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Add a unit test for json_disconnect

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json_disconnect() is documented in jsonpull.h as the supported way to
splice a subtree out of the parser's tree and take ownership of it, but
nothing calls it: read_filter() and parse_filter() used to, and now get
the same guarantee from json_read_tree() clearing back-pointers on the way
out. Cover the behavior rather than leave the primitive dead and untested.

The test pins that the subtree is removed from its parent, that the parser
keeps the rest of the tree, and that the detached subtree stays readable
after the json_pull is destroyed.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_017KNxyHKasyWrWcvre2yK4r
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Claude
2026-08-12 18:16:37 +00:00
parent f85cb9e049
commit ff01e872ef
1 changed files with 56 additions and 0 deletions
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unit.cpp
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@@ -247,6 +247,62 @@ TEST_CASE("json_free releases a top-level value held by the parser", "[jsonpull]
REQUIRE(jp->root == nullptr);
}
// json_disconnect() is the documented way to splice a subtree out of the
// parser's tree and take ownership of it so that it can outlive the
// json_pull it came from. Nothing in tippecanoe calls it today -- the
// filter loaders get the same guarantee from json_read_tree, which clears
// back-pointers on the way out -- so cover it here rather than leave a
// documented ownership primitive untested.
TEST_CASE("json_disconnect hands a subtree to the caller", "[jsonpull][ownership]") {
json_object_ptr taken;
json_object *outer = nullptr;
json_pull_ptr jp = json_begin_string("[[1, 2], [3, 4]]");
int arrays_seen = 0;
json_object *j;
while ((j = json_read(jp)) != nullptr) {
if (j->type != JSON_ARRAY) {
continue;
}
arrays_seen++;
if (arrays_seen == 2) {
// This is [3, 4]; take it away from the enclosing array.
taken = json_disconnect(j);
REQUIRE(taken != nullptr);
REQUIRE(taken.get() == j);
} else if (j->parent == nullptr) {
outer = j;
break;
}
}
// The outer array is left holding only the element we didn't take,
// and the parser is still the owner of it.
REQUIRE(outer != nullptr);
REQUIRE(jp->root.get() == outer);
REQUIRE(outer->array().size() == 1);
REQUIRE(outer->array()[0]->array().size() == 2);
REQUIRE(outer->array()[0]->array()[0]->number() == 1);
REQUIRE(outer->array()[0]->array()[1]->number() == 2);
// The detached subtree holds no back-pointers into the parser...
REQUIRE(taken->parent == nullptr);
REQUIRE(taken->parser == nullptr);
REQUIRE(taken->array()[0]->parser == nullptr);
REQUIRE(taken->array()[1]->parser == nullptr);
// ...so it stays valid once the parser, and the tree the parser still
// owns, are destroyed.
jp.reset();
// outer is dangling now; do not dereference.
REQUIRE(taken->type == JSON_ARRAY);
REQUIRE(taken->array().size() == 2);
REQUIRE(taken->array()[0]->number() == 3);
REQUIRE(taken->array()[1]->number() == 4);
}
TEST_CASE("Polygon cleaning drops a hole that no ring can parent", "[wagyu]") {
// Two mutually reversed self-intersecting rings whose union leaves a hole
// that wagyu's topology correction cannot assign to any surviving parent