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

1 files changed, 17 insertions, 35 deletions

diff --git a/src/backend/executor/execExpr.c b/src/backend/executor/execExpr.c
index 2bf86d06ef5..ccd48637784 100644
--- a/src/backend/executor/execExpr.c
+++ b/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);
 }