10 files changed, 112 insertions, 95 deletions

diff --git a/src/nvim/api/vimscript.c b/src/nvim/api/vimscript.c
index 2438a5cf1d..1740429ef6 100644
--- a/src/nvim/api/vimscript.c
+++ b/src/nvim/api/vimscript.c
@@ -172,7 +172,7 @@ Object nvim_eval(String expr, Error *err)
   int ok;
 
   TRY_WRAP(err, {
-    ok = eval0(expr.data, &rettv, NULL, true);
+    ok = eval0(expr.data, &rettv, NULL, EVAL_EVALUATE);
   });
 
   if (!ERROR_SET(err)) {
@@ -290,7 +290,7 @@ Object nvim_call_dict_function(Object dict, String fn, Array args, Error *err)
   switch (dict.type) {
   case kObjectTypeString:
     try_start();
-    if (eval0(dict.data.string.data, &rettv, NULL, true) == FAIL) {
+    if (eval0(dict.data.string.data, &rettv, NULL, EVAL_EVALUATE) == FAIL) {
       api_set_error(err, kErrorTypeException,
                     "Failed to evaluate dict expression");
     }
diff --git a/src/nvim/eval.c b/src/nvim/eval.c
index ff33fdeccb..796c010f74 100644
--- a/src/nvim/eval.c
+++ b/src/nvim/eval.c
@@ -706,7 +706,7 @@ int eval_to_bool(char *arg, bool *error, char **nextcmd, int skip)
   if (skip) {
     emsg_skip++;
   }
-  if (eval0(arg, &tv, nextcmd, !skip) == FAIL) {
+  if (eval0(arg, &tv, nextcmd, skip ? 0 : EVAL_EVALUATE) == FAIL) {
     *error = true;
   } else {
     *error = false;
@@ -730,7 +730,7 @@ static int eval1_emsg(char **arg, typval_T *rettv, bool evaluate)
   const int did_emsg_before = did_emsg;
   const int called_emsg_before = called_emsg;
 
-  const int ret = eval1(arg, rettv, evaluate);
+  const int ret = eval1(arg, rettv, evaluate ? EVAL_EVALUATE : 0);
   if (ret == FAIL) {
     // Report the invalid expression unless the expression evaluation has
     // been cancelled due to an aborting error, an interrupt, or an
@@ -832,7 +832,7 @@ char *eval_to_string_skip(const char *arg, const char **nextcmd, const bool skip
   if (skip) {
     emsg_skip++;
   }
-  if (eval0((char *)arg, &tv, (char **)nextcmd, !skip) == FAIL || skip) {
+  if (eval0((char *)arg, &tv, (char **)nextcmd, skip ? 0 : EVAL_EVALUATE) == FAIL || skip) {
     retval = NULL;
   } else {
     retval = xstrdup(tv_get_string(&tv));
@@ -853,7 +853,7 @@ int skip_expr(char **pp)
   typval_T rettv;
 
   *pp = skipwhite(*pp);
-  return eval1(pp, &rettv, false);
+  return eval1(pp, &rettv, 0);
 }
 
 /// Top level evaluation function, returning a string.
@@ -868,7 +868,7 @@ char *eval_to_string(char *arg, char **nextcmd, bool convert)
   char *retval;
   garray_T ga;
 
-  if (eval0(arg, &tv, nextcmd, true) == FAIL) {
+  if (eval0(arg, &tv, nextcmd, EVAL_EVALUATE) == FAIL) {
     retval = NULL;
   } else {
     if (convert && tv.v_type == VAR_LIST) {
@@ -929,7 +929,7 @@ varnumber_T eval_to_number(char *expr)
 
   emsg_off++;
 
-  if (eval1(&p, &rettv, true) == FAIL) {
+  if (eval1(&p, &rettv, EVAL_EVALUATE) == FAIL) {
     retval = -1;
   } else {
     retval = tv_get_number_chk(&rettv, NULL);
@@ -947,7 +947,7 @@ varnumber_T eval_to_number(char *expr)
 typval_T *eval_expr(char *arg)
 {
   typval_T *tv = xmalloc(sizeof(*tv));
-  if (eval0(arg, tv, NULL, true) == FAIL) {
+  if (eval0(arg, tv, NULL, EVAL_EVALUATE) == FAIL) {
     XFREE_CLEAR(tv);
   }
   return tv;
@@ -1024,7 +1024,7 @@ list_T *eval_spell_expr(char *badword, char *expr)
     emsg_off++;
   }
 
