Fix for GitHub issue #239 - segfault when library file has syntax errors.

If there are errors when parsing a file, it is not safe to elaborate any
modules that have been found in that file.

elaborate.cc

@@ -2233,7 +2233,8 @@ void PGModule::elaborate_scope(Design*des, NetScope*sc) const
 	// Not a module or primitive that I know about yet, so try to
 	// load a library module file (which parses some new Verilog
 	// code) and try again.
-      if (load_module(type_)) {
+      int parser_errors = 0;
+      if (load_module(type_, parser_errors)) {
 
 	      // Try again to find the module type
 	    mod = pform_modules.find(type_);
@@ -2248,6 +2249,10 @@ void PGModule::elaborate_scope(Design*des, NetScope*sc) const
 		  return;
       }
 
+      if (parser_errors) {
+            cerr << get_fileline() << ": error: Failed to parse library file." << endl;
+            des->errors += parser_errors + 1;
+      }
 
 	// Not a module or primitive that I know about or can find by
 	// any means, so give up.

load_module.cc

@@ -54,11 +54,13 @@ extern FILE *depend_file;
  * Use the type name as a key, and search the module library for a
  * file name that has that key.
  */
-bool load_module(const char*type)
+bool load_module(const char*type, int&parser_errors)
 {
       char path[4096];
       char*ltype = strdup(type);
 
+      parser_errors = 0;
+
       for (char*tmp = ltype ; *tmp ;  tmp += 1)
 	    *tmp = tolower(*tmp);
 
@@ -85,12 +87,12 @@ bool load_module(const char*type)
 	    if (verbose_flag)
 		  cerr << "Loading library file " << path << "." << endl;
 
-	    pform_parse(path);
+	    parser_errors = pform_parse(path);
 
 	    if (verbose_flag)
 		  cerr << "... Load module complete." << endl << flush;
 
-	    return true;
+	    return parser_errors == 0;
       }
 
       return false;

util.h

@@ -34,7 +34,7 @@ class NetScope;
  * looking for a plausible Verilog file to hold the module, and
  * invoking the parser to bring in that file's contents.
  */
-extern bool load_module(const char*type);
+extern bool load_module(const char*type, int&parser_errors);