Re: remaining sql/json patches

Hi,

On 2023-09-29 13:57:46 +0900, Amit Langote wrote:
> Thanks. I will push the attached 0001 shortly.

Sorry for not looking at this earlier.

Have you done benchmarking to verify that 0001 does not cause performance
regressions? I'd not be suprised if it did. I'd split the soft-error path into
a separate opcode. For JIT it can largely be implemented using the same code,
eliding the check if it's the non-soft path. Or you can just put it into an
out-of-line function.

I don't like adding more stuff to ExprState. This one seems particularly
awkward, because it might be used by more than one level in an expression
subtree, which means you really need to save/restore old values when
recursing.

> @@ -1579,25 +1582,13 @@ ExecInitExprRec(Expr *node, ExprState *state,
>
> /* lookup the result type's input function */
> scratch.d.iocoerce.finfo_in = palloc0(sizeof(FmgrInfo));
> - scratch.d.iocoerce.fcinfo_data_in = palloc0(SizeForFunctionCallInfo(3));
> -
> getTypeInputInfo(iocoerce->resulttype,
> - &iofunc, &typioparam);
> + &iofunc, &scratch.d.iocoerce.typioparam);
> fmgr_info(iofunc, scratch.d.iocoerce.finfo_in);
> fmgr_info_set_expr((Node *) node, scratch.d.iocoerce.finfo_in);
> - InitFunctionCallInfoData(*scratch.d.iocoerce.fcinfo_data_in,
> - scratch.d.iocoerce.finfo_in,
> - 3, InvalidOid, NULL, NULL);
>
> - /*
> - * We can preload the second and third arguments for the input
> - * function, since they're constants.
> - */
> - fcinfo_in = scratch.d.iocoerce.fcinfo_data_in;
> - fcinfo_in->args[1].value = ObjectIdGetDatum(typioparam);
> - fcinfo_in->args[1].isnull = false;
> - fcinfo_in->args[2].value = Int32GetDatum(-1);
> - fcinfo_in->args[2].isnull = false;
> + /* Use the ErrorSaveContext passed by the caller. */
> + scratch.d.iocoerce.escontext = state->escontext;
>
> ExprEvalPushStep(state, &scratch);
> break;

I think it's likely that removing the optimization of not needing to set these
arguments ahead of time will result in a performance regression. Not to speak
of initializing the fcinfo from scratch on every evaluation of the expression.

I think this shouldn't not be merged as is.

> src/backend/parser/gram.y | 348 +++++-

This causes a nontrivial increase in the size of the parser (~5% in an
optimized build here), I wonder if we can do better.

> +/*
> + * Push steps to evaluate a JsonExpr and its various subsidiary expressions.
> + */
> +static void
> +ExecInitJsonExpr(JsonExpr *jexpr, ExprState *state,
> + Datum *resv, bool *resnull,
> + ExprEvalStep *scratch)
> +{
> + JsonExprState *jsestate = palloc0(sizeof(JsonExprState));
> + JsonExprPreEvalState *pre_eval = &jsestate->pre_eval;
> + ListCell *argexprlc;
> + ListCell *argnamelc;
> + int skip_step_off = -1;
> + int passing_args_step_off = -1;
> + int coercion_step_off = -1;
> + int coercion_finish_step_off = -1;
> + int behavior_step_off = -1;
> + int onempty_expr_step_off = -1;
> + int onempty_jump_step_off = -1;
> + int onerror_expr_step_off = -1;
> + int onerror_jump_step_off = -1;
> + int result_coercion_jump_step_off = -1;
> + List *adjust_jumps = NIL;
> + ListCell *lc;
> + ExprEvalStep *as;
> +
> + jsestate->jsexpr = jexpr;
> +
> + /*
> + * Add steps to compute formatted_expr, pathspec, and PASSING arg
> + * expressions as things that must be evaluated *before* the actual JSON
> + * path expression.
> + */
> + ExecInitExprRec((Expr *) jexpr->formatted_expr, state,
> + &pre_eval->formatted_expr.value,
> + &pre_eval->formatted_expr.isnull);
> + ExecInitExprRec((Expr *) jexpr->path_spec, state,
> + &pre_eval->pathspec.value,
> + &pre_eval->pathspec.isnull);
> +
> + /*
> + * Before pushing steps for PASSING args, push a step to decide whether to
> + * skip evaluating the args and the JSON path expression depending on
> + * whether either of formatted_expr and pathspec is NULL; see
> + * ExecEvalJsonExprSkip().
> + */
> + scratch->opcode = EEOP_JSONEXPR_SKIP;
> + scratch->d.jsonexpr_skip.jsestate = jsestate;
> + skip_step_off = state->steps_len;
> + ExprEvalPushStep(state, scratch);

