C++: less verbose error-recovery for version conflict markers

gcc/cp/ChangeLog:
	* parser.c (cp_parser_error_1): After issuing a conflict marker
	error, consume tokens until the end of the source line.

gcc/testsuite/ChangeLog:
	* g++.dg/conflict-markers-2.C: New test.

From-SVN: r262232

gcc/cp/ChangeLog

+2018-06-28  David Malcolm  <dmalcolm@redhat.com>
+
+	* parser.c (cp_parser_error_1): After issuing a conflict marker
+	error, consume tokens until the end of the source line.
+
 2018-06-28  Jason Merrill  <jason@redhat.com>
 
 	PR c++/86342 - -Wdeprecated-copy and system headers.

gcc/cp/parser.c

@@ -2862,6 +2862,20 @@ cp_parser_error_1 (cp_parser* parser, const char* gmsgid,
       if (cp_lexer_peek_conflict_marker (parser->lexer, token->type, &loc))
 	{
 	  error_at (loc, "version control conflict marker in file");
+	  expanded_location token_exploc = expand_location (token->location);
+	  /* Consume tokens until the end of the source line.  */
+	  while (1)
+	    {
+	      cp_lexer_consume_token (parser->lexer);
+	      cp_token *next = cp_lexer_peek_token (parser->lexer);
+	      if (next == NULL)
+		break;
+	      expanded_location next_exploc = expand_location (next->location);
+	      if (next_exploc.file != token_exploc.file)
+		break;
+	      if (next_exploc.line != token_exploc.line)
+		break;
+	    }
 	  return;
 	}
     }

gcc/testsuite/g++.dg/conflict-markers-2.C

+// { dg-do compile { target c++11 } }
+
+extern void f1 (void);
+extern void f2 (void);
+extern void f3 (void);
+extern void f4 (void);
+
+void test ()
+{
+  f1 ();
+<<<<<<< HEAD // { dg-error "conflict marker" }
+  f2 ();
+======= // { dg-error "conflict marker" }
+  f3 ();
+>>>>>>> 252be53... Some commit message // { dg-error "conflict marker" }
+  f4 ();
+}