1 files changed, 64 insertions, 15 deletions

diff --git a/src/backend/utils/misc/guc.c b/src/backend/utils/misc/guc.c
index 01f373815e0..eaa4bf2c304 100644
--- a/src/backend/utils/misc/guc.c
+++ b/src/backend/utils/misc/guc.c
@@ -150,6 +150,8 @@ extern bool optimize_bounded_sort;
 
 static int	GUC_check_errcode_value;
 
+static List *reserved_class_prefix = NIL;
+
 /* global variables for check hook support */
 char	   *GUC_check_errmsg_string;
 char	   *GUC_check_errdetail_string;
@@ -5590,18 +5592,44 @@ find_option(const char *name, bool create_placeholders, bool skip_errors,
 		 * doesn't contain a separator, don't assume that it was meant to be a
 		 * placeholder.
 		 */
-		if (strchr(name, GUC_QUALIFIER_SEPARATOR) != NULL)
+		const char *sep = strchr(name, GUC_QUALIFIER_SEPARATOR);
+
+		if (sep != NULL)
 		{
-			if (valid_custom_variable_name(name))
-				return add_placeholder_variable(name, elevel);
-			/* A special error message seems desirable here */
-			if (!skip_errors)
-				ereport(elevel,
-						(errcode(ERRCODE_INVALID_NAME),
-						 errmsg("invalid configuration parameter name \"%s\"",
-								name),
-						 errdetail("Custom parameter names must be two or more simple identifiers separated by dots.")));
-			return NULL;
+			size_t		classLen = sep - name;
+			ListCell   *lc;
+
+			/* The name must be syntactically acceptable ... */
+			if (!valid_custom_variable_name(name))
+			{
+				if (!skip_errors)
+					ereport(elevel,
+							(errcode(ERRCODE_INVALID_NAME),
+							 errmsg("invalid configuration parameter name \"%s\"",
+									name),
+							 errdetail("Custom parameter names must be two or more simple identifiers separated by dots.")));
+				return NULL;
+			}
+			/* ... and it must not match any previously-reserved prefix */
+			foreach(lc, reserved_class_prefix)
+			{
+				const char *rcprefix = lfirst(lc);
+
+				if (strlen(rcprefix) == classLen &&
+					strncmp(name, rcprefix, classLen) == 0)
+				{
+					if (!skip_errors)
+						ereport(elevel,
+								(errcode(ERRCODE_INVALID_NAME),
+								 errmsg("invalid configuration parameter name \"%s\"",
+										name),
+								 errdetail("\"%s\" is a reserved prefix.",
+										   rcprefix)));
+					return NULL;
+				}
+			}
+			/* OK, create it */
+			return add_placeholder_variable(name, elevel);
 		}
 	}
 
@@ -9355,15 +9383,26 @@ DefineCustomEnumVariable(const char *name,
 }
 
 /*
+ * Mark the given GUC prefix as "reserved".
+ *
+ * This deletes 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.
  */
 void
-EmitWarningsOnPlaceholders(const char *className)
+MarkGUCPrefixReserved(const char *className)
 {
 	int			classLen = strlen(className);
 	int			i;
+	MemoryContext oldcontext;
 
+	/*
+	 * Check for existing placeholders.  We must actually remove invalid
+	 * placeholders, else future parallel worker startups will fail.  (We
+	 * don't bother trying to free associated memory, since this shouldn't
+	 * happen often.)
+	 */
 	for (i = 0; i < num_guc_variables; i++)
 	{
 		struct config_generic *var = guc_variables[i];
@@ -9373,11 +9412,21 @@ EmitWarningsOnPlaceholders(const char *className)
 			var->name[classLen] == GUC_QUALIFIER_SEPARATOR)
 		{
 			ereport(WARNING,
-					(errcode(ERRCODE_UNDEFINED_OBJECT),
-					 errmsg("unrecognized configuration parameter \"%s\"",
-							var->name)));
+					(errcode(ERRCODE_INVALID_NAME),
+					 errmsg("invalid configuration parameter name \"%s\", removing it",
+							var->name),
+					 errdetail("\"%s\" is now a reserved prefix.",
+							   className)));
+			num_guc_variables--;
+			memmove(&guc_variables[i], &guc_variables[i + 1],
+					(num_guc_variables - i) * sizeof(struct config_generic *));
 		}
 	}
+
+	/* And remember the name so we can prevent future mistakes. */
+	oldcontext = MemoryContextSwitchTo(TopMemoryContext);
+	reserved_class_prefix = lappend(reserved_class_prefix, pstrdup(className));
+	MemoryContextSwitchTo(oldcontext);
 }