fix(runtime): don't use regexes inside lua require'mod'

Fixes #15147 and fixes #15497. Also sketch "subdir" caching. Currently
this only caches whether an rtp entry has a "lua/" subdir but we could
consider cache other subdirs potentially or even "lua/mybigplugin/"
possibly.

Note: the async_leftpad test doesn't actually fail on master, at least
not deterministically (even when disabling the fast_breakcheck
throttling). It's still useful as a regression test for further changes
and included as such.

1 files changed, 10 insertions, 1 deletions

diff --git a/test/functional/lua/vim_spec.lua b/test/functional/lua/vim_spec.lua
index 8651a38025..a739992611 100644
--- a/test/functional/lua/vim_spec.lua
+++ b/test/functional/lua/vim_spec.lua
@@ -2255,7 +2255,7 @@ end)
 
 describe('lua: require("mod") from packages', function()
   before_each(function()
-    command('set rtp+=test/functional/fixtures')
+    command('set rtp+=test/functional/fixtures pp+=test/functional/fixtures')
   end)
 
   it('propagates syntax error', function()
@@ -2266,4 +2266,13 @@ describe('lua: require("mod") from packages', function()
 
     matches("unexpected symbol", syntax_error_msg)
   end)
+
+  it('uses the right order of mod.lua vs mod/init.lua', function()
+    -- lua/fancy_x.lua takes precedence over lua/fancy_x/init.lua
+    eq('I am fancy_x.lua', exec_lua [[ return require'fancy_x' ]])
+    -- but lua/fancy_y/init.lua takes precedence over after/lua/fancy_y.lua
+    eq('I am init.lua of fancy_y!', exec_lua [[ return require'fancy_y' ]])
+    -- safety check: after/lua/fancy_z.lua is still loaded
+    eq('I am fancy_z.lua', exec_lua [[ return require'fancy_z' ]])
+  end)
 end)