Implement new gdb/lldb pretty-printers

Replace old GDB and LLDB pretty-printers with new ones
which were originally written for IntelliJ Rust.
New LLDB pretty-printers support synthetic children.
New GDB/LLDB pretty-printers support all Rust types
supported by old pretty-printers, and also support:
Rc, Arc, Cell, Ref, RefCell, RefMut, HashMap, HashSet.

1 files changed, 715 insertions, 0 deletions

diff --git a/src/etc/lldb_providers.py b/src/etc/lldb_providers.py
new file mode 100644
index 00000000000..3c7817b3a61
--- /dev/null
+++ b/src/etc/lldb_providers.py
@@ -0,0 +1,715 @@
+import sys
+
+from lldb import SBValue, SBData, SBError, eBasicTypeLong, eBasicTypeUnsignedLong, \
+    eBasicTypeUnsignedChar
+
+# from lldb.formatters import Logger
+
+####################################################################################################
+# This file contains two kinds of pretty-printers: summary and synthetic.
+#
+# Important classes from LLDB module:
+#   SBValue: the value of a variable, a register, or an expression
+#   SBType:  the data type; each SBValue has a corresponding SBType
+#
+# Summary provider is a function with the type `(SBValue, dict) -> str`.
+#   The first parameter is the object encapsulating the actual variable being displayed;
+#   The second parameter is an internal support parameter used by LLDB, and you should not touch it.
+#
+# Synthetic children is the way to provide a children-based representation of the object's value.
+# Synthetic provider is a class that implements the following interface:
+#
+#     class SyntheticChildrenProvider:
+#         def __init__(self, SBValue, dict)
+#         def num_children(self)
+#         def get_child_index(self, str)
+#         def get_child_at_index(self, int)
+#         def update(self)
+#         def has_children(self)
+#         def get_value(self)
+#
+#
+# You can find more information and examples here:
+#   1. https://lldb.llvm.org/varformats.html
+#   2. https://lldb.llvm.org/python-reference.html
+#   3. https://lldb.llvm.org/python_reference/lldb.formatters.cpp.libcxx-pysrc.html
+#   4. https://github.com/llvm-mirror/lldb/tree/master/examples/summaries/cocoa
+####################################################################################################
+
+PY3 = sys.version_info[0] == 3
+
+
+class ValueBuilder:
+    def __init__(self, valobj):
+        # type: (SBValue) -> ValueBuilder
+        self.valobj = valobj
+        process = valobj.GetProcess()
+        self.endianness = process.GetByteOrder()
+        self.pointer_size = process.GetAddressByteSize()
+
+    def from_int(self, name, value):
+        # type: (str, int) -> SBValue
+        type = self.valobj.GetType().GetBasicType(eBasicTypeLong)
+        data = SBData.CreateDataFromSInt64Array(self.endianness, self.pointer_size, [value])
+        return self.valobj.CreateValueFromData(name, data, type)
+
+    def from_uint(self, name, value):
+        # type: (str, int) -> SBValue
+        type = self.valobj.GetType().GetBasicType(eBasicTypeUnsignedLong)
+        data = SBData.CreateDataFromUInt64Array(self.endianness, self.pointer_size, [value])
+        return self.valobj.CreateValueFromData(name, data, type)
+
+
+def unwrap_unique_or_non_null(unique_or_nonnull):
+    # BACKCOMPAT: rust 1.32
+    # https://github.com/rust-lang/rust/commit/7a0911528058e87d22ea305695f4047572c5e067
+    ptr = unique_or_nonnull.GetChildMemberWithName("pointer")
+    return ptr if ptr.TypeIsPointerType() else ptr.GetChildAtIndex(0)
+
+
+class DefaultSynthteticProvider:
+    def __init__(self, valobj, dict):
+        # type: (SBValue, dict) -> DefaultSynthteticProvider
+        # logger = Logger.Logger()
+        # logger >> "Default synthetic provider for " + str(valobj.GetName())
+        self.valobj = valobj
+
