Fix get_name_for_var_field() to deal with RECORD Params.

With 9.1's use of Params to pass down values from NestLoop join nodes
to their inner plans, it is possible for a Param to have type RECORD, in
which case the set of fields comprising the value isn't determinable by
inspection of the Param alone.  However, just as with a Var of type RECORD,
we can find out what we need to know if we can locate the expression that
the Param represents.  We already knew how to do this in get_parameter(),
but I'd overlooked the need to be able to cope in get_name_for_var_field(),
which led to EXPLAIN failing with "record type has not been registered".

To fix, refactor the search code in get_parameter() so it can be used by
both functions.

Per report from Marti Raudsepp.

Author: tglsfdc

src/backend/utils/adt/ruleutils.c

@@ -207,9 +207,9 @@ static char *get_variable(Var *var, int levelsup, bool showstar,
 			 deparse_context *context);
 static RangeTblEntry *find_rte_by_refname(const char *refname,
 					deparse_context *context);
+static Node *find_param_referent(Param *param, deparse_context *context,
+					deparse_namespace **dpns_p, ListCell **ancestor_cell_p);
 static void get_parameter(Param *param, deparse_context *context);
-static void print_parameter_expr(Node *expr, ListCell *ancestor_cell,
-					 deparse_namespace *dpns, deparse_context *context);
 static const char *get_simple_binary_op_name(OpExpr *expr);
 static bool isSimpleNode(Node *node, Node *parentNode, int prettyFlags);
 static void appendContextKeyword(deparse_context *context, const char *str,
@@ -3892,15 +3892,21 @@ get_variable(Var *var, int levelsup, bool showstar, deparse_context *context)
 
 
 /*
- * Get the name of a field of an expression of composite type.
- *
- * This is fairly straightforward except for the case of a Var of type RECORD.
- * Since no actual table or view column is allowed to have type RECORD, such
- * a Var must refer to a JOIN or FUNCTION RTE or to a subquery output.	We
- * drill down to find the ultimate defining expression and attempt to infer
- * the field name from it.	We ereport if we can't determine the name.
+ * Get the name of a field of an expression of composite type.  The
+ * expression is usually a Var, but we handle other cases too.
  *
  * levelsup is an extra offset to interpret the Var's varlevelsup correctly.
+ *
+ * This is fairly straightforward when the expression has a named composite
+ * type; we need only look up the type in the catalogs.  However, the type
+ * could also be RECORD.  Since no actual table or view column is allowed to
+ * have type RECORD, a Var of type RECORD must refer to a JOIN or FUNCTION RTE
+ * or to a subquery output.  We drill down to find the ultimate defining
+ * expression and attempt to infer the field name from it.  We ereport if we
+ * can't determine the name.
+ *
+ * Similarly, a PARAM of type RECORD has to refer to some expression of
+ * a determinable composite type.
  */
 static const char *
 get_name_for_var_field(Var *var, int fieldno,
@@ -3925,6 +3931,29 @@ get_name_for_var_field(Var *var, int fieldno,
 			return strVal(list_nth(r->colnames, fieldno - 1));
 	}
 
+	/*
+	 * If it's a Param of type RECORD, try to find what the Param refers to.
+	 */
+	if (IsA(var, Param))
+	{
+		Param	   *param = (Param *) var;
+		ListCell   *ancestor_cell;
+
+		expr = find_param_referent(param, context, &dpns, &ancestor_cell);
+		if (expr)
+		{
+			/* Found a match, so recurse to decipher the field name */
+			deparse_namespace save_dpns;
+			const char *result;
+
+			push_ancestor_plan(dpns, ancestor_cell, &save_dpns);
+			result = get_name_for_var_field((Var *) expr, fieldno,
+											0, context);
+			pop_ancestor_plan(dpns, &save_dpns);
+			return result;
+		}
+	}
+
 	/*
 	 * If it's a Var of type RECORD, we have to find what the Var refers to;
 	 * if not, we can use get_expr_result_type. If that fails, we try
@@ -4279,17 +4308,25 @@ find_rte_by_refname(const char *refname, deparse_context *context)
 }
 
 /*
- * Display a Param appropriately.
+ * Try to find the referenced expression for a PARAM_EXEC Param that might
+ * reference a parameter supplied by an upper NestLoop or SubPlan plan node.
+ *
+ * If successful, return the expression and set *dpns_p and *ancestor_cell_p
+ * appropriately for calling push_ancestor_plan().  If no referent can be
+ * found, return NULL.
  */
-static void
-get_parameter(Param *param, deparse_context *context)
+static Node *
+find_param_referent(Param *param, deparse_context *context,
+					deparse_namespace **dpns_p, ListCell **ancestor_cell_p)
 {
+	/* Initialize output parameters to prevent compiler warnings */
+	*dpns_p = NULL;
+	*ancestor_cell_p = NULL;
+
 	/*
-	 * If it's a PARAM_EXEC parameter, try to locate the expression from which
-	 * the parameter was computed.	This will necessarily be in some ancestor
-	 * of the current expression's PlanState.  Note that failing to find a
-	 * referent isn't an error, since the Param might well be a subplan output
-	 * rather than an input.
+	 * If it's a PARAM_EXEC parameter, look for a matching NestLoopParam or
+	 * SubPlan argument.  This will necessarily be in some ancestor of the
+	 * current expression's PlanState.
 	 */
 	if (param->paramkind == PARAM_EXEC)
 	{
@@ -4324,10 +4361,10 @@ get_parameter(Param *param, deparse_context *context)
 
