Don't include CaseTestExpr in JsonValueExpr.formatted_expr

A CaseTestExpr is currently being put into
JsonValueExpr.formatted_expr as placeholder for the result of
evaluating JsonValueExpr.raw_expr, which in turn is evaluated
separately.  Though, there's no need for this indirection if
raw_expr itself can be embedded into formatted_expr and evaluated
as part of evaluating the latter, especially as there is no
special reason to evaluate it separately.  So this commit makes it
so.  As a result, JsonValueExpr.raw_expr no longer needs to be
evaluated in ExecInterpExpr(), eval_const_exprs_mutator() etc. and
is now only used for displaying the original "unformatted"
expression in ruleutils.c.  Comments about and the code manipulating
formatted_expr is updated to mention that it is now always set and
is the expression that gives a JsonValueExpr its runtime value.

While at it, this also removes the function makeCaseTestExpr(),
because the code in makeJsonConstructorExpr() looks more readable
without it IMO and isn't used by anyone else either.

Finally, a note is added in the comment above CaseTestExpr's
definition that JsonConstructorExpr is also using it.

Backpatched to 16 from the development branch to keep the code in
sync across branches.

Reviewed-by: Álvaro Herrera <alvherre@alvh.no-ip.org>
Discussion: https://postgr.es/m/CA+HiwqE4XTdfb1nW=Ojoy_tQSRhYt-q_kb6i5d4xcKyrLC1Nbg@mail.gmail.com

src/backend/executor/execExpr.c

@@ -2294,21 +2294,8 @@ ExecInitExprRec(Expr *node, ExprState *state,
 			{
 				JsonValueExpr *jve = (JsonValueExpr *) node;
 
-				ExecInitExprRec(jve->raw_expr, state, resv, resnull);
-
-				if (jve->formatted_expr)
-				{
-					Datum	   *innermost_caseval = state->innermost_caseval;
-					bool	   *innermost_isnull = state->innermost_casenull;
-
-					state->innermost_caseval = resv;
-					state->innermost_casenull = resnull;
-
-					ExecInitExprRec(jve->formatted_expr, state, resv, resnull);
-
-					state->innermost_caseval = innermost_caseval;
-					state->innermost_casenull = innermost_isnull;
-				}
+				Assert(jve->formatted_expr != NULL);
+				ExecInitExprRec(jve->formatted_expr, state, resv, resnull);
 				break;
 			}
 

src/backend/nodes/makefuncs.c

@@ -848,12 +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;
-	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/optimizer/util/clauses.c

@@ -2827,25 +2827,12 @@ eval_const_expressions_mutator(Node *node,
 		case T_JsonValueExpr:
 			{
 				JsonValueExpr *jve = (JsonValueExpr *) node;
-				Node	   *raw;
+				Node	   *formatted;
 
-				raw = eval_const_expressions_mutator((Node *) jve->raw_expr,
-													 context);
-				if (raw && IsA(raw, Const))
-				{
-					Node	   *formatted;
-					Node	   *save_case_val = context->case_val;
-
-					context->case_val = raw;
-
-					formatted = eval_const_expressions_mutator((Node *) jve->formatted_expr,
-															   context);
-
-					context->case_val = save_case_val;
-
-					if (formatted && IsA(formatted, Const))
-						return formatted;
-				}
+				formatted = eval_const_expressions_mutator((Node *) jve->formatted_expr,
+														   context);
+				if (formatted && IsA(formatted, Const))
+					return formatted;
 				break;
 			}
 

src/backend/parser/gram.y

@@ -16353,7 +16353,9 @@ 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

@@ -3202,24 +3202,13 @@ makeJsonByteaToTextConversion(Node *expr, JsonFormat *format, int location)
 	return (Node *) fexpr;
 }
 
