nvim: lua: plugins: Add diffview

Also add a helper on lines similar to Git difftool from fugitive.

nvim/.config/nvim/after/ftplugin/git.vim

@@ -3,7 +3,8 @@ autocmd! BufEnter <buffer> DisableWhitespace
 
 nmap <buffer> <Leader>gb :call git#git_branch_checkout()<CR>
 nmap <buffer> <Leader>gB :call git#git_branch_delete()<CR>
-nmap <buffer> <Leader>gd :call git#git_diff_commit()<CR>
+nmap <buffer> <Leader>gd :call git#git_diffview_commit()<CR>
+nmap <buffer> <Leader>gD :call git#git_diff_commit()<CR>
 nmap <buffer> <Leader>gl :call git#git_branch_log()<CR>
 nmap <buffer> <Leader>gL :call git#git_branch_log_pretty()<CR>
 nmap <buffer> <Leader>gp :call git#git_cherry_pick()<CR>

nvim/.config/nvim/autoload/git.vim

@@ -103,6 +103,15 @@ function! git#git_diff_commit() abort
   silent execute "Git difftool -y " . commit[1] . "^!"
 endfunction
 
+" Run DiffviewOpen on the commit in the line which we are at. To be used after
+" running some variation of Git log.
+function! git#git_diffview_commit() abort
+  " A line in Git log is of the form commit <SHA>
+  let line = trim(getline('.'))
+  let commit = split(line, " ")
+  silent execute "DiffviewOpen " . commit[1] . "^!"
+endfunction
+
 " The next two functions allow scoping diffs by line range of a file and named
 " block in a file. Inspired by reading the following article.
 " https://susanpotter.net/software/tracking-diffs-by-scoping-to-file-range-function-method-or-class-changes-in-git/

nvim/.config/nvim/lua/plugins.lua

@@ -45,6 +45,7 @@ local init = function ()
   use 'rhysd/conflict-marker.vim'
   use 'salcode/vim-interactive-rebase-reverse'
   use 'whiteinge/diffconflicts'
+  use 'sindrets/diffview.nvim'
   -- Boost vim command line mode
   use 'vim-utils/vim-husk'
   -- Rainbow Parentheses