fix: bind an empty JSON array as the quoted '{}' literal (#86)

src/binding.rs

@@ -436,6 +436,16 @@ fn decode_blob_wire_format(value: &str) -> Option<Vec<u8>> {
 /// Convert a JSON array to a PostgreSQL `ARRAY[...]` literal string.
 /// Recursively handles nested arrays (multi-dimensional PG arrays).
 fn json_array_to_pg_literal(arr: &[Value]) -> Result<String, String> {
+    // `ARRAY[]` (an ARRAY constructor with no elements) is only accepted
+    // when the target column type is unambiguous — in many contexts
+    // (e.g. INSERT ... VALUES) it's a syntax/type error. `'{}'` is the
+    // canonical PostgreSQL empty-array literal the server always accepts;
+    // it must be quoted — a bare `{}` is itself a syntax error. Matches the
+    // builtin driver's `json_array_to_pg_literal` exactly.
+    if arr.is_empty() {
+        return Ok("'{}'".to_string());
+    }
+
     let mut parts = Vec::with_capacity(arr.len());
     for elem in arr {
         let part = match elem {

src/binding_tests.rs

@@ -48,6 +48,24 @@ mod bind_pg_value_tests {
         assert_eq!(bound.sql, "ARRAY[ARRAY[1, 2], ARRAY[3, 4]]");
     }
 
+    #[test]
+    fn empty_array_binds_as_quoted_empty_literal_not_array_constructor() {
+        // ARRAY[] (an ARRAY constructor with no elements) is only accepted
+        // when the target column type is unambiguous -- in many contexts
+        // (e.g. plain INSERT ... VALUES) it's a syntax/type error. '{}' is
+        // the canonical PostgreSQL empty-array literal the server always
+        // accepts. See #86.
+        let bound = bind_pg_value(json!([]), 1, &BindOptions::default()).unwrap();
+        assert_eq!(bound.sql, "'{}'");
+        assert!(bound.param.is_none());
+    }
+
+    #[test]
+    fn nested_empty_array_binds_as_quoted_empty_literal_at_every_level() {
+        let bound = bind_pg_value(json!([[]]), 1, &BindOptions::default()).unwrap();
+        assert_eq!(bound.sql, "ARRAY['{}']");
+    }
+
     #[test]
     fn string_array_escapes_single_quotes() {
         let bound = bind_pg_value(json!(["it's", "ok"]), 1, &BindOptions::default()).unwrap();
@@ -260,6 +278,15 @@ mod bind_pg_value_tests {
         assert!(bound.param.is_none());
     }
 
+    #[test]
+    fn empty_array_literal_embedded_in_string_binds_as_quoted_empty_literal() {
+        // Same #86 guard, reached via bind_pg_string's inline array-literal
+        // parse ("[]") rather than a native JSON array value.
+        let bound = bind_pg_value(json!("[]"), 1, &BindOptions::default()).unwrap();
+        assert_eq!(bound.sql, "'{}'");
+        assert!(bound.param.is_none());
+    }
+
     #[test]
     fn plain_string_falls_through_to_text_binding() {
         let bound = bind_pg_value(json!("hello world"), 1, &BindOptions::default()).unwrap();