Make I/O errors fatal instead of mere warnings (#63)

An input/output error indicates a fatal condition, even if it
occurs when closing a file. Awk should not return success on I/O
error, but treat I/O errors as it already treats write errors.

Test case:

$ (trap '' PIPE; awk 'BEGIN { print "hi"; }'; echo "E $?" >&2) | :
awk: i/o error occurred while closing /dev/stdout
 source line number 1
E 2

The test case pipes a line into a dummy command that reads no
input, with SIGPIPE ignored so we rely on awk's own I/O checking.
No write error is detected, because the pipe is buffered; the
broken pipe is only detected as an I/O error on closing stdout.

Before this commit, "E 0" was printed (indicating status 0/success)
because an I/O error merely produced a warning. A shell script
was unable to detect the I/O error using the exit status.

1 files changed, 5 insertions, 0 deletions

diff --git a/testdir/T.misc b/testdir/T.misc
index 7fc196a..a191ae2 100755
--- a/testdir/T.misc
+++ b/testdir/T.misc
@@ -466,3 +466,8 @@ echo '' >foo0
 $awk 'END { print NF, $0 }' foo0 >foo1
 awk '{ print NF, $0 }' foo0| tail -1 >foo2
 cmp -s foo1 foo2 || echo 'BAD: T.misc END must preserve $0'
+
+# Check for nonzero exit status on I/O error.
+echo 'E 2' >foo1
+(trap '' PIPE; "$awk" 'BEGIN { print "hi"; }' 2>/dev/null; echo "E $?" >foo2) | :
+cmp -s foo1 foo2 || echo 'BAD: T.misc exit status on I/O error'