pg: More verbose error traces

Partly because some errors currently appeared to come from within FU::PG
itself, which is useless, and partly because it's common to wrap
database access methods, while that's exactly the kind of operation
where you *really* want to know where the error originated from.

(Source: too much time wasted debugging VNDB errors)

FU.xs

@@ -15,10 +15,10 @@
 
 
 #define FUPG_CONN_COOKIE \
-    if (c->cookie) croak("Invalid attempt to run a query on the top-level connection while a transaction object exists")
+    if (c->cookie) fu_confess("Invalid attempt to run a query on the top-level connection while a transaction object exists")
 
 #define FUPG_ST_COOKIE \
-    if (st->cookie != st->conn->cookie) croak("Invalid cross-transaction operation on statement object")
+    if (st->cookie != st->conn->cookie) fu_confess("Invalid cross-transaction operation on statement object")
 
 typedef fupg_conn *fupg_txn;
 
@@ -37,14 +37,14 @@ fupg_st *     FUPG_ST
 INPUT
 FUPG_CONN
     if (sv_derived_from($arg, \"FU::PG::conn\")) $var = (fupg_conn *)SvIVX(SvRV($arg));
-    else croak(\"invalid connection object\");
+    else fu_confess(\"invalid connection object\");
 
 FUPG_TXN
     $var = fupg_get_transaction(aTHX_ $arg);
 
 FUPG_ST
     if (sv_derived_from($arg, \"FU::PG::st\")) $var = (fupg_st *)SvIVX(SvRV($arg));
-    else croak(\"invalid statement object\");
+    else fu_confess(\"invalid statement object\");
 #"
 EOT
 

FU/PG.pm

@@ -15,7 +15,7 @@ package FU::PG::conn {
 };
 
 package FU::PG::txn {
-    use Carp 'croak';
+    use Carp 'confess';
 
     my $COUNTER = 0;
 
@@ -27,19 +27,19 @@ package FU::PG::txn {
     # 2: $parent, undef if this is a top-level transaction.
 
     sub commit($t) {
-        croak "Unable to commit transaction that has already finished" if !$t->[1];
+        confess "Unable to commit transaction that has already finished" if !$t->[1];
         $t->exec($t->[2] ? "RELEASE SAVEPOINT fupg_$t->[1]" : 'COMMIT');
         $t->[1] = undef;
     }
 
     sub rollback($t) {
-        croak "Unable to rollback transaction that has already finished" if !$t->[1];
+        confess "Unable to rollback transaction that has already finished" if !$t->[1];
         $t->exec($t->[2] ? "ROLLBACK TO SAVEPOINT fupg_$t->[1]" : 'ROLLBACK');
         $t->[1] = undef;
     }
 
     sub txn($t) {
-        croak "Unable to create sub-transaction when current transaction has already finished" if !$t->[1];
+        confess "Unable to create sub-transaction when current transaction has already finished" if !$t->[1];
         $COUNTER++;
         $t->exec("SAVEPOINT fupg_$COUNTER");
         $t->[0]->_set_cookie($COUNTER);
@@ -80,7 +80,7 @@ FU::PG - Another PostgreSQL client module
 
   $conn->q('INSERT INTO books (title) VALUES ($1)', 'Revelation Space')->exec;
 
-  for my ($id, $title) ($conn->q('SELECT * FROM books')->flat) {
+  for my ($id, $title) ($conn->q('SELECT * FROM books')->flat->@*) {
     print "$id:  $title\n";
   }
 
@@ -365,8 +365,6 @@ handling, that is still available:
 Just don't try to use transaction objects and manual transaction commands at
 the same time, that won't end well.
 
-=back
-
 
 =head2 Errors
 

c/common.c

@@ -26,7 +26,7 @@ static SV *fu_croak_hv(HV *hv, const char *klass, const char *message, ...) {
     ENTER;
     SAVETMPS;
     PUSHMARK(SP);
-    XPUSHs(sv_2mortal(sv));
+    mXPUSHs(sv);
     PUTBACK;
     call_pv("Carp::longmess", G_SCALAR);
     hv_stores(hv, "full_message", SvREFCNT_inc(POPs));
@@ -36,6 +36,27 @@ static SV *fu_croak_hv(HV *hv, const char *klass, const char *message, ...) {
     return sv_bless(sv_2mortal(newRV_noinc((SV *)hv)), gv_stashpv(klass, GV_ADD));
 }
 
+__attribute__((noreturn, format (printf, 1, 2)))
+static void fu_confess(const char *message, ...) {
+    va_list args;
+    SV *sv;
+    dTHX;
+    dSP;
+
+    va_start(args, message);
+    sv = vnewSVpvf(message, &args);
+    va_end(args);
+
+    ENTER;
+    SAVETMPS;
+    PUSHMARK(SP);
+    mXPUSHs(sv);
+    PUTBACK;
+    call_pv("Carp::confess", G_DISCARD);
+    /* Won't happen, but a safe fallback */
+    croak("%s", SvPV_nolen(sv));
+}
+
 
 
 /* Custom string builder, should be slightly faster than using Sv* macros directly. */

c/pgconn.c

@@ -142,11 +142,11 @@ static fupg_conn *fupg_get_transaction(pTHX_ SV *sv) {
 
     v = av_fetch(av, 1, 0);
     if (!v || !*v) goto invalid;
-    if (!SvOK(*v)) croak("Invalid attempt to run a query on a transaction that has already finished");
-    if (c->cookie != SvUV(*v)) croak("Invalid cross-transaction operation");
+    if (!SvOK(*v)) fu_confess("Invalid attempt to run a query on a transaction that has already finished");
+    if (c->cookie != SvUV(*v)) fu_confess("Invalid cross-transaction operation");
     return c;
 invalid:
-    croak("invalid transaction object");
+    fu_confess("invalid transaction object");
 }
 
