Unbreak interactive GPG prompt upon signing

With the recent update in efee955 (gpg-interface: check gpg signature
creation status, 2016-06-17), we ask GPG to send all status updates to
stderr, and then catch the stderr in an strbuf.

But GPG might fail, and send error messages to stderr. And we simply
do not show them to the user.

Even worse: this swallows any interactive prompt for a passphrase. And
detaches stderr from the tty so that the passphrase cannot be read.

So while the first problem could be fixed (by printing the captured
stderr upon error), the second problem cannot be easily fixed, and
presents a major regression.

So let's just revert commit efee9553a4.

This fixes https://github.com/git-for-windows/git/issues/871

Cc: Michael J Gruber <git@drmicha.warpmail.net>
Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>

gpg-interface.c

@@ -950,12 +950,9 @@ static int sign_buffer_gpg(struct strbuf *buffer, struct strbuf *signature,
 	struct child_process gpg = CHILD_PROCESS_INIT;
 	int ret;
 	size_t bottom;
-	const char *cp;
-	struct strbuf gpg_status = STRBUF_INIT;
 
 	strvec_pushl(&gpg.args,
 		     use_format->program,
-		     "--status-fd=2",
 		     "-bsau", signing_key,
 		     NULL);
 
@@ -967,18 +964,10 @@ static int sign_buffer_gpg(struct strbuf *buffer, struct strbuf *signature,
 	 */
 	sigchain_push(SIGPIPE, SIG_IGN);
 	ret = pipe_command(&gpg, buffer->buf, buffer->len,
-			   signature, 1024, &gpg_status, 0);
+			   signature, 1024, NULL, 0);
 	sigchain_pop(SIGPIPE);
 
-	for (cp = gpg_status.buf;
-	     cp && (cp = strstr(cp, "[GNUPG:] SIG_CREATED "));
-	     cp++) {
-		if (cp == gpg_status.buf || cp[-1] == '\n')
-			break; /* found */
-	}
-	ret |= !cp;
-	strbuf_release(&gpg_status);
-	if (ret)
+	if (ret || signature->len == bottom)
 		return error(_("gpg failed to sign the data"));
 
 	/* Strip CR from the line endings, in case we are on Windows. */

t/t7004-tag.sh

@@ -1375,30 +1375,6 @@ test_expect_success GPG \
 	'test_config user.signingkey BobTheMouse &&
 	test_must_fail git tag -s -m tail tag-gpg-failure'
 
-# try to produce invalid signature
-test_expect_success GPG \
-	'git tag -s fails if gpg is misconfigured (bad signature format)' \
-	'test_config gpg.program echo &&
-	 test_must_fail git tag -s -m tail tag-gpg-failure'
-
-# try to produce invalid signature
-test_expect_success GPG 'git verifies tag is valid with double signature' '
-	git tag -s -m tail tag-gpg-double-sig &&
-	git cat-file tag tag-gpg-double-sig >tag &&
-	othersigheader=$(test_oid othersigheader) &&
-	sed -ne "/^\$/q;p" tag >new-tag &&
-	cat <<-EOM >>new-tag &&
-	$othersigheader -----BEGIN PGP SIGNATURE-----
-	 someinvaliddata
-	 -----END PGP SIGNATURE-----
-	EOM
-	sed -e "1,/^tagger/d" tag >>new-tag &&
-	new_tag=$(git hash-object -t tag -w new-tag) &&
-	git update-ref refs/tags/tag-gpg-double-sig $new_tag &&
-	git verify-tag tag-gpg-double-sig &&
-	git fsck
-'
-
 # try to sign with bad user.signingkey
 test_expect_success GPGSM \
 	'git tag -s fails if gpgsm is misconfigured (bad key)' \
@@ -1406,13 +1382,6 @@ test_expect_success GPGSM \
 	 test_config gpg.format x509 &&
 	 test_must_fail git tag -s -m tail tag-gpg-failure'
 
-# try to produce invalid signature
-test_expect_success GPGSM \
-	'git tag -s fails if gpgsm is misconfigured (bad signature format)' \
-	'test_config gpg.x509.program echo &&
-	 test_config gpg.format x509 &&
-	 test_must_fail git tag -s -m tail tag-gpg-failure'
-
 # try to verify without gpg:
 
 rm -rf gpghome