Allow creation of constants from extensions.

1 files changed, 40 insertions, 2 deletions

diff --git a/gawkapi.c b/gawkapi.c
index b6d83acb..e8d50e8c 100644
--- a/gawkapi.c
+++ b/gawkapi.c
@@ -26,6 +26,7 @@
 #include "awk.h"
 
 static awk_bool_t node_to_awk_value(NODE *node, awk_value_t *result, awk_valtype_t wanted);
+static void set_constant();
 
 /*
  * Get the count'th paramater, zero-based.
@@ -460,10 +461,13 @@ api_sym_lookup_scalar(awk_ext_id_t id,
 	return node_to_awk_value(node, result, wanted);
 }
 
-/* api_sym_update --- update a symbol's value, see gawkapi.h for semantics */
+/* api_sym_update_real --- update a symbol's value, see gawkapi.h for semantics */
 
 static awk_bool_t
-api_sym_update(awk_ext_id_t id, const char *name, awk_value_t *value)
+sym_update_real(awk_ext_id_t id,
+		const char *name,
+		awk_value_t *value,
+		bool is_const)
 {
 	NODE *node;
 	NODE *array_node;
@@ -503,6 +507,8 @@ api_sym_update(awk_ext_id_t id, const char *name, awk_value_t *value)
 					Node_var);
 			unref(node->var_value);
 			node->var_value = awk_value_to_node(value);
+			if (is_const)
+				node->var_assign = set_constant;
 		}
 		return true;
 	}
@@ -518,6 +524,9 @@ api_sym_update(awk_ext_id_t id, const char *name, awk_value_t *value)
 		if (node->type == Node_var || node->type == Node_var_new) {
 			unref(node->var_value);
 			node->var_value = awk_value_to_node(value);
+			/* let the extension change its own variable */
+			if (is_const)
+				node->var_assign = set_constant;
 		} else {
 			return false;
 		}
@@ -530,6 +539,26 @@ api_sym_update(awk_ext_id_t id, const char *name, awk_value_t *value)
 	return true;
 }
 
+/* api_sym_update --- update a symbol, non-constant */
+
+static awk_bool_t
+api_sym_update(awk_ext_id_t id,
+		const char *name,
+		awk_value_t *value)
+{
+	return sym_update_real(id, name, value, false);
+}
+
+/* api_sym_update --- update a symbol, constant */
+
+static awk_bool_t
+api_sym_constant(awk_ext_id_t id,
+		const char *name,
+		awk_value_t *value)
+{
+	return sym_update_real(id, name, value, true);
+}
+
 /* api_sym_update_scalar --- update a scalar cookie */
 
 static awk_bool_t
@@ -864,6 +893,7 @@ gawk_api_t api_impl = {
 	api_sym_lookup,
 	api_sym_lookup_scalar,
 	api_sym_update,
+	api_sym_constant,
 	api_sym_update_scalar,
 
 	api_get_array_element,
@@ -897,3 +927,11 @@ update_ext_api()
 {
 	api_impl.do_flags[0] = (do_lint ? 1 : 0);
 }
+
+/* set_constant --- prevent awk code from changing a constant */
+
+static void
+set_constant()
+{
+	fatal(_("cannot assign to defined constant"));
+}