 /* Read a Perl value from a PGresult.
@@ -196,7 +196,7 @@ static SV *fupg_q(pTHX_ fupg_conn *c, const char *query, I32 ax, I32 argc) {
 
 static void fupg_st_prepare(pTHX_ fupg_st *st) {
     if (st->describe) return;
-    if (st->prepared) croak("invalid attempt to re-prepare invalid statement");
+    if (st->prepared) fu_confess("invalid attempt to re-prepare invalid statement");
 
     /* TODO: This is where we check for any cached prepared statements */
 
@@ -253,7 +253,7 @@ static void fupg_st_check_dupcols(pTHX_ PGresult *r) {
         int len = -strlen(key);
         if (hv_exists(hv, key, len)) {
             SvREFCNT_dec((SV *)hv);
-            croak("Query returns multiple columns with the same name ('%s')", key);
+            fu_confess("Query returns multiple columns with the same name ('%s')", key);
         }
         hv_store(hv, key, len, &PL_sv_yes, 0);
     }
@@ -264,7 +264,7 @@ static void fupg_st_execute(pTHX_ fupg_st *st) {
     /* Disallow fetching the results more than once. I don't see a reason why
      * someone would need that and disallowing it leaves room for fetching the
      * results in a streaming fashion without breaking API compat. */
-    if (st->result) croak("Invalid attempt to execute statement multiple times");
+    if (st->result) fu_confess("Invalid attempt to execute statement multiple times");
 
     /* TODO: prepare can be skipped when prepared statement caching is disabled and (text-format queries or no bind params) */
     fupg_st_prepare(aTHX_ st);
@@ -302,10 +302,10 @@ static SV *fupg_st_exec(pTHX_ fupg_st *st) {
 
 static SV *fupg_st_val(pTHX_ fupg_st *st) {
     fupg_st_prepare(aTHX_ st);
-    if (PQnfields(st->describe) > 1) croak("Invalid use of $st->val() on query returning more than one column");
-    if (PQnfields(st->describe) == 0) croak("Invalid use of $st->val() on query returning no data");
+    if (PQnfields(st->describe) > 1) fu_confess("Invalid use of $st->val() on query returning more than one column");
+    if (PQnfields(st->describe) == 0) fu_confess("Invalid use of $st->val() on query returning no data");
     fupg_st_execute(aTHX_ st);
-    if (PQntuples(st->result) > 1) croak("Invalid use of $st->val() on query returning more than one row");
+    if (PQntuples(st->result) > 1) fu_confess("Invalid use of $st->val() on query returning more than one row");
     SV *sv = PQntuples(st->result) == 0 ? newSV(0) : fupg_val(aTHX_ st->result, 0, 0);
     return sv_2mortal(sv);
 }
@@ -313,8 +313,8 @@ static SV *fupg_st_val(pTHX_ fupg_st *st) {
 static I32 fupg_st_rowl(pTHX_ fupg_st *st, I32 ax) {
     dSP;
     fupg_st_execute(aTHX_ st);
-    if (PQntuples(st->result) == 0) croak("Invalid use of $st->rowl() on query returning zero rows");
-    if (PQntuples(st->result) > 1) croak("Invalid use of $st->rowl() on query returning more than one row");
+    if (PQntuples(st->result) == 0) fu_confess("Invalid use of $st->rowl() on query returning zero rows");
+    if (PQntuples(st->result) > 1) fu_confess("Invalid use of $st->rowl() on query returning more than one row");
     if (GIMME_V != G_LIST) {
         ST(0) = sv_2mortal(newSViv(PQnfields(st->result)));
         return 1;
@@ -328,8 +328,8 @@ static I32 fupg_st_rowl(pTHX_ fupg_st *st, I32 ax) {
 
 static SV *fupg_st_rowa(pTHX_ fupg_st *st) {
     fupg_st_execute(aTHX_ st);
-    if (PQntuples(st->result) == 0) croak("Invalid use of $st->rowl() on query returning zero rows");
-    if (PQntuples(st->result) > 1) croak("Invalid use of $st->rowl() on query returning more than one row");
+    if (PQntuples(st->result) == 0) fu_confess("Invalid use of $st->rowl() on query returning zero rows");
+    if (PQntuples(st->result) > 1) fu_confess("Invalid use of $st->rowl() on query returning more than one row");
     int i, nfields = PQnfields(st->result);
     AV *av = newAV_alloc_x(nfields);
     SV *sv = sv_2mortal(newRV_noinc((SV *)av));
@@ -341,8 +341,8 @@ static SV *fupg_st_rowh(pTHX_ fupg_st *st) {
     fupg_st_prepare(aTHX_ st);
     fupg_st_check_dupcols(aTHX_ st->describe);
     fupg_st_execute(aTHX_ st);
-    if (PQntuples(st->result) == 0) croak("Invalid use of $st->rowh() on query returning zero rows");
-    if (PQntuples(st->result) > 1) croak("Invalid use of $st->rowh() on query returning more than one row");
+    if (PQntuples(st->result) == 0) fu_confess("Invalid use of $st->rowh() on query returning zero rows");
+    if (PQntuples(st->result) > 1) fu_confess("Invalid use of $st->rowh() on query returning more than one row");
     int i, nfields = PQnfields(st->result);
     HV *hv = newHV();
     SV *sv = sv_2mortal(newRV_noinc((SV *)hv));