Detect generate regions within generate schemes.

Generate schemes may nest freely, but generate regions
(an anachronistic concept from 1364-2001) cannot nest,
not within schemes or other regions. Have the parser detect
the nesting and print an error message.

parse.y

@@ -2425,9 +2425,19 @@ module_item
 
   /* A generate region can contain further module items. Actually, it
      is supposed to be limited to certain kinds of module items, but
-     the semantic tests will check that for us. */
+     the semantic tests will check that for us. Do check that the
+     generate/endgenerate regions do not nest. Generate schemes nest,
+     but generate regions do not. */
 
   | K_generate module_item_list_opt K_endgenerate
+     { // Test for bad nesting. I understand it, but it is illegal.
+       if (pform_parent_generate()) {
+	     cerr << @1 << ": error: Generate/endgenerate regions cannot nest." << endl;
+	     cerr << @1 << ":      : Try removing optional generate/endgenerate keywords," << endl;
+	     cerr << @1 << ":      : or move them to surround the parent generate scheme." << endl;
+	     error_count += 1;
+	}
+      }
 
   | K_genvar list_of_identifiers ';'
       { pform_genvars(@1, $2); }

pform.cc

@@ -342,6 +342,11 @@ PBlock* pform_push_block_scope(char*name, PBlock::BL_TYPE bt)
       return block;
 }
 
+PGenerate* pform_parent_generate(void)
+{
+      return pform_cur_generate;
+}
+
 void pform_bind_attributes(map<perm_string,PExpr*>&attributes,
 			   svector<named_pexpr_t*>*attr)
 {

pform.h

@@ -214,6 +214,12 @@ extern void pform_generate_case_item(const struct vlltype&lp, svector<PExpr*>*te
 extern void pform_generate_block_name(char*name);
 extern void pform_endgenerate();
 
+/*
+ * This function returns the lexically containing generate scheme, if
+ * there is one. The parser may use this to check if we are within a
+ * generate scheme.
+ */
+extern PGenerate* pform_parent_generate(void);
 
 /*
  * The makewire functions announce to the pform code new wires. These