-  if (eval1(&p, &rettv, true) == OK) {
+  if (eval1(&p, &rettv, EVAL_EVALUATE) == OK) {
     if (rettv.v_type != VAR_LIST) {
       tv_clear(&rettv);
     } else {
@@ -1171,7 +1171,7 @@ int eval_foldexpr(char *arg, int *cp)
   }
   textlock++;
   *cp = NUL;
-  if (eval0(arg, &tv, NULL, true) == FAIL) {
+  if (eval0(arg, &tv, NULL, EVAL_EVALUATE) == FAIL) {
     retval = 0;
   } else {
     // If the result is a number, just return the number.
@@ -1346,7 +1346,7 @@ char *get_lval(char *const name, typval_T *const rettv, lval_T *const lp, const
         empty1 = true;
       } else {
         empty1 = false;
-        if (eval1(&p, &var1, true) == FAIL) {  // Recursive!
+        if (eval1(&p, &var1, EVAL_EVALUATE) == FAIL) {  // Recursive!
           return NULL;
         }
         if (!tv_check_str(&var1)) {
@@ -1380,7 +1380,8 @@ char *get_lval(char *const name, typval_T *const rettv, lval_T *const lp, const
           lp->ll_empty2 = true;
         } else {
           lp->ll_empty2 = false;
-          if (eval1(&p, &var2, true) == FAIL) {  // Recursive!
+          // Recursive!
+          if (eval1(&p, &var2, EVAL_EVALUATE) == FAIL) {
             tv_clear(&var1);
             return NULL;
           }
@@ -1799,7 +1800,7 @@ void *eval_for_line(const char *arg, bool *errp, char **nextcmdp, int skip)
   if (skip) {
     emsg_skip++;
   }
-  if (eval0(skipwhite(expr + 2), &tv, nextcmdp, !skip) == OK) {
+  if (eval0(skipwhite(expr + 2), &tv, nextcmdp, skip ? 0 : EVAL_EVALUATE) == OK) {
     *errp = false;
     if (!skip) {
       if (tv.v_type == VAR_LIST) {
@@ -2164,9 +2165,10 @@ int pattern_match(const char *pat, const char *text, bool ic)
 ///
 /// @return OK or FAIL.
 static int eval_func(char **const arg, char *const name, const int name_len, typval_T *const rettv,
-                     const bool evaluate, typval_T *const basetv)
+                     const int flags, typval_T *const basetv)
   FUNC_ATTR_NONNULL_ARG(1, 2, 4)
 {
+  const bool evaluate = flags & EVAL_EVALUATE;
   char *s = name;
   int len = name_len;
 
@@ -2223,8 +2225,10 @@ static int eval_func(char **const arg, char *const name, const int name_len, typ
 /// Put the result in "rettv" when returning OK and "evaluate" is true.
 /// Note: "rettv.v_lock" is not set.
 ///
+/// @param flags  has EVAL_EVALUATE and similar flags.
+///
 /// @return OK or FAIL.
-int eval0(char *arg, typval_T *rettv, char **nextcmd, int evaluate)
+int eval0(char *arg, typval_T *rettv, char **nextcmd, const int flags)
 {
   int ret;
   char *p;
@@ -2233,7 +2237,7 @@ int eval0(char *arg, typval_T *rettv, char **nextcmd, int evaluate)
   bool end_error = false;
 
   p = skipwhite(arg);
-  ret = eval1(&p, rettv, evaluate);
+  ret = eval1(&p, rettv, flags);
 
   if (ret != FAIL) {
     end_error = !ends_excmd(*p);
@@ -2246,7 +2250,8 @@ int eval0(char *arg, typval_T *rettv, char **nextcmd, int evaluate)
     // been cancelled due to an aborting error, an interrupt, or an
     // exception, or we already gave a more specific error.
     // Also check called_emsg for when using assert_fails().
-    if (!aborting() && did_emsg == did_emsg_before
+    if (!aborting()
+        && did_emsg == did_emsg_before
         && called_emsg == called_emsg_before) {
       if (end_error) {
         semsg(_(e_trailing_arg), p);
@@ -2272,18 +2277,20 @@ int eval0(char *arg, typval_T *rettv, char **nextcmd, int evaluate)
 /// Note: "rettv.v_lock" is not set.
 ///
 /// @return  OK or FAIL.
-int eval1(char **arg, typval_T *rettv, int evaluate)
+int eval1(char **arg, typval_T *rettv, const int flags)
 {
   typval_T var2;
 
   // Get the first variable.
-  if (eval2(arg, rettv, evaluate) == FAIL) {
+  if (eval2(arg, rettv, flags) == FAIL) {
     return FAIL;
   }
 
   if ((*arg)[0] == '?') {
+    const bool evaluate = flags & EVAL_EVALUATE;
+
     bool result = false;
-    if (evaluate) {
+    if (flags & EVAL_EVALUATE) {
       bool error = false;
 
       if (tv_get_number_chk(rettv, &error) != 0) {
@@ -2295,9 +2302,9 @@ int eval1(char **arg, typval_T *rettv, int evaluate)
       }
     }
 
-    // Get the second variable.
+    // Get the second variable.  Recursive!
     *arg = skipwhite(*arg + 1);
-    if (eval1(arg, rettv, evaluate && result) == FAIL) {  // recursive!
+    if (eval1(arg, rettv, result ? flags : flags & ~EVAL_EVALUATE) == FAIL) {
       return FAIL;
     }
 
