schemagen: handle WeaselJsonParser_create failure in RootBuilder

If WeaselJsonParser_create returns nullptr (e.g. negative stack size or allocation failure), set the existing error_ flag so that subsequent feed()/finish() calls return WeaselJson_REJECT instead of dereferencing the null parser_.

Also add a regression test in test_gen.cpp that constructs a RootBuilder with an invalid stack size and verifies it rejects without crashing.

Closes #36

contrib/schemagen/test_gen.cpp

@@ -68,6 +68,15 @@ int main() {
     expectReject(json, "unknown key in strict root");
   }
 
+  // ---- invalid stack size is rejected without crashing ----
+  {
+    RootBuilder b(-1);
+    char buf[] = "null";
+    WeaselJsonStatus s = b.feed(buf, sizeof(buf) - 1);
+    CHECK(s == WeaselJson_REJECT);
+    printf("ok   invalid stack size rejected, not crashed\n");
+  }
+
   {
     std::string json = R"({
       "name": "Ada É",

contrib/schemagen/weaseljson_schemagen.py

@@ -892,6 +892,10 @@ public:
   explicit RootBuilder(int stackSize = 1024) {{
     cb_ = makeCallbacks();
     parser_ = WeaselJsonParser_create(stackSize, &cb_, this, 0);
+    if (!parser_) {{
+      error_ = true;
+      return;
+    }}
 {self._ctor_body()}
   }}
   ~RootBuilder() {{ if (parser_) WeaselJsonParser_destroy(parser_); }}

src/json_value.h

@@ -1,6 +1,7 @@
 #pragma once
 
 #include <cstddef>
+#include <cstdint>
 #include <map>
 #include <memory>
 #include <optional>

src/lib.cpp

@@ -29,11 +29,17 @@ 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/test.cpp

@@ -246,6 +246,20 @@ 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);

test_python_bindings.py

@@ -95,8 +95,20 @@ 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

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