feat(nvim): use diffview-nvim for diffs and merges

git/default.nix

@@ -44,7 +44,8 @@
         merge.ff = false;
         merge.tool = "nvim";
 
-        mergetool.nvim.cmd = "nvim -f -c \"Gdiffsplit!\" \"$MERGED\"";
+        mergetool.nvim.cmd = "nvim -d $BASE $LOCAL $REMOTE $MERGED -c 'DiffviewOpen'";
+        mergetool.nvim.trustExitCode = false;
         mergetool.prompt = false;
 
         pager.difftool = true;

neovim/default.nix

@@ -55,6 +55,7 @@
         vim-flog
         git-blame-nvim
         nvim-web-devicons # used by diffview-nvim
+        diffview-nvim
 
         # snippets
         friendly-snippets
@@ -175,6 +176,14 @@
         require("local_firenvim")
 
         require("CopilotChat").setup()
+        require("diffview").setup({
+          view = {
+            merge_tool = {
+              layout = "diff4_mixed",
+              disable_diagnostics = true,
+            }
+          }
+        })
       '';
     };
   };