use `const` in graminit.c (GH-12713)

Include/grammar.h

@@ -13,7 +13,7 @@ extern "C" {
 
 typedef struct {
     int          lb_type;
-    char        *lb_str;
+    const char  *lb_str;
 } label;
 
 #define EMPTY 0         /* Label number 0 is by definition the empty label */
@@ -22,7 +22,7 @@ typedef struct {
 
 typedef struct {
     int          ll_nlabels;
-    label       *ll_label;
+    const label *ll_label;
 } labellist;
 
 /* An arc from one state to another */
@@ -36,7 +36,7 @@ typedef struct {
 
 typedef struct {
     int          s_narcs;
-    arc         *s_arc;         /* Array of arcs */
+    const arc   *s_arc;         /* Array of arcs */
 
     /* Optional accelerators */
     int          s_lower;       /* Lowest label index */
@@ -59,8 +59,8 @@ typedef struct {
 
 typedef struct {
     int          g_ndfas;
-    dfa         *g_dfa;         /* Array of DFAs */
-    labellist    g_ll;
+    const dfa   *g_dfa;         /* Array of DFAs */
+    const labellist g_ll;
     int          g_start;       /* Start symbol of the grammar */
     int          g_accel;       /* Set if accelerators present */
 } grammar;

Parser/pgen/grammar.py

@@ -76,7 +76,7 @@ class Grammar:
 
     def print_labels(self, writer):
         writer(
-            "static label labels[{n_labels}] = {{\n".format(n_labels=len(self.labels))
+            "static const label labels[{n_labels}] = {{\n".format(n_labels=len(self.labels))
         )
         for label, name in self.labels:
             label_name = '"{}"'.format(name) if name is not None else 0
@@ -89,7 +89,7 @@ class Grammar:
 
     def print_dfas(self, writer):
         self.print_states(writer)
-        writer("static dfa dfas[{}] = {{\n".format(len(self.dfas)))
+        writer("static const dfa dfas[{}] = {{\n".format(len(self.dfas)))
         for dfaindex, dfa_elem in enumerate(self.dfas.items()):
             symbol, (dfa, first_sets) = dfa_elem
             writer(
@@ -131,7 +131,7 @@ class Grammar:
         for stateindex, state in enumerate(states):
             narcs = len(state)
             write(
-                "static arc arcs_{dfa_index}_{state_index}[{n_arcs}] = {{\n".format(
+                "static const arc arcs_{dfa_index}_{state_index}[{n_arcs}] = {{\n".format(
                     dfa_index=dfaindex, state_index=stateindex, n_arcs=narcs
                 )
             )