@@ -2310,9 +2317,9 @@ int eval1(char **arg, typval_T *rettv, int evaluate)
       return FAIL;
     }
 
-    // Get the third variable.
+    // Get the third variable.  Recursive!
     *arg = skipwhite(*arg + 1);
-    if (eval1(arg, &var2, evaluate && !result) == FAIL) {  // Recursive!
+    if (eval1(arg, &var2, !result ? flags : flags & ~EVAL_EVALUATE) == FAIL) {
       if (evaluate && result) {
         tv_clear(rettv);
       }
@@ -2333,13 +2340,13 @@ int eval1(char **arg, typval_T *rettv, int evaluate)
 /// "arg" is advanced to the next non-white after the recognized expression.
 ///
 /// @return  OK or FAIL.
-static int eval2(char **arg, typval_T *rettv, int evaluate)
+static int eval2(char **arg, typval_T *rettv, const int flags)
 {
   typval_T var2;
   bool error = false;
 
   // Get the first variable.
-  if (eval3(arg, rettv, evaluate) == FAIL) {
+  if (eval3(arg, rettv, flags) == FAIL) {
     return FAIL;
   }
 
@@ -2347,6 +2354,8 @@ static int eval2(char **arg, typval_T *rettv, int evaluate)
   bool first = true;
   bool result = false;
   while ((*arg)[0] == '|' && (*arg)[1] == '|') {
+    const bool evaluate = flags & EVAL_EVALUATE;
+
     if (evaluate && first) {
       if (tv_get_number_chk(rettv, &error) != 0) {
         result = true;
@@ -2360,7 +2369,7 @@ static int eval2(char **arg, typval_T *rettv, int evaluate)
 
     // Get the second variable.
     *arg = skipwhite(*arg + 2);
-    if (eval3(arg, &var2, evaluate && !result) == FAIL) {
+    if (eval3(arg, &var2, !result ? flags : flags & ~EVAL_EVALUATE) == FAIL) {
       return FAIL;
     }
 
@@ -2390,13 +2399,13 @@ static int eval2(char **arg, typval_T *rettv, int evaluate)
 ///             `arg` is advanced to the next non-white after the recognized expression.
 ///
 /// @return  OK or FAIL.
-static int eval3(char **arg, typval_T *rettv, int evaluate)
+static int eval3(char **arg, typval_T *rettv, const int flags)
 {
   typval_T var2;
   bool error = false;
 
   // Get the first variable.
-  if (eval4(arg, rettv, evaluate) == FAIL) {
+  if (eval4(arg, rettv, flags) == FAIL) {
     return FAIL;
   }
 
@@ -2404,6 +2413,8 @@ static int eval3(char **arg, typval_T *rettv, int evaluate)
   bool first = true;
   bool result = true;
   while ((*arg)[0] == '&' && (*arg)[1] == '&') {
+    const bool evaluate = flags & EVAL_EVALUATE;
+
     if (evaluate && first) {
       if (tv_get_number_chk(rettv, &error) == 0) {
         result = false;
@@ -2417,7 +2428,7 @@ static int eval3(char **arg, typval_T *rettv, int evaluate)
 
     // Get the second variable.
     *arg = skipwhite(*arg + 2);
-    if (eval4(arg, &var2, evaluate && result) == FAIL) {
+    if (eval4(arg, &var2, result ? flags : flags & ~EVAL_EVALUATE) == FAIL) {
       return FAIL;
     }
 
@@ -2456,7 +2467,7 @@ static int eval3(char **arg, typval_T *rettv, int evaluate)
 /// "arg" is advanced to the next non-white after the recognized expression.
 ///
 /// @return  OK or FAIL.
-static int eval4(char **arg, typval_T *rettv, int evaluate)
+static int eval4(char **arg, typval_T *rettv, const int flags)
 {
   typval_T var2;
   char *p;
@@ -2464,7 +2475,7 @@ static int eval4(char **arg, typval_T *rettv, int evaluate)
   int len = 2;
 
   // Get the first variable.
-  if (eval5(arg, rettv, evaluate) == FAIL) {
+  if (eval5(arg, rettv, flags) == FAIL) {
     return FAIL;
   }
 
@@ -2528,11 +2539,11 @@ static int eval4(char **arg, typval_T *rettv, int evaluate)
 
     // Get the second variable.
     *arg = skipwhite(p + len);
-    if (eval5(arg, &var2, evaluate) == FAIL) {
+    if (eval5(arg, &var2, flags) == FAIL) {
       tv_clear(rettv);
       return FAIL;
     }
-    if (evaluate) {
+    if (flags & EVAL_EVALUATE) {
       const int ret = typval_compare(rettv, &var2, type, ic);
 
       tv_clear(&var2);
@@ -2586,7 +2597,7 @@ static int eval_addlist(typval_T *tv1, typval_T *tv2)
 ///             `arg` is advanced to the next non-white after the recognized expression.
 ///
 /// @return  OK or FAIL.
-static int eval5(char **arg, typval_T *rettv, int evaluate)
+static int eval5(char **arg, typval_T *rettv, const int flags)
 {
   typval_T var2;
   varnumber_T n1, n2;
@@ -2594,7 +2605,7 @@ static int eval5(char **arg, typval_T *rettv, int evaluate)
   char *p;
 
