highlight program with: | ||
|
||
--------------------------------------------- | ||
git log -p --color | /path/to/diff-highlight | ||
--------------------------------------------- | ||
|
||
If you want to use it all the time, drop it in your $PATH and put the | ||
following in your git configuration: | ||
|
||
--------------------------------------------- | ||
[pager] | ||
log = diff-highlight | less | ||
show = diff-highlight | less | ||
diff = diff-highlight | less | ||
--------------------------------------------- | ||
|
||
|
||
Color Config | ||
------------ | ||
|
||
You can configure the highlight colors and attributes using git's | ||
config. The colors for "old" and "new" lines can be specified | ||
independently. There are two "modes" of configuration: | ||
|
||
1. You can specify a "highlight" color and a matching "reset" color. | ||
This will retain any existing colors in the diff, and apply the | ||
"highlight" and "reset" colors before and after the highlighted | ||
portion. | ||
|
||
2. You can specify a "normal" color and a "highlight" color. In this | ||
case, existing colors are dropped from that line. The non-highlighted | ||
bits of the line get the "normal" color, and the highlights get the | ||
"highlight" color. | ||
|
||
If no "new" colors are specified, they default to the "old" colors. If | ||
no "old" colors are specified, the default is to reverse the foreground | ||
and background for highlighted portions. | ||
|
||
Examples: | ||
|
||
--------------------------------------------- | ||
# Underline highlighted portions | ||
[color "diff-highlight"] | ||
oldHighlight = ul | ||
oldReset = noul | ||
--------------------------------------------- | ||
|
||
--------------------------------------------- | ||
# Varying background intensities | ||
[color "diff-highlight"] | ||
oldNormal = "black #f8cbcb" | ||
oldHighlight = "black #ffaaaa" | ||
newNormal = "black #cbeecb" | ||
newHighlight = "black #aaffaa" | ||
--------------------------------------------- | ||
|
||
|
||
Bugs | ||
---- | ||
|
||
Because diff-highlight relies on heuristics to guess which parts of | ||
changes are important, there are some cases where the highlighting is | ||
more distracting than useful. Fortunately, these cases are rare in | ||
practice, and when they do occur, the worst case is simply a little | ||
extra highlighting. This section documents some cases known to be | ||
sub-optimal, in case somebody feels like working on improving the | ||
heuristics. | ||
|
||
1. Two changes on the same line get highlighted in a blob. For example, | ||
highlighting: | ||
|
||
---------------------------------------------- | ||
-foo(buf, size); | ||
+foo(obj->buf, obj->size); | ||
---------------------------------------------- | ||
|
||
yields (where the inside of "+{}" would be highlighted): | ||
|
||
---------------------------------------------- | ||
-foo(buf, size); | ||
+foo(+{obj->buf, obj->}size); | ||
---------------------------------------------- | ||
|
||
whereas a more semantically meaningful output would be: | ||
|
||
---------------------------------------------- | ||
-foo(buf, size); | ||
+foo(+{obj->}buf, +{obj->}size); | ||
---------------------------------------------- | ||
|
||
Note that doing this right would probably involve a set of | ||
content-specific boundary patterns, similar to word-diff. Otherwise | ||
you get junk like: | ||
|
||
----------------------------------------------------- | ||
-this line has some -{i}nt-{ere}sti-{ng} text on it | ||
+this line has some +{fa}nt+{a}sti+{c} text on it | ||
----------------------------------------------------- | ||
|
||
which is less readable than the current output. | ||
|
||
2. The multi-line matching assumes that lines in the pre- and post-image | ||
match by position. This is often the case, but can be fooled when a | ||
line is removed from the top and a new one added at the bottom (or | ||
vice versa). Unless the lines in the middle are also changed, diffs | ||
will show this as two hunks, and it will not get highlighted at all | ||
(which is good). But if the lines in the middle are changed, the | ||
highlighting can be misleading. Here's a pathological case: | ||
|
||
----------------------------------------------------- | ||
-one | ||
-two | ||
-three | ||
-four | ||
+two 2 | ||
+three 3 | ||
+four 4 | ||
+five 5 | ||
----------------------------------------------------- | ||
|
||
which gets highlighted as: | ||
|
||
----------------------------------------------------- | ||
-one | ||
-t-{wo} | ||
-three | ||
-f-{our} | ||
+two 2 | ||
+t+{hree 3} | ||
+four 4 | ||
+f+{ive 5} | ||
----------------------------------------------------- | ||
|
||
because it matches "two" to "three 3", and so forth. It would be | ||
nicer as: | ||
|
||
----------------------------------------------------- | ||
-one | ||
-two | ||
-three | ||
-four | ||
+two +{2} | ||
+three +{3} | ||
+four +{4} | ||
+five 5 | ||
----------------------------------------------------- | ||
|
||
which would probably involve pre-matching the lines into pairs | ||
according to some heuristic. |
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Original file line number | Diff line number | Diff line change |
---|---|---|
@@ -0,0 +1,4 @@ | ||
#!/bin/bash | ||
|
||
curl -o "third_party/diff-highlight/diff-highlight" "https://raw.githubusercontent.com/git/git/master/contrib/diff-highlight/diff-highlight" | ||
curl -o "third_party/diff-highlight/README" "https://raw.githubusercontent.com/git/git/master/contrib/diff-highlight/README" |