Fix a bug where unknown data readers in non-selected reader conditional branches prevented reading altogether

CHANGELOG.md

@@ -12,6 +12,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
  * Fix a bug where `basilisp test` command fails due to an invalid `argparse` configuration (#1119)
  * Fix a bug where `basilisp.walk/walk` (and any functions that depend on it) did not preserve collection metadata (#1123)
  * Fix a bug where the private `postwalk` implementation in the reader did not preserve collection metadata (#1123)
+ * Fix a bug where unknown data reader tags in non-selected reader conditional branches prevented reading the forms (#1118)
 
 ## [v0.3.1]
 ### Added

src/basilisp/lang/reader.py

@@ -51,6 +51,7 @@
     lrepr,
 )
 from basilisp.lang.source import format_source_context
+from basilisp.lang.tagged import TaggedLiteral, tagged_literal
 from basilisp.lang.typing import IterableLispForm, LispForm, ReaderForm
 from basilisp.lang.util import munge
 from basilisp.util import Maybe, partition
@@ -363,6 +364,7 @@ class ReaderContext:
         "_default_data_reader_fn",
         "_features",
         "_process_reader_cond",
+        "_process_tagged_literals",
         "_reader",
         "_resolve",
         "_in_anon_fn",
@@ -389,6 +391,7 @@ def __init__(  # pylint: disable=too-many-arguments
         self._process_reader_cond = process_reader_cond
         self._reader = reader
         self._resolve = Maybe(resolver).or_else_get(lambda x: x)
+        self._process_tagged_literals: collections.deque[bool] = collections.deque([])
         self._in_anon_fn: collections.deque[bool] = collections.deque([])
         self._syntax_quoted: collections.deque[bool] = collections.deque([])
         self._gensym_env: collections.deque[GenSymEnvironment] = collections.deque([])
@@ -434,6 +437,19 @@ def is_in_anon_fn(self) -> bool:
         except IndexError:
             return False
 
+    @contextlib.contextmanager
+    def process_tagged_literals(self, v: bool):
+        self._process_tagged_literals.append(v)
+        yield
+        self._process_tagged_literals.pop()
+
+    @property
+    def should_process_tagged_literals(self) -> bool:
+        try:
+            return self._process_tagged_literals[-1] is True
+        except IndexError:
+            return True
+
     @property
     def gensym_env(self) -> GenSymEnvironment:
         return self._gensym_env[-1]
@@ -655,7 +671,7 @@ def _read_coll(
             continue
         elif _should_splice_reader_conditional(ctx, elem):
             assert isinstance(elem, ReaderConditional)
-            selected_feature = elem.select_feature(ctx.reader_features)
+            selected_feature = _select_reader_conditional_branch(ctx, elem)
             if selected_feature is ReaderConditional.FEATURE_NOT_PRESENT:
                 continue
             elif isinstance(selected_feature, vec.PersistentVector):
@@ -726,7 +742,7 @@ def __read_map_elems(ctx: ReaderContext) -> Iterable[RawReaderForm]:
             continue
         elif _should_splice_reader_conditional(ctx, v):
             assert isinstance(v, ReaderConditional)
-            selected_feature = v.select_feature(ctx.reader_features)
+            selected_feature = _select_reader_conditional_branch(ctx, v)
             if selected_feature is ReaderConditional.FEATURE_NOT_PRESENT:
                 continue
             elif isinstance(selected_feature, vec.PersistentVector):
@@ -1443,6 +1459,23 @@ def _read_numeric_constant(ctx: ReaderContext) -> float:
     return c
 
 
+def _select_reader_conditional_branch(
+    ctx: ReaderContext, reader_cond: ReaderConditional
+) -> LispReaderForm:
+    """Select the reader conditional branch by feature and then resolve any tagged
+    literals for the selected feature."""
+
+    def resolve_tagged_literals(form: LispReaderForm):
+        if isinstance(form, TaggedLiteral):
+            resolved = _postwalk(resolve_tagged_literals, form.form)
+            return _resolve_tagged_literal(ctx, form.tag, resolved)
+        return form
+
+    return _postwalk(
+        resolve_tagged_literals, reader_cond.select_feature(ctx.reader_features)
+    )
+
+
 def _should_splice_reader_conditional(ctx: ReaderContext, form: LispReaderForm) -> bool:
     """Return True if and only if form is a ReaderConditional which should be spliced
     into a surrounding collection context."""
@@ -1453,9 +1486,61 @@ def _should_splice_reader_conditional(ctx: ReaderContext, form: LispReaderForm)
     )
 