+    def num_children(self):
+        # type: () -> int
+        return self.valobj.GetNumChildren()
+
+    def get_child_index(self, name):
+        # type: (str) -> int
+        return self.valobj.GetIndexOfChildWithName(name)
+
+    def get_child_at_index(self, index):
+        # type: (int) -> SBValue
+        return self.valobj.GetChildAtIndex(index)
+
+    def update(self):
+        # type: () -> None
+        pass
+
+    def has_children(self):
+        # type: () -> bool
+        return self.valobj.MightHaveChildren()
+
+
+class EmptySyntheticProvider:
+    def __init__(self, valobj, dict):
+        # type: (SBValue, dict) -> EmptySyntheticProvider
+        # logger = Logger.Logger()
+        # logger >> "[EmptySyntheticProvider] for " + str(valobj.GetName())
+        self.valobj = valobj
+
+    def num_children(self):
+        # type: () -> int
+        return 0
+
+    def get_child_index(self, name):
+        # type: (str) -> int
+        return None
+
+    def get_child_at_index(self, index):
+        # type: (int) -> SBValue
+        return None
+
+    def update(self):
+        # type: () -> None
+        pass
+
+    def has_children(self):
+        # type: () -> bool
+        return False
+
+
+def SizeSummaryProvider(valobj, dict):
+    # type: (SBValue, dict) -> str
+    return 'size=' + str(valobj.GetNumChildren())
+
+
+def vec_to_string(vec):
+    length = vec.GetNumChildren()
+    chars = [vec.GetChildAtIndex(i).GetValueAsUnsigned() for i in range(length)]
+    return bytes(chars).decode(errors='replace') if PY3 else "".join(chr(char) for char in chars)
+
+
+def StdStringSummaryProvider(valobj, dict):
+    # type: (SBValue, dict) -> str
+    # logger = Logger.Logger()
+    # logger >> "[StdStringSummaryProvider] for " + str(valobj.GetName())
+    vec = valobj.GetChildAtIndex(0)
+    return '"%s"' % vec_to_string(vec)
+
+
+def StdOsStringSummaryProvider(valobj, dict):
+    # type: (SBValue, dict) -> str
+    # logger = Logger.Logger()
+    # logger >> "[StdOsStringSummaryProvider] for " + str(valobj.GetName())
+    buf = valobj.GetChildAtIndex(0).GetChildAtIndex(0)
+    is_windows = "Wtf8Buf" in buf.type.name
+    vec = buf.GetChildAtIndex(0) if is_windows else buf
+    return '"%s"' % vec_to_string(vec)
+
+
+def StdStrSummaryProvider(valobj, dict):
+    # type: (SBValue, dict) -> str
+    # logger = Logger.Logger()
+    # logger >> "[StdStrSummaryProvider] for " + str(valobj.GetName())
+
+    length = valobj.GetChildMemberWithName("length").GetValueAsUnsigned()
+    if length == 0:
+        return '""'
+
+    data_ptr = valobj.GetChildMemberWithName("data_ptr")
+
+    start = data_ptr.GetValueAsUnsigned()
+    error = SBError()
+    process = data_ptr.GetProcess()
+    data = process.ReadMemory(start, length, error)
+    data = data.decode(encoding='UTF-8') if PY3 else data
+    return '"%s"' % data
+
+
+class StructSyntheticProvider:
+    """Pretty-printer for structs and struct enum variants"""
+
+    def __init__(self, valobj, dict, is_variant=False):
+        # type: (SBValue, dict, bool) -> StructSyntheticProvider
+        # logger = Logger.Logger()
+        self.valobj = valobj
+        self.is_variant = is_variant
+        self.type = valobj.GetType()
+        self.fields = {}
+
+        if is_variant:
+            self.fields_count = self.type.GetNumberOfFields() - 1
+            real_fields = self.type.fields[1:]
+        else:
+            self.fields_count = self.type.GetNumberOfFields()
+            real_fields = self.type.fields
+
+        for number, field in enumerate(real_fields):
+            self.fields[field.name] = number
+
+    def num_children(self):
+        # type: () -> int
+        return self.fields_count
+
+    def get_child_index(self, name):
+        # type: (str) -> int
+        return self.fields.get(name, -1)
