vim.current.buffer.append() has inconsistent behavior with vim

[Yggdroot]

• nvim --version:

NVIM v0.2.2
Build type: Release
LuaJIT 2.0.5
Compilation: /usr/local/Homebrew/Library/Homebrew/shims/super/clang -Wconversion -U_FORTIFY_SOURCE -D_FORTIFY_SOURCE=1 -DNVIM_MSGPACK_HAS_FLOAT32 -DNVIM_UNIBI_HAS_VAR_FROM -DNDEBUG -DMIN_LOG_LEVEL=3 -Wall -Wextra -pedantic -Wno-unused-parameter -Wstrict-prototypes -std=gnu99 -Wimplicit-fallthrough -Wvla -fstack-protector-strong -fdiagnostics-color=auto -DINCLUDE_GENERATED_DECLARATIONS -I/tmp/neovim-20180209-64704-1ao8lfl/neovim-0.2.2/build/config -I/tmp/neovim-20180209-64704-1ao8lfl/neovim-0.2.2/src -I/usr/local/include -I/usr/local/include -I/usr/local/include -I/usr/local/include -I/usr/local/include -I/usr/local/include -I/usr/local/opt/gettext/include -I/usr/include -I/tmp/neovim-20180209-64704-1ao8lfl/neovim-0.2.2/build/src/nvim/auto -I/tmp/neovim-20180209-64704-1ao8lfl/neovim-0.2.2/build/include
编译者 brew@ElCapitan.local

Features: +acl +iconv +jemalloc +tui
See ":help feature-compile"

     系统 vimrc 文件: "$VIM/sysinit.vim"
         $VIM 预设值: "/usr/local/Cellar/neovim/0.2.2_1/share/nvim"

• Vim (version: ) behaves differently? yes
• Operating system/version: MacOS
• Terminal name/version:
• $TERM:

Steps to reproduce using nvim -u NORC

nvim -u NORC

:py import vim
:py print vim.current.window.cursor[0]
:py vim.current.buffer.append('aaa', 0)
:py print vim.current.window.cursor[0]

Actual behaviour

output is: 1, 2

Expected behaviour

vim's output is 1,1

[justinmk]

@phodge Is this the same as #7756 ? (why does that issue mention multiple windows?)

[ipod825]

I guess they are related. I mentioned multiple windows because that's how I spotted the issue and didn't try just a single window.

[dimbleby]

This looks deliberate. Code is here.

Doesn't seem unreasonable to me that in the given test case neovim should prefer to preserve the position of the cursor on the original line of text, rather than on the original line number.

[dimbleby]

Having said that, this code is only imperfectly achieving that aim. Eg consider:

:py3 import vim
:py3 vim.current.window.cursor = (2, 2)
:py3 print(vim.current.window.cursor[0])
:py3 vim.current.buffer[:] = ['shorter', 'buffer', 'contents']
:py3 print(vim.current.window.cursor[0])

which results in the cursor moving from line 2 to line 1, though you'd think that it could have stayed where it was. (This example is, I think, consistent with vim).

[Yggdroot]

@dimbleby Your example is not the same as mine.

[dimbleby]

@Yggdroot - of course! It was a second example.

Apparently I was unclear, so I'll try again:

• I agree that your example shows neovim behaving differently from vim
• I'm noting that this deviation actually makes some sense, because trying to keep the cursor on the same line of text that it started on is pretty reasonable - perhaps more reasonable than the vim behaviour of keeping it on the same line number that it started on.
• But I'm then giving a second example in which IMO neither vim nor neovim does a great job of deciding where the cursor should be after the buffer manipulation.

Make sense?

[ipod825]

I just realized that this issue is different from #7756. This one inserts a line to a buffer while #7756 modifies a line in a buffer. Inserting a line does not move the cursor in a second window viewing the same buffer.

[Yggdroot]

The inconsistency does not mean wrong. But we should think about that should neovim deviate from vim at this point?

[justinmk]

Fixed by #9674.