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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.

--- a/FIXES

+++ b/FIXES

@@ -25,6 +25,10 @@

 This file lists all bug fixes, changes, etc., made since the AWK book

 was sent to the printers in August, 1987.

+January 9, 2020:

+	Input/output errors on closing files are now fatal instead of

+	mere warnings. Thanks to Martijn Dekker <martijn@inlv.org>.

+

 January 5, 2020:

 	Fix a bug in the concatentation of two string constants into

 	one done in the grammar.  Fixes GitHub issue #61.  Thanks

--- a/run.c

+++ b/run.c

@@ -1769,13 +1769,13 @@

 	for (i = 0; i < nfiles; i++) {

 		if (files[i].fname && strcmp(x->sval, files[i].fname) == 0) {

 			if (ferror(files[i].fp))

-				WARNING( "i/o error occurred on %s", files[i].fname );

+				FATAL( "i/o error occurred on %s", files[i].fname );

 			if (files[i].mode == '|' || files[i].mode == LE)

 				stat = pclose(files[i].fp);

 			else

 				stat = fclose(files[i].fp);

 			if (stat == EOF)

-				WARNING( "i/o error occurred closing %s", files[i].fname );

+				FATAL( "i/o error occurred closing %s", files[i].fname );

 			if (i > 2)	/* don't do /dev/std... */

 				xfree(files[i].fname);

 			files[i].fname = NULL;	/* watch out for ref thru this */

@@ -1795,13 +1795,13 @@

 	for (i = 0; i < FOPEN_MAX; i++) {

 		if (files[i].fp) {

 			if (ferror(files[i].fp))

-				WARNING( "i/o error occurred on %s", files[i].fname );

+				FATAL( "i/o error occurred on %s", files[i].fname );

 			if (files[i].mode == '|' || files[i].mode == LE)

 				stat = pclose(files[i].fp);

 			else

 				stat = fclose(files[i].fp);

 			if (stat == EOF)

-				WARNING( "i/o error occurred while closing %s", files[i].fname );

+				FATAL( "i/o error occurred while closing %s", files[i].fname );

 		}

 	}

 }

--- a/testdir/T.misc

+++ b/testdir/T.misc

@@ -466,3 +466,8 @@

 $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'

-- 

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