+
+    def get_child_at_index(self, index):
+        # type: (int) -> SBValue
+        if self.is_variant:
+            field = self.type.GetFieldAtIndex(index + 1)
+        else:
+            field = self.type.GetFieldAtIndex(index)
+        return self.valobj.GetChildMemberWithName(field.name)
+
+    def update(self):
+        # type: () -> None
+        pass
+
+    def has_children(self):
+        # type: () -> bool
+        return True
+
+
+class TupleSyntheticProvider:
+    """Pretty-printer for tuples and tuple enum variants"""
+
+    def __init__(self, valobj, dict, is_variant=False):
+        # type: (SBValue, dict, bool) -> TupleSyntheticProvider
+        # logger = Logger.Logger()
+        self.valobj = valobj
+        self.is_variant = is_variant
+        self.type = valobj.GetType()
+
+        if is_variant:
+            self.size = self.type.GetNumberOfFields() - 1
+        else:
+            self.size = self.type.GetNumberOfFields()
+
+    def num_children(self):
+        # type: () -> int
+        return self.size
+
+    def get_child_index(self, name):
+        # type: (str) -> int
+        if name.isdigit():
+            return int(name)
+        else:
+            return -1
+
+    def get_child_at_index(self, index):
+        # type: (int) -> SBValue
+        if self.is_variant:
+            field = self.type.GetFieldAtIndex(index + 1)
+        else:
+            field = self.type.GetFieldAtIndex(index)
+        element = self.valobj.GetChildMemberWithName(field.name)
+        return self.valobj.CreateValueFromData(str(index), element.GetData(), element.GetType())
+
+    def update(self):
+        # type: () -> None
+        pass
+
+    def has_children(self):
+        # type: () -> bool
+        return True
+
+
+class StdVecSyntheticProvider:
+    """Pretty-printer for alloc::vec::Vec<T>
+
+    struct Vec<T> { buf: RawVec<T>, len: usize }
+    struct RawVec<T> { ptr: Unique<T>, cap: usize, ... }
+    rust 1.31.1: struct Unique<T: ?Sized> { pointer: NonZero<*const T>, ... }
+    rust 1.33.0: struct Unique<T: ?Sized> { pointer: *const T, ... }
+    struct NonZero<T>(T)
+    """
+
+    def __init__(self, valobj, dict):
+        # type: (SBValue, dict) -> StdVecSyntheticProvider
+        # logger = Logger.Logger()
+        # logger >> "[StdVecSyntheticProvider] for " + str(valobj.GetName())
+        self.valobj = valobj
+        self.update()
+
+    def num_children(self):
+        # type: () -> int
+        return self.length
+
+    def get_child_index(self, name):
+        # type: (str) -> int
+        index = name.lstrip('[').rstrip(']')
+        if index.isdigit():
+            return int(index)
+        else:
+            return -1
+
+    def get_child_at_index(self, index):
+        # type: (int) -> SBValue
+        start = self.data_ptr.GetValueAsUnsigned()
+        address = start + index * self.element_type_size
+        element = self.data_ptr.CreateValueFromAddress("[%s]" % index, address, self.element_type)
+        return element
+
+    def update(self):
+        # type: () -> None
+        self.length = self.valobj.GetChildMemberWithName("len").GetValueAsUnsigned()
+        self.buf = self.valobj.GetChildMemberWithName("buf")
+
+        self.data_ptr = unwrap_unique_or_non_null(self.buf.GetChildMemberWithName("ptr"))
+
+        self.element_type = self.data_ptr.GetType().GetPointeeType()
+        self.element_type_size = self.element_type.GetByteSize()
+
+    def has_children(self):
+        # type: () -> bool
+        return True
+
+
+class StdSliceSyntheticProvider:
+    def __init__(self, valobj, dict):
+        self.valobj = valobj
+        self.update()
+
+    def num_children(self):
+        # type: () -> int
+        return self.length
+
+    def get_child_index(self, name):
+        # type: (str) -> int
