1 files changed, 77 insertions, 0 deletions
diff --git a/lib/spack/external/attr/setters.py b/lib/spack/external/attr/setters.py
new file mode 100644
index 0000000000..240014b3c1
--- /dev/null
+++ b/lib/spack/external/attr/setters.py
@@ -0,0 +1,77 @@
+"""
+Commonly used hooks for on_setattr.
+"""
+
+from __future__ import absolute_import, division, print_function
+
+from . import _config
+from .exceptions import FrozenAttributeError
+
+
+def pipe(*setters):
+    """
+    Run all *setters* and return the return value of the last one.
+
+    .. versionadded:: 20.1.0
+    """
+
+    def wrapped_pipe(instance, attrib, new_value):
+        rv = new_value
+
+        for setter in setters:
+            rv = setter(instance, attrib, rv)
+
+        return rv
+
+    return wrapped_pipe
+
+
+def frozen(_, __, ___):
+    """
+    Prevent an attribute to be modified.
+
+    .. versionadded:: 20.1.0
+    """
+    raise FrozenAttributeError()
+
+
+def validate(instance, attrib, new_value):
+    """
+    Run *attrib*'s validator on *new_value* if it has one.
+
+    .. versionadded:: 20.1.0
+    """
+    if _config._run_validators is False:
+        return new_value
+
+    v = attrib.validator
+    if not v:
+        return new_value
+
+    v(instance, attrib, new_value)
+
+    return new_value
+
+
+def convert(instance, attrib, new_value):
+    """
+    Run *attrib*'s converter -- if it has one --  on *new_value* and return the
+    result.
+
+    .. versionadded:: 20.1.0
+    """
+    c = attrib.converter
+    if c:
+        return c(new_value)
+
+    return new_value
+
+
+NO_OP = object()
+"""
+Sentinel for disabling class-wide *on_setattr* hooks for certain attributes.
+
+Does not work in `pipe` or within lists.
+
+.. versionadded:: 20.1.0
+"""