fix(logs): avoid modifying custom per-log attributes (#1500)

Allow reusing attribute objects across multiple log calls, as documented.

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

Author: jpnurmi

src/sentry_logs.c

@@ -243,10 +243,7 @@ static sentry_value_t
 construct_log(sentry_level_t level, const char *message, va_list args)
 {
     sentry_value_t log = sentry_value_new_object();
-    sentry_value_t attributes = sentry_value_new_null();
-    SENTRY_WITH_SCOPE (scope) {
-        attributes = sentry__value_clone(scope->attributes);
-    }
+    sentry_value_t attributes = sentry_value_new_object();
 
     SENTRY_WITH_OPTIONS (options) {
         // Extract custom attributes if the option is enabled
@@ -258,16 +255,15 @@ construct_log(sentry_level_t level, const char *message, va_list args)
             va_end(args_copy);
             if (sentry_value_get_type(custom_attributes)
                 == SENTRY_VALUE_TYPE_OBJECT) {
-                // Merge global attributes INTO per-log attributes
-                // (per-log attributes take precedence for conflicts)
-                sentry__value_merge_objects(custom_attributes, attributes);
+                // Clone custom attributes first (per-log attributes take
+                // precedence for conflicts)
                 sentry_value_decref(attributes);
-                attributes = custom_attributes;
+                attributes = sentry__value_clone(custom_attributes);
             } else {
                 SENTRY_DEBUG("Discarded custom attributes on log: non-object "
                              "sentry_value_t passed in");
-                sentry_value_decref(custom_attributes);
             }
+            sentry_value_decref(custom_attributes);
         }
 
         // Format the message with remaining args (or all args if not using

src/sentry_scope.c

@@ -779,6 +779,8 @@ void
 sentry__scope_apply_attributes(const sentry_scope_t *scope,
     sentry_value_t telemetry, sentry_value_t attributes)
 {
+    sentry__value_merge_objects(attributes, scope->attributes);
+
     sentry_value_t trace_id = sentry_value_get_by_key(
         sentry_value_get_by_key(scope->propagation_context, "trace"),
         "trace_id");

tests/unit/test_logs.c

@@ -379,3 +379,34 @@ SENTRY_TEST(logs_custom_attributes_with_format_strings)
     TEST_CHECK(!validation_data.has_validation_error);
     TEST_CHECK_INT_EQUAL(validation_data.called_count, 1);
 }
+
+SENTRY_TEST(logs_custom_attributes_not_modified)
+{
+    SENTRY_TEST_OPTIONS_NEW(options);
+    sentry_options_set_dsn(options, "https://foo@sentry.invalid/42");
+    sentry_options_set_enable_logs(options, true);
+    sentry_options_set_logs_with_attributes(options, true);
+    sentry_init(options);
+
+    sentry_set_attribute("global.key",
+        sentry_value_new_attribute(
+            sentry_value_new_string("global_value"), NULL));
+
+    sentry_value_t attrs = sentry_value_new_object();
+    sentry_value_set_by_key(attrs, "local.key",
+        sentry_value_new_attribute(
+            sentry_value_new_string("local_value"), NULL));
+    sentry_value_incref(attrs);
+
+    sentry_log_info("Test message", attrs);
+
+    // attrs should still contain only local.key, not global.key
+    TEST_CHECK_INT_EQUAL(sentry_value_get_length(attrs), 1);
+    TEST_CHECK(
+        !sentry_value_is_null(sentry_value_get_by_key(attrs, "local.key")));
+    TEST_CHECK(
+        sentry_value_is_null(sentry_value_get_by_key(attrs, "global.key")));
+
+    sentry_value_decref(attrs);
+    sentry_close();
+}

tests/unit/tests.inc

@@ -93,6 +93,7 @@ XX(iso_time)
 XX(lazy_attachments)
 XX(logger_enable_disable_functionality)
 XX(logger_level)
+XX(logs_custom_attributes_not_modified)
 XX(logs_custom_attributes_with_format_strings)
 XX(logs_disabled_by_default)
 XX(logs_force_flush)