Add a demo ext showing that ereport doesn't eval its args on errlevel

Author: Craig Ringer

postgresql/ereport_skip/.gitignore

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+log
+regress.*
+tmp_check
+*.so
+*.o

postgresql/ereport_skip/Makefile

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+# src/test/modules/ereport_skip/Makefile
+
+MODULES = ereport_skip
+PGFILEDESC = "ereport_skip"
+
+EXTENSION = ereport_skip
+DATA = ereport_skip--1.0.sql
+
+REGRESS = ereport_skip_constexpr \
+	  ereport_skip_nonconst
+
+ifdef USE_PGXS
+PG_CONFIG = pg_config
+PGXS := $(shell $(PG_CONFIG) --pgxs)
+include $(PGXS)
+else
+subdir = src/test/modules/ereport_skip
+top_builddir = ../../../..
+include $(top_builddir)/src/Makefile.global
+include $(top_srcdir)/contrib/contrib-global.mk
+endif

postgresql/ereport_skip/README.md

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+# `ereport_skip`
+
+Demo extension showing that evaluation of ereport() arguments is bypassed
+when elevel is low enough that they are not required.
+
+Put it in src/test/modules and "make check", or run with PGXS using
+installcheck.

postgresql/ereport_skip/ereport_skip--1.0.sql

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+CREATE FUNCTION ereport_skip_test() RETURNS void LANGUAGE c AS 'MODULE_PATHNAME','ereport_skip_test';
+CREATE FUNCTION ereport_skip_test2() RETURNS void LANGUAGE c AS 'MODULE_PATHNAME','ereport_skip_test2';

postgresql/ereport_skip/ereport_skip.c

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+#include "postgres.h"
+
+#include "commands/seclabel.h"
+#include "fmgr.h"
+#include "miscadmin.h"
+#include "utils/guc.h"
+
+PG_MODULE_MAGIC;
+
+static const char *
+expensive_function(void)
+{
+	pg_usleep(2000000L);
+	return "expensive";
+}
+
+PG_FUNCTION_INFO_V1(ereport_skip_test);
+
+Datum
+ereport_skip_test(PG_FUNCTION_ARGS)
+{
+	/* Constant expression */
+	ereport(DEBUG1,
+		(errmsg("%s", expensive_function())));
+	PG_RETURN_VOID();
+}
+
+PG_FUNCTION_INFO_V1(ereport_skip_test2);
+
+Datum
+ereport_skip_test2(PG_FUNCTION_ARGS)
+{
+	/* Non-constant expression */
+	ereport(client_min_messages,
+		(errmsg("%s", expensive_function())));
+	PG_RETURN_VOID();
+}

postgresql/ereport_skip/ereport_skip.control

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+comment = 'Test code for ereport skip'
+default_version = '1.0'
+module_pathname = '$libdir/ereport_skip'
+relocatable = true

postgresql/ereport_skip/expected/ereport_skip_constexpr.sql

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+CREATE EXTENSION ereport_skip;
+
+SET client_min_messages = 'info';
+
+SELECT clock_timestamp() AS before_ts \gset
+SELECT ereport_skip_test();
+SELECT clock_timestamp() AS after_ts \gset
+
+SELECT (TIMESTAMP :'after_ts' - TIMESTAMP :'before_ts') > INTERVAL '1' SECOND AS did_delay_when_no_output;
+
+SET client_min_messages = 'debug1';
+
+SELECT clock_timestamp() AS before_ts \gset
+SELECT ereport_skip_test();
+SELECT clock_timestamp() AS after_ts \gset
+
+SELECT (TIMESTAMP :'after_ts' - TIMESTAMP :'before_ts') > INTERVAL '1' SECOND AS did_delay_when_output;

postgresql/ereport_skip/expected/ereport_skip_nonconst.sql

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+-- Test with non-constexpr elevel to make sure we still elide calls.
+
+SET client_min_messages = 'info';
+
+SELECT clock_timestamp() AS before_ts \gset
+SELECT ereport_skip_test2();
+SELECT clock_timestamp() AS after_ts \gset
+
+SELECT (TIMESTAMP :'after_ts' - TIMESTAMP :'before_ts') > INTERVAL '1' SECOND AS did_delay_when_no_output;
+
+SET client_min_messages = 'debug1';
+
+SELECT clock_timestamp() AS before_ts \gset
+SELECT ereport_skip_test2();
+SELECT clock_timestamp() AS after_ts \gset
+
+SELECT (TIMESTAMP :'after_ts' - TIMESTAMP :'before_ts') > INTERVAL '1' SECOND AS did_delay_when_output;