 
-def _read_reader_conditional_preserving(ctx: ReaderContext) -> ReaderConditional:
-    """Read a reader conditional form and return the unprocessed reader
-    conditional object."""
+def _read_reader_conditional_preserving(
+    ctx: ReaderContext, is_splicing: bool
+) -> ReaderConditional:
+    """Read a reader conditional form and return the reader conditional object."""
+    coll: list = []
+    reader = ctx.reader
+    while True:
+        char = reader.peek()
+        if char == "":
+            raise ctx.eof_error("Unexpected EOF in reader conditional")
+        if whitespace_chars.match(char):
+            reader.advance()
+            continue
+        if char == ")":
+            reader.next_char()
+            return ReaderConditional(llist.list(coll), is_splicing=is_splicing)
+
+        with ctx.process_tagged_literals(False):
+            elem = _read_next(ctx)
+
+        if elem is COMMENT or isinstance(elem, Comment):
+            continue
+        elif _should_splice_reader_conditional(ctx, elem):
+            assert isinstance(elem, ReaderConditional)
+            selected_feature = _select_reader_conditional_branch(ctx, elem)
+            if selected_feature is ReaderConditional.FEATURE_NOT_PRESENT:
+                continue
+            elif isinstance(selected_feature, vec.PersistentVector):
+                coll.extend(selected_feature)
+            else:
+                raise ctx.syntax_error(
+                    "Expecting Vector for splicing reader conditional "
+                    f"form; got {type(selected_feature)}"
+                )
+        else:
+            assert (
+                not isinstance(elem, ReaderConditional)
+                or not ctx.should_process_reader_cond
+            ), "Reader conditionals must be processed if specified"
+            coll.append(elem)
+
+
+def _read_reader_conditional(ctx: ReaderContext) -> LispReaderForm:
+    """Read a reader conditional form and either return it or process it and
+    return the resulting form.
+
+    If the reader is not set to process the reader conditional, it will always
+    be returned as a ReaderConditional object.
+
+    If the reader is set to process reader conditionals, only non-splicing reader
+    conditionals are processed here. If no matching feature is found in a
+    non-splicing reader conditional, a comment will be emitted (which is ultimately
+    discarded downstream in the reader).
+
+    Splicing reader conditionals are processed in the respective collection readers."""
     reader = ctx.reader
     start = reader.advance()
     assert start == "?"
@@ -1477,27 +1562,9 @@ def _read_reader_conditional_preserving(ctx: ReaderContext) -> ReaderConditional
             f"Expected opening '(' for reader conditional; got '{open_char}'"
         )
 
-    feature_list = _read_coll(ctx, llist.list, ")", "reader conditional")
-    assert isinstance(feature_list, llist.PersistentList)
-    return ReaderConditional(feature_list, is_splicing=is_splicing)
-
-
-def _read_reader_conditional(ctx: ReaderContext) -> LispReaderForm:
-    """Read a reader conditional form and either return it or process it and
-    return the resulting form.
-
-    If the reader is not set to process the reader conditional, it will always
-    be returned as a ReaderConditional object.
-
-    If the reader is set to process reader conditionals, only non-splicing reader
-    conditionals are processed here. If no matching feature is found in a
-    non-splicing reader conditional, a comment will be emitted (which is ultimately
-    discarded downstream in the reader).
-
-    Splicing reader conditionals are processed in the respective collection readers."""
-    reader_cond = _read_reader_conditional_preserving(ctx)
+    reader_cond = _read_reader_conditional_preserving(ctx, is_splicing)
     if ctx.should_process_reader_cond and not reader_cond.is_splicing:
-        form = reader_cond.select_feature(ctx.reader_features)
+        form = _select_reader_conditional_branch(ctx, reader_cond)
         return cast(
             LispReaderForm,
             COMMENT if form is ReaderConditional.FEATURE_NOT_PRESENT else form,
@@ -1544,9 +1611,32 @@ def _load_record_or_type(
         raise ctx.syntax_error("Records may only be constructed from Vectors and Maps")
 
