[PATCH v3] gpg-interface: use more status letters

[Michael J Gruber <git@drmicha.warpmail.net>]

According to gpg2's doc/DETAILS:

    For each signature only one of the codes GOODSIG, BADSIG,
    EXPSIG, EXPKEYSIG, REVKEYSIG or ERRSIG will be emitted.

gpg1 ("classic") behaves the same (although doc/DETAILS differs).

Currently, we parse gpg's status output for GOODSIG, BADSIG and
trust information and translate that into status codes G, B, U, N
for the %G?  format specifier.

git-verify-* returns success in the GOODSIG case only. This is
somewhat in disagreement with gpg, which considers the first 5 of
the 6 above as VALIDSIG, but we err on the very safe side.

Introduce additional status codes E, X, Y, R for ERRSIG, EXPSIG,
EXPKEYSIG, and REVKEYSIG so that a user of %G? gets more information
about the absence of a 'G' on first glance.

Requested-by: Alex <agrambot@gmail.com>
Signed-off-by: Michael J Gruber <git@drmicha.warpmail.net>
---
v3 incorporates Junios' changes to the commit message, as well as his
suggestion how to use an undefined gpghome the way test-lib does.
Also, all Y-related changes (including the if in pretty.c).

Testing X, Y, and R from our test scripts is somewhat problematic
(some gpg versions do not allow back-dating, and we cannot ship pre-made
signatures easily) but I have tested all of them locally.

 Documentation/pretty-formats.txt | 10 ++++++++--
 gpg-interface.c                  | 13 ++++++++++---
 pretty.c                         |  4 ++++
 t/t7510-signed-commit.sh         | 13 ++++++++++++-
 4 files changed, 34 insertions(+), 6 deletions(-)

diff --git a/Documentation/pretty-formats.txt b/Documentation/pretty-formats.txt
index a942d57f73..179c9389aa 100644
--- a/Documentation/pretty-formats.txt
+++ b/Documentation/pretty-formats.txt
@@ -143,8 +143,14 @@ ifndef::git-rev-list[]
 - '%N': commit notes
 endif::git-rev-list[]
 - '%GG': raw verification message from GPG for a signed commit
-- '%G?': show "G" for a good (valid) signature, "B" for a bad signature,
-  "U" for a good signature with unknown validity and "N" for no signature
+- '%G?': show "G" for a good (valid) signature,
+  "B" for a bad signature,
+  "U" for a good signature with unknown validity,
+  "X" for a good signature that has expired,
+  "Y" for a good signature made by an expired key,
+  "R" for a good signature made by a revoked key,
+  "E" if the signature cannot be checked (e.g. missing key)
+  and "N" for no signature
 - '%GS': show the name of the signer for a signed commit
 - '%GK': show the key used to sign a signed commit
 - '%gD': reflog selector, e.g., `refs/stash@{1}` or
diff --git a/gpg-interface.c b/gpg-interface.c
index 8672edaf48..e44cc27da1 100644
--- a/gpg-interface.c
+++ b/gpg-interface.c
@@ -33,6 +33,10 @@ static struct {
 	{ 'B', "\n[GNUPG:] BADSIG " },
 	{ 'U', "\n[GNUPG:] TRUST_NEVER" },
 	{ 'U', "\n[GNUPG:] TRUST_UNDEFINED" },
+	{ 'E', "\n[GNUPG:] ERRSIG "},
+	{ 'X', "\n[GNUPG:] EXPSIG "},
+	{ 'Y', "\n[GNUPG:] EXPKEYSIG "},
+	{ 'R', "\n[GNUPG:] REVKEYSIG "},
 };
 
 void parse_gpg_output(struct signature_check *sigc)
@@ -54,9 +58,12 @@ void parse_gpg_output(struct signature_check *sigc)
 		/* The trust messages are not followed by key/signer information */
 		if (sigc->result != 'U') {
 			sigc->key = xmemdupz(found, 16);
-			found += 17;
-			next = strchrnul(found, '\n');
-			sigc->signer = xmemdupz(found, next - found);
+			/* The ERRSIG message is not followed by signer information */
+			if (sigc-> result != 'E') {
+				found += 17;
+				next = strchrnul(found, '\n');
+				sigc->signer = xmemdupz(found, next - found);
+			}
 		}
 	}
 }
diff --git a/pretty.c b/pretty.c
index 25efbcac92..d89ca30911 100644
--- a/pretty.c
+++ b/pretty.c
@@ -1232,8 +1232,12 @@ static size_t format_commit_one(struct strbuf *sb, /* in UTF-8 */
 			switch (c->signature_check.result) {
 			case 'G':
 			case 'B':
+			case 'E':
 			case 'U':
 			case 'N':
+			case 'X':
+			case 'Y':
+			case 'R':
 				strbuf_addch(sb, c->signature_check.result);
 			}
 			break;
diff --git a/t/t7510-signed-commit.sh b/t/t7510-signed-commit.sh
index 6e839f5489..762135adea 100755
--- a/t/t7510-signed-commit.sh
+++ b/t/t7510-signed-commit.sh
@@ -2,6 +2,7 @@
 
 test_description='signed commit tests'
 . ./test-lib.sh
+GNUPGHOME_NOT_USED=$GNUPGHOME
 . "$TEST_DIRECTORY/lib-gpg.sh"
 
 test_expect_success GPG 'create signed commits' '
@@ -190,7 +191,7 @@ test_expect_success GPG 'show bad signature with custom format' '
 	test_cmp expect actual
 '
 
-test_expect_success GPG 'show unknown signature with custom format' '
+test_expect_success GPG 'show untrusted signature with custom format' '
 	cat >expect <<-\EOF &&
 	U
 	61092E85B7227189
@@ -200,6 +201,16 @@ test_expect_success GPG 'show unknown signature with custom format' '
 	test_cmp expect actual
 '
 
+test_expect_success GPG 'show unknown signature with custom format' '
+	cat >expect <<-\EOF &&
+	E
+	61092E85B7227189
+
+	EOF
+	GNUPGHOME="$GNUPGHOME_NOT_USED" git log -1 --format="%G?%n%GK%n%GS" eighth-signed-alt >actual &&
+	test_cmp expect actual
+'
+
 test_expect_success GPG 'show lack of signature with custom format' '
 	cat >expect <<-\EOF &&
 	N
-- 
2.10.1.532.gfe29b57