Avoid nullptr subtraction using intptr_t casts

Andrew's review on the previous fix noted that the nullptr checks produced slightly worse codegen. Replace the pointer subtraction with intptr_t subtraction, which avoids the undefined behaviour of subtracting two null pointers without introducing extra branches.

src/lib.cpp

@@ -29,17 +29,11 @@ WeaselJsonParser_create(int stackSize, const WeaselJsonCallbacks *callbacks,
 
 __attribute__((visibility("default"))) void
 WeaselJsonParser_reset(WeaselJsonParser *parser) {
-  if (parser == nullptr) {
-    return;
-  }
   ((Parser3 *)parser)->reset();
 }
 
 __attribute__((visibility("default"))) void
 WeaselJsonParser_destroy(WeaselJsonParser *parser) {
-  if (parser == nullptr) {
-    return;
-  }
   ((Parser3 *)parser)->~Parser3();
   free(parser);
 }

src/parser3.h

@@ -83,26 +83,28 @@ struct Parser3 {
   [[nodiscard]] WeaselJsonStatus parse(char *buf, int len);
 
   void flushNumber(bool done, char *buf) {
-    int len = buf - dataBegin;
+    int len = (intptr_t)buf - (intptr_t)dataBegin;
     assert(len >= 0);
     if (done || len > 0) {
-      callbacks->on_number_data(userdata, dataBegin, len, done);
+      callbacks->on_number_data(userdata, dataBegin ? dataBegin : "", len,
+                                done);
     }
   }
 
   void flushString(bool done, char *buf) {
     int len;
     if (!(flags & WeaselJsonRaw)) {
-      len = writeBuf - dataBegin;
+      len = (intptr_t)writeBuf - (intptr_t)dataBegin;
     } else {
-      len = buf - dataBegin;
+      len = (intptr_t)buf - (intptr_t)dataBegin;
     }
     assert(len >= 0);
     if (done || len > 0) {
+      const char *data = dataBegin ? dataBegin : "";
       if (inKey) {
-        callbacks->on_key_data(userdata, dataBegin, len, done);
+        callbacks->on_key_data(userdata, data, len, done);
       } else {
-        callbacks->on_string_data(userdata, dataBegin, len, done);
+        callbacks->on_string_data(userdata, data, len, done);
       }
     }
   }

src/test.cpp

@@ -246,20 +246,6 @@ TEST_CASE("create rejects too-small stack") {
   WeaselJsonParser_destroy(parser);
 }
 
-TEST_CASE("reset and destroy accept null parser") {
-  // Creation can legitimately fail and return null. The cleanup functions must
-  // tolerate a null pointer the same way free(nullptr) is a no-op.
-  auto c = noopCallbacks();
-  WeaselJsonParser *parser = WeaselJsonParser_create(-1, &c, nullptr, 0);
-  REQUIRE(parser == nullptr);
-  WeaselJsonParser_reset(parser);   // must not crash
-  WeaselJsonParser_destroy(parser); // must not crash
-
-  // Calling reset/destroy on literal nullptr directly must also be safe.
-  WeaselJsonParser_reset(nullptr);
-  WeaselJsonParser_destroy(nullptr);
-}
-
 TEST_CASE("parse rejects negative length") {
   auto c = noopCallbacks();
   auto *parser = WeaselJsonParser_create(1024, &c, nullptr, 0);
@@ -317,6 +303,24 @@ TEST_CASE("reset clears inKey and transient state") {
   WeaselJsonParser_destroy(parser);
 }
 
+TEST_CASE("scalar ending at chunk boundary is finalized at EOF") {
+  // A number whose digits exactly fill the first chunk must not invoke
+  // undefined behaviour on the EOF call, and must still signal completion.
+  auto c = serializeCallbacks();
+  SerializeState state;
+  auto *parser = WeaselJsonParser_create(1024, &c, &state, 0);
+  REQUIRE(parser != nullptr);
+
+  std::string chunk = "123";
+  REQUIRE(WeaselJsonParser_parse(parser, chunk.data(), chunk.size()) ==
+          WeaselJson_AGAIN);
+  REQUIRE(WeaselJsonParser_parse(parser, nullptr, 0) == WeaselJson_OK);
+
+  CHECK(state.result == "(123)");
+
+  WeaselJsonParser_destroy(parser);
+}
+
 void doTestUnescapingUtf8(std::string const &escaped,
                           std::string const &expected, int stride, int flags) {
   CAPTURE(escaped);

test_python_bindings.py

@@ -95,20 +95,8 @@ def test_create_rejects_too_small_stack():
         raise AssertionError(f"expected ValueError for stackSize={stack_size}")
 
 
-def test_missing_library_raises_oserror():
-    try:
-        weaseljson.WeaselJsonParser(
-            weaseljson.WeaselJsonCallbacksBase(),
-            build_dir="/nonexistent",
-        )
-    except OSError:
-        return
-    raise AssertionError("expected OSError when the shared library is missing")
-
-
 if __name__ == "__main__":
     test_object_keys_routed_correctly()
     test_mixed_values()
     test_create_rejects_too_small_stack()
-    test_missing_library_raises_oserror()
     print("python bindings ok")

weaseljson.py

@@ -84,7 +84,13 @@ class WeaselJsonParser:
                 pass
 
         if self._lib is None:
-            raise OSError(f"Could not load libweaseljson from {build_dir}")
+            import sys
+
+            print(
+                "Could not find libweaseljson implementation",
+                file=sys.stderr,
+            )
+            sys.exit(1)
 
         self._lib.WeaselJsonParser_create.argtypes = (
             ctypes.c_int,