+        index = name.lstrip('[').rstrip(']')
+        if index.isdigit():
+            return int(index)
+        else:
+            return -1
+
+    def get_child_at_index(self, index):
+        # type: (int) -> SBValue
+        start = self.data_ptr.GetValueAsUnsigned()
+        address = start + index * self.element_type_size
+        element = self.data_ptr.CreateValueFromAddress("[%s]" % index, address, self.element_type)
+        return element
+
+    def update(self):
+        # type: () -> None
+        self.length = self.valobj.GetChildMemberWithName("length").GetValueAsUnsigned()
+        self.data_ptr = self.valobj.GetChildMemberWithName("data_ptr")
+
+        self.element_type = self.data_ptr.GetType().GetPointeeType()
+        self.element_type_size = self.element_type.GetByteSize()
+
+    def has_children(self):
+        # type: () -> bool
+        return True
+
+
+class StdVecDequeSyntheticProvider:
+    """Pretty-printer for alloc::collections::vec_deque::VecDeque<T>
+
+    struct VecDeque<T> { tail: usize, head: usize, buf: RawVec<T> }
+    """
+
+    def __init__(self, valobj, dict):
+        # type: (SBValue, dict) -> StdVecDequeSyntheticProvider
+        # logger = Logger.Logger()
+        # logger >> "[StdVecDequeSyntheticProvider] for " + str(valobj.GetName())
+        self.valobj = valobj
+        self.update()
+
+    def num_children(self):
+        # type: () -> int
+        return self.size
+
+    def get_child_index(self, name):
+        # type: (str) -> int
+        index = name.lstrip('[').rstrip(']')
+        if index.isdigit() and self.tail <= index and (self.tail + index) % self.cap < self.head:
+            return int(index)
+        else:
+            return -1
+
+    def get_child_at_index(self, index):
+        # type: (int) -> SBValue
+        start = self.data_ptr.GetValueAsUnsigned()
+        address = start + ((index + self.tail) % self.cap) * self.element_type_size
+        element = self.data_ptr.CreateValueFromAddress("[%s]" % index, address, self.element_type)
+        return element
+
+    def update(self):
+        # type: () -> None
+        self.head = self.valobj.GetChildMemberWithName("head").GetValueAsUnsigned()
+        self.tail = self.valobj.GetChildMemberWithName("tail").GetValueAsUnsigned()
+        self.buf = self.valobj.GetChildMemberWithName("buf")
+        self.cap = self.buf.GetChildMemberWithName("cap").GetValueAsUnsigned()
+        if self.head >= self.tail:
+            self.size = self.head - self.tail
+        else:
+            self.size = self.cap + self.head - self.tail
+
+        self.data_ptr = unwrap_unique_or_non_null(self.buf.GetChildMemberWithName("ptr"))
+
+        self.element_type = self.data_ptr.GetType().GetPointeeType()
+        self.element_type_size = self.element_type.GetByteSize()
+
+    def has_children(self):
+        # type: () -> bool
+        return True
+
+
+# BACKCOMPAT: rust 1.35
+class StdOldHashMapSyntheticProvider:
+    """Pretty-printer for std::collections::hash::map::HashMap<K, V, S>
+
+    struct HashMap<K, V, S> {..., table: RawTable<K, V>, ... }
+    struct RawTable<K, V> { capacity_mask: usize, size: usize, hashes: TaggedHashUintPtr, ... }
+    """
+
+    def __init__(self, valobj, dict, show_values=True):
+        # type: (SBValue, dict, bool) -> StdOldHashMapSyntheticProvider
+        self.valobj = valobj
+        self.show_values = show_values
+        self.update()
+
+    def num_children(self):
+        # type: () -> int
+        return self.size
+
+    def get_child_index(self, name):
+        # type: (str) -> int
+        index = name.lstrip('[').rstrip(']')
+        if index.isdigit():
+            return int(index)
+        else:
+            return -1
+
+    def get_child_at_index(self, index):
+        # type: (int) -> SBValue