   // Get the first variable.
-  if (eval6(arg, rettv, evaluate, false) == FAIL) {
+  if (eval6(arg, rettv, flags, false) == FAIL) {
     return FAIL;
   }
 
@@ -2606,7 +2617,7 @@ static int eval5(char **arg, typval_T *rettv, int evaluate)
     }
 
     if ((op != '+' || (rettv->v_type != VAR_LIST && rettv->v_type != VAR_BLOB))
-        && (op == '.' || rettv->v_type != VAR_FLOAT) && evaluate) {
+        && (op == '.' || rettv->v_type != VAR_FLOAT) && (flags & EVAL_EVALUATE)) {
       // For "list + ...", an illegal use of the first operand as
       // a number cannot be determined before evaluating the 2nd
       // operand: if this is also a list, all is ok.
@@ -2625,12 +2636,12 @@ static int eval5(char **arg, typval_T *rettv, int evaluate)
       (*arg)++;
     }
     *arg = skipwhite(*arg + 1);
-    if (eval6(arg, &var2, evaluate, op == '.') == FAIL) {
+    if (eval6(arg, &var2, flags, op == '.') == FAIL) {
       tv_clear(rettv);
       return FAIL;
     }
 
-    if (evaluate) {
+    if (flags & EVAL_EVALUATE) {
       // Compute the result.
       if (op == '.') {
         char buf1[NUMBUFLEN];
@@ -2724,11 +2735,10 @@ static int eval5(char **arg, typval_T *rettv, int evaluate)
 ///                      expression.  Is advanced to the next non-whitespace
 ///                      character after the recognized expression.
 /// @param[out]  rettv  Location where result is saved.
-/// @param[in]  evaluate  If not true, rettv is not populated.
 /// @param[in]  want_string  True if "." is string_concatenation, otherwise
 ///                          float
 /// @return  OK or FAIL.
-static int eval6(char **arg, typval_T *rettv, int evaluate, int want_string)
+static int eval6(char **arg, typval_T *rettv, const int flags, bool want_string)
   FUNC_ATTR_NO_SANITIZE_UNDEFINED
 {
   typval_T var2;
@@ -2739,7 +2749,7 @@ static int eval6(char **arg, typval_T *rettv, int evaluate, int want_string)
   bool error = false;
 
   // Get the first variable.
-  if (eval7(arg, rettv, evaluate, want_string) == FAIL) {
+  if (eval7(arg, rettv, flags, want_string) == FAIL) {
     return FAIL;
   }
 
@@ -2750,7 +2760,7 @@ static int eval6(char **arg, typval_T *rettv, int evaluate, int want_string)
       break;
     }
 
-    if (evaluate) {
+    if (flags & EVAL_EVALUATE) {
       if (rettv->v_type == VAR_FLOAT) {
         f1 = rettv->vval.v_float;
         use_float = true;
@@ -2768,11 +2778,11 @@ static int eval6(char **arg, typval_T *rettv, int evaluate, int want_string)
 
     // Get the second variable.
     *arg = skipwhite(*arg + 1);
-    if (eval7(arg, &var2, evaluate, false) == FAIL) {
+    if (eval7(arg, &var2, flags, false) == FAIL) {
       return FAIL;
     }
 
-    if (evaluate) {
+    if (flags & EVAL_EVALUATE) {
       if (var2.v_type == VAR_FLOAT) {
         if (!use_float) {
           f1 = (float_T)n1;
@@ -2859,8 +2869,9 @@ static int eval6(char **arg, typval_T *rettv, int evaluate, int want_string)
 /// @param want_string  after "." operator
 ///
 /// @return  OK or FAIL.
-static int eval7(char **arg, typval_T *rettv, int evaluate, int want_string)
+static int eval7(char **arg, typval_T *rettv, const int flags, bool want_string)
 {
+  const bool evaluate = flags & EVAL_EVALUATE;
   int ret = OK;
   static int recurse = 0;
 
@@ -2922,14 +2933,14 @@ static int eval7(char **arg, typval_T *rettv, int evaluate, int want_string)
 
   // List: [expr, expr]
   case '[':
-    ret = get_list_tv(arg, rettv, evaluate);
+    ret = get_list_tv(arg, rettv, flags);
     break;
 
