From 3c2c25d19da3b39f57c7d04b17077e015aa82758 Mon Sep 17 00:00:00 2001 From: "Chao Li (Evan)" Date: Mon, 15 Dec 2025 17:00:59 +0800 Subject: [PATCH v1] Add sanity check for duplicate enum values in GUC definitions Add a backend startup check that scans enum-type GUCs and reports cases where multiple enum labels map to the same numeric value. Historically, duplicate enum values have occasionally been introduced unintentionally, which can make enum lookup ambiguous and harder to reason about. This change detects such cases early, after the GUC hash table is built, and errors out to prevent silently accepting ambiguous definitions. A small number of existing enum GUCs intentionally reuse values (for example, to provide backward-compatible aliases). These are explicitly excluded from the check via a whitelist. This check is intended as a developer-facing sanity guard to catch mistakes in GUC enum tables. Author: Chao Li --- src/backend/utils/misc/guc.c | 63 +++++++++++++++++++++++++++++ src/backend/utils/misc/guc_tables.c | 10 +++++ src/include/utils/guc_tables.h | 2 + 3 files changed, 75 insertions(+) diff --git a/src/backend/utils/misc/guc.c b/src/backend/utils/misc/guc.c index 935c235e1b3..58d1eada183 100644 --- a/src/backend/utils/misc/guc.c +++ b/src/backend/utils/misc/guc.c @@ -238,6 +238,7 @@ static int guc_name_match(const void *key1, const void *key2, Size keysize); static void InitializeGUCOptionsFromEnvironment(void); static void InitializeOneGUCOption(struct config_generic *gconf); static void RemoveGUCFromLists(struct config_generic *gconf); +static void check_enum_duplicates(void); static void set_guc_source(struct config_generic *gconf, GucSource newsource); static void pg_timezone_abbrev_initialize(void); static void push_old_value(struct config_generic *gconf, GucAction action); @@ -860,6 +861,63 @@ get_guc_variables(int *num_vars) return result; } +/* + * If an enum-typed GUC has duplicate values for different names, raise an error. + * There are a few exceptions, listed in enum_dup_whitelist. + */ +static void +check_enum_duplicates(void) +{ + HASH_SEQ_STATUS status; + GUCHashEntry *hentry; + + Assert(guc_hashtab != NULL); + + hash_seq_init(&status, guc_hashtab); + while ((hentry = (GUCHashEntry *) hash_seq_search(&status)) != NULL) + { + const struct config_generic *gconf = hentry->gucvar; + + if (gconf->vartype == PGC_ENUM) + { + bool allow_dups = false; + + for (const char *const *p = enum_dup_whitelist; *p; p++) + { + if (strcmp(gconf->name, *p) == 0) + { + allow_dups = true; + break; + } + } + if (allow_dups) + continue; + + for (const struct config_enum_entry *opt1 = gconf->_enum.options; opt1->name; opt1++) + { + if (opt1->hidden) + continue; + + for (const struct config_enum_entry *opt2 = opt1 + 1; opt2->name; opt2++) + { + if (opt2->hidden) + continue; + + if (opt1->val == opt2->val) + { + elog(ERROR, + "GUC enum \"%s\" has duplicate value %d for \"%s\" and \"%s\"", + gconf->name, + opt1->val, + opt1->name, + opt2->name); + } + } + } + } + } +} + /* * Build the GUC hash table. This is split out so that help_config.c can @@ -1420,6 +1478,11 @@ InitializeGUCOptions(void) */ build_guc_variables(); + /* + * Check for enum GUCs with duplicate values. + */ + check_enum_duplicates(); + /* * Load all variables with their compiled-in defaults, and initialize * status fields as needed. diff --git a/src/backend/utils/misc/guc_tables.c b/src/backend/utils/misc/guc_tables.c index f87b558c2c6..0eb8dfdf9ff 100644 --- a/src/backend/utils/misc/guc_tables.c +++ b/src/backend/utils/misc/guc_tables.c @@ -764,6 +764,16 @@ const char *const config_type_names[] = [PGC_ENUM] = "enum", }; +/* + * Enum GUCs where duplicate numeric values are expected, so they will be + * skipped in enum sanity checks. Hidden enum values are not checked, as they + * are not exposed to users. + */ +const char *enum_dup_whitelist[] = { + "wal_compression", + NULL +}; + StaticAssertDecl(lengthof(config_type_names) == (PGC_ENUM + 1), "array length mismatch"); diff --git a/src/include/utils/guc_tables.h b/src/include/utils/guc_tables.h index 04cc60eb526..04f5330fee4 100644 --- a/src/include/utils/guc_tables.h +++ b/src/include/utils/guc_tables.h @@ -327,6 +327,8 @@ extern struct config_generic **get_guc_variables(int *num_vars); extern void build_guc_variables(void); +extern const char *enum_dup_whitelist[]; + /* search in enum options */ extern const char *config_enum_lookup_by_value(const struct config_generic *record, int val); extern bool config_enum_lookup_by_name(const struct config_enum *record, -- 2.39.5 (Apple Git-154)