fix: db-pre-config function failing with pg reserved words

When db-pre-config is accidentally set to a pg reserved word
like "true", it fails with a confusing error. The function
names should be properly quoted to avoid such errors. This commit
resolves this by quoting the pre-config function name.

Signed-off-by: Taimoor Zaeem <taimoorzaeem@gmail.com>

CHANGELOG.md

@@ -4,6 +4,10 @@ All notable changes to this project will be documented in this file. From versio
 
 ## Unreleased
 
+## Fixed
+
+- Fix `db-pre-config` function failing when function names are pg reserved words by @taimoorzaeem #4380
+
 ## [14.0] - 2025-10-24
 
 ### Added

src/PostgREST/AppState.hs

@@ -69,7 +69,7 @@ import PostgREST.Config.PgVersion        (PgVersion (..),
 import PostgREST.SchemaCache             (SchemaCache (..),
                                           querySchemaCache,
                                           showSummary)
-import PostgREST.SchemaCache.Identifiers (dumpQi)
+import PostgREST.SchemaCache.Identifiers (quoteQi)
 import PostgREST.Unix                    (createAndBindDomainSocket)
 
 import Data.Streaming.Network (bindPortTCP, bindRandomPortTCP)
@@ -441,7 +441,7 @@ readInDbConfig startingUp appState@AppState{stateObserver=observer} = do
   pgVer <- getPgVersion appState
   dbSettings <-
     if configDbConfig conf then do
-      qDbSettings <- usePool appState (queryDbSettings (dumpQi <$> configDbPreConfig conf) (configDbPreparedStatements conf))
+      qDbSettings <- usePool appState (queryDbSettings (quoteQi <$> configDbPreConfig conf) (configDbPreparedStatements conf))
       case qDbSettings of
         Left e -> do
           observer $ ConfigReadErrorObs e

src/PostgREST/SchemaCache/Identifiers.hs

@@ -10,6 +10,7 @@ module PostgREST.SchemaCache.Identifiers
   , dumpQi
   , escapeIdent
   , isAnyElement
+  , quoteQi
   , toQi
   , trimNullChars
   ) where
@@ -41,6 +42,10 @@ dumpQi :: QualifiedIdentifier -> Text
 dumpQi (QualifiedIdentifier s i) =
   (if T.null s then mempty else s <> ".") <> i
 
+quoteQi :: QualifiedIdentifier -> Text
+quoteQi (QualifiedIdentifier s i) =
+  (if T.null s then mempty else escapeIdent s <> ".") <> escapeIdent i
+
 -- TODO: Handle a case where the QI comes like this: "my.fav.schema"."my.identifier"
 -- Right now it only handles the schema.identifier case
 toQi :: Text -> QualifiedIdentifier

test/io/__snapshots__/test_cli/test_schema_cache_snapshot[dbRoutines].yaml

@@ -461,6 +461,23 @@
       pdSchema: public
       pdVolatility: Volatile
 
+- - qiName: 'true'
+    qiSchema: public
+  - - pdDescription: null
+      pdFuncSettings: []
+      pdHasVariadic: false
+      pdName: 'true'
+      pdParams: []
+      pdReturnType:
+        contents:
+          contents:
+            qiName: bool
+            qiSchema: pg_catalog
+          tag: Scalar
+        tag: Single
+      pdSchema: public
+      pdVolatility: Volatile
+
 - - qiName: create_function
     qiSchema: public
   - - pdDescription: null

test/io/fixtures.sql

@@ -256,3 +256,7 @@ select * from projects;
 
 create or replace view infinite_recursion as
 select * from infinite_recursion;
+
+create or replace function "true"() returns boolean as $_$
+  select true;
+$_$ language sql;

test/io/test_io.py

@@ -2046,3 +2046,29 @@ def test_log_listener_connection_errors(defaultenv):
             in line
             for line in output
         )
+
+
+def test_db_pre_config_with_pg_reserved_words(defaultenv):
+    "The db-pre-config should not fail unexpectedly when function name is a postgres reserved word"
+
+    env = {
+        **defaultenv,
+        "PGRST_DB_PRE_CONFIG": "true",  # call true function
+    }
+
+    with run(env=env) as postgrest:
+        response = postgrest.session.post("/rpc/true")
+        assert response.status_code == 200
+
+    env = {
+        **defaultenv,
+        "PGRST_DB_PRE_CONFIG": "select",  # no "select" function in our fixtures, fail gracefully at startup
+    }
+
+    with run(env=env, no_startup_stdout=False, wait_for_readiness=False) as postgrest:
+        output = postgrest.read_stdout(nlines=8)
+        assert any(
+            'Failed to query database settings for the config parameters.{"code":"42883","details":null,"hint":"No function matches the given name and argument types. You might need to add explicit type casts.","message":"function select() does not exist"}'
+            in line
+            for line in output
+        )