feat(v:lua): support calling v:lua as a method

runtime/doc/lua.txt

@@ -391,6 +391,10 @@ where the args are converted to Lua values. The expression >
 is equivalent to the Lua chunk >
     return somemod.func(...)
 
+The `v:lua` prefix may be used to call Lua functions as |method|s. For
+example: >
+    arg1->v:lua.somemod.func(arg2)
+
 You can use `v:lua` in "func" options like 'tagfunc', 'omnifunc', etc.
 For example consider the following Lua omnifunc handler: >
 

src/nvim/eval.c

@@ -4212,7 +4212,7 @@ static int eval_lambda(char_u **const arg, typval_T *const rettv,
   return ret;
 }
 
-/// Evaluate "->method()".
+/// Evaluate "->method()" or "->v:lua.method()".
 /// @note "*arg" points to the '-'.
 /// @return FAIL or OK. "*arg" is advanced to after the ')'.
 static int eval_method(char_u **const arg, typval_T *const rettv,
@@ -4225,19 +4225,30 @@ static int eval_method(char_u **const arg, typval_T *const rettv,
   rettv->v_type = VAR_UNKNOWN;
 
   // Locate the method name.
+  int len;
   char_u *name = *arg;
+  char_u *lua_funcname = NULL;
+  if (STRNCMP(name, "v:lua.", 6) == 0) {
+    lua_funcname = name + 6;
+    *arg = (char_u *)skip_luafunc_name((const char *)lua_funcname);
+    *arg = skipwhite(*arg);  // to detect trailing whitespace later
+    len = *arg - lua_funcname;
+  } else {
     char_u *alias;
-
+    len = get_name_len((const char **)arg, (char **)&alias, evaluate, true);
-  const int len
-      = get_name_len((const char **)arg, (char **)&alias, evaluate, true);
     if (alias != NULL) {
       name = alias;
     }
+  }
 
   int ret;
   if (len <= 0) {
     if (verbose) {
+      if (lua_funcname == NULL) {
         EMSG(_("E260: Missing name after ->"));
+      } else {
+        EMSG2(_(e_invexpr2), name);
+      }
     }
     ret = FAIL;
   } else {
@@ -4251,6 +4262,13 @@ static int eval_method(char_u **const arg, typval_T *const rettv,
         EMSG(_(e_nowhitespace));
       }
       ret = FAIL;
+    } else if (lua_funcname != NULL) {
+      if (evaluate) {
+        rettv->v_type = VAR_PARTIAL;
+        rettv->vval.v_partial = vvlua_partial;
+        rettv->vval.v_partial->pt_refcount++;
+      }
+      ret = call_func_rettv(arg, rettv, evaluate, NULL, &base, lua_funcname);
     } else {
       ret = eval_func(arg, name, len, rettv, evaluate, &base);
     }
@@ -8591,13 +8609,23 @@ static bool tv_is_luafunc(typval_T *tv)
   return tv->v_type == VAR_PARTIAL && is_luafunc(tv->vval.v_partial);
 }
 
-/// check the function name after "v:lua."
+/// Skips one character past the end of the name of a v:lua function.
-int check_luafunc_name(const char *str, bool paren)
+/// @param p  Pointer to the char AFTER the "v:lua." prefix.
+/// @return Pointer to the char one past the end of the function's name.
+const char *skip_luafunc_name(const char *p)
+  FUNC_ATTR_NONNULL_ALL FUNC_ATTR_PURE FUNC_ATTR_WARN_UNUSED_RESULT
 {
-  const char *p = str;
   while (ASCII_ISALNUM(*p) || *p == '_' || *p == '.' || *p == '\'') {
     p++;
   }
+  return p;
+}
+
+/// check the function name after "v:lua."
+int check_luafunc_name(const char *const str, const bool paren)
+  FUNC_ATTR_NONNULL_ALL FUNC_ATTR_PURE FUNC_ATTR_WARN_UNUSED_RESULT
+{
+  const char *const p = skip_luafunc_name(str);
   if (*p != (paren ? '(' : NUL)) {
     return 0;
   } else {

src/nvim/eval/userfunc.c

@@ -1423,6 +1423,23 @@ static void user_func_error(int error, const char_u *name)
   }
 }
 
