diff-frag

Take a big diff with or without a 2-line header and turn it into frags with only a reasonable amount of context

For example, you might have a program that spits out a diff like this:

1some header data
2Author: Bobo The Cat <bobo@cat.kitty>
3Date: Wed Nov 20 20:13:08 2019 -0800
4
5diff --git a/bowl.txt b/bowl.txt
6index glorp..prolg 100655
7--- a/bowl.txt
8+++ b/bowl.txt
9 space-prefixed lines are the same in both
10 but we were sloppy in what got included in the diff
11
12 this can happen if you tell git to output a LOT of context, or if you
13 have a program that diffs objects in a naive way.
14
15 so you get 1000 lines of identical output ...
16
17 but dumping that all to ta teerminal is so ruuuuuude
18
19-what you want
20+what you want is just this bit
21+ just the changes
22
23 more more more more more.... it goes on and on for a long time...

In that case, what you'd really prefer is something like:

1some header data
2Author: Bobo The Cat <bobo@cat.kitty>
3Date: Wed Nov 20 20:13:08 2019 -0800
4
5diff --git a/bowl.txt b/bowl.txt
6index glorp..prolg 100655
7--- a/bowl.txt
8+++ b/bowl.txt
9@@ -1000,6 +1000,7 @@ so you get 1000 lines of identical...
10
11 but dumping that all to ta teerminal is so ruuuuuude
12
13-what you want
14+what you want is just this bit
15+just the changes
16
17 more more more more more.... it goes on and on for a long time...
18@@ -2456,5 +2567,5 @@ another bit of context here
19
20+ added line
21+ well, you get
22- removed line
23- the idea
24
25 just the changes, is what I'm saying, not the 1000 lines between.

This function will take the first kind of string, and turn it into the second. It's useful for test frameworks that pretty-print object diffs, for object matching assertions, and want to make them prettier when the object is really big.

USAGE

1const diffFrag = require('diff-frag')
2// options are optional, you don't have to pass that in
3const fraggedDiff = diffFrag(rawDiff, options)
4// that's it, it's just the one function

OPTIONS

• contextLines How many lines of context to show? Default = 3
• hasHeader Set to true to indicate that there is a header separated by --- oldName\n+++ newName\n lines. Set to false to indicate that you're definitely only sending just the +/-/' '-prefixed diff parts. Leave it as the default null to tell diffFrag to try to figure it out.
• oldName Only relevant if the header can't be found, otherwise it'll use the oldName in the header that the diff already has.
• oldHeader Only relevant if the header can't be found, otherwise it'll use the oldHeader in the header that the diff already has.
• newName Only relevant if the header can't be found, otherwise it'll use the newName in the header that the diff already has.
• newHeader Only relevant if the header can't be found, otherwise it'll use the newHeader in the header that the diff already has.

A ---/+++ header is always attached to the diff it returns. If a header is found in the diff you provide, then it'll use the names it finds, otherwise it's generated as:

1`---${oldName}\t${oldHeader}\n+++${newName}\t${newHeader}`