Could SKIP be implemented using EEOP_JUMP_IF_NULL with a bit of work? I see
that it sets jsestate->post_eval.jcstate, but I don't understand why it needs
to be done that way. /* ExecEvalJsonExprCoercion() depends on this. */ doesn't
explain that much.

> + /* PASSING args. */
> + jsestate->pre_eval.args = NIL;
> + passing_args_step_off = state->steps_len;
> + forboth(argexprlc, jexpr->passing_values,
> + argnamelc, jexpr->passing_names)
> + {
> + Expr *argexpr = (Expr *) lfirst(argexprlc);
> + String *argname = lfirst_node(String, argnamelc);
> + JsonPathVariable *var = palloc(sizeof(*var));
> +
> + var->name = pstrdup(argname->sval);

Why does this need to be strdup'd?

> + /* Step for the actual JSON path evaluation; see ExecEvalJsonExpr(). */
> + scratch->opcode = EEOP_JSONEXPR_PATH;
> + scratch->d.jsonexpr.jsestate = jsestate;
> + ExprEvalPushStep(state, scratch);
> +
> + /*
> + * Step to handle ON ERROR and ON EMPTY behavior. Also, to handle errors
> + * that may occur during coercion handling.
> + *
> + * See ExecEvalJsonExprBehavior().
> + */
> + scratch->opcode = EEOP_JSONEXPR_BEHAVIOR;
> + scratch->d.jsonexpr_behavior.jsestate = jsestate;
> + behavior_step_off = state->steps_len;
> + ExprEvalPushStep(state, scratch);

From what I can tell there a) can never be a step between EEOP_JSONEXPR_PATH
and EEOP_JSONEXPR_BEHAVIOR b) EEOP_JSONEXPR_PATH ends with an unconditional
branch. What's the point of the two different steps here?

>
> + EEO_CASE(EEOP_JSONEXPR_PATH)
> + {
> + /* too complex for an inline implementation */
> + ExecEvalJsonExpr(state, op, econtext);
> + EEO_NEXT();
> + }

Why does EEOP_JSONEXPR_PATH call ExecEvalJsonExpr, the names don't match...

> + EEO_CASE(EEOP_JSONEXPR_SKIP)
> + {
> + /* too complex for an inline implementation */
> + EEO_JUMP(ExecEvalJsonExprSkip(state, op));
> + }
...

> + EEO_CASE(EEOP_JSONEXPR_COERCION_FINISH)
> + {
> + /* too complex for an inline implementation */
> + EEO_JUMP(ExecEvalJsonExprCoercionFinish(state, op));
> + }

This seems to just return op->d.jsonexpr_coercion_finish.jump_coercion_error
or op->d.jsonexpr_coercion_finish.jump_coercion_done. Which makes me think
it'd be better to return a boolean? Particularly because that's how you
already implemented it for JIT (except that you did it by hardcoding the jump
step to compare to, which seems odd).

Separately, why do we even need a jump for both cases, and not just for the
error case?

> + EEO_CASE(EEOP_JSONEXPR_BEHAVIOR)
> + {
> + /* too complex for an inline implementation */
> + EEO_JUMP(ExecEvalJsonExprBehavior(state, op));
> + }
> +
> + EEO_CASE(EEOP_JSONEXPR_COERCION)
> + {
> + /* too complex for an inline implementation */
> + EEO_JUMP(ExecEvalJsonExprCoercion(state, op, econtext,
> + *op->resvalue, *op->resnull));
> + }

I wonder if this is the right design for this op - you're declaring this to be
op not worth implementing inline, yet you then have it implemented by hand for JIT.