   // Dictionary: #{key: val, key: val}
   case '#':
     if ((*arg)[1] == '{') {
       (*arg)++;
-      ret = eval_dict(arg, rettv, evaluate, true);
+      ret = eval_dict(arg, rettv, flags, true);
     } else {
       ret = NOTDONE;
     }
@@ -2940,7 +2951,7 @@ static int eval7(char **arg, typval_T *rettv, int evaluate, int want_string)
   case '{':
     ret = get_lambda_tv(arg, rettv, evaluate);
     if (ret == NOTDONE) {
-      ret = eval_dict(arg, rettv, evaluate, false);
+      ret = eval_dict(arg, rettv, flags, false);
     }
     break;
 
@@ -2968,7 +2979,7 @@ static int eval7(char **arg, typval_T *rettv, int evaluate, int want_string)
   // nested expression: (expression).
   case '(':
     *arg = skipwhite(*arg + 1);
-    ret = eval1(arg, rettv, evaluate);                  // recursive!
+    ret = eval1(arg, rettv, flags);  // recursive!
     if (**arg == ')') {
       (*arg)++;
     } else if (ret == OK) {
@@ -2997,7 +3008,7 @@ static int eval7(char **arg, typval_T *rettv, int evaluate, int want_string)
       ret = FAIL;
     } else {
       if (**arg == '(') {               // recursive!
-        ret = eval_func(arg, s, len, rettv, evaluate, NULL);
+        ret = eval_func(arg, s, len, rettv, flags, NULL);
       } else if (evaluate) {
         ret = get_var_tv(s, len, rettv, NULL, true, false);
       } else {
@@ -3013,7 +3024,7 @@ static int eval7(char **arg, typval_T *rettv, int evaluate, int want_string)
   // Handle following '[', '(' and '.' for expr[expr], expr.name,
   // expr(expr), expr->name(expr)
   if (ret == OK) {
-    ret = handle_subscript((const char **)arg, rettv, evaluate, true);
+    ret = handle_subscript((const char **)arg, rettv, flags, true);
   }
 
   // Apply logical NOT and unary '-', from right to left, ignore '+'.
@@ -3238,7 +3249,7 @@ static int eval_method(char **const arg, typval_T *const rettv, const bool evalu
       }
       ret = call_func_rettv(arg, rettv, evaluate, NULL, &base, lua_funcname);
     } else {
-      ret = eval_func(arg, name, len, rettv, evaluate, &base);
+      ret = eval_func(arg, name, len, rettv, evaluate ? EVAL_EVALUATE : 0, &base);
     }
   }
 
@@ -3257,8 +3268,9 @@ static int eval_method(char **const arg, typval_T *const rettv, const bool evalu
 /// @param verbose  give error messages
 ///
 /// @returns FAIL or OK. "*arg" is advanced to after the ']'.
-static int eval_index(char **arg, typval_T *rettv, int evaluate, int verbose)
+static int eval_index(char **arg, typval_T *rettv, const int flags, bool verbose)
 {
+  const bool evaluate = flags & EVAL_EVALUATE;
   bool empty1 = false;
   bool empty2 = false;
   ptrdiff_t len = -1;
@@ -3313,7 +3325,7 @@ static int eval_index(char **arg, typval_T *rettv, int evaluate, int verbose)
     *arg = skipwhite(*arg + 1);
     if (**arg == ':') {
       empty1 = true;
-    } else if (eval1(arg, &var1, evaluate) == FAIL) {  // Recursive!
+    } else if (eval1(arg, &var1, flags) == FAIL) {  // Recursive!
       return FAIL;
     } else if (evaluate && !tv_check_str(&var1)) {
       // Not a number or string.
@@ -3327,7 +3339,7 @@ static int eval_index(char **arg, typval_T *rettv, int evaluate, int verbose)
       *arg = skipwhite(*arg + 1);
       if (**arg == ']') {
         empty2 = true;
-      } else if (eval1(arg, &var2, evaluate) == FAIL) {  // Recursive!
+      } else if (eval1(arg, &var2, flags) == FAIL) {  // Recursive!
         if (!empty1) {
           tv_clear(&var1);
         }
@@ -3930,8 +3942,9 @@ void partial_unref(partial_T *pt)
 /// Allocate a variable for a List and fill it from "*arg".
 ///
 /// @return  OK or FAIL.
-static int get_list_tv(char **arg, typval_T *rettv, int evaluate)
+static int get_list_tv(char **arg, typval_T *rettv, const int flags)
 {
+  const bool evaluate = flags & EVAL_EVALUATE;
   list_T *l = NULL;
 