+        # logger = Logger.Logger()
+        start = self.data_ptr.GetValueAsUnsigned() & ~1
+
+        # See `libstd/collections/hash/table.rs:raw_bucket_at
+        hashes = self.hash_uint_size * self.capacity
+        align = self.pair_type_size
+        # See `libcore/alloc.rs:padding_needed_for`
+        len_rounded_up = (((((hashes + align) % self.modulo - 1) % self.modulo) & ~(
+                (align - 1) % self.modulo)) % self.modulo - hashes) % self.modulo
+        # len_rounded_up = ((hashes + align - 1) & ~(align - 1)) - hashes
+
+        pairs_offset = hashes + len_rounded_up
+        pairs_start = start + pairs_offset
+
+        table_index = self.valid_indices[index]
+        idx = table_index & self.capacity_mask
+        address = pairs_start + idx * self.pair_type_size
+        element = self.data_ptr.CreateValueFromAddress("[%s]" % index, address, self.pair_type)
+        if self.show_values:
+            return element
+        else:
+            key = element.GetChildAtIndex(0)
+            return self.valobj.CreateValueFromData("[%s]" % index, key.GetData(), key.GetType())
+
+    def update(self):
+        # type: () -> None
+        # logger = Logger.Logger()
+
+        self.table = self.valobj.GetChildMemberWithName("table")  # type: SBValue
+        self.size = self.table.GetChildMemberWithName("size").GetValueAsUnsigned()
+        self.hashes = self.table.GetChildMemberWithName("hashes")
+        self.hash_uint_type = self.hashes.GetType()
+        self.hash_uint_size = self.hashes.GetType().GetByteSize()
+        self.modulo = 2 ** self.hash_uint_size
+        self.data_ptr = self.hashes.GetChildAtIndex(0).GetChildAtIndex(0)
+
+        self.capacity_mask = self.table.GetChildMemberWithName("capacity_mask").GetValueAsUnsigned()
+        self.capacity = (self.capacity_mask + 1) % self.modulo
+
+        marker = self.table.GetChildMemberWithName("marker").GetType()  # type: SBType
+        self.pair_type = marker.template_args[0]
+        self.pair_type_size = self.pair_type.GetByteSize()
+
+        self.valid_indices = []
+        for idx in range(self.capacity):
+            address = self.data_ptr.GetValueAsUnsigned() + idx * self.hash_uint_size
+            hash_uint = self.data_ptr.CreateValueFromAddress("[%s]" % idx, address,
+                                                             self.hash_uint_type)
+            hash_ptr = hash_uint.GetChildAtIndex(0).GetChildAtIndex(0)
+            if hash_ptr.GetValueAsUnsigned() != 0:
+                self.valid_indices.append(idx)
+
+        # logger >> "Valid indices: {}".format(str(self.valid_indices))
+
+    def has_children(self):
+        # type: () -> bool
+        return True
+
+
+class StdHashMapSyntheticProvider:
+    """Pretty-printer for hashbrown's HashMap"""
+
+    def __init__(self, valobj, dict, show_values=True):
+        # type: (SBValue, dict, bool) -> StdHashMapSyntheticProvider
+        self.valobj = valobj
+        self.show_values = show_values
+        self.update()
+
+    def num_children(self):
+        # type: () -> int
+        return self.size
+
+    def get_child_index(self, name):
+        # type: (str) -> int
+        index = name.lstrip('[').rstrip(']')
+        if index.isdigit():
+            return int(index)
+        else:
+            return -1
+
+    def get_child_at_index(self, index):
+        # type: (int) -> SBValue
+        pairs_start = self.data_ptr.GetValueAsUnsigned()
+        idx = self.valid_indices[index]
+        address = pairs_start + idx * self.pair_type_size
+        element = self.data_ptr.CreateValueFromAddress("[%s]" % index, address, self.pair_type)
+        if self.show_values:
+            return element
+        else:
+            key = element.GetChildAtIndex(0)