> +/*
> + * Evaluate given JsonExpr by performing the specified JSON operation.
> + *
> + * This also populates the JsonExprPostEvalState with the information needed
> + * by the subsequent steps that handle the specified JsonBehavior.
> + */
> +void
> +ExecEvalJsonExpr(ExprState *state, ExprEvalStep *op, ExprContext *econtext)
> +{
> + JsonExprState *jsestate = op->d.jsonexpr.jsestate;
> + JsonExprPreEvalState *pre_eval = &jsestate->pre_eval;
> + JsonExprPostEvalState *post_eval = &jsestate->post_eval;
> + JsonExpr *jexpr = jsestate->jsexpr;
> + Datum item;
> + Datum res = (Datum) 0;
> + bool resnull = true;
> + JsonPath *path;
> + bool throw_error = (jexpr->on_error->btype == JSON_BEHAVIOR_ERROR);
> + bool *error = &post_eval->error;
> + bool *empty = &post_eval->empty;
> +
> + item = pre_eval->formatted_expr.value;
> + path = DatumGetJsonPathP(pre_eval->pathspec.value);
> +
> + /* Reset JsonExprPostEvalState for this evaluation. */
> + memset(post_eval, 0, sizeof(*post_eval));
> +
> + switch (jexpr->op)
> + {
> + case JSON_EXISTS_OP:
> + {
> + bool exists = JsonPathExists(item, path,
> + !throw_error ? error : NULL,
> + pre_eval->args);
> +
> + post_eval->jcstate = jsestate->result_jcstate;
> + if (*error)
> + {
> + *op->resnull = true;
> + *op->resvalue = (Datum) 0;
> + return;
> + }
> +
> + resnull = false;
> + res = BoolGetDatum(exists);
> + break;
> + }

Kinda seems there should be a EEOP_JSON_EXISTS/JSON_QUERY_OP op, instead of
implementing it all inside ExecEvalJsonExpr. I think this might obsolete
needing to rediscover that the value is null in SKIP etc?

> + case JSON_QUERY_OP:
> + res = JsonPathQuery(item, path, jexpr->wrapper, empty,
> + !throw_error ? error : NULL,
> + pre_eval->args);
> +
> + post_eval->jcstate = jsestate->result_jcstate;
> + if (*error)
> + {
> + *op->resnull = true;
> + *op->resvalue = (Datum) 0;
> + return;
> + }
> + resnull = !DatumGetPointer(res);

Shoulnd't this check empty?

FWIW, it's also pretty odd that JsonPathQuery() once
return (Datum) 0;
and later does
return PointerGetDatum(NULL);