 
+def _resolve_tagged_literal(
+    ctx: ReaderContext, s: sym.Symbol, v: RawReaderForm
+) -> LispReaderForm:
+    """Resolve a tagged literal into whatever value is returned by the associated data reader."""
+    data_reader = None
+    if s in ctx.data_readers:
+        data_reader = ctx.data_readers[s]
+    elif s in ReaderContext._DATA_READERS:
+        data_reader = ReaderContext._DATA_READERS[s]
+
+    if data_reader is not None:
+        try:
+            return data_reader(v)
+        except SyntaxError as e:
+            raise ctx.syntax_error(e.message).with_traceback(e.__traceback__) from None
+    elif s.ns is None and "." in s.name:
+        return _load_record_or_type(ctx, s, v)
+    else:
+        try:
+            return ctx.default_data_reader_fn(s, v)
+        except SyntaxError as e:
+            raise ctx.syntax_error(e.message).with_traceback(e.__traceback__) from None
+
+
 def _read_reader_macro(ctx: ReaderContext) -> LispReaderForm:  # noqa: MC0001
-    """Return a data structure evaluated as a reader
-    macro from the input stream."""
+    """Return a data structure evaluated as a reader macro from the input stream."""
     start = ctx.reader.advance()
     assert start == "#"
     char = ctx.reader.peek()
@@ -1587,28 +1677,10 @@ def _read_reader_macro(ctx: ReaderContext) -> LispReaderForm:  # noqa: MC0001
 
         v = _read_next_consuming_comment(ctx)
 
-        data_reader = None
-        if s in ctx.data_readers:
-            data_reader = ctx.data_readers[s]
-        elif s in ReaderContext._DATA_READERS:
-            data_reader = ReaderContext._DATA_READERS[s]
+        if not ctx.should_process_tagged_literals:
+            return tagged_literal(s, v)
 
-        if data_reader is not None:
-            try:
-                return data_reader(v)
-            except SyntaxError as e:
-                raise ctx.syntax_error(e.message).with_traceback(
-                    e.__traceback__
-                ) from None
-        elif s.ns is None and "." in s.name:
-            return _load_record_or_type(ctx, s, v)
-        else:
-            try:
-                return ctx.default_data_reader_fn(s, v)
-            except SyntaxError as e:
-                raise ctx.syntax_error(e.message).with_traceback(
-                    e.__traceback__
-                ) from None
+        return _resolve_tagged_literal(ctx, s, v)
 
     raise ctx.syntax_error(f"Unexpected char '{char}' in reader macro")
 

src/basilisp/lang/typing.py

@@ -19,6 +19,7 @@
     ISeq,
     IType,
 )
+from basilisp.lang.tagged import TaggedLiteral
 
 CompilerOpts = IPersistentMap[kw.Keyword, bool]
 
@@ -48,7 +49,7 @@
     uuid.UUID,
 ]
 PyCollectionForm = Union[dict, list, set, tuple]
-ReaderForm = Union[LispForm, IRecord, ISeq, IType, PyCollectionForm]
+ReaderForm = Union[LispForm, IRecord, ISeq, IType, PyCollectionForm, TaggedLiteral]
 SpecialForm = Union[llist.PersistentList, ISeq]
 
 

tests/basilisp/reader_test.py

@@ -22,6 +22,7 @@
 from basilisp.lang import vector as vec
 from basilisp.lang.exception import format_exception
 from basilisp.lang.interfaces import IPersistentSet
+from basilisp.lang.tagged import tagged_literal
 
