Confusing coloring: Add support for diffSubname

[swnakamura]

Environment:

• OS: Arch Linux
• Vim (:version): nvim v0.7.0-dev+920-g7e2ce35e3
• Terminal: GNOME Terminal

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When I diff files (e.g. with fugitive.vim), coloring is confusing.

For example, I have a text file

hello world.
hello world.
hello world.

deleted

then change the line deleted with added. When I compare the difference with fugitive.vim, I see this:

Here, the first hello world. line is highlighted green, but is not the added line. This is confusing.

Solution?

This happens because iceberg.vim doesn't have a highlight for diffSubname.
It is defined here and linked to PreProc later in the file.
Then PreProc is highlighted as green in iceberg.vim.

I suppose we can use a different color for diffSubname?

[swnakamura]

https://vi.stackexchange.com/questions/4883/overwrite-colorscheme-syntax-highlighting
The same issue is discussed here. Maybe I should fix this locally by inserting something like hi! link diffSubname NONE to my .vimrc.