> + case JSON_VALUE_OP:
> + {
> + JsonbValue *jbv = JsonPathValue(item, path, empty,
> + !throw_error ? error : NULL,
> + pre_eval->args);
> +
> + /* Might get overridden below by an item_jcstate. */
> + post_eval->jcstate = jsestate->result_jcstate;
> + if (*error)
> + {
> + *op->resnull = true;
> + *op->resvalue = (Datum) 0;
> + return;
> + }
> +
> + if (!jbv) /* NULL or empty */
> + {
> + resnull = true;
> + break;
> + }
> +
> + Assert(!*empty);
> +
> + resnull = false;
> +
> + /* Coerce scalar item to the output type */
> +
> + /*
> + * If the requested output type is json(b), use
> + * JsonExprState.result_coercion to do the coercion.
> + */
> + if (jexpr->returning->typid == JSONOID ||
> + jexpr->returning->typid == JSONBOID)
> + {
> + /* Use result_coercion from json[b] to the output type */
> + res = JsonbPGetDatum(JsonbValueToJsonb(jbv));
> + break;
> + }
> +
> + /*
> + * Else, use one of the item_coercions.
> + *
> + * Error out if no cast exists to coerce SQL/JSON item to the
> + * the output type.
> + */
> + res = ExecPrepareJsonItemCoercion(jbv,
> + jsestate->item_jcstates,
> + &post_eval->jcstate);
> + if (post_eval->jcstate &&
> + post_eval->jcstate->coercion &&
> + (post_eval->jcstate->coercion->via_io ||
> + post_eval->jcstate->coercion->via_populate))
> + {
> + if (!throw_error)
> + {
> + *op->resnull = true;
> + *op->resvalue = (Datum) 0;
> + return;
> + }
> +
> + /*
> + * Coercion via I/O means here that the cast to the target
> + * type simply does not exist.
> + */
> + ereport(ERROR,
> + (errcode(ERRCODE_SQL_JSON_ITEM_CANNOT_BE_CAST_TO_TARGET_TYPE),
> + errmsg("SQL/JSON item cannot be cast to target type")));
> + }
> + break;
> + }
> +
> + default:
> + elog(ERROR, "unrecognized SQL/JSON expression op %d", jexpr->op);
> + *op->resnull = true;
> + *op->resvalue = (Datum) 0;
> + return;
> + }
> +
> + /*
> + * If the ON EMPTY behavior is to cause an error, do so here. Other
> + * behaviors will be handled in ExecEvalJsonExprBehavior().
> + */
> + if (*empty)
> + {
> + Assert(jexpr->on_empty); /* it is not JSON_EXISTS */
> +
> + if (jexpr->on_empty->btype == JSON_BEHAVIOR_ERROR)
> + {
> + if (!throw_error)
> + {
> + *op->resnull = true;
> + *op->resvalue = (Datum) 0;
> + return;
> + }
> +
> + ereport(ERROR,
> + (errcode(ERRCODE_NO_SQL_JSON_ITEM),
> + errmsg("no SQL/JSON item")));
> + }
> + }
> +
> + *op->resvalue = res;
> + *op->resnull = resnull;
> +}
> +
> +/*
> + * Skip calling ExecEvalJson() on the given JsonExpr?

I don't think that function exists.

> + * Returns the step address to be performed next.
> + */
> +int
> +ExecEvalJsonExprSkip(ExprState *state, ExprEvalStep *op)
> +{
> + JsonExprState *jsestate = op->d.jsonexpr_skip.jsestate;
> +
> + /*
> + * Skip if either of the input expressions has turned out to be NULL,
> + * though do execute domain checks for NULLs, which are handled by the
> + * coercion step.
> + */
> + if (jsestate->pre_eval.formatted_expr.isnull ||
> + jsestate->pre_eval.pathspec.isnull)
> + {
> + *op->resvalue = (Datum) 0;
> + *op->resnull = true;
> +
> + /* ExecEvalJsonExprCoercion() depends on this. */
> + jsestate->post_eval.jcstate = jsestate->result_jcstate;
> +
> + return op->d.jsonexpr_skip.jump_coercion;
> + }
> +
> + /*
> + * Go evaluate the PASSING args if any and subsequently JSON path itself.
> + */
> + return op->d.jsonexpr_skip.jump_passing_args;
> +}
> +
> +/*
> + * Returns the step address to perform the JsonBehavior applicable to
> + * the JSON item that resulted from evaluating the given JsonExpr.
> + *
> + * Returns the step address to be performed next.
> + */
> +int
> +ExecEvalJsonExprBehavior(ExprState *state, ExprEvalStep *op)
> +{
> + JsonExprState *jsestate = op->d.jsonexpr_behavior.jsestate;
> + JsonExprPostEvalState *post_eval = &jsestate->post_eval;
> + JsonBehavior *behavior = NULL;
> + int jump_to = -1;
> +
> + if (post_eval->error || post_eval->coercion_error)
> + {
> + behavior = jsestate->jsexpr->on_error;
> + jump_to = op->d.jsonexpr_behavior.jump_onerror_expr;
> + }
> + else if (post_eval->empty)
> + {
> + behavior = jsestate->jsexpr->on_empty;
> + jump_to = op->d.jsonexpr_behavior.jump_onempty_expr;
> + }
> + else if (!post_eval->coercion_done)
> + {
> + /*
> + * If no error or the JSON item is not empty, directly go to the
> + * coercion step to coerce the item as is.
> + */
> + return op->d.jsonexpr_behavior.jump_coercion;
> + }
> +
> + Assert(behavior);
> +
> + /*
> + * Set up for coercion step that will run to coerce a non-default behavior
> + * value. It should use result_coercion, if any. Errors that may occur
> + * should be thrown for JSON ops other than JSON_VALUE_OP.
> + */
> + if (behavior->btype != JSON_BEHAVIOR_DEFAULT)
> + {
> + post_eval->jcstate = jsestate->result_jcstate;
> + post_eval->coercing_behavior_expr = true;
> + }
> +
> + Assert(jump_to >= 0);
> + return jump_to;
> +}
> +
> +/*
> + * Evaluate or return the step address to evaluate a coercion of a JSON item
> + * to the target type. The former if the coercion must be done right away by
> + * calling the target type's input function, and for some types, by calling
> + * json_populate_type().
> + *
> + * Returns the step address to be performed next.
> + */
> +int
> +ExecEvalJsonExprCoercion(ExprState *state, ExprEvalStep *op,
> + ExprContext *econtext,
> + Datum res, bool resnull)
> +{
> + JsonExprState *jsestate = op->d.jsonexpr_coercion.jsestate;
> + JsonExpr *jexpr = jsestate->jsexpr;
> + JsonExprPostEvalState *post_eval = &jsestate->post_eval;
> + JsonCoercionState *jcstate = post_eval->jcstate;
> + char *val_string = NULL;
> + bool omit_quotes = false;
> +
> + switch (jexpr->op)
> + {
> + case JSON_EXISTS_OP:
> + if (jcstate && jcstate->jump_eval_expr >= 0)
> + return jcstate->jump_eval_expr;

