Make SPI_fnumber() reject dropped columns.

There's basically no scenario where it's sensible for this to match
dropped columns, so put a test for dropped-ness into SPI_fnumber()
itself, and excise the test from the small number of callers that
were paying attention to the case.  (Most weren't :-(.)

In passing, normalize tests at call sites: always reject attnum <= 0
if we're disallowing system columns.  Previously there was a mixture
of "< 0" and "<= 0" tests.  This makes no practical difference since
SPI_fnumber() never returns 0, but I'm feeling pedantic today.

Also, in the places that are actually live user-facing code and not
legacy cruft, distinguish "column not found" from "can't handle
system column".

Per discussion with Jim Nasby; thi supersedes his original patch
that just changed the behavior at one call site.

Discussion: <b2de8258-c4c0-1cb8-7b97-e8538e5c975c@BlueTreble.com>

src/backend/executor/spi.c

@@ -824,7 +824,8 @@ SPI_fnumber(TupleDesc tupdesc, const char *fname)
 
 	for (res = 0; res < tupdesc->natts; res++)
 	{
-		if (namestrcmp(&tupdesc->attrs[res]->attname, fname) == 0)
+		if (namestrcmp(&tupdesc->attrs[res]->attname, fname) == 0 &&
+			!tupdesc->attrs[res]->attisdropped)
 			return res + 1;
 	}
 

src/backend/utils/adt/tsvector_op.c

@@ -2242,6 +2242,7 @@ tsvector_update_trigger(PG_FUNCTION_ARGS, bool config_column)
 				(errcode(ERRCODE_UNDEFINED_COLUMN),
 				 errmsg("tsvector column \"%s\" does not exist",
 						trigger->tgargs[0])));
+	/* This will effectively reject system columns, so no separate test: */
 	if (!IsBinaryCoercible(SPI_gettypeid(rel->rd_att, tsvector_attr_num),
 						   TSVECTOROID))
 		ereport(ERROR,

src/pl/plperl/plperl.c

@@ -1062,11 +1062,16 @@ plperl_build_tuple_result(HV *perlhash, TupleDesc td)
 		char	   *key = hek2cstr(he);
 		int			attn = SPI_fnumber(td, key);
 
-		if (attn <= 0 || td->attrs[attn - 1]->attisdropped)
+		if (attn == SPI_ERROR_NOATTRIBUTE)
 			ereport(ERROR,
 					(errcode(ERRCODE_UNDEFINED_COLUMN),
 					 errmsg("Perl hash contains nonexistent column \"%s\"",
 							key)));
+		if (attn <= 0)
+			ereport(ERROR,
+					(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
+					 errmsg("cannot set system attribute \"%s\"",
+							key)));
 
 		values[attn - 1] = plperl_sv_to_datum(val,
 											  td->attrs[attn - 1]->atttypid,

src/pl/tcl/pltcl.c

@@ -603,6 +603,7 @@ pltcl_init_load_unknown(Tcl_Interp *interp)
 	 * leave this code as DString - it's only executed once per session
 	 ************************************************************/
 	fno = SPI_fnumber(SPI_tuptable->tupdesc, "modsrc");
+	Assert(fno > 0);
 
 	Tcl_DStringInit(&unknown_src);
 
@@ -1259,12 +1260,6 @@ pltcl_trigger_handler(PG_FUNCTION_ARGS, pltcl_call_state *call_state,
 					 errmsg("cannot set system attribute \"%s\"",
 							ret_name)));
 
-		/************************************************************
-		 * Ignore dropped columns
-		 ************************************************************/
-		if (tupdesc->attrs[attnum - 1]->attisdropped)
-			continue;
-
 		/************************************************************
 		 * Lookup the attribute type's input function
 		 ************************************************************/
@@ -3077,10 +3072,6 @@ pltcl_build_tuple_result(Tcl_Interp *interp, Tcl_Obj **kvObjv, int kvObjc,
 					 errmsg("cannot set system attribute \"%s\"",
 							fieldName)));
 
-		/* Ignore dropped attributes */
-		if (call_state->ret_tupdesc->attrs[attn - 1]->attisdropped)
-			continue;
-
 		values[attn - 1] = utf_e2u(Tcl_GetString(kvObjv[i + 1]));
 	}
 

src/test/regress/regress.c

@@ -523,11 +523,12 @@ ttdummy(PG_FUNCTION_ARGS)
 	for (i = 0; i < 2; i++)
 	{
 		attnum[i] = SPI_fnumber(tupdesc, args[i]);
-		if (attnum[i] < 0)
-			elog(ERROR, "ttdummy (%s): there is no attribute %s", relname, args[i]);
+		if (attnum[i] <= 0)
+			elog(ERROR, "ttdummy (%s): there is no attribute %s",
+				 relname, args[i]);
 		if (SPI_gettypeid(tupdesc, attnum[i]) != INT4OID)
-			elog(ERROR, "ttdummy (%s): attributes %s and %s must be of abstime type",
-				 relname, args[0], args[1]);
+			elog(ERROR, "ttdummy (%s): attribute %s must be of integer type",
+				 relname, args[i]);
 	}
 
 	oldon = SPI_getbinval(trigtuple, tupdesc, attnum[0], &isnull);