Function plpgsql_post_column_ref

src/pl/plpgsql/src/pl_comp.c:1126–1165

* plpgsql_post_column_ref parser callback after parsing a ColumnRef */

 * plpgsql_post_column_ref		parser callback after parsing a ColumnRef
 */
static Node *
plpgsql_post_column_ref(ParseState *pstate, ColumnRef *cref, Node *var)
{
	PLpgSQL_expr *expr = (PLpgSQL_expr *) pstate->p_ref_hook_state;
	Node	   *myvar;

	if (expr->func->resolve_option == PLPGSQL_RESOLVE_VARIABLE)
		return NULL;			/* we already found there's no match */

	if (expr->func->resolve_option == PLPGSQL_RESOLVE_COLUMN && var != NULL)
		return NULL;			/* there's a table column, prefer that */

	/*
	 * If we find a record/row variable but can't match a field name, throw
	 * error if there was no core resolution for the ColumnRef either.  In
	 * that situation, the reference is inevitably going to fail, and
	 * complaining about the record/row variable is likely to be more on-point
	 * than the core parser's error message.  (It's too bad we don't have
	 * access to transformColumnRef's internal crerr state here, as in case of
	 * a conflict with a table name this could still be less than the most
	 * helpful error message possible.)
	 */
	myvar = resolve_column_ref(pstate, expr, cref, (var == NULL));

	if (myvar != NULL && var != NULL)
	{
		/*
		 * We could leave it to the core parser to throw this error, but we
		 * can add a more useful detail message than the core could.
		 */
		ereport(ERROR,
				(errcode(ERRCODE_AMBIGUOUS_COLUMN),
				 errmsg("column reference \"%s\" is ambiguous",
						NameListToString(cref->fields)),
				 errdetail("It could refer to either a PL/pgSQL variable or a table column."),
				 parser_errposition(pstate, cref->location)));
	}

	return myvar;
}

/*
 * plpgsql_param_ref		parser callback for ParamRefs ($n symbols)