io.c: reopen stdio streams correctly when given "w+"

* io.c (rb_io_oflags_modestr): handle O_TRUNC correctly
* test/ruby/test_io.rb (test_reopen_stdio): new test

Patch-by: cremno phobia <[email protected]>

[ruby-core:69779] [Bug #11319]

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@51066 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

1 files changed, 3 insertions, 0 deletions

diff --git a/io.c b/io.c
index dfdb422b56..8358c74ff9 100644
--- a/io.c
+++ b/io.c
@@ -5046,6 +5046,9 @@ rb_io_oflags_modestr(int oflags)
       case O_WRONLY:
 	return MODE_BINARY("w", "wb");
       case O_RDWR:
+	if (oflags & O_TRUNC) {
+	    return MODE_BINARY("w+", "wb+");
+	}
 	return MODE_BINARY("r+", "rb+");
     }
 }