SQL/JSON: Always coerce JsonExpr result at runtime

Instead of looking up casts at parse time for converting the result
of JsonPath* query functions to the specified or the default
RETURNING type, always perform the conversion at runtime using either
the target type's input function or the function
json_populate_type().

There are two motivations for this change:

1. json_populate_type() coerces to types with typmod such that any
   string values that exceed length limit cause an error instead of
   silent truncation, which is necessary to be standard-conforming.

2. It was possible to end up with a cast expression that doesn't
   support soft handling of errors causing bugs in the of handling
   ON ERROR clause.

JsonExpr.coercion_expr which would store the cast expression is no
longer necessary, so remove.

Bump catversion because stored rules change because of the above
removal.

Reported-by: Alvaro Herrera <alvherre@alvh.no-ip.org>
Reviewed-by: Jian He <jian.universality@gmail.com>
Discussion: Discussion: https://postgr.es/m/202405271326.5a5rprki64aw%40alvherre.pgsql

Author: amitlan

src/backend/executor/execExpr.c

@@ -92,7 +92,7 @@ static void ExecInitJsonExpr(JsonExpr *jsexpr, ExprState *state,
 							 Datum *resv, bool *resnull,
 							 ExprEvalStep *scratch);
 static void ExecInitJsonCoercion(ExprState *state, JsonReturning *returning,
-								 ErrorSaveContext *escontext,
+								 ErrorSaveContext *escontext, bool omit_quotes,
 								 Datum *resv, bool *resnull);
 
 
@@ -4313,13 +4313,15 @@ ExecInitJsonExpr(JsonExpr *jsexpr, ExprState *state,
 	ExprEvalPushStep(state, scratch);
 
 	/*
-	 * Jump to coerce the NULL using coercion_expr if present.  Coercing NULL
-	 * is only interesting when the RETURNING type is a domain whose
-	 * constraints must be checked.  jsexpr->coercion_expr containing a
-	 * CoerceToDomain node must have been set in that case.
+	 * Jump to coerce the NULL using json_populate_type() if needed.  Coercing
+	 * NULL is only interesting when the RETURNING type is a domain whose
+	 * constraints must be checked.  jsexpr->use_json_coercion must have been
+	 * set in that case.
 	 */
-	if (jsexpr->coercion_expr)
+	if (get_typtype(jsexpr->returning->typid) == TYPTYPE_DOMAIN &&
+		DomainHasConstraints(jsexpr->returning->typid))
 	{
+		Assert(jsexpr->use_json_coercion);
 		scratch->opcode = EEOP_JUMP;
 		scratch->d.jump.jumpdone = state->steps_len + 1;
 		ExprEvalPushStep(state, scratch);
@@ -4337,33 +4339,12 @@ ExecInitJsonExpr(JsonExpr *jsexpr, ExprState *state,
 	 * NULL returned on NULL input as described above.
 	 */
 	jsestate->jump_eval_coercion = -1;
-	if (jsexpr->coercion_expr)
-	{
-		Datum	   *save_innermost_caseval;
-		bool	   *save_innermost_casenull;
-		ErrorSaveContext *save_escontext;
-
-		jsestate->jump_eval_coercion = state->steps_len;
-
-		save_innermost_caseval = state->innermost_caseval;
-		save_innermost_casenull = state->innermost_casenull;
-		save_escontext = state->escontext;
-
-		state->innermost_caseval = resv;
-		state->innermost_casenull = resnull;
-		state->escontext = escontext;
-
-		ExecInitExprRec((Expr *) jsexpr->coercion_expr, state, resv, resnull);
-
-		state->innermost_caseval = save_innermost_caseval;
-		state->innermost_casenull = save_innermost_casenull;
-		state->escontext = save_escontext;
-	}
-	else if (jsexpr->use_json_coercion)
+	if (jsexpr->use_json_coercion)
 	{
 		jsestate->jump_eval_coercion = state->steps_len;
 
-		ExecInitJsonCoercion(state, jsexpr->returning, escontext, resv, resnull);
+		ExecInitJsonCoercion(state, jsexpr->returning, escontext,
+							 jsexpr->omit_quotes, resv, resnull);
 	}
 	else if (jsexpr->use_io_coercion)
 	{
@@ -4435,8 +4416,8 @@ ExecInitJsonExpr(JsonExpr *jsexpr, ExprState *state,
 