 
 @pytest.fixture
@@ -1551,14 +1552,18 @@ class TestReaderConditional:
             "#?(clj 1 :lpy 2 :default)",
         ],
     )
-    def test_basic_form_syntax(self, v: str):
+    def test_invalid_basic_form_syntax(self, v: str):
         with pytest.raises(reader.SyntaxError):
             read_str_first(v)
 
     def test_basic_form(self):
         assert 2 == read_str_first("#?(:clj 1 :lpy 2 :default 3)")
+        assert 2 == read_str_first("#?(:clj #_1 1 #_:lpy :lpy 2 :default 3)")
         assert 1 == read_str_first("#?(:default 1 :lpy 2)")
         assert None is read_str_first("#?(:clj 1 :cljs 2)")
+        assert [[], (), {}, set()] == read_str_first(
+            "#?(:cljs #js [] :lpy #py [#py [] #py () #py {} #py #{}] :default [])"
+        )
 
     def test_basic_form_preserving(self):
         c = read_str_first("#?(:clj 1 :lpy 2 :default 3)", process_reader_cond=False)
@@ -1570,6 +1575,72 @@ def test_basic_form_preserving(self):
         ) == c.val_at(reader.READER_COND_FORM_KW)
         assert "#?(:clj 1 :lpy 2 :default 3)" == c.lrepr()
 
+    def test_form_preserving_with_unknown_data_readers(self):
+        c = read_str_first(
+            "#?(:cljs #js [] :lpy #py [] :default [])", process_reader_cond=False
+        )
+        assert isinstance(c, reader.ReaderConditional)
+        assert not c.is_splicing
+        assert False is c.val_at(reader.READER_COND_SPLICING_KW)
+        assert llist.l(
+            kw.keyword("cljs"),
+            tagged_literal(sym.symbol("js"), vec.EMPTY),
+            kw.keyword("lpy"),
+            tagged_literal(sym.symbol("py"), vec.EMPTY),
+            kw.keyword("default"),
+            vec.EMPTY,
+        ) == c.val_at(reader.READER_COND_FORM_KW)
+        assert "#?(:cljs #js [] :lpy #py [] :default [])" == c.lrepr()
+
+    def test_ignore_unknown_data_readers_in_non_selected_conditional(self):
+        v = read_str_first("#?(:cljs #js [] :default [])")
+        assert isinstance(v, vec.PersistentVector)
+        assert v == vec.EMPTY
+
+    @pytest.mark.parametrize(
+        "s,expected",
+        [
+            (
+                "#?(:cljs [#?(:lpy :py :default :other)] :default :none)",
+                kw.keyword("none"),
+            ),
+            (
+                "#?(:lpy [#?(:lpy :py :default :other)] :default :none)",
+                vec.v(kw.keyword("py")),
+            ),
+            (
+                "#?(:lpy [#?(:clj :py :default :other)] :default :none)",
+                vec.v(kw.keyword("other")),
+            ),
+            (
+                "#?(:cljs [#?@(:clj [1 2] :default [3 4])] :default :none)",
+                kw.keyword("none"),
+            ),
+            (
+                "#?(:lpy [#?@(:clj [1 2] :default [3 4])] :default :none)",
+                vec.v(3, 4),
+            ),
+            (
+                "#?(:lpy [#?@(:clj [1 2] :cljs [3 4])] :default :none)",
+                vec.EMPTY,
+            ),
+            (
+                "#?(#?@(:clj [:clj [1 2]] :lpy [:lpy [3 4]]) :default [])",
+                vec.v(3, 4),
+            ),
+            (
+                "#?(#?@(:clj [:clj [1 2]] :lpy [:cljs [3 4]]) :default [])",
+                vec.EMPTY,
+            ),
+            (
+                "#?(#?@(:clj [1 2]) :default :none)",
+                kw.keyword("none"),
+            ),
+        ],
+    )
+    def test_nested_reader_conditionals(self, s: str, expected):
+        assert expected == read_str_first(s)
+
     @pytest.mark.parametrize(
         "v",
         [
@@ -1598,6 +1669,8 @@ def test_basic_form_preserving(self):
             "#?@(:clj)",
             "#?@(:clj [1] lpy)",
             "#?@(clj [1] :lpy [2] :default)",
+            # Invalid splice connection (in nested reader conditional)
+            "#?(#?@(:lpy (:lpy [])) :default :none)",
         ],
     )
     def test_splicing_form_syntax(self, v: str):