Shouldn't this be a compile-time check and instead be handled by simply not
emitting a step instead?

> + /* No coercion needed. */
> + post_eval->coercion_done = true;
> + return op->d.jsonexpr_coercion.jump_coercion_done;

Which then means we also don't need to emit anything here, no?

> +/*
> + * Prepare SQL/JSON item coercion to the output type. Returned a datum of the
> + * corresponding SQL type and a pointer to the coercion state.
> + */
> +static Datum
> +ExecPrepareJsonItemCoercion(JsonbValue *item, List *item_jcstates,
> + JsonCoercionState **p_item_jcstate)

I might have missed it, but if not: The whole way the coercion stuff works
needs a decent comment explaining how things fit together.

What does "item" really mean here?

> +{
> + JsonCoercionState *item_jcstate;
> + Datum res;
> + JsonbValue buf;
> +
> + if (item->type == jbvBinary &&
> + JsonContainerIsScalar(item->val.binary.data))
> + {
> + bool res PG_USED_FOR_ASSERTS_ONLY;
> +
> + res = JsonbExtractScalar(item->val.binary.data, &buf);
> + item = &buf;
> + Assert(res);
> + }
> +
> + /* get coercion state reference and datum of the corresponding SQL type */
> + switch (item->type)
> + {
> + case jbvNull:
> + item_jcstate = list_nth(item_jcstates, JsonItemTypeNull);

This seems quite odd. We apparently have a fixed-length array, where specific
offsets have specific meanings, yet it's encoded as a list that's then
accessed with constant offsets?

Right now ExecEvalJsonExpr() stores what ExecPrepareJsonItemCoercion() chooses
in post_eval->jcstate. Which the immediately following
ExecEvalJsonExprBehavior() then digs out again. Then there's also control flow
via post_eval->coercing_behavior_expr. This is ... not nice.

ISTM that jsestate should have an array of jump targets, indexed by
item->type. Which, for llvm IR, you can encode as a switch statement, instead
of doing control flow via JsonExprState/JsonExprPostEvalState. There's
obviously a bit more needed, but I think something like that should work, and
simplify things a fair bit.