 					if (nlp->paramno == param->paramid)
 					{
-						/* Found a match, so print it */
-						print_parameter_expr((Node *) nlp->paramval, lc,
-											 dpns, context);
-						return;
+						/* Found a match, so return it */
+						*dpns_p = dpns;
+						*ancestor_cell_p = lc;
+						return (Node *) nlp->paramval;
 					}
 				}
 			}
@@ -4353,9 +4390,10 @@ get_parameter(Param *param, deparse_context *context)
 
 					if (paramid == param->paramid)
 					{
-						/* Found a match, so print it */
-						print_parameter_expr(arg, lc, dpns, context);
-						return;
+						/* Found a match, so return it */
+						*dpns_p = dpns;
+						*ancestor_cell_p = lc;
+						return arg;
 					}
 				}
 
@@ -4390,50 +4428,71 @@ get_parameter(Param *param, deparse_context *context)
 		}
 	}
 
-	/*
-	 * Not PARAM_EXEC, or couldn't find referent: just print $N.
-	 */
-	appendStringInfo(context->buf, "$%d", param->paramid);
+	/* No referent found */
+	return NULL;
 }
 
-/* Print a parameter reference expression found by get_parameter */
+/*
+ * Display a Param appropriately.
+ */
 static void
-print_parameter_expr(Node *expr, ListCell *ancestor_cell,
-					 deparse_namespace *dpns, deparse_context *context)
+get_parameter(Param *param, deparse_context *context)
 {
-	deparse_namespace save_dpns;
-	bool		save_varprefix;
-	bool		need_paren;
-
-	/* Switch attention to the ancestor plan node */
-	push_ancestor_plan(dpns, ancestor_cell, &save_dpns);
+	Node	   *expr;
+	deparse_namespace *dpns;
+	ListCell   *ancestor_cell;
 
 	/*
-	 * Force prefixing of Vars, since they won't belong to the relation being
-	 * scanned in the original plan node.
+	 * If it's a PARAM_EXEC parameter, try to locate the expression from which
+	 * the parameter was computed.  Note that failing to find a referent isn't
+	 * an error, since the Param might well be a subplan output rather than an
+	 * input.
 	 */
-	save_varprefix = context->varprefix;
-	context->varprefix = true;
+	expr = find_param_referent(param, context, &dpns, &ancestor_cell);
+	if (expr)
+	{
+		/* Found a match, so print it */
+		deparse_namespace save_dpns;
+		bool		save_varprefix;
+		bool		need_paren;
 
-	/*
-	 * A Param's expansion is typically a Var, Aggref, or upper-level Param,
-	 * which wouldn't need extra parentheses.  Otherwise, insert parens to
-	 * ensure the expression looks atomic.
-	 */
-	need_paren = !(IsA(expr, Var) ||
-				   IsA(expr, Aggref) ||
-				   IsA(expr, Param));
-	if (need_paren)
-		appendStringInfoChar(context->buf, '(');
+		/* Switch attention to the ancestor plan node */
+		push_ancestor_plan(dpns, ancestor_cell, &save_dpns);
 
-	get_rule_expr(expr, context, false);
+		/*
+		 * Force prefixing of Vars, since they won't belong to the relation
+		 * being scanned in the original plan node.
+		 */
+		save_varprefix = context->varprefix;
+		context->varprefix = true;
 
-	if (need_paren)
-		appendStringInfoChar(context->buf, ')');
+		/*
+		 * A Param's expansion is typically a Var, Aggref, or upper-level
+		 * Param, which wouldn't need extra parentheses.  Otherwise, insert
+		 * parens to ensure the expression looks atomic.
+		 */
+		need_paren = !(IsA(expr, Var) ||
+					   IsA(expr, Aggref) ||
+					   IsA(expr, Param));
+		if (need_paren)
+			appendStringInfoChar(context->buf, '(');
+
+		get_rule_expr(expr, context, false);
+
+		if (need_paren)
+			appendStringInfoChar(context->buf, ')');
+
+		context->varprefix = save_varprefix;
 
-	context->varprefix = save_varprefix;
+		pop_ancestor_plan(dpns, &save_dpns);
 
-	pop_ancestor_plan(dpns, &save_dpns);
+		return;
+	}
+
+	/*
+	 * Not PARAM_EXEC, or couldn't find referent: just print $N.
+	 */
+	appendStringInfo(context->buf, "$%d", param->paramid);
 }
 
 /*