Allow reify types to be mutable to avoid FrozenInstanceError from attrs

CHANGELOG.md

@@ -5,6 +5,8 @@ The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/),
 and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.html).
 
 ## [Unreleased]
+### Changed
+ * Types generated by `reify` may optionally be marked as `^:mutable` now to prevent `attrs.exceptions.FrozenInstanceError`s being thrown when mutating methods inherited from the supertype(s) are called (#1088)
 
 ## [v0.3.0]
 ### Added

docs/concepts.rst

@@ -1342,6 +1342,13 @@ Reified types always implement :py:class:`basilisp.lang.interfaces.IWithMeta` an
 
    While ``reify`` and ``deftype`` are broadly similar, ``reify`` types may not define class or static methods.
 
+.. warning::
+
+   If a reified type is defined with a mutable "abstract" supertype (such as :external:py:class:`io.IOBase`), users may experience errors arising from the ``attrs``-generated ``__setattr__`` method for the underlying type when mutating methods are called on the resulting object.
+   Reified types are immutable (or "frozen" in ``attrs`` lingo) by default.
+   When a mutating method, such as :external:py:meth:`io.IOBase.close`, is called on the type (which may be called manually or it may be called at VM shutdown), the mutation will fail due to ``attrs`` replacing the ``__setattr__`` method on the type.
+   It is possible to force Basilisp to generate a mutable (non-frozen) type for reified types by applying the ``^:mutable`` metadata on the ``reify`` symbol.
+
 .. _defrecord:
 
 ``defrecord``

src/basilisp/core.lpy

@@ -6742,9 +6742,10 @@
   the body of a method should not include that parameter, as it will be supplied
   automatically."
   [& method-impls]
-  (let [{:keys [interfaces methods]} (collect-methods method-impls)]
+  (let [{:keys [interfaces methods]} (collect-methods method-impls)
+        reify-sym                    (with-meta 'reify* (meta (first &form)))]
     (with-meta
-      `(reify* :implements [~@interfaces python/object]
+      `(~reify-sym :implements [~@interfaces python/object]
                ~@methods)
       (meta &form))))
 

src/basilisp/lang/compiler/analyzer.py

@@ -3107,6 +3107,7 @@ def _reify_ast(form: ISeq, ctx: AnalyzerContext) -> Reify:
             members=vec.vector(members),
             verified_abstract=type_abstractness.is_statically_verified_as_abstract,
             artificially_abstract=type_abstractness.artificially_abstract_supertypes,
+            is_frozen=not _is_mutable(form.first),
             use_weakref_slot=not type_abstractness.supertype_already_weakref,
             env=ctx.get_node_env(pos=ctx.syntax_position),
         )

src/basilisp/lang/compiler/generator.py

@@ -2771,7 +2771,7 @@ def _reify_to_py_ast(
                             ),
                             verified_abstract=node.verified_abstract,
                             artificially_abstract_bases=artificially_abstract_bases,
-                            is_frozen=True,
+                            is_frozen=node.is_frozen,
                             use_slots=True,
                             use_weakref_slot=node.use_weakref_slot,
                         )

src/basilisp/lang/compiler/nodes.py

@@ -815,6 +815,7 @@ class Reify(Node[SpecialForm]):
     env: NodeEnv
     verified_abstract: bool = False
     artificially_abstract: IPersistentSet[DefTypeBase] = lset.PersistentSet.empty()
+    is_frozen: bool = True
     use_weakref_slot: bool = True
     meta: NodeMeta = None
     children: Sequence[kw.Keyword] = vec.v(MEMBERS)

tests/basilisp/compiler_test.py

@@ -4937,21 +4937,21 @@ def test_reify_disallows_extra_methods_if_not_in_a_super_type(
                 (
                     """
                     (import* io)
-                    (reify* :implements [^:abstract ^{:abstract-members '(:read)} io/IOBase]
+                    (^:mutable reify* :implements [^:abstract ^{:abstract-members '(:read)} io/IOBase]
                       (read [this v]))""",
                     compiler.CompilerException,
                 ),
                 (
                     """
                     (import* io)
-                    (reify* :implements [^:abstract ^{:abstract-members [:read]} io/IOBase]
+                    (^:mutable reify* :implements [^:abstract ^{:abstract-members [:read]} io/IOBase]
                       (read [this v]))""",
                     compiler.CompilerException,
                 ),
                 (
                     """
                     (import* io)
-                    (reify* :implements [^:abstract ^{:abstract-members #py [:read]} io/IOBase]
+                    (^:mutable reify* :implements [^:abstract ^{:abstract-members #py [:read]} io/IOBase]
                       (read [this v]))""",
                     compiler.CompilerException,
                 ),
@@ -4968,7 +4968,7 @@ def test_reify_abstract_members_must_have_elements(self, lcompile: CompileFn):
                 lcompile(
                     """
                     (import* io)
-                    (reify* :implements [^:abstract ^{:abstract-members #{}} io/IOBase]
+                    (^:mutable reify* :implements [^:abstract ^{:abstract-members #{}} io/IOBase]
                       (read [this v]))
                     """
                 )
@@ -4979,7 +4979,7 @@ def test_reify_abstract_should_not_have_namespaces(
             lcompile(
                 """
                 (import* io)
-                (reify* :implements [^:abstract ^{:abstract-members #{:io/read}} io/IOBase]
+                (^:mutable reify* :implements [^:abstract ^{:abstract-members #{:io/read}} io/IOBase]
                   (read [this v]))
                 """
             )
@@ -4997,7 +4997,7 @@ def test_reify_abstract_members_names_must_be_str_keyword_or_symbol(
                 lcompile(
                     """
                     (import* io)
-                    (reify* :implements [^:abstract ^{:abstract-members #{1 :read}} io/IOBase]
+                    (^:mutable reify* :implements [^:abstract ^{:abstract-members #{1 :read}} io/IOBase]
                       (read [this v]))
                     """,
                 )
@@ -5007,19 +5007,19 @@ def test_reify_abstract_members_names_must_be_str_keyword_or_symbol(
             [
                 """
                 (import* io)
-                (reify* :implements [^:abstract ^{:abstract-members #{:read :write}} io/IOBase]
+                (^:mutable reify* :implements [^:abstract ^{:abstract-members #{:read :write}} io/IOBase]
                   (read [this n])
                   (write [this v]))
                 """,
                 """
                 (import* io)
-                (reify* :implements [^:abstract ^{:abstract-members #{read write}} io/IOBase]
+                (^:mutable reify* :implements [^:abstract ^{:abstract-members #{read write}} io/IOBase]
                   (read [this n])
                   (write [this v]))
                 """,
                 """
                 (import* io)
-                (reify* :implements [^:abstract ^{:abstract-members #{"read" "write"}} io/IOBase]
+                (^:mutable reify* :implements [^:abstract ^{:abstract-members #{"read" "write"}} io/IOBase]
                   (read [this n])
                   (write [this v]))
                 """,