To make output better, also add some (temporary?) String() functions and
fix an assumption about the smallest fragment header I discovered was
wrong while looking at sample patches.
Track leading and trailing context lines because it's easy and Git
includes this information in the fragment type. Add validation for when
the fragment does not agree with the header or with the new/deleted
state of the file.
After considering fragment parsing, it made sense to change the
invariant estabilished in the previous commit. Specifically, parser
functions now assume they are call on the first line of their object and
return with the parser on the first line after their object. This means
code can call parse function immediately after each other without
advancing the parser in between.
It's possible this will change back later on... there seem to be
annoying edge cases with either choice, but I think making the functions
consistent is important.
The parsed OIDs are usually prefixes, not full hashes, so rename the
fields appropriately. Also note that values that are too long to be
valid OIDs are still accepted by the library.
I believe the structure is correct, but there are a lot of details to
fill in - translating the C string parsing logic into Go is not always
straightforward.
Billy Keyes