Warning on SET of nonexisting setting with a prefix reserved by an extension

An extension can already de facto reserve a GUC prefix using
EmitWarningsOnPlaceholders().  But this was only checked against
settings that exist at the time the extension is loaded (or the
extension chooses to call this).  No diagnostic is given when a SET
command later uses a nonexisting setting with a custom prefix.

With this change, EmitWarningsOnPlaceholders() saves the prefixes it
reserves in a list, and SET checks when it finds a "placeholder"
setting whether it belongs to a reserved prefix and issues a warning
in that case.

Add a regression test that checks the patch using the "plpgsql"
registered prefix.

Author: Florin Irion <florin.irion@enterprisedb.com>
Discussion: https://www.postgresql.org/message-id/flat/CA+HEvJDhWuuTpGTJT9Tgbdzm4QS4EzPAwDBScWK18H2Q=FVJFw@mail.gmail.com

1 files changed, 47 insertions, 0 deletions

diff --git a/src/backend/utils/misc/guc.c b/src/backend/utils/misc/guc.c
index 25ac4ca85ba..a292498e2f7 100644
--- a/src/backend/utils/misc/guc.c
+++ b/src/backend/utils/misc/guc.c
@@ -235,6 +235,8 @@ static bool check_recovery_target_lsn(char **newval, void **extra, GucSource sou
 static void assign_recovery_target_lsn(const char *newval, void *extra);
 static bool check_primary_slot_name(char **newval, void **extra, GucSource source);
 static bool check_default_with_oids(bool *newval, void **extra, GucSource source);
+static void check_reserved_prefixes(const char *varName);
+static List *reserved_class_prefix = NIL;
 
 /* Private functions in guc-file.l that need to be called from guc.c */
 static ConfigVariable *ProcessConfigFileInternal(GucContext context,
@@ -8755,6 +8757,7 @@ ExecSetVariableStmt(VariableSetStmt *stmt, bool isTopLevel)
 									 (superuser() ? PGC_SUSET : PGC_USERSET),
 									 PGC_S_SESSION,
 									 action, true, 0, false);
+			check_reserved_prefixes(stmt->name);
 			break;
 		case VAR_SET_MULTI:
 
@@ -8840,6 +8843,8 @@ ExecSetVariableStmt(VariableSetStmt *stmt, bool isTopLevel)
 									 (superuser() ? PGC_SUSET : PGC_USERSET),
 									 PGC_S_SESSION,
 									 action, true, 0, false);
+
+			check_reserved_prefixes(stmt->name);
 			break;
 		case VAR_RESET_ALL:
 			ResetAllOptions();
@@ -9326,6 +9331,7 @@ EmitWarningsOnPlaceholders(const char *className)
 {
 	int			classLen = strlen(className);
 	int			i;
+	MemoryContext	oldcontext;
 
 	for (i = 0; i < num_guc_variables; i++)
 	{
@@ -9341,8 +9347,49 @@ EmitWarningsOnPlaceholders(const char *className)
 							var->name)));
 		}
 	}
+
+	oldcontext = MemoryContextSwitchTo(TopMemoryContext);
+	reserved_class_prefix = lappend(reserved_class_prefix, pstrdup(className));
+	MemoryContextSwitchTo(oldcontext);
 }
 
+/*
+ * Check a setting name against prefixes previously reserved by
+ * EmitWarningsOnPlaceholders() and throw a warning if matching.
+ */
+static void
+check_reserved_prefixes(const char *varName)
+{
+	char	   *sep = strchr(varName, GUC_QUALIFIER_SEPARATOR);
+
+	if (sep)
+	{
+		size_t		classLen = sep - varName;
+		ListCell   *lc;
+
+		foreach(lc, reserved_class_prefix)
+		{
+			char	   *rcprefix = lfirst(lc);
+
+			if (strncmp(varName, rcprefix, classLen) == 0)
+			{
+				for (int i = 0; i < num_guc_variables; i++)
+				{
+					struct config_generic *var = guc_variables[i];
+
+					if ((var->flags & GUC_CUSTOM_PLACEHOLDER) != 0 &&
+						strcmp(varName, var->name) == 0)
+					{
+						ereport(WARNING,
+								(errcode(ERRCODE_UNDEFINED_OBJECT),
+								 errmsg("unrecognized configuration parameter \"%s\"", var->name),
+								 errdetail("\"%.*s\" is a reserved prefix.", (int) classLen, var->name)));
+					}
+				}
+			}
+		}
+	}
+}
 
 /*
  * SHOW command