Fix crash and leak in DiffHunk.lines and Patch.hunks

On allocation failure PyList_New() returns NULL, and the previous code
dereferenced it while setting items. Also, the partially built list was
leaked on every mid-loop early return.

Fixes #1479

Assisted-by: Kimi Code

Author: jdavid

CHANGELOG.md

@@ -17,6 +17,10 @@
   instead of producing wrong results, `SystemError`, or crashes
   [#1478](https://github.com/libgit2/pygit2/issues/1478).
 
+- Fix potential crash and memory leak in `DiffHunk.lines` and `Patch.hunks`
+  on allocation or per-item failure
+  [#1479](https://github.com/libgit2/pygit2/issues/1479).
+
 
 # 1.20.0 (2026-08-08)
 

src/diff.c

@@ -832,14 +832,21 @@ DiffHunk_lines__get__(DiffHunk *self)
 
     // TODO Replace by an iterator
     py_lines = PyList_New(self->n_lines);
+    if (py_lines == NULL)
+        return NULL;
+
     for (i = 0; i < self->n_lines; ++i) {
         err = git_patch_get_line_in_hunk(&line, self->patch->patch, self->idx, i);
-        if (err < 0)
+        if (err < 0) {
+            Py_DECREF(py_lines);
             return Error_set(err);
+        }
 
         py_line = wrap_diff_line(line, self);
-        if (py_line == NULL)
+        if (py_line == NULL) {
+            Py_DECREF(py_lines);
             return NULL;
+        }
 
         PyList_SetItem(py_lines, i, py_line);
    }

src/patch.c

@@ -223,10 +223,15 @@ Patch_hunks__get__(Patch *self)
 
     hunk_amounts = git_patch_num_hunks(self->patch);
     py_hunks = PyList_New(hunk_amounts);
+    if (py_hunks == NULL)
+        return NULL;
+
     for (i = 0; i < hunk_amounts; i++) {
         py_hunk = wrap_diff_hunk(self, i);
-        if (py_hunk == NULL)
+        if (py_hunk == NULL) {
+            Py_DECREF(py_hunks);
             return NULL;
+        }
 
         PyList_SET_ITEM((PyObject*) py_hunks, i, py_hunk);
     }