   if (evaluate) {
@@ -3941,7 +3954,7 @@ static int get_list_tv(char **arg, typval_T *rettv, int evaluate)
   *arg = skipwhite(*arg + 1);
   while (**arg != ']' && **arg != NUL) {
     typval_T tv;
-    if (eval1(arg, &tv, evaluate) == FAIL) {  // Recursive!
+    if (eval1(arg, &tv, flags) == FAIL) {  // Recursive!
       goto failret;
     }
     if (evaluate) {
@@ -4576,8 +4589,9 @@ static int get_literal_key(char **arg, typval_T *tv)
 /// "literal" is true for #{key: val}
 ///
 /// @return  OK or FAIL.  Returns NOTDONE for {expr}.
-static int eval_dict(char **arg, typval_T *rettv, int evaluate, bool literal)
+static int eval_dict(char **arg, typval_T *rettv, const int flags, bool literal)
 {
+  const bool evaluate = flags & EVAL_EVALUATE;
   typval_T tv;
   char *key = NULL;
   char *curly_expr = skipwhite(*arg + 1);
@@ -4591,7 +4605,7 @@ static int eval_dict(char **arg, typval_T *rettv, int evaluate, bool literal)
   // "#{abc}" is never a curly-braces expression.
   if (*curly_expr != '}'
       && !literal
-      && eval1(&curly_expr, &tv, false) == OK
+      && eval1(&curly_expr, &tv, 0) == OK
       && *skipwhite(curly_expr) == '}') {
     return NOTDONE;
   }
@@ -4608,7 +4622,7 @@ static int eval_dict(char **arg, typval_T *rettv, int evaluate, bool literal)
   while (**arg != '}' && **arg != NUL) {
     if ((literal
          ? get_literal_key(arg, &tvkey)
-         : eval1(arg, &tvkey, evaluate)) == FAIL) {  // recursive!
+         : eval1(arg, &tvkey, flags)) == FAIL) {  // recursive!
       goto failret;
     }
     if (**arg != ':') {
@@ -4626,7 +4640,7 @@ static int eval_dict(char **arg, typval_T *rettv, int evaluate, bool literal)
     }
 
     *arg = skipwhite(*arg + 1);
-    if (eval1(arg, &tv, evaluate) == FAIL) {  // Recursive!
+    if (eval1(arg, &tv, flags) == FAIL) {  // Recursive!
       if (evaluate) {
         tv_clear(&tvkey);
       }
@@ -6937,12 +6951,12 @@ int check_luafunc_name(const char *const str, const bool paren)
 ///
 /// Can all be combined in any order: dict.func(expr)[idx]['func'](expr)->len()
 ///
-/// @param evaluate  do more than finding the end
 /// @param verbose  give error messages
 /// @param start_leader  start of '!' and '-' prefixes
 /// @param end_leaderp  end of '!' and '-' prefixes
-int handle_subscript(const char **const arg, typval_T *rettv, int evaluate, int verbose)
+int handle_subscript(const char **const arg, typval_T *rettv, const int flags, bool verbose)
 {
+  const bool evaluate = flags & EVAL_EVALUATE;
   int ret = OK;
   dict_T *selfdict = NULL;
   const char *lua_funcname = NULL;
@@ -7002,7 +7016,7 @@ int handle_subscript(const char **const arg, typval_T *rettv, int evaluate, int
       } else {
         selfdict = NULL;
       }
-      if (eval_index((char **)arg, rettv, evaluate, verbose) == FAIL) {
+      if (eval_index((char **)arg, rettv, flags, verbose) == FAIL) {
         tv_clear(rettv);
         ret = FAIL;
       }
@@ -7385,7 +7399,7 @@ void ex_echo(exarg_T *eap)
 
     {
       char *p = arg;
-      if (eval1(&arg, &rettv, !eap->skip) == FAIL) {
+      if (eval1(&arg, &rettv, eap->skip ? 0 : EVAL_EVALUATE) == FAIL) {
         // Report the invalid expression unless the expression evaluation
         // has been cancelled due to an aborting error, an interrupt, or an
         // exception.
diff --git a/src/nvim/eval.h b/src/nvim/eval.h
index aa034cb2b3..973a4a1fc3 100644
--- a/src/nvim/eval.h
+++ b/src/nvim/eval.h
@@ -266,6 +266,11 @@ typedef int (*ex_unletlock_callback)(lval_T *, char *, exarg_T *, int);
 // Used for checking if local variables or arguments used in a lambda.
 extern bool *eval_lavars_used;
 
+/// Flag for expression evaluation.
+enum {
+  EVAL_EVALUATE = 1,  ///< when missing don't actually evaluate
+};
+
 #ifdef INCLUDE_GENERATED_DECLARATIONS
 # include "eval.h.generated.h"
 #endif
diff --git a/src/nvim/eval/funcs.c b/src/nvim/eval/funcs.c
index 7f224f371c..52e38b73ba 100644
--- a/src/nvim/eval/funcs.c
+++ b/src/nvim/eval/funcs.c
@@ -1550,7 +1550,7 @@ static void f_eval(typval_T *argvars, typval_T *rettv, EvalFuncData fptr)
   }
 
   const char *const expr_start = s;
-  if (s == NULL || eval1((char **)&s, rettv, true) == FAIL) {
+  if (s == NULL || eval1((char **)&s, rettv, EVAL_EVALUATE) == FAIL) {
     if (expr_start != NULL && !aborting()) {
       semsg(_(e_invexpr2), expr_start);
     }
diff --git a/src/nvim/eval/userfunc.c b/src/nvim/eval/userfunc.c
index f09da6b79b..f82ab08d2d 100644
--- a/src/nvim/eval/userfunc.c
+++ b/src/nvim/eval/userfunc.c
@@ -152,7 +152,7 @@ static int get_function_args(char **argp, char endchar, garray_T *newargs, int *
         p = skipwhite(p) + 1;
         p = skipwhite(p);
         char *expr = p;
-        if (eval1(&p, &rettv, false) != FAIL) {
+        if (eval1(&p, &rettv, 0) != FAIL) {
           ga_grow(default_args, 1);
 
