This only updates to Go 1.21 baseline, which is what the module still
specifies as the minimum version. I'll need to run this again when
moving to Go 1.25 or 1.26 as minimum.
If a file was an exact multiple of 1024 bytes (the size of an internal
buffer) and was missing a final newline, the LineReaderAt implementation
would drop the last line, leading to an unexpected EOF error on apply.
In addition to fixing the bug, slightly change the behavior of
ReadLineAt to reflect how it is actually used:
1. Clarify that the return value n includes all lines instead of only
lines with a final newline. This was already true except in the
case of the bug fixed by this commit.
2. Only return io.EOF if fewer lines are read than requested. The
previous implementation also returned io.EOF if the last line was
missing a final newline, but this was confusing and didn't really
serve a purpose.
This is technically a breaking change for external implementations but
an implementation that exactly followed the "spec" was already broken in
certain edge cases.
LineReader is a wrapper around StringReader that counts line numbers.
This is not currently used by the parser, but will be used by the apply
functions.
Billy Keyes