+/// Used by call_func to add a method base (if any) to a function argument list
+/// as the first argument. @see call_func
+static void argv_add_base(typval_T *const basetv, typval_T **const argvars,
+                          int *const argcount, typval_T *const new_argvars,
+                          int *const argv_base)
+  FUNC_ATTR_NONNULL_ARG(2, 3, 4, 5)
+{
+  if (basetv != NULL) {
+    // Method call: base->Method()
+    memmove(&new_argvars[1], *argvars, sizeof(typval_T) * (*argcount));
+    new_argvars[0] = *basetv;
+    (*argcount)++;
+    *argvars = new_argvars;
+    *argv_base = 1;
+  }
+}
+
 /// Call a function with its resolved parameters
 ///
 /// @return FAIL if function cannot be called, else OK (even if an error
@@ -1515,6 +1532,7 @@ call_func(
     if (is_luafunc(partial)) {
       if (len > 0) {
         error = ERROR_NONE;
+        argv_add_base(funcexe->basetv, &argvars, &argcount, argv, &argv_base);
         nlua_typval_call((const char *)funcname, len, argvars, argcount, rettv);
       } else {
         // v:lua was called directly; show its name in the emsg
@@ -1553,14 +1571,7 @@ call_func(
                                         fp->uf_args.ga_len);
         }
 
-        if (funcexe->basetv != NULL) {
+        argv_add_base(funcexe->basetv, &argvars, &argcount, argv, &argv_base);
-          // Method call: base->Method()
-          memmove(&argv[1], argvars, sizeof(typval_T) * argcount);
-          argv[0] = *funcexe->basetv;
-          argcount++;
-          argvars = argv;
-          argv_base = 1;
-        }
 
         if (fp->uf_flags & FC_RANGE && funcexe->doesrange != NULL) {
           *funcexe->doesrange = true;

test/functional/lua/luaeval_spec.lua

@@ -481,6 +481,21 @@ describe('v:lua', function()
        pcall_err(eval, 'v:lua.mymod.crashy()'))
   end)
 
+  it('works when called as a method', function()
+    eq(123, eval('110->v:lua.foo(13)'))
+    eq(true, exec_lua([[return _G.val == nil]]))
+
+    eq(321, eval('300->v:lua.foo(21, "boop")'))
+    eq("boop", exec_lua([[return _G.val]]))
+
+    eq(NIL, eval('"there"->v:lua.mymod.noisy()'))
+    eq("hey there", meths.get_current_line())
+    eq({5, 10, 15, 20}, eval('[[1], [2, 3], [4]]->v:lua.vim.tbl_flatten()->map({_, v -> v * 5})'))
+
+    eq("Vim:E5108: Error executing lua [string \"<nvim>\"]:0: attempt to call global 'nonexistent' (a nil value)",
+       pcall_err(eval, '"huh?"->v:lua.mymod.crashy()'))
+  end)
+
   it('works in :call', function()
     command(":call v:lua.mymod.noisy('command')")
     eq("hey command", meths.get_current_line())
@@ -522,5 +537,11 @@ describe('v:lua', function()
 
     eq("Vim(let):E46: Cannot change read-only variable \"v:['lua']\"", pcall_err(command, "let v:['lua'] = 'xx'"))
     eq("Vim(let):E46: Cannot change read-only variable \"v:lua\"", pcall_err(command, "let v:lua = 'xx'"))
+
+    eq("Vim:E107: Missing parentheses: v:lua.func", pcall_err(eval, "'bad'->v:lua.func"))
+    eq("Vim:E274: No white space allowed before parenthesis", pcall_err(eval, "'bad'->v:lua.func ()"))
+    eq("Vim:E107: Missing parentheses: v:lua", pcall_err(eval, "'bad'->v:lua"))
+    eq("Vim:E117: Unknown function: v:lua", pcall_err(eval, "'bad'->v:lua()"))
+    eq("Vim:E15: Invalid expression: v:lua.()", pcall_err(eval, "'bad'->v:lua.()"))
   end)
 end)