           // trim trailing whitespace
@@ -463,7 +463,8 @@ int get_func_tv(const char *name, int len, typval_T *rettv, char **arg, funcexe_
     if (*argp == ')' || *argp == ',' || *argp == NUL) {
       break;
     }
-    if (eval1(&argp, &argvars[argcount], funcexe->fe_evaluate) == FAIL) {
+    if (eval1(&argp, &argvars[argcount],
+              funcexe->fe_evaluate ? EVAL_EVALUATE : 0) == FAIL) {
       ret = FAIL;
       break;
     }
@@ -972,7 +973,7 @@ void call_user_func(ufunc_T *fp, int argcount, typval_T *argvars, typval_T *rett
 
         default_expr = ((char **)(fp->uf_def_args.ga_data))
                        [ai + fp->uf_def_args.ga_len];
-        if (eval1(&default_expr, &def_rettv, true) == FAIL) {
+        if (eval1(&default_expr, &def_rettv, EVAL_EVALUATE) == FAIL) {
           default_arg_err = true;
           break;
         }
@@ -1109,7 +1110,7 @@ void call_user_func(ufunc_T *fp, int argcount, typval_T *argvars, typval_T *rett
     // A Lambda always has the command "return {expr}".  It is much faster
     // to evaluate {expr} directly.
     ex_nesting_level++;
-    (void)eval1(&p, rettv, true);
+    (void)eval1(&p, rettv, EVAL_EVALUATE);
     ex_nesting_level--;
   } else {
     // call do_cmdline() to execute the lines
@@ -2953,7 +2954,7 @@ void ex_return(exarg_T *eap)
 
   eap->nextcmd = NULL;
   if ((*arg != NUL && *arg != '|' && *arg != '\n')
-      && eval0(arg, &rettv, &eap->nextcmd, !eap->skip) != FAIL) {
+      && eval0(arg, &rettv, &eap->nextcmd, eap->skip ? 0 : EVAL_EVALUATE) != FAIL) {
     if (!eap->skip) {
       returning = do_return(eap, false, true, &rettv);
     } else {
@@ -3004,7 +3005,7 @@ void ex_call(exarg_T *eap)
     // instead to skip to any following command, e.g. for:
     //   :if 0 | call dict.foo().bar() | endif.
     emsg_skip++;
-    if (eval0(eap->arg, &rettv, &eap->nextcmd, false) != FAIL) {
+    if (eval0(eap->arg, &rettv, &eap->nextcmd, 0) != FAIL) {
       tv_clear(&rettv);
     }
     emsg_skip--;
@@ -3071,7 +3072,7 @@ void ex_call(exarg_T *eap)
     }
 
