Re: format_datum debugging function

[Paul Jungwirth]

On 8/12/24 04:32, Aleksander Alekseev wrote:

[...] This function takes a Datum and the appropriate out function, and returns 
a char *. So you
can do this:

(gdb) call format_datum(range_out, $1)
$2 = 0x59162692d938 "[1,4)"

I assume a patch like this doesn't need documentation. Does it need a test? 
Anything else?

I think you forgot to attach the patch. Or is it just a proposal?

Sorry, patch attached here.

Yours,

--
Paul              ~{:-)
p...@illuminatedcomputing.com
From 38a5e20e1481aa42d746b088cc6802f99d6d4276 Mon Sep 17 00:00:00 2001
From: "Paul A. Jungwirth" <p...@illuminatedcomputing.com>
Date: Fri, 9 Aug 2024 15:46:58 -0700
Subject: [PATCH v1] Add format_datum debugging function

This function lets you say `call format_datum(foo_out, foo)` in your
debugger to get a Datum as a readable string. It returns a char *
instead of printing itself, since that seems more flexible.
---
 src/backend/nodes/print.c | 19 +++++++++++++++++++
 src/include/nodes/print.h |  1 +
 2 files changed, 20 insertions(+)

diff --git a/src/backend/nodes/print.c b/src/backend/nodes/print.c
index 02798f4482d..d810e31d1b1 100644
--- a/src/backend/nodes/print.c
+++ b/src/backend/nodes/print.c
@@ -25,6 +25,7 @@
 #include "nodes/pathnodes.h"
 #include "nodes/print.h"
 #include "parser/parsetree.h"
+#include "pgstat.h"
 #include "utils/lsyscache.h"
 
 
@@ -246,6 +247,24 @@ pretty_format_node_dump(const char *dump)
 #undef LINELEN
 }
 
+char *
+format_datum(PGFunction outfunc, Datum val)
+{
+	FmgrInfo flinfo;
+
+	flinfo.fn_addr = outfunc;
+	flinfo.fn_oid = InvalidOid;
+	flinfo.fn_nargs = 1;
+	flinfo.fn_strict = true;
+	flinfo.fn_retset = false;
+	flinfo.fn_stats = TRACK_FUNC_ALL;
+	flinfo.fn_extra = NULL;
+	flinfo.fn_mcxt = CurrentMemoryContext;
+	flinfo.fn_expr = NULL;
+
+	return OutputFunctionCall(&flinfo, val);
+}
+
 /*
  * print_rt
  *	  print contents of range table
diff --git a/src/include/nodes/print.h b/src/include/nodes/print.h
index 333103a4051..27d165edafc 100644
--- a/src/include/nodes/print.h
+++ b/src/include/nodes/print.h
@@ -23,6 +23,7 @@ extern void print(const void *obj);
 extern void pprint(const void *obj);
 extern void elog_node_display(int lev, const char *title,
 							  const void *obj, bool pretty);
+extern char *format_datum(PGFunction outfunc, Datum val);
 extern char *format_node_dump(const char *dump);
 extern char *pretty_format_node_dump(const char *dump);
 extern void print_rt(const List *rtable);
-- 
2.42.0