Re: a problem with git diff
- From
brian m. carlson <sandals@crustytoothpaste.net>
- Date
- Apr 16, 2020, 22:55 UTC
- Message-ID
- <20200416225502.GJ2751707@camp.crustytoothpaste.net>
- In-Reply-To
- <65cbee30-fa37-1422-98f2-2c2b5aa094bd@maurel.de>
On 2020-04-16 at 16:43:40, Guy Maurel wrote:
Show 13 quoted lines
> Hello! > > Using the appended two files: > git diff combine.cpp-2020-04-16-A combine.cpp-2020-04-16-R > git-diff.diff-Y > > doesn't show the same differences as with: > meld combine.cpp-2020-04-16-R combine.cpp-2020-04-16-A > > Have a look at git-diff.diff-Y at line 210: > -static void process_returns(void) > +static void mark_lvalue(chunk_t *pc) > > which is NOT correct.
It looks like there's some additional code that gets inserted before the process_returns function. In this case, the diff is accurate in that applying it to the old file will result in the new file, but it's not very helpful.
The reason is that the default diff algorithm, myers, looks for common lines and finds them in the blank lines in both process_returns and the new code above it. It then writes the diff as a set of deletions of the lines in process_returns and an addition of the lines in the new code, plus a final addition of the process_returns function. While correct, this is, as you noted, confusing.
If you're looking for a more helpful output, you can use --diff-algorithm=patience (or diff.algorithm=patience), which results in a diff output that more logically matches what most humans would like to see. You can also use the histogram diff algorithm, which is based on patience but has some additional heuristics. Which one produces better output differs depending on the circumstance.
-- brian m. carlson: Houston, Texas, US OpenPGP: https://keybase.io/bk2204