     // Handle a function returning a Funcref, Dictionary or List.
-    if (handle_subscript((const char **)&arg, &rettv, true, true)
+    if (handle_subscript((const char **)&arg, &rettv, EVAL_EVALUATE, true)
         == FAIL) {
       failed = true;
       break;
diff --git a/src/nvim/eval/vars.c b/src/nvim/eval/vars.c
index 9120cc4471..a3dc0cfc04 100644
--- a/src/nvim/eval/vars.c
+++ b/src/nvim/eval/vars.c
@@ -175,21 +175,13 @@ static list_T *heredoc_get(exarg_T *eap, char *cmd)
 /// ":let var ..= expr" assignment command.
 /// ":let [var1, var2] = expr" unpack list.
 /// ":let [name, ..., ; lastname] = expr" unpack list.
-void ex_let(exarg_T *eap)
-{
-  ex_let_const(eap, false);
-}
-
+///
 /// ":cons[t] var = expr1" define constant
 /// ":cons[t] [name1, name2, ...] = expr1" define constants unpacking list
 /// ":cons[t] [name, ..., ; lastname] = expr" define constants unpacking list
-void ex_const(exarg_T *eap)
-{
-  ex_let_const(eap, true);
-}
-
-static void ex_let_const(exarg_T *eap, const bool is_const)
+void ex_let(exarg_T *eap)
 {
+  const bool is_const = eap->cmdidx == CMD_const;
   char *arg = eap->arg;
   char *expr = NULL;
   typval_T rettv;
@@ -208,8 +200,10 @@ static void ex_let_const(exarg_T *eap, const bool is_const)
     argend--;
   }
   expr = skipwhite(argend);
-  if (*expr != '=' && !((vim_strchr("+-*/%.", (uint8_t)(*expr)) != NULL
-                         && expr[1] == '=') || strncmp(expr, "..=", 3) == 0)) {
+  bool concat = strncmp(expr, "..=", 3) == 0;
+  bool has_assign = *expr == '=' || (vim_strchr("+-*/%.", (uint8_t)(*expr)) != NULL
+                                     && expr[1] == '=');
+  if (!has_assign && !concat) {
     // ":let" without "=": list variables
     if (*arg == '[') {
       emsg(_(e_invarg));
@@ -240,6 +234,8 @@ static void ex_let_const(exarg_T *eap, const bool is_const)
       tv_clear(&rettv);
     }
   } else {
+    rettv.v_type = VAR_UNKNOWN;
+
     op[0] = '=';
     op[1] = NUL;
     if (*expr != '=') {
@@ -259,7 +255,8 @@ static void ex_let_const(exarg_T *eap, const bool is_const)
     if (eap->skip) {
       emsg_skip++;
     }
-    i = eval0(expr, &rettv, &eap->nextcmd, !eap->skip);
+    int eval_flags = eap->skip ? 0 : EVAL_EVALUATE;
+    i = eval0(expr, &rettv, &eap->nextcmd, eval_flags);
     if (eap->skip) {
       if (i != FAIL) {
         tv_clear(&rettv);
@@ -506,7 +503,7 @@ static const char *list_arg_vars(exarg_T *eap, const char *arg, int *first)
         } else {
           // handle d.key, l[idx], f(expr)
           const char *const arg_subsc = arg;
-          if (handle_subscript(&arg, &tv, true, true) == FAIL) {
+          if (handle_subscript(&arg, &tv, EVAL_EVALUATE, true) == FAIL) {
             error = true;
           } else {
             if (arg == arg_subsc && len == 2 && name[1] == ':') {
@@ -1713,7 +1710,7 @@ bool var_exists(const char *var)
     n = get_var_tv(name, len, &tv, NULL, false, true) == OK;
     if (n) {
       // Handle d.key, l[idx], f(expr).
-      n = handle_subscript(&var, &tv, true, false) == OK;
+      n = handle_subscript(&var, &tv, EVAL_EVALUATE, false) == OK;
       if (n) {
         tv_clear(&tv);
       }
diff --git a/src/nvim/ex_cmds.lua b/src/nvim/ex_cmds.lua
index bdc1174de3..be6299db0e 100644
--- a/src/nvim/ex_cmds.lua
+++ b/src/nvim/ex_cmds.lua
@@ -634,7 +634,7 @@ module.cmds = {
     command='const',
     flags=bit.bor(EXTRA, NOTRLCOM, SBOXOK, CMDWIN, LOCK_OK),
     addr_type='ADDR_NONE',
-    func='ex_const',
+    func='ex_let',
   },
   {
     command='copen',
diff --git a/src/nvim/ex_eval.c b/src/nvim/ex_eval.c
index fed8f549e6..6772b78c33 100644
--- a/src/nvim/ex_eval.c
+++ b/src/nvim/ex_eval.c
@@ -793,7 +793,7 @@ void ex_eval(exarg_T *eap)
 {
   typval_T tv;
 
-  if (eval0(eap->arg, &tv, &eap->nextcmd, !eap->skip) == OK) {
+  if (eval0(eap->arg, &tv, &eap->nextcmd, eap->skip ? 0 : EVAL_EVALUATE) == OK) {
     tv_clear(&tv);
   }
 }
diff --git a/src/nvim/quickfix.c b/src/nvim/quickfix.c
index 262d87ba61..cfaa3b5781 100644
--- a/src/nvim/quickfix.c
+++ b/src/nvim/quickfix.c
@@ -6958,7 +6958,7 @@ void ex_cexpr(exarg_T *eap)
   // Evaluate the expression.  When the result is a string or a list we can
   // use it to fill the errorlist.
   typval_T tv;
-  if (eval0(eap->arg, &tv, &eap->nextcmd, true) == FAIL) {
+  if (eval0(eap->arg, &tv, &eap->nextcmd, EVAL_EVALUATE) == FAIL) {
     return;
   }
 
diff --git a/test/unit/eval/helpers.lua b/test/unit/eval/helpers.lua
index 9dd6b76de2..0694fceaec 100644
--- a/test/unit/eval/helpers.lua
+++ b/test/unit/eval/helpers.lua
@@ -512,7 +512,7 @@ end
 local function eval0(expr)
   local tv = ffi.gc(ffi.new('typval_T', {v_type=eval.VAR_UNKNOWN}),
                     eval.tv_clear)
-  if eval.eval0(to_cstr(expr), tv, nil, true) == 0 then
+  if eval.eval0(to_cstr(expr), tv, nil, eval.EVAL_EVALUATE) == 0 then
     return nil
   else
     return tv