feat(runtime): Allow lua to be used in compiler

runtime/doc/quickfix.txt

@@ -1208,8 +1208,8 @@ not "b:current_compiler".  What the command actually does is the following:
 - Delete the "current_compiler" and "b:current_compiler" variables.
 - Define the "CompilerSet" user command.  With "!" it does ":set", without "!"
   it does ":setlocal".
-- Execute ":runtime! compiler/{name}.vim".  The plugins are expected to set
+- Execute ":runtime! compiler/{name}.(vim|lua)".  The plugins are expected to
-  options with "CompilerSet" and set the "current_compiler" variable to the
+  set options with "CompilerSet" and set the "current_compiler" variable to the
   name of the compiler.
 - Delete the "CompilerSet" user command.
 - Set "b:current_compiler" to the value of "current_compiler".

src/nvim/ex_cmds2.c

@@ -2421,6 +2421,7 @@ void ex_compiler(exarg_T *eap)
   if (*eap->arg == NUL) {
     // List all compiler scripts.
     do_cmdline_cmd("echo globpath(&rtp, 'compiler/*.vim')");  // NOLINT
+    do_cmdline_cmd("echo globpath(&rtp, 'compiler/*.lua')");  // NOLINT
   } else {
     size_t bufsize = STRLEN(eap->arg) + 14;
     buf = xmalloc(bufsize);
@@ -2445,7 +2446,11 @@ void ex_compiler(exarg_T *eap)
 
     snprintf((char *)buf, bufsize, "compiler/%s.vim", eap->arg);
     if (source_in_path(p_rtp, buf, DIP_ALL) == FAIL) {
-      EMSG2(_("E666: compiler not supported: %s"), eap->arg);
+      // Try lua compiler
+      snprintf((char *)buf, bufsize, "compiler/%s.lua", eap->arg);
+      if (source_in_path(p_rtp, buf, DIP_ALL) == FAIL) {
+        EMSG2(_("E666: compiler not supported: %s"), eap->arg);
+      }
     }
     xfree(buf);
 

test/functional/lua/runtime_spec.lua

@@ -85,5 +85,35 @@ describe('runtime:', function()
     end)
   end)
 
+  describe('compiler', function()
+    local compiler_folder = table.concat({xconfig, 'nvim', 'compiler'}, pathsep)
+
+    it('loads lua compilers', function()
+      local compiler_file = table.concat({compiler_folder, 'new_compiler.lua'},
+                                            pathsep)
+      mkdir_p(compiler_folder)
+      write_file(compiler_file, [[vim.g.lua_compiler = 1]])
+
+      clear{ args_rm={'-' }, env={ XDG_CONFIG_HOME=xconfig }}
+      exec('compiler new_compiler')
+
+      eq(1, eval('g:lua_compiler'))
+      rmdir(compiler_folder)
+    end)
+
+    it('loads vim compilers when both lua and vim version exist', function()
+      local compiler_file = table.concat({compiler_folder, 'new_compiler'},
+                                            pathsep)
+      mkdir_p(compiler_folder)
+      write_file(compiler_file..'.vim', [[let g:compiler = 'vim']])
+      write_file(compiler_file..'.lua', [[vim.g.compiler = 'lua']])
+
+      clear{ args_rm={'-u' }, env={ XDG_CONFIG_HOME=xconfig }}
+      exec('compiler new_compiler')
+
+      eq('vim', eval('g:compiler'))
+      rmdir(compiler_folder)
+    end)
+  end)
 end)