Avoid doing catalog lookups in postgres_fdw's conversion_error_callback.

As in 50371df26, this is a bad idea since the callback can't really
know what error is being thrown and thus whether or not it is safe
to attempt catalog accesses.  Rather than pushing said accesses into
the mainline code where they'd usually be a waste of cycles, we can
look at the query's rangetable instead.

This change does mean that we'll be printing query aliases (if any
were used) rather than the table or column's true name.  But that
doesn't seem like a bad thing: it's certainly a more useful definition
in self-join cases, for instance.  In any case, it seems unlikely that
any applications would be depending on this detail, so it seems safe
to change.

Patch by me.  Original complaint by Andres Freund; Bharath Rupireddy
noted the connection to conversion_error_callback.

Discussion: https://postgr.es/m/20210106020229.ne5xnuu6wlondjpe@alap3.anarazel.de

1 files changed, 8 insertions, 6 deletions

diff --git a/contrib/postgres_fdw/expected/postgres_fdw.out b/contrib/postgres_fdw/expected/postgres_fdw.out
index d52e5da234e..6a19c5cd08a 100644
--- a/contrib/postgres_fdw/expected/postgres_fdw.out
+++ b/contrib/postgres_fdw/expected/postgres_fdw.out
@@ -2869,15 +2869,17 @@ DROP FUNCTION f_test(int);
 -- conversion error
 -- ===================================================================
 ALTER FOREIGN TABLE ft1 ALTER COLUMN c8 TYPE int;
-SELECT * FROM ft1 WHERE c1 = 1;  -- ERROR
+SELECT * FROM ft1 ftx(x1,x2,x3,x4,x5,x6,x7,x8) WHERE x1 = 1;  -- ERROR
 ERROR:  invalid input syntax for integer: "foo"
-CONTEXT:  column "c8" of foreign table "ft1"
-SELECT  ft1.c1,  ft2.c2, ft1.c8 FROM ft1, ft2 WHERE ft1.c1 = ft2.c1 AND ft1.c1 = 1; -- ERROR
+CONTEXT:  column "x8" of foreign table "ftx"
+SELECT ftx.x1, ft2.c2, ftx.x8 FROM ft1 ftx(x1,x2,x3,x4,x5,x6,x7,x8), ft2
+  WHERE ftx.x1 = ft2.c1 AND ftx.x1 = 1; -- ERROR
 ERROR:  invalid input syntax for integer: "foo"
-CONTEXT:  column "c8" of foreign table "ft1"
-SELECT  ft1.c1,  ft2.c2, ft1 FROM ft1, ft2 WHERE ft1.c1 = ft2.c1 AND ft1.c1 = 1; -- ERROR
+CONTEXT:  column "x8" of foreign table "ftx"
+SELECT ftx.x1, ft2.c2, ftx FROM ft1 ftx(x1,x2,x3,x4,x5,x6,x7,x8), ft2
+  WHERE ftx.x1 = ft2.c1 AND ftx.x1 = 1; -- ERROR
 ERROR:  invalid input syntax for integer: "foo"
-CONTEXT:  whole-row reference to foreign table "ft1"
+CONTEXT:  whole-row reference to foreign table "ftx"
 ALTER FOREIGN TABLE ft1 ALTER COLUMN c8 TYPE user_enum;
 -- ===================================================================
 -- subtransaction