 		/* Step to coerce the ON ERROR expression if needed */
 		if (jsexpr->on_error->coerce)
-			ExecInitJsonCoercion(state, jsexpr->returning, escontext, resv,
-								 resnull);
+			ExecInitJsonCoercion(state, jsexpr->returning, escontext,
+								 jsexpr->omit_quotes, resv, resnull);
 
 		/* JUMP to end to skip the ON EMPTY steps added below. */
 		jumps_to_end = lappend_int(jumps_to_end, state->steps_len);
@@ -4468,8 +4449,8 @@ ExecInitJsonExpr(JsonExpr *jsexpr, ExprState *state,
 
 		/* Step to coerce the ON EMPTY expression if needed */
 		if (jsexpr->on_empty->coerce)
-			ExecInitJsonCoercion(state, jsexpr->returning, escontext, resv,
-								 resnull);
+			ExecInitJsonCoercion(state, jsexpr->returning, escontext,
+								 jsexpr->omit_quotes, resv, resnull);
 	}
 
 	foreach(lc, jumps_to_end)
@@ -4488,7 +4469,7 @@ ExecInitJsonExpr(JsonExpr *jsexpr, ExprState *state,
  */
 static void
 ExecInitJsonCoercion(ExprState *state, JsonReturning *returning,
-					 ErrorSaveContext *escontext,
+					 ErrorSaveContext *escontext, bool omit_quotes,
 					 Datum *resv, bool *resnull)
 {
 	ExprEvalStep scratch = {0};
@@ -4501,5 +4482,6 @@ ExecInitJsonCoercion(ExprState *state, JsonReturning *returning,
 	scratch.d.jsonexpr_coercion.targettypmod = returning->typmod;
 	scratch.d.jsonexpr_coercion.json_populate_type_cache = NULL;
 	scratch.d.jsonexpr_coercion.escontext = escontext;
+	scratch.d.jsonexpr_coercion.omit_quotes = omit_quotes;
 	ExprEvalPushStep(state, &scratch);
 }

src/backend/executor/execExprInterp.c

@@ -4303,8 +4303,14 @@ ExecEvalJsonExprPath(ExprState *state, ExprEvalStep *op,
 
 				if (!error)
 				{
-					*op->resvalue = BoolGetDatum(exists);
 					*op->resnull = false;
+					if (jsexpr->use_json_coercion)
+						*op->resvalue = DirectFunctionCall1(jsonb_in,
+															BoolGetDatum(exists) ?
+															CStringGetDatum("true") :
+															CStringGetDatum("false"));
+					else
+						*op->resvalue = BoolGetDatum(exists);
 				}
 			}
 			break;
@@ -4316,22 +4322,6 @@ ExecEvalJsonExprPath(ExprState *state, ExprEvalStep *op,
 										  jsexpr->column_name);
 
 			*op->resnull = (DatumGetPointer(*op->resvalue) == NULL);
-
-			/* Handle OMIT QUOTES. */
-			if (!*op->resnull && jsexpr->omit_quotes)
-			{
-				val_string = JsonbUnquote(DatumGetJsonbP(*op->resvalue));
-
-				/*
-				 * Pass the string as a text value to the cast expression if
-				 * one present.  If not, use the input function call below to
-				 * do the coercion.
-				 */
-				if (jump_eval_coercion >= 0)
-					*op->resvalue =
-						DirectFunctionCall1(textin,
-											PointerGetDatum(val_string));
-			}
 			break;
 
 		case JSON_VALUE_OP:
@@ -4343,7 +4333,7 @@ ExecEvalJsonExprPath(ExprState *state, ExprEvalStep *op,
 
 				if (jbv == NULL)
 				{
-					/* Will be coerced with coercion_expr, if any. */
+					/* Will be coerced with json_populate_type(), if needed. */
 					*op->resvalue = (Datum) 0;
 					*op->resnull = true;
 				}
@@ -4355,18 +4345,22 @@ ExecEvalJsonExprPath(ExprState *state, ExprEvalStep *op,
 						val_string = DatumGetCString(DirectFunctionCall1(jsonb_out,
 																		 JsonbPGetDatum(JsonbValueToJsonb(jbv))));
 					}
+					else if (jsexpr->use_json_coercion)
+					{
+						*op->resvalue = JsonbPGetDatum(JsonbValueToJsonb(jbv));
+						*op->resnull = false;
+					}
 					else
 					{
 						val_string = ExecGetJsonValueItemString(jbv, op->resnull);
 
