Rename EmitWarningsOnPlaceholders() to MarkGUCPrefixReserved().

This seems like a clearer name for what it does now.

Provide a compatibility macro so that extensions don't have to convert
to the new name right away.

Discussion: https://postgr.es/m/116024.1640111629@sss.pgh.pa.us

src/backend/utils/misc/guc.c

@@ -9360,11 +9360,15 @@ DefineCustomEnumVariable(const char *name,
 }
 
 /*
+ * Mark the given GUC prefix as "reserved".
+ *
+ * This prints warnings if there are any existing placeholders matching
+ * the prefix, and then prevents new ones from being created.
  * Extensions should call this after they've defined all of their custom
- * GUCs, to help catch misspelled config-file entries,
+ * GUCs, to help catch misspelled config-file entries.
  */
 void
-EmitWarningsOnPlaceholders(const char *className)
+MarkGUCPrefixReserved(const char *className)
 {
 	int			classLen = strlen(className);
 	int			i;

src/include/utils/guc.h

@@ -354,7 +354,10 @@ extern void DefineCustomEnumVariable(const char *name,
 									 GucEnumAssignHook assign_hook,
 									 GucShowHook show_hook);
 
-extern void EmitWarningsOnPlaceholders(const char *className);
+extern void MarkGUCPrefixReserved(const char *className);
+
+/* old name for MarkGUCPrefixReserved, for backwards compatibility: */
+#define EmitWarningsOnPlaceholders(className) MarkGUCPrefixReserved(className)
 
 extern const char *GetConfigOption(const char *name, bool missing_ok,
 								   bool restrict_privileged);

src/pl/plperl/plperl.c

@@ -453,7 +453,7 @@ _PG_init(void)
 							   PGC_SUSET, 0,
 							   NULL, NULL, NULL);
 
-	EmitWarningsOnPlaceholders("plperl");
+	MarkGUCPrefixReserved("plperl");
 
 	/*
 	 * Create hash tables.

src/pl/plpgsql/src/pl_handler.c

@@ -197,7 +197,7 @@ _PG_init(void)
 							   plpgsql_extra_errors_assign_hook,
 							   NULL);
 
-	EmitWarningsOnPlaceholders("plpgsql");
+	MarkGUCPrefixReserved("plpgsql");
 
 	plpgsql_HashTableInit();
 	RegisterXactCallback(plpgsql_xact_cb, NULL);

src/pl/tcl/pltcl.c

@@ -474,8 +474,8 @@ _PG_init(void)
 							   PGC_SUSET, 0,
 							   NULL, NULL, NULL);
 
-	EmitWarningsOnPlaceholders("pltcl");
-	EmitWarningsOnPlaceholders("pltclu");
+	MarkGUCPrefixReserved("pltcl");
+	MarkGUCPrefixReserved("pltclu");
 
 	pltcl_pm_init_done = true;
 }

src/test/modules/delay_execution/delay_execution.c

@@ -91,7 +91,7 @@ _PG_init(void)
 							NULL,
 							NULL);
 
-	EmitWarningsOnPlaceholders("delay_execution");
+	MarkGUCPrefixReserved("delay_execution");
 
 	/* Install our hook */
 	prev_planner_hook = planner_hook;

src/test/modules/ssl_passphrase_callback/ssl_passphrase_func.c

@@ -49,7 +49,7 @@ _PG_init(void)
 							   NULL,
 							   NULL);
 
-	EmitWarningsOnPlaceholders("ssl_passphrase");
+	MarkGUCPrefixReserved("ssl_passphrase");
 
 	if (ssl_passphrase)
 		openssl_tls_init_hook = set_rot13;

src/test/modules/worker_spi/worker_spi.c

@@ -322,7 +322,7 @@ _PG_init(void)
 							   0,
 							   NULL, NULL, NULL);
 
-	EmitWarningsOnPlaceholders("worker_spi");
+	MarkGUCPrefixReserved("worker_spi");
 
 	/* set up common data for all our workers */
 	memset(&worker, 0, sizeof(worker));