test: allow exec_lua to handle functions

Problem:

Tests have lots of exec_lua calls which input blocks of code
provided as unformatted strings.

Solution:

Teach exec_lua how to handle functions.

test/functional/lua/fs_spec.lua

@@ -141,19 +141,14 @@ describe('vim.fs', function()
     it('works', function()
       eq(
         true,
-        exec_lua(
-          [[
-        local dir, nvim = ...
-        for name, type in vim.fs.dir(dir) do
-          if name == nvim and type == 'file' then
-            return true
+        exec_lua(function(dir, nvim)
+          for name, type in vim.fs.dir(dir) do
+            if name == nvim and type == 'file' then
+              return true
+            end
           end
-        end
-        return false
-      ]],
-          nvim_dir,
-          nvim_prog_basename
-        )
+          return false
+        end, nvim_dir, nvim_prog_basename)
       )
     end)
 
@@ -172,27 +167,21 @@ describe('vim.fs', function()
       io.open('testd/a/b/c/c4', 'w'):close()
 
       local function run(dir, depth, skip)
-        local r = exec_lua(
-          [[
-          local dir, depth, skip = ...
+        local r = exec_lua(function(dir0, depth0, skip0)
           local r = {}
           local skip_f
-          if skip then
-            skip_f = function(n)
-              if vim.tbl_contains(skip or {}, n) then
+          if skip0 then
+            skip_f = function(n0)
+              if vim.tbl_contains(skip0 or {}, n0) then
                 return false
               end
             end
           end
-          for name, type_ in vim.fs.dir(dir, { depth = depth, skip = skip_f }) do
+          for name, type_ in vim.fs.dir(dir0, { depth = depth0, skip = skip_f }) do
             r[name] = type_
           end
           return r
-        ]],
-          dir,
-          depth,
-          skip
-        )
+        end, dir, depth, skip)
         return r
       end
 
@@ -263,13 +252,9 @@ describe('vim.fs', function()
 
       opts = { path = test_source_path .. '/contrib', limit = math.huge }
       eq(
-        exec_lua(
-          [[
-          local dir = ...
-          return vim.tbl_map(vim.fs.basename, vim.fn.glob(dir..'/contrib/*', false, true))
-        ]],
-          test_source_path
-        ),
+        exec_lua(function(dir)
+          return vim.tbl_map(vim.fs.basename, vim.fn.glob(dir .. '/contrib/*', false, true))
+        end, test_source_path),
         vim.tbl_map(
           vim.fs.basename,
           vim.fs.find(function(_, d)
@@ -299,11 +284,11 @@ describe('vim.fs', function()
 
     it('works with a function', function()
       ---@type string
-      local result = exec_lua([[
-        return vim.fs.root(0, function(name, path)
+      local result = exec_lua(function()
+        return vim.fs.root(0, function(name, _)
           return name:match('%.txt$')
         end)
-      ]])
+      end)
       eq(vim.fs.joinpath(test_source_path, 'test/functional/fixtures'), result)
     end)
 
@@ -352,13 +337,10 @@ describe('vim.fs', function()
       local xdg_config_home = test_build_dir .. '/.config'
       eq(
         xdg_config_home .. '/nvim',
-        exec_lua(
-          [[
-        vim.env.XDG_CONFIG_HOME = ...
-        return vim.fs.normalize('$XDG_CONFIG_HOME/nvim')
-      ]],
-          xdg_config_home
-        )
+        exec_lua(function(...)
+          vim.env.XDG_CONFIG_HOME = ...
+          return vim.fs.normalize('$XDG_CONFIG_HOME/nvim')
+        end, xdg_config_home)
       )
     end)