nvim: Improve snippet jumping

Snippets can be jumped through more easily now since jumping between
snippets (with <tab> and <s-tab>) takes precedence over completions and
jumping through completions. That means when a snippet has been expanded
we can now cycle through its insertion points without worrying about
activating completion items instead.

Additionally, only jump through insertion points as long as we are
within the snippet boundaries with the cursor, so it doesn't surprise
jump later when pressing <tab> from somewhere else in the file.

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

@@ -135,12 +135,12 @@ return {
 						}), -- disable selection in cmd mode
 					}),
 					["<Tab>"] = cmp.mapping(function(fallback)
-						if cmp.visible() then
+						-- expand_or_jumpable() will always jump
-							cmp.select_next_item()
+						-- expand_or_locally_jumpable() only jumps when still inside snippet region
-						-- You could replace the expand_or_jumpable() calls with expand_or_locally_jumpable()
+						if luasnip.expand_or_locally_jumpable() then
-						-- they way you will only jump inside the snippet region
-						elseif luasnip.expand_or_jumpable() then
 							luasnip.expand_or_jump()
+						elseif cmp.visible() then
+							cmp.select_next_item()
 						elseif has_words_before() then
 							cmp.complete()
 						else
@@ -148,10 +148,10 @@ return {
 						end
 					end, { "i", "s" }),
 					["<S-Tab>"] = cmp.mapping(function(fallback)
-						if cmp.visible() then
+						if luasnip.jumpable(-1) then
-							cmp.select_prev_item()
-						elseif luasnip.jumpable(-1) then
 							luasnip.jump(-1)
+						elseif cmp.visible() then
+							cmp.select_prev_item()
 						else
 							fallback()
 						end