Code review for commit b6e1157e7d

b6e1157e7d made some changes to enforce that
JsonValueExpr.formatted_expr is always set and is the expression that
gives a JsonValueExpr its runtime value, but that's not really
apparent from the comments about and the code manipulating
formatted_expr.  This commit fixes that.

Per suggestion from Álvaro Herrera.

Discussion: https://postgr.es/m/20230718155313.3wqg6encgt32adqb%40alvherre.pgsql

src/backend/nodes/makefuncs.c

@@ -848,16 +848,13 @@ makeJsonFormat(JsonFormatType type, JsonEncoding encoding, int location)
  *	  creates a JsonValueExpr node
  */
 JsonValueExpr *
-makeJsonValueExpr(Expr *expr, JsonFormat *format)
+makeJsonValueExpr(Expr *raw_expr, Expr *formatted_expr,
+				  JsonFormat *format)
 {
 	JsonValueExpr *jve = makeNode(JsonValueExpr);
 
-	jve->raw_expr = expr;
-
-	/*
-	 * Set after checking the format, if needed, in transformJsonValueExpr().
-	 */
-	jve->formatted_expr = NULL;
+	jve->raw_expr = raw_expr;
+	jve->formatted_expr = formatted_expr;
 	jve->format = format;
 
 	return jve;

src/backend/nodes/nodeFuncs.c

@@ -225,9 +225,7 @@ exprType(const Node *expr)
 			{
 				const JsonValueExpr *jve = (const JsonValueExpr *) expr;
 
-				type = exprType((Node *)
-								(jve->formatted_expr ? jve->formatted_expr :
-								 jve->raw_expr));
+				type = exprType((Node *) jve->formatted_expr);
 			}
 			break;
 		case T_JsonConstructorExpr:

src/backend/parser/gram.y

@@ -16362,7 +16362,9 @@ opt_asymmetric: ASYMMETRIC
 json_value_expr:
 			a_expr json_format_clause_opt
 			{
-				$$ = (Node *) makeJsonValueExpr((Expr *) $1, castNode(JsonFormat, $2));
+				/* formatted_expr will be set during parse-analysis. */
+				$$ = (Node *) makeJsonValueExpr((Expr *) $1, NULL,
+												castNode(JsonFormat, $2));
 			}
 		;
 

src/backend/parser/parse_expr.c

@@ -3205,6 +3205,10 @@ makeJsonByteaToTextConversion(Node *expr, JsonFormat *format, int location)
 /*
  * Transform JSON value expression using specified input JSON format or
  * default format otherwise.
+ *
+ * Returned expression is either ve->raw_expr coerced to text (if needed) or
+ * a JsonValueExpr with formatted_expr set to the coerced copy of raw_expr
+ * if the specified format requires it.
  */
 static Node *
 transformJsonValueExpr(ParseState *pstate, const char *constructName,
@@ -3304,6 +3308,10 @@ transformJsonValueExpr(ParseState *pstate, const char *constructName,
 		}
 	}
 
+	/* If returning a JsonValueExpr, formatted_expr must have been set. */
+	Assert(!IsA(expr, JsonValueExpr) ||
+		   ((JsonValueExpr *) expr)->formatted_expr != NULL);
+
 	return expr;
 }
 
@@ -3631,13 +3639,12 @@ transformJsonArrayQueryConstructor(ParseState *pstate,
 								makeString(pstrdup("a")));
 	colref->location = ctor->location;
 
-	agg->arg = makeJsonValueExpr((Expr *) colref, ctor->format);
-
 	/*
 	 * No formatting necessary, so set formatted_expr to be the same as
 	 * raw_expr.
 	 */
-	agg->arg->formatted_expr = agg->arg->raw_expr;
+	agg->arg = makeJsonValueExpr((Expr *) colref, (Expr *) colref,
+								 ctor->format);
 	agg->absent_on_null = ctor->absent_on_null;
 	agg->constructor = makeNode(JsonAggConstructor);
 	agg->constructor->agg_order = NIL;
@@ -3906,9 +3913,7 @@ transformJsonParseArg(ParseState *pstate, Node *jsexpr, JsonFormat *format,
 		expr = makeJsonByteaToTextConversion(expr, format, exprLocation(expr));
 		*exprtype = TEXTOID;
 
-		jve = makeJsonValueExpr((Expr *) raw_expr, format);
-
-		jve->formatted_expr = (Expr *) expr;
+		jve = makeJsonValueExpr((Expr *) raw_expr, (Expr *) expr, format);
 		expr = (Node *) jve;
 	}
 	else

src/include/nodes/makefuncs.h

@@ -110,7 +110,8 @@ extern VacuumRelation *makeVacuumRelation(RangeVar *relation, Oid oid, List *va_
 
 extern JsonFormat *makeJsonFormat(JsonFormatType type, JsonEncoding encoding,
 								  int location);
-extern JsonValueExpr *makeJsonValueExpr(Expr *expr, JsonFormat *format);
+extern JsonValueExpr *makeJsonValueExpr(Expr *raw_expr, Expr *formatted_expr,
+										JsonFormat *format);
 extern Node *makeJsonKeyValue(Node *key, Node *value);
 extern Node *makeJsonIsPredicate(Node *expr, JsonFormat *format,
 								 JsonValueType item_type, bool unique_keys,

src/include/nodes/primnodes.h

@@ -1596,8 +1596,9 @@ typedef struct JsonReturning
  * JsonValueExpr -
  *		representation of JSON value expression (expr [FORMAT JsonFormat])
  *
- * Note that raw_expr is only there for displaying and is not evaluated by
- * ExecInterpExpr() and eval_const_exprs_mutator().
+ * The actual value is obtained by evaluating formatted_expr.  raw_expr is
+ * only there for displaying the original user-written expression and is not
+ * evaluated by ExecInterpExpr() and eval_const_exprs_mutator().
  */
 typedef struct JsonValueExpr
 {