 						/*
-						 * Pass the string as a text value to the cast
-						 * expression if one present.  If not, use the input
-						 * function call below to do the coercion.
+						 * Simply convert to the default RETURNING type (text)
+						 * if no coercion needed.
 						 */
-						*op->resvalue = PointerGetDatum(val_string);
-						if (jump_eval_coercion >= 0)
-							*op->resvalue = DirectFunctionCall1(textin, *op->resvalue);
+						if (!jsexpr->use_io_coercion)
+							*op->resvalue = DirectFunctionCall1(textin,
+																CStringGetDatum(val_string));
 					}
 				}
 				break;
@@ -4545,13 +4539,14 @@ ExecEvalJsonCoercion(ExprState *state, ExprEvalStep *op,
 									   op->d.jsonexpr_coercion.targettypmod,
 									   &op->d.jsonexpr_coercion.json_populate_type_cache,
 									   econtext->ecxt_per_query_memory,
-									   op->resnull, (Node *) escontext);
+									   op->resnull,
+									   op->d.jsonexpr_coercion.omit_quotes,
+									   (Node *) escontext);
 }
 
 /*
- * Checks if an error occurred either when evaluating JsonExpr.coercion_expr or
- * in ExecEvalJsonCoercion().  If so, this sets JsonExprState.error to trigger
- * the ON ERROR handling steps.
+ * Checks if an error occurred in ExecEvalJsonCoercion().  If so, this sets
+ * JsonExprState.error to trigger the ON ERROR handling steps.
  */
 void
 ExecEvalJsonCoercionFinish(ExprState *state, ExprEvalStep *op)

src/backend/jit/llvm/llvmjit_expr.c

@@ -2010,7 +2010,7 @@ llvm_compile_expr(ExprState *state)
 							v_jump_coercion = l_int32_const(lc, jsestate->jump_eval_coercion);
 							LLVMAddCase(v_switch, v_jump_coercion, b_coercion);
 						}
-						/* coercion_expr code */
+						/* jump_eval_coercion code */
 						LLVMPositionBuilderAtEnd(b, b_coercion);
 						if (jsestate->jump_eval_coercion >= 0)
 							LLVMBuildBr(b, opblocks[jsestate->jump_eval_coercion]);

src/backend/nodes/nodeFuncs.c

@@ -1006,10 +1006,7 @@ exprCollation(const Node *expr)
 			{
 				const JsonExpr *jsexpr = (JsonExpr *) expr;
 
-				if (jsexpr->coercion_expr)
-					coll = exprCollation(jsexpr->coercion_expr);
-				else
-					coll = jsexpr->collation;
+				coll = jsexpr->collation;
 			}
 			break;
 		case T_JsonBehavior:
@@ -1265,10 +1262,7 @@ exprSetCollation(Node *expr, Oid collation)
 			{
 				JsonExpr   *jexpr = (JsonExpr *) expr;
 
-				if (jexpr->coercion_expr)
-					exprSetCollation((Node *) jexpr->coercion_expr, collation);
-				else
-					jexpr->collation = collation;
+				jexpr->collation = collation;
 			}
 			break;
 		case T_JsonBehavior:
@@ -2368,8 +2362,6 @@ expression_tree_walker_impl(Node *node,
 					return true;
 				if (WALK(jexpr->path_spec))
 					return true;
-				if (WALK(jexpr->coercion_expr))
-					return true;
 				if (WALK(jexpr->passing_values))
 					return true;
 				/* we assume walker doesn't care about passing_names */
@@ -3411,7 +3403,6 @@ expression_tree_mutator_impl(Node *node,
 				FLATCOPY(newnode, jexpr, JsonExpr);
 				MUTATE(newnode->formatted_expr, jexpr->formatted_expr, Node *);
 				MUTATE(newnode->path_spec, jexpr->path_spec, Node *);
-				MUTATE(newnode->coercion_expr, jexpr->coercion_expr, Node *);
 				MUTATE(newnode->passing_values, jexpr->passing_values, List *);
 				/* assume mutator does not care about passing_names */
 				MUTATE(newnode->on_empty, jexpr->on_empty, JsonBehavior *);