patch 8.2.4669: in compiled code len('string') is not inlined

Problem:    In compiled code len('string') is not inlined.
Solution:   Compute the length at compile time if possible. (closes #10065)

src/evalfunc.c

@@ -90,7 +90,6 @@ static void f_interrupt(typval_T *argvars, typval_T *rettv);
 static void f_invert(typval_T *argvars, typval_T *rettv);
 static void f_islocked(typval_T *argvars, typval_T *rettv);
 static void f_last_buffer_nr(typval_T *argvars, typval_T *rettv);
-static void f_len(typval_T *argvars, typval_T *rettv);
 static void f_libcall(typval_T *argvars, typval_T *rettv);
 static void f_libcallnr(typval_T *argvars, typval_T *rettv);
 static void f_line(typval_T *argvars, typval_T *rettv);
@@ -7019,7 +7018,7 @@ f_last_buffer_nr(typval_T *argvars UNUSED, typval_T *rettv)
 /*
  * "len()" function
  */
-    static void
+    void
 f_len(typval_T *argvars, typval_T *rettv)
 {
     switch (argvars[0].v_type)

src/proto/evalfunc.pro

@@ -20,6 +20,7 @@ void execute_cmds_from_string(char_u *str);
 void execute_common(typval_T *argvars, typval_T *rettv, int arg_off);
 void f_exists(typval_T *argvars, typval_T *rettv);
 void f_has(typval_T *argvars, typval_T *rettv);
+void f_len(typval_T *argvars, typval_T *rettv);
 int dynamic_feature(char_u *feature);
 void mzscheme_call_vim(char_u *name, typval_T *args, typval_T *rettv);
 void range_list_materialize(list_T *list);

src/testdir/test_vim9_disassemble.vim

@@ -1015,9 +1015,20 @@ def s:HasGuiRunning()
   endif
 enddef
 
+def s:LenConstant(): number
+  return len("foo") + len("fighters")
+enddef
+
 def Test_disassemble_const_expr()
+  var instr = execute('disassemble LenConstant')
+  assert_match('LenConstant\_s*' ..
+    'return len("foo") + len("fighters")\_s*' ..
+    '\d PUSHNR 11\_s*',
+    instr)
+  assert_notmatch('BCALL len', instr)
+
   assert_equal("\nyes", execute('HasEval()'))
-  var instr = execute('disassemble HasEval')
+  instr = execute('disassemble HasEval')
   assert_match('HasEval\_s*' ..
         'if has("eval")\_s*' ..
         'echo "yes"\_s*' ..

src/version.c

@@ -750,6 +750,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    4669,
 /**/
     4668,
 /**/

src/vim9expr.c

@@ -724,13 +724,16 @@ compile_call(
     }
 
     // We can evaluate "has('name')" at compile time.
+    // We can evaluate "len('string')" at compile time.
     // We always evaluate "exists_compiled()" at compile time.
-    if ((varlen == 3 && STRNCMP(*arg, "has", 3) == 0)
+    if ((varlen == 3
+	     && (STRNCMP(*arg, "has", 3) == 0 || STRNCMP(*arg, "len", 3) == 0))
 	    || (varlen == 15 && STRNCMP(*arg, "exists_compiled", 6) == 0))
     {
 	char_u	    *s = skipwhite(*arg + varlen + 1);
 	typval_T    argvars[2];
 	int	    is_has = **arg == 'h';
+	int	    is_len = **arg == 'l';
 
 	argvars[0].v_type = VAR_UNKNOWN;
 	if (*s == '"')
@@ -750,6 +753,8 @@ compile_call(
 	    tv->vval.v_number = 0;
 	    if (is_has)
 		f_has(argvars, tv);
+	    else if (is_len)
+		f_len(argvars, tv);
 	    else
 		f_exists(argvars, tv);
 	    clear_tv(&argvars[0]);
@@ -757,7 +762,7 @@ compile_call(
 	    return OK;
 	}
 	clear_tv(&argvars[0]);
-	if (!is_has)
+	if (!is_has && !is_len)
 	{
 	    emsg(_(e_argument_of_exists_compiled_must_be_literal_string));
 	    return FAIL;