-/*
- * Make a CaseTestExpr node.
- */
-static Node *
-makeCaseTestExpr(Node *expr)
-{
-	CaseTestExpr *placeholder = makeNode(CaseTestExpr);
-
-	placeholder->typeId = exprType(expr);
-	placeholder->typeMod = exprTypmod(expr);
-	placeholder->collation = exprCollation(expr);
-
-	return (Node *) placeholder;
-}
-
 /*
  * 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,
@@ -3268,11 +3257,8 @@ transformJsonValueExpr(ParseState *pstate, const char *constructName,
 	if (format != JS_FORMAT_DEFAULT)
 	{
 		Oid			targettype = format == JS_FORMAT_JSONB ? JSONBOID : JSONOID;
-		Node	   *orig = makeCaseTestExpr(expr);
 		Node	   *coerced;
 
-		expr = orig;
-
 		if (exprtype != BYTEAOID && typcategory != TYPCATEGORY_STRING)
 			ereport(ERROR,
 					errcode(ERRCODE_DATATYPE_MISMATCH),
@@ -3310,7 +3296,7 @@ transformJsonValueExpr(ParseState *pstate, const char *constructName,
 			coerced = (Node *) fexpr;
 		}
 
-		if (coerced == orig)
+		if (coerced == expr)
 			expr = rawexpr;
 		else
 		{
@@ -3322,6 +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;
 }
 
@@ -3537,8 +3527,22 @@ makeJsonConstructorExpr(ParseState *pstate, JsonConstructorType type,
 	jsctor->absent_on_null = absent_on_null;
 	jsctor->location = location;
 
+	/*
+	 * Coerce to the RETURNING type and format, if needed.  We abuse
+	 * CaseTestExpr here as placeholder to pass the result of either
+	 * evaluating 'fexpr' or whatever is produced by ExecEvalJsonConstructor()
+	 * that is of type JSON or JSONB to the coercion function.
+	 */
 	if (fexpr)
-		placeholder = makeCaseTestExpr((Node *) fexpr);
+	{
+		CaseTestExpr *cte = makeNode(CaseTestExpr);
+
+		cte->typeId = exprType((Node *) fexpr);
+		cte->typeMod = exprTypmod((Node *) fexpr);
+		cte->collation = exprCollation((Node *) fexpr);
+
+		placeholder = (Node *) cte;
+	}
 	else
 	{
 		CaseTestExpr *cte = makeNode(CaseTestExpr);
@@ -3635,7 +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 = makeJsonValueExpr((Expr *) colref, (Expr *) colref,
+								 ctor->format);
 	agg->absent_on_null = ctor->absent_on_null;
 	agg->constructor = makeNode(JsonAggConstructor);
 	agg->constructor->agg_order = NIL;
@@ -3900,13 +3909,11 @@ transformJsonParseArg(ParseState *pstate, Node *jsexpr, JsonFormat *format,
 	{
 		JsonValueExpr *jve;
 
-		expr = makeCaseTestExpr(raw_expr);
+		expr = raw_expr;
 		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

@@ -1264,6 +1264,8 @@ typedef struct CaseWhen
  *	  see build_coercion_expression().
  *	* Nested FieldStore/SubscriptingRef assignment expressions in INSERT/UPDATE;
  *	  see transformAssignmentIndirection().
+ *	* Placeholder for intermediate results in some SQL/JSON expression nodes,
+ *	  such as JsonConstructorExpr.
  *
  * The uses in CaseExpr and ArrayCoerceExpr are safe only to the extent that
  * there is not any other CaseExpr or ArrayCoerceExpr between the value source
@@ -1593,12 +1595,16 @@ typedef struct JsonReturning
 /*
  * JsonValueExpr -
  *		representation of JSON value expression (expr [FORMAT JsonFormat])
+ *
+ * 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
 {
 	NodeTag		type;
 	Expr	   *raw_expr;		/* raw expression */
-	Expr	   *formatted_expr; /* formatted expression or NULL */
+	Expr	   *formatted_expr; /* formatted expression */
 	JsonFormat *format;			/* FORMAT clause, if specified */
 } JsonValueExpr;