plv8 swallows error stack

[bendiy]

If PostgreSQL throws an error up the stack from a plv8.execute(...), the actual error stack is swallowed and hidden. When using plpgsql, the actual error line is reported.

Here's an example to demonstrate this:

CREATE OR REPLACE FUNCTION public._anerror()
  RETURNS boolean AS
$BODY$
BEGIN

  RAISE EXCEPTION 'my error';

  RETURN true;

END;
$BODY$
LANGUAGE plpgsql;

CREATE OR REPLACE FUNCTION public._callsanerror()
  RETURNS boolean AS
$BODY$
DECLARE
  something boolean;
BEGIN
  something := _anerror();

  RETURN something;
END;
$BODY$
  LANGUAGE plpgsql;

Then call _callsanerror() function either directly or through plpgsql:

SELECT _callsanerror();

Outputs the message:

ERROR:  my error
CONTEXT:  PL/pgSQL function _callsanerror() line 5 at assignment
********** Error **********

ERROR: my error
SQL state: P0001
Context: PL/pgSQL function _callsanerror() line 5 at assignment

DO $$
BEGIN
  SELECT _callsanerror();
END;
$$ LANGUAGE plpgsql;

Outputs the message:

ERROR:  my error
CONTEXT:  PL/pgSQL function _callsanerror() line 5 at assignment
SQL statement "SELECT _callsanerror()"
PL/pgSQL function inline_code_block line 3 at SQL statement
********** Error **********

ERROR: my error
SQL state: P0001
Context: PL/pgSQL function _callsanerror() line 5 at assignment
SQL statement "SELECT _callsanerror()"
PL/pgSQL function inline_code_block line 3 at SQL statement

When called from plv8, the relevate stack line that actually threw the error is swallowed:

DO $$
  plv8.execute("SELECT _callsanerror();");
$$ LANGUAGE plv8;

Outputs the message:

ERROR:  my error
DETAIL:  undefined() LINE 2:   plv8.execute("SELECT _callsanerror();");
********** Error **********

ERROR: my error
SQL state: XX000
Detail: undefined() LINE 2:   plv8.execute("SELECT _callsanerror();");

No reference to Context: PL/pgSQL function _callsanerror() line 5 at assignment.

Is there any way to make use of PG_EXCEPTION_CONTEXT and return the full stack?
https://www.postgresql.org/docs/current/static/plpgsql-control-structures.html#PLPGSQL-EXCEPTION-DIAGNOSTICS

[JerrySievert]

it hasn't been super high priority - I will try to spend some time on it, but if anyone else wants to send a PR, I'd be happy to look at it.

[bendiy]

Calling:

    RAISE EXCEPTION USING
      MESSAGE = 'A First Name is required.',
      DETAIL = 'A detailed message??',
      HINT = 'Do this to avoid that.',
      COLUMN = 'firstName'
      ;

Right now, the error object looks like:

{
  "column_name":"firstName",
  "constraint_name":null,
  "datatype_name":null,
  "message": "A First Name is required.",
  "schema_name":null,
  "sqlerrcode":"P0001",
  "stack": "some stack trace here...",
  "table_name":null
}

It would be nice to also include the following:
DETAIL
HINT

[bendiy]

Error messages are reported here:

plv8/plv8.cc

Lines 1769 to 1773 in 57db50d

	if (strstr(m_msg, "Error: ") == m_msg)
	m_msg += 7;
	appendStringInfo(&str, "%s() LINE %d: %s",
	script.str("?"), lineno - 1, source.str("?"));
	m_detail = str.data;

[bendiy]

Looking at how psycopg2 does it, they use libpg and call PQerrorMessage():
https://www.postgresql.org/docs/current/static/libpq-status.html#LIBPQ-PQERRORMESSAGE

[bendiy]

PostgreSQL's CopyErrorData() has:
detail
detail_log
hint
context
internalquery
assoc_context
https://doxygen.postgresql.org/elog_8c_source.html#l01497
And a few more that might exist:
https://doxygen.postgresql.org/elog_8h_source.html#l00329

I think edata->context is the stack:
https://doxygen.postgresql.org/elog_8h.html#ad811b6bbae02e9f946cef448df4f6701

That can be added here:

plv8/plv8_func.cc

Line 262 in 57db50d

ErrorData *edata = CopyErrorData();