Test rejection of incorrect modes

Tests/test_arrow.py

@@ -68,6 +68,26 @@ def test_to_array(mode: str, dtype: Any, mask: Any) -> None:
 
     assert_image_equal(img, reloaded)
 
+@pytest.mark.parametrize(
+    "mode, dest_modes",
+    (
+        ("L", ["I", "F", "LA", "RGB", "RGBA", "RGBX", "CMYK", "YCbCr", "HSV"]),
+        ("I", ["L", "F"]), # Technically I32 can work for any 4x8bit storage.
+        ("F", ["I", "L", "LA", "RGB", "RGBA", "RGBX", "CMYK", "YCbCr", "HSV"]),
+        ("LA", ["L", "F"]),
+        ("RGB", ["L", "F"]),
+        ("RGBA", ["L", "F"]),
+        ("RGBX", ["L", "F"]),
+        ("CMYK", ["L", "F"]),
+        ("YCbCr", ["L", "F"]),
+        ("HSV", ["L", "F"]),
+    ),
+)
+def test_invalid_array_type(mode: str, dest_modes: List[str]) -> None:
+    img = hopper(mode)
+    for dest_mode in dest_modes:
+        with pytest.raises(ValueError):
+            Image.fromarrow(img, dest_mode, img.size)
 
 def test_lifetime():
     # valgrind shouldn't error out here.

src/_imaging.c

@@ -290,6 +290,7 @@ _new_arrow(PyObject *self, PyObject *args) {
     if (!ret && array->release) {
         array->release(array);
         array->release = NULL;
+        return ImagingError_ValueError("Invalid arrow array mode or size mismatch");
     }
     return ret;
 }

src/libImaging/Storage.c

@@ -705,25 +705,36 @@ ImagingNewArrow(
 
     int64_t pixels = (int64_t)xsize * (int64_t)ysize;
 
-    if (((strcmp(schema->format, "i") == 0 && im->pixelsize == 4) ||
+    // fmt:off   // don't reformat this
-         (strcmp(schema->format, im->arrow_band_format) == 0 && im->bands == 1)) &&
+    if (((strcmp(schema->format, "I") == 0
-        pixels == external_array->length) {
+          && im->pixelsize == 4
+          && im->bands >= 2) // INT32 into any INT32 Storage mode
+         ||
+         (strcmp(schema->format, im->arrow_band_format) == 0
+          && im->bands == 1)) // Single band match
+        && pixels == external_array->length) {
         // one arrow element per, and it matches a pixelsize*char
         if (ImagingAllocateArrow(im, external_array)) {
             return im;
         }
     }
-    if (strcmp(schema->format, "+w:4") == 0 && im->pixelsize == 4 &&
+    // linter: don't mess with the formatting here
-        schema->n_children > 0 && schema->children &&
+    if (strcmp(schema->format, "+w:4") == 0 // 4 up array
-        strcmp(schema->children[0]->format, "C") == 0 &&
+        && im->pixelsize == 4  // storage as 32 bpc
-        pixels == external_array->length && external_array->n_children == 1 &&
+        && schema->n_children > 0  // make sure schema is well formed.
-        external_array->children && 4 * pixels == external_array->children[0]->length) {
+        && schema->children        // make sure schema is well formed
+        && strcmp(schema->children[0]->format, "C") == 0 // Expected format
+        && strcmp(im->arrow_band_format, "C") == 0 // Expected Format
+        && pixels == external_array->length // expected length
+        && external_array->n_children == 1 // array is well formed
+        && external_array->children        // array is well formed
+        && 4 * pixels == external_array->children[0]->length) {
         // 4 up element of char into pixelsize == 4
         if (ImagingAllocateArrow(im, external_array)) {
             return im;
         }
     }
-
+    // fmt: on
     ImagingDelete(im);
     return NULL;
 }