> @@ -15711,6 +15721,192 @@ func_expr_common_subexpr:
> n->location = @1;
> $$ = (Node *) n;
> }
> + | JSON_QUERY '('
> + json_api_common_syntax
> + json_returning_clause_opt
> + json_wrapper_behavior
> + json_quotes_clause_opt
> + ')'
> + {
> + JsonFuncExpr *n = makeNode(JsonFuncExpr);
> +
> + n->op = JSON_QUERY_OP;
> + n->common = (JsonCommon *) $3;
> + n->output = (JsonOutput *) $4;
> + n->wrapper = $5;
> + if (n->wrapper != JSW_NONE && $6 != JS_QUOTES_UNSPEC)
> + ereport(ERROR,
> + (errcode(ERRCODE_SYNTAX_ERROR),
> + errmsg("SQL/JSON QUOTES behavior must not be specified when WITH WRAPPER is used"),
> + parser_errposition(@6)));
> + n->quotes = $6;
> + n->location = @1;
> + $$ = (Node *) n;
> + }
> + | JSON_QUERY '('
> + json_api_common_syntax
> + json_returning_clause_opt
> + json_wrapper_behavior
> + json_quotes_clause_opt
> + json_query_behavior ON EMPTY_P
> + ')'
> + {
> + JsonFuncExpr *n = makeNode(JsonFuncExpr);
> +
> + n->op = JSON_QUERY_OP;
> + n->common = (JsonCommon *) $3;
> + n->output = (JsonOutput *) $4;
> + n->wrapper = $5;
> + if (n->wrapper != JSW_NONE && $6 != JS_QUOTES_UNSPEC)
> + ereport(ERROR,
> + (errcode(ERRCODE_SYNTAX_ERROR),
> + errmsg("SQL/JSON QUOTES behavior must not be specified when WITH WRAPPER is used"),
> + parser_errposition(@6)));
> + n->quotes = $6;
> + n->on_empty = $7;
> + n->location = @1;
> + $$ = (Node *) n;
> + }
> + | JSON_QUERY '('
> + json_api_common_syntax
> + json_returning_clause_opt
> + json_wrapper_behavior
> + json_quotes_clause_opt
> + json_query_behavior ON ERROR_P
> + ')'
> + {
> + JsonFuncExpr *n = makeNode(JsonFuncExpr);
> +
> + n->op = JSON_QUERY_OP;
> + n->common = (JsonCommon *) $3;
> + n->output = (JsonOutput *) $4;
> + n->wrapper = $5;
> + if (n->wrapper != JSW_NONE && $6 != JS_QUOTES_UNSPEC)
> + ereport(ERROR,
> + (errcode(ERRCODE_SYNTAX_ERROR),
> + errmsg("SQL/JSON QUOTES behavior must not be specified when WITH WRAPPER is used"),
> + parser_errposition(@6)));
> + n->quotes = $6;
> + n->on_error = $7;
> + n->location = @1;
> + $$ = (Node *) n;
> + }
> + | JSON_QUERY '('
> + json_api_common_syntax
> + json_returning_clause_opt
> + json_wrapper_behavior
> + json_quotes_clause_opt
> + json_query_behavior ON EMPTY_P
> + json_query_behavior ON ERROR_P
> + ')'
> + {
> + JsonFuncExpr *n = makeNode(JsonFuncExpr);
> +
> + n->op = JSON_QUERY_OP;
> + n->common = (JsonCommon *) $3;
> + n->output = (JsonOutput *) $4;
> + n->wrapper = $5;
> + if (n->wrapper != JSW_NONE && $6 != JS_QUOTES_UNSPEC)
> + ereport(ERROR,
> + (errcode(ERRCODE_SYNTAX_ERROR),
> + errmsg("SQL/JSON QUOTES behavior must not be specified when WITH WRAPPER is used"),
> + parser_errposition(@6)));
> + n->quotes = $6;
> + n->on_empty = $7;
> + n->on_error = $10;
> + n->location = @1;
> + $$ = (Node *) n;
> + }

I'm sure we can find a way to deduplicate this.

