vim-patch:8.2.3689: ex_let_one() is too long (#23830)

Problem:    ex_let_one() is too long.
Solution:   Split into multiple functions.

3ccb579516

Co-authored-by: Bram Moolenaar <Bram@vim.org>

src/nvim/eval/vars.c

@@ -701,30 +701,18 @@ static const char *list_arg_vars(exarg_T *eap, const char *arg, int *first)
   return arg;
 }
 
-/// Set one item of `:let var = expr` or `:let [v1, v2] = list` to its value
+/// Set an environment variable, part of ex_let_one().
-///
+static char *ex_let_env(char *arg, typval_T *const tv, const bool is_const,
-/// @param[in]  arg  Start of the variable name.
-/// @param[in]  tv  Value to assign to the variable.
-/// @param[in]  copy  If true, copy value from `tv`.
-/// @param[in]  endchars  Valid characters after variable name or NULL.
-/// @param[in]  op  Operation performed: *op is `+`, `-`, `.` for `+=`, etc.
-///                 NULL for `=`.
-///
-/// @return a pointer to the char just after the var name or NULL in case of
-///         error.
-static char *ex_let_one(char *arg, typval_T *const tv, const bool copy, const bool is_const,
                         const char *const endchars, const char *const op)
   FUNC_ATTR_NONNULL_ARG(1, 2) FUNC_ATTR_WARN_UNUSED_RESULT
 {
-  char *arg_end = NULL;
-
-  // ":let $VAR = expr": Set environment variable.
-  if (*arg == '$') {
   if (is_const) {
     emsg(_("E996: Cannot lock an environment variable"));
     return NULL;
   }
+
   // Find the end of the name.
+  char *arg_end = NULL;
   arg++;
   char *name = arg;
   int len = get_env_len((const char **)&arg);
@@ -757,15 +745,21 @@ static char *ex_let_one(char *arg, typval_T *const tv, const bool copy, const bo
       xfree(tofree);
     }
   }
-    // ":let &option = expr": Set option value.
+  return arg_end;
-    // ":let &l:option = expr": Set local option value.
+}
-    // ":let &g:option = expr": Set global option value.
+
-  } else if (*arg == '&') {
+/// Set an option, part of ex_let_one().
+static char *ex_let_option(char *arg, typval_T *const tv, const bool is_const,
+                           const char *const endchars, const char *const op)
+  FUNC_ATTR_NONNULL_ARG(1, 2) FUNC_ATTR_WARN_UNUSED_RESULT
+{
   if (is_const) {
     emsg(_("E996: Cannot lock an option"));
     return NULL;
   }
+
   // Find the end of the name.
+  char *arg_end = NULL;
   int scope;
   char *const p = (char *)find_option_end((const char **)&arg, &scope);
   if (p == NULL
@@ -850,12 +844,20 @@ static char *ex_let_one(char *arg, typval_T *const tv, const bool copy, const bo
     xfree(stringval);
     xfree(tofree);
   }
-    // ":let @r = expr": Set register contents.
+  return arg_end;
-  } else if (*arg == '@') {
+}
+
+/// Set a register, part of ex_let_one().
+static char *ex_let_register(char *arg, typval_T *const tv, const bool is_const,
+                             const char *const endchars, const char *const op)
+  FUNC_ATTR_NONNULL_ARG(1, 2) FUNC_ATTR_WARN_UNUSED_RESULT
+{
   if (is_const) {
     emsg(_("E996: Cannot lock a register"));
     return NULL;
   }
+
+  char *arg_end = NULL;
   arg++;
   if (op != NULL && vim_strchr("+-*/%", (uint8_t)(*op)) != NULL) {
     semsg(_(e_letwrong), op);
@@ -879,11 +881,41 @@ static char *ex_let_one(char *arg, typval_T *const tv, const bool copy, const bo
     }
     xfree(ptofree);
   }
+  return arg_end;
+}
+
+/// Set one item of `:let var = expr` or `:let [v1, v2] = list` to its value
+///
+/// @param[in]  arg  Start of the variable name.
+/// @param[in]  tv  Value to assign to the variable.
+/// @param[in]  copy  If true, copy value from `tv`.
+/// @param[in]  endchars  Valid characters after variable name or NULL.
+/// @param[in]  op  Operation performed: *op is `+`, `-`, `.` for `+=`, etc.
+///                 NULL for `=`.
+///
+/// @return a pointer to the char just after the var name or NULL in case of
+///         error.
+static char *ex_let_one(char *arg, typval_T *const tv, const bool copy, const bool is_const,
+                        const char *const endchars, const char *const op)
+  FUNC_ATTR_NONNULL_ARG(1, 2) FUNC_ATTR_WARN_UNUSED_RESULT
+{
+  char *arg_end = NULL;
+
+  if (*arg == '$') {
+    // ":let $VAR = expr": Set environment variable.
+    return ex_let_env(arg, tv, is_const, endchars, op);
+  } else if (*arg == '&') {
+    // ":let &option = expr": Set option value.
+    // ":let &l:option = expr": Set local option value.
+    // ":let &g:option = expr": Set global option value.
+    return ex_let_option(arg, tv, is_const, endchars, op);
+  } else if (*arg == '@') {
+    // ":let @r = expr": Set register contents.
+    return ex_let_register(arg, tv, is_const, endchars, op);
+  } else if (eval_isnamec1(*arg) || *arg == '{') {
     // ":let var = expr": Set internal variable.
     // ":let {expr} = expr": Idem, name made with curly braces
-  } else if (eval_isnamec1(*arg) || *arg == '{') {
     lval_T lv;
-
     char *const p = get_lval(arg, tv, &lv, false, false, 0, FNE_CHECK_START);
     if (p != NULL && lv.ll_name != NULL) {
       if (endchars != NULL && vim_strchr(endchars, (uint8_t)(*skipwhite(p))) == NULL) {