ENH: Use int64_error flag to raise ValueError

Author: effigies

nibabel/nifti1.py

@@ -26,6 +26,7 @@
 from . import analyze  # module import
 from .spm99analyze import SpmAnalyzeHeader
 from .casting import have_binary128
+from nibabel.__future__ import future_flags
 
 pdcm, have_dicom, _ = optional_package("pydicom")
 
@@ -1757,11 +1758,18 @@ def __init__(self, dataobj, affine, header=None,
                  extra=None, file_map=None, dtype=None):
         danger_dts = (np.dtype("int64"), np.dtype("uint64"))
         if header is None and dtype is None and dataobj.dtype in danger_dts:
-            msg = (f"Image data has type {dataobj.dtype}, which may cause "
-                   "incompatibilities with other tools. This will error in "
-                   "future versions of Nibabel. This warning can be silenced "
-                   f"by passing the dtype argument to {self.__class__.__name__}().")
-            warnings.warn(msg, FutureWarning)
+            if future_flags['int64_error']:
+                raise ValueError(
+                    f"Image data has type {dataobj.dtype}, which may cause "
+                    "incompatibilities with other tools. To set an alternative "
+                    f"on-disk dtype or force use of {dataobj.dtype}, pass a "
+                    f"dtype argument to {self.__class__.__name__}().")
+            warnings.warn(
+                f"Image data has type {dataobj.dtype}, which may cause "
+                "incompatibilities with other tools. This will error in "
+                "future versions of Nibabel. This warning can be silenced "
+                f"by passing the dtype argument to {self.__class__.__name__}().",
+                FutureWarning)
         super(Nifti1Pair, self).__init__(dataobj,
                                          affine,
                                          header,