> + | JSON_EXISTS '('
> + json_api_common_syntax
> + json_returning_clause_opt
> + ')'
> + {
> + JsonFuncExpr *p = makeNode(JsonFuncExpr);
> +
> + p->op = JSON_EXISTS_OP;
> + p->common = (JsonCommon *) $3;
> + p->output = (JsonOutput *) $4;
> + p->location = @1;
> + $$ = (Node *) p;
> + }
> + | JSON_EXISTS '('
> + json_api_common_syntax
> + json_returning_clause_opt
> + json_exists_behavior ON ERROR_P
> + ')'
> + {
> + JsonFuncExpr *p = makeNode(JsonFuncExpr);
> +
> + p->op = JSON_EXISTS_OP;
> + p->common = (JsonCommon *) $3;
> + p->output = (JsonOutput *) $4;
> + p->on_error = $5;
> + p->location = @1;
> + $$ = (Node *) p;
> + }
> + | JSON_VALUE '('
> + json_api_common_syntax
> + json_returning_clause_opt
> + ')'
> + {
> + JsonFuncExpr *n = makeNode(JsonFuncExpr);
> +
> + n->op = JSON_VALUE_OP;
> + n->common = (JsonCommon *) $3;
> + n->output = (JsonOutput *) $4;
> + n->location = @1;
> + $$ = (Node *) n;
> + }
> +
> + | JSON_VALUE '('
> + json_api_common_syntax
> + json_returning_clause_opt
> + json_value_behavior ON EMPTY_P
> + ')'
> + {
> + JsonFuncExpr *n = makeNode(JsonFuncExpr);
> +
> + n->op = JSON_VALUE_OP;
> + n->common = (JsonCommon *) $3;
> + n->output = (JsonOutput *) $4;
> + n->on_empty = $5;
> + n->location = @1;
> + $$ = (Node *) n;
> + }
> + | JSON_VALUE '('
> + json_api_common_syntax
> + json_returning_clause_opt
> + json_value_behavior ON ERROR_P
> + ')'
> + {
> + JsonFuncExpr *n = makeNode(JsonFuncExpr);
> +
> + n->op = JSON_VALUE_OP;
> + n->common = (JsonCommon *) $3;
> + n->output = (JsonOutput *) $4;
> + n->on_error = $5;
> + n->location = @1;
> + $$ = (Node *) n;
> + }
> +
> + | JSON_VALUE '('
> + json_api_common_syntax
> + json_returning_clause_opt
> + json_value_behavior ON EMPTY_P
> + json_value_behavior ON ERROR_P
> + ')'
> + {
> + JsonFuncExpr *n = makeNode(JsonFuncExpr);
> +
> + n->op = JSON_VALUE_OP;
> + n->common = (JsonCommon *) $3;
> + n->output = (JsonOutput *) $4;
> + n->on_empty = $5;
> + n->on_error = $8;
> + n->location = @1;
> + $$ = (Node *) n;
> + }
> ;

And this.

> +json_query_behavior:
> + ERROR_P { $$ = makeJsonBehavior(JSON_BEHAVIOR_ERROR, NULL, @1); }
> + | NULL_P { $$ = makeJsonBehavior(JSON_BEHAVIOR_NULL, NULL, @1); }
> + | DEFAULT a_expr { $$ = makeJsonBehavior(JSON_BEHAVIOR_DEFAULT, $2, @1); }
> + | EMPTY_P ARRAY { $$ = makeJsonBehavior(JSON_BEHAVIOR_EMPTY_ARRAY, NULL, @1); }
> + | EMPTY_P OBJECT_P { $$ = makeJsonBehavior(JSON_BEHAVIOR_EMPTY_OBJECT, NULL, @1); }
> + /* non-standard, for Oracle compatibility only */
> + | EMPTY_P { $$ = makeJsonBehavior(JSON_BEHAVIOR_EMPTY_ARRAY, NULL, @1); }
> + ;

> +json_exists_behavior:
> + ERROR_P { $$ = makeJsonBehavior(JSON_BEHAVIOR_ERROR, NULL, @1); }
> + | TRUE_P { $$ = makeJsonBehavior(JSON_BEHAVIOR_TRUE, NULL, @1); }
> + | FALSE_P { $$ = makeJsonBehavior(JSON_BEHAVIOR_FALSE, NULL, @1); }
> + | UNKNOWN { $$ = makeJsonBehavior(JSON_BEHAVIOR_UNKNOWN, NULL, @1); }
> + ;
> +
> +json_value_behavior:
> + NULL_P { $$ = makeJsonBehavior(JSON_BEHAVIOR_NULL, NULL, @1); }
> + | ERROR_P { $$ = makeJsonBehavior(JSON_BEHAVIOR_ERROR, NULL, @1); }
> + | DEFAULT a_expr { $$ = makeJsonBehavior(JSON_BEHAVIOR_DEFAULT, $2, @1); }
> + ;

This also seems like it could use some dedup.

Greetings,

Andres Freund