Fix invalid load path breaks later good paths

Loader `paths` can be a list, invalid path within (e.g., the directory
doesn't exist) will be omitted, and other valid items should be kept.

There is a problem that valid paths AFTER a bad one are omitted, too.

The cause is after normalize paths, invalid item become nil hole, then
`ipairs` in deduplicate function unexpectedly stopped there.

Solution: remove nil before dedup.

Small note: lua and snipmate loaders share
`loader.util.get_load_paths_snipmate_like` helper thus fixed together.

However vscode loader has its own `package.json` parsing logic so can't
be treated the same.

doc/luasnip.txt

@@ -1,4 +1,4 @@
-*luasnip.txt*           For NVIM v0.8.0           Last change: 2023 January 16
+*luasnip.txt*           For NVIM v0.8.0           Last change: 2023 January 18
 
 ==============================================================================
 Table of Contents                                  *luasnip-table-of-contents*

lua/luasnip/loaders/from_vscode.lua

@@ -205,7 +205,10 @@ local function get_snippet_files(opts)
 		paths = opts.paths
 	end
 	paths = vim.tbl_map(Path.expand, paths) -- Expand before deduping, fake paths will become nil
-	paths = util.deduplicate(paths) -- Remove doppelgänger paths and ditch nil ones
+	paths = vim.tbl_filter(function(v)
+		return v
+	end, paths) -- ditch nil
+	paths = util.deduplicate(paths) -- Remove doppelgänger paths
 
 	local ft_paths = {}
 

lua/luasnip/loaders/util.lua

@@ -37,6 +37,10 @@ local function split_lines(filestring)
 	)
 end
 
+local function _is_present(v)
+	return v ~= nil
+end
+
 local function normalize_paths(paths, rtp_dirname)
 	if not paths then
 		paths = vim.api.nvim_get_runtime_file(rtp_dirname, true)
@@ -45,6 +49,7 @@ local function normalize_paths(paths, rtp_dirname)
 	end
 
 	paths = vim.tbl_map(Path.expand, paths)
+	paths = vim.tbl_filter(_is_present, paths)
 	paths = util.deduplicate(paths)
 
 	return paths

tests/integration/loaders_spec.lua

@@ -236,6 +236,27 @@ describe("loaders:", function()
 		assert.are.same(3, exec_lua('return #ls.get_snippets("vim")'))
 	end)
 
+	it("loads paths with invalid paths ditched (vscode)", function()
+		exec_lua(string.format(
+			[[require("luasnip.loaders.from_vscode").load({paths={"%s", "%s"}})]],
+			os.getenv("LUASNIP_SOURCE") .. "/tests/data/invalid-not-exists",
+			os.getenv("LUASNIP_SOURCE") .. "/tests/data/vscode-snippets" -- has 5 prio snippets
+		))
+
+		assert.are.same(5, exec_lua('return #ls.get_snippets("prio")'))
+	end)
+
+	it("loads paths with invalid paths ditched (lua)", function()
+		exec_lua(string.format(
+			[[require("luasnip.loaders.from_lua").load({paths={"%s", "%s"}})]],
+			os.getenv("LUASNIP_SOURCE") .. "/tests/data/invalid-not-exists",
+			os.getenv("LUASNIP_SOURCE")
+				.. "/tests/data/lua-snippets/luasnippets" -- has 1 prio snippet
+		))
+
+		assert.are.same(1, exec_lua('return #ls.get_snippets("prio")'))
+	end)
+
 	it("respects {override,default}_priority", function()
 		-- just the filetype the test-snippets are added for.
 		exec("set ft=prio")