| 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. |