SQL/JSON: Fix error-handling of some JsonBehavior expressions

To ensure that the errors of executing a JsonBehavior expression that
is coerced in the parser are caught instead of being thrown directly,
pass ErrorSaveContext to ExecInitExprRec() when initializing it.
Also, add a EEOP_JSONEXPR_COERCION_FINISH step to handle the errors
that are caught that way.

Discussion: https://postgr.es/m/CACJufxEo4sUjKCYtda0_qt9tazqqKPmF1cqhW9KBOUeJFqQd2g@mail.gmail.com
Backpatch-through: 17

src/backend/executor/execExpr.c

@@ -4400,6 +4400,8 @@ ExecInitJsonExpr(JsonExpr *jsexpr, ExprState *state,
 	if (jsexpr->on_error &&
 		jsexpr->on_error->btype != JSON_BEHAVIOR_ERROR)
 	{
+		ErrorSaveContext *saved_escontext;
+
 		jsestate->jump_error = state->steps_len;
 
 		/* JUMP to end if false, that is, skip the ON ERROR expression. */
@@ -4410,15 +4412,36 @@ ExecInitJsonExpr(JsonExpr *jsexpr, ExprState *state,
 		scratch->d.jump.jumpdone = -1;	/* set below */
 		ExprEvalPushStep(state, scratch);
 
-		/* Steps to evaluate the ON ERROR expression */
+		/*
+		 * Steps to evaluate the ON ERROR expression; handle errors softly to
+		 * rethrow them in COERCION_FINISH step that will be added later.
+		 */
+		saved_escontext = state->escontext;
+		state->escontext = escontext;
 		ExecInitExprRec((Expr *) jsexpr->on_error->expr,
 						state, resv, resnull);
+		state->escontext = saved_escontext;
 
 		/* Step to coerce the ON ERROR expression if needed */
 		if (jsexpr->on_error->coerce)
 			ExecInitJsonCoercion(state, jsexpr->returning, escontext,
 								 jsexpr->omit_quotes, resv, resnull);
 
+		/*
+		 * Add a COERCION_FINISH step to check for errors that may occur when
+		 * coercing and rethrow them.
+		 */
+		if (jsexpr->on_error->coerce ||
+			IsA(jsexpr->on_error->expr, CoerceViaIO) ||
+			IsA(jsexpr->on_error->expr, CoerceToDomain))
+		{
+			scratch->opcode = EEOP_JSONEXPR_COERCION_FINISH;
+			scratch->resvalue = resv;
+			scratch->resnull = resnull;
+			scratch->d.jsonexpr.jsestate = jsestate;
+			ExprEvalPushStep(state, scratch);
+		}
+
 		/* JUMP to end to skip the ON EMPTY steps added below. */
 		jumps_to_end = lappend_int(jumps_to_end, state->steps_len);
 		scratch->opcode = EEOP_JUMP;
@@ -4433,6 +4456,8 @@ ExecInitJsonExpr(JsonExpr *jsexpr, ExprState *state,
 	if (jsexpr->on_empty != NULL &&
 		jsexpr->on_empty->btype != JSON_BEHAVIOR_ERROR)
 	{
+		ErrorSaveContext *saved_escontext;
+
 		jsestate->jump_empty = state->steps_len;
 
 		/* JUMP to end if false, that is, skip the ON EMPTY expression. */
@@ -4443,14 +4468,36 @@ ExecInitJsonExpr(JsonExpr *jsexpr, ExprState *state,
 		scratch->d.jump.jumpdone = -1;	/* set below */
 		ExprEvalPushStep(state, scratch);
 
-		/* Steps to evaluate the ON EMPTY expression */
+		/*
+		 * Steps to evaluate the ON EMPTY expression; handle errors softly to
+		 * rethrow them in COERCION_FINISH step that will be added later.
+		 */
+		saved_escontext = state->escontext;
+		state->escontext = escontext;
 		ExecInitExprRec((Expr *) jsexpr->on_empty->expr,
 						state, resv, resnull);
+		state->escontext = saved_escontext;
 
 		/* Step to coerce the ON EMPTY expression if needed */
 		if (jsexpr->on_empty->coerce)
 			ExecInitJsonCoercion(state, jsexpr->returning, escontext,
 								 jsexpr->omit_quotes, resv, resnull);
+
+		/*
+		 * Add a COERCION_FINISH step to check for errors that may occur when
+		 * coercing and rethrow them.
+		 */
+		if (jsexpr->on_empty->coerce ||
+			IsA(jsexpr->on_empty->expr, CoerceViaIO) ||
+			IsA(jsexpr->on_empty->expr, CoerceToDomain))
+		{
+
+			scratch->opcode = EEOP_JSONEXPR_COERCION_FINISH;
+			scratch->resvalue = resv;
+			scratch->resnull = resnull;
+			scratch->d.jsonexpr.jsestate = jsestate;
+			ExprEvalPushStep(state, scratch);
+		}
 	}
 
 	foreach(lc, jumps_to_end)

src/backend/executor/execExprInterp.c

@@ -4558,6 +4558,12 @@ ExecEvalJsonCoercionFinish(ExprState *state, ExprEvalStep *op)
 		*op->resvalue = (Datum) 0;
 		*op->resnull = true;
 		jsestate->error.value = BoolGetDatum(true);
+
+		/*
+		 * Reset for next use such as for catching errors when coercing a
+		 * JsonBehavior expression.
+		 */
+		jsestate->escontext.error_occurred = false;
 	}
 }
 

src/test/regress/expected/sqljson_jsontable.out

@@ -227,7 +227,11 @@ SELECT * FROM JSON_TABLE(jsonb '{"d1": "H"}', '$'
 
 SELECT * FROM JSON_TABLE(jsonb '{"d1": "H"}', '$'
     COLUMNS (js1 jsonb_test_domain PATH '$.a2' DEFAULT 'foo'::jsonb_test_domain ON EMPTY));
-ERROR:  value for domain jsonb_test_domain violates check constraint "jsonb_test_domain_check"
+ js1 
+-----
+ 
+(1 row)
+
 SELECT * FROM JSON_TABLE(jsonb '{"d1": "H"}', '$'
     COLUMNS (js1 jsonb_test_domain PATH '$.a2' DEFAULT 'foo1'::jsonb_test_domain ON EMPTY));
  js1  

src/test/regress/expected/sqljson_queryfuncs.out

@@ -1232,7 +1232,11 @@ DROP TABLE test_jsonb_mutability;
 DROP FUNCTION ret_setint;
 CREATE DOMAIN queryfuncs_test_domain AS text CHECK (value <> 'foo');
 SELECT JSON_VALUE(jsonb '{"d1": "H"}', '$.a2' RETURNING queryfuncs_test_domain DEFAULT 'foo'::queryfuncs_test_domain ON EMPTY);
-ERROR:  value for domain queryfuncs_test_domain violates check constraint "queryfuncs_test_domain_check"
+ json_value 
+------------
+ 
+(1 row)
+
 SELECT JSON_VALUE(jsonb '{"d1": "H"}', '$.a2' RETURNING queryfuncs_test_domain DEFAULT 'foo1'::queryfuncs_test_domain ON EMPTY);
  json_value 
 ------------