From d3f497906daf1c405059b2c292f1eeb5cfeb742b Mon Sep 17 00:00:00 2001
From: Nathan Bossart <nathandbossart@gmail.com>
Date: Wed, 15 Feb 2023 14:28:53 -0800
Subject: [PATCH v19 1/5] introduce routine for checking mutually exclusive
 string GUCs

---
 src/backend/postmaster/pgarch.c |  8 +++-----
 src/backend/utils/misc/guc.c    | 22 ++++++++++++++++++++++
 src/include/utils/guc.h         |  3 +++
 3 files changed, 28 insertions(+), 5 deletions(-)

diff --git a/src/backend/postmaster/pgarch.c b/src/backend/postmaster/pgarch.c
index f97035ca03..dcb5222bbe 100644
--- a/src/backend/postmaster/pgarch.c
+++ b/src/backend/postmaster/pgarch.c
@@ -815,11 +815,9 @@ LoadArchiveLibrary(void)
 {
 	ArchiveModuleInit archive_init;
 
-	if (XLogArchiveLibrary[0] != '\0' && XLogArchiveCommand[0] != '\0')
-		ereport(ERROR,
-				(errcode(ERRCODE_INVALID_PARAMETER_VALUE),
-				 errmsg("both archive_command and archive_library set"),
-				 errdetail("Only one of archive_command, archive_library may be set.")));
+	(void) CheckMutuallyExclusiveStringGUCs(XLogArchiveLibrary, "archive_library",
+											XLogArchiveCommand, "archive_command",
+											ERROR);
 
 	/*
 	 * If shell archiving is enabled, use our special initialization function.
diff --git a/src/backend/utils/misc/guc.c b/src/backend/utils/misc/guc.c
index 391866145e..ac507008ce 100644
--- a/src/backend/utils/misc/guc.c
+++ b/src/backend/utils/misc/guc.c
@@ -2659,6 +2659,28 @@ ReportGUCOption(struct config_generic *record)
 	pfree(val);
 }
 
+/*
+ * If both parameters are set, emits a log message at 'elevel' and returns
+ * false.  Otherwise, returns true.
+ */
+bool
+CheckMutuallyExclusiveStringGUCs(const char *p1val, const char *p1name,
+								 const char *p2val, const char *p2name,
+								 int elevel)
+{
+	if (p1val[0] != '\0' && p2val[0] != '\0')
+	{
+		ereport(elevel,
+				(errcode(ERRCODE_INVALID_PARAMETER_VALUE),
+				 errmsg("cannot set both %s and %s", p1name, p2name),
+				 errdetail("Only one of %s or %s may be set.",
+						   p1name, p2name)));
+		return false;
+	}
+
+	return true;
+}
+
 /*
  * Convert a value from one of the human-friendly units ("kB", "min" etc.)
  * to the given base unit.  'value' and 'unit' are the input value and unit
diff --git a/src/include/utils/guc.h b/src/include/utils/guc.h
index 3712aba09b..3088ada610 100644
--- a/src/include/utils/guc.h
+++ b/src/include/utils/guc.h
@@ -376,6 +376,9 @@ extern void RestrictSearchPath(void);
 extern void AtEOXact_GUC(bool isCommit, int nestLevel);
 extern void BeginReportingGUCOptions(void);
 extern void ReportChangedGUCOptions(void);
+extern bool CheckMutuallyExclusiveStringGUCs(const char *p1val, const char *p1name,
+											 const char *p2val, const char *p2name,
+											 int elevel);
 extern void ParseLongOption(const char *string, char **name, char **value);
 extern const char *get_config_unit_name(int flags);
 extern bool parse_int(const char *value, int *result, int flags,
-- 
2.25.1