+            return self.valobj.CreateValueFromData("[%s]" % index, key.GetData(), key.GetType())
+
+    def update(self):
+        # type: () -> None
+        table = self.valobj.GetChildMemberWithName("base").GetChildMemberWithName("table")
+        capacity = table.GetChildMemberWithName("bucket_mask").GetValueAsUnsigned() + 1
+        ctrl = table.GetChildMemberWithName("ctrl").GetChildAtIndex(0)
+
+        self.size = table.GetChildMemberWithName("items").GetValueAsUnsigned()
+        self.data_ptr = table.GetChildMemberWithName("data").GetChildAtIndex(0)
+        self.pair_type = self.data_ptr.Dereference().GetType()
+        self.pair_type_size = self.pair_type.GetByteSize()
+
+        u8_type = self.valobj.GetTarget().GetBasicType(eBasicTypeUnsignedChar)
+        u8_type_size = self.valobj.GetTarget().GetBasicType(eBasicTypeUnsignedChar).GetByteSize()
+
+        self.valid_indices = []
+        for idx in range(capacity):
+            address = ctrl.GetValueAsUnsigned() + idx * u8_type_size
+            value = ctrl.CreateValueFromAddress("ctrl[%s]" % idx, address,
+                                                u8_type).GetValueAsUnsigned()
+            is_present = value & 128 == 0
+            if is_present:
+                self.valid_indices.append(idx)
+
+    def has_children(self):
+        # type: () -> bool
+        return True
+
+
+def StdRcSummaryProvider(valobj, dict):
+    # type: (SBValue, dict) -> str
+    strong = valobj.GetChildMemberWithName("strong").GetValueAsUnsigned()
+    weak = valobj.GetChildMemberWithName("weak").GetValueAsUnsigned()
+    return "strong={}, weak={}".format(strong, weak)
+
+
+class StdRcSyntheticProvider:
+    """Pretty-printer for alloc::rc::Rc<T> and alloc::sync::Arc<T>
+
+    struct Rc<T> { ptr: NonNull<RcBox<T>>, ... }
+    rust 1.31.1: struct NonNull<T> { pointer: NonZero<*const T> }
+    rust 1.33.0: struct NonNull<T> { pointer: *const T }
+    struct NonZero<T>(T)
+    struct RcBox<T> { strong: Cell<usize>, weak: Cell<usize>, value: T }
+    struct Cell<T> { value: UnsafeCell<T> }
+    struct UnsafeCell<T> { value: T }
+
+    struct Arc<T> { ptr: NonNull<ArcInner<T>>, ... }
+    struct ArcInner<T> { strong: atomic::AtomicUsize, weak: atomic::AtomicUsize, data: T }
+    struct AtomicUsize { v: UnsafeCell<usize> }
+    """
+
+    def __init__(self, valobj, dict, is_atomic=False):
+        # type: (SBValue, dict, bool) -> StdRcSyntheticProvider
+        self.valobj = valobj
+
+        self.ptr = unwrap_unique_or_non_null(self.valobj.GetChildMemberWithName("ptr"))
+
+        self.value = self.ptr.GetChildMemberWithName("data" if is_atomic else "value")
+
+        self.strong = self.ptr.GetChildMemberWithName("strong").GetChildAtIndex(
+            0).GetChildMemberWithName("value")
+        self.weak = self.ptr.GetChildMemberWithName("weak").GetChildAtIndex(
+            0).GetChildMemberWithName("value")
+
+        self.value_builder = ValueBuilder(valobj)
+
+        self.update()
+
+    def num_children(self):
+        # type: () -> int
+        # Actually there are 3 children, but only the `value` should be shown as a child
+        return 1
+
+    def get_child_index(self, name):
+        # type: (str) -> int
+        if name == "value":
+            return 0
+        if name == "strong":
+            return 1
+        if name == "weak":
+            return 2
+        return -1
+
+    def get_child_at_index(self, index):
+        # type: (int) -> SBValue
+        if index == 0:
+            return self.value
+        if index == 1:
+            return self.value_builder.from_uint("strong", self.strong_count)
+        if index == 2:
+            return self.value_builder.from_uint("weak", self.weak_count)
+
+        return None
+
+    def update(self):
+        # type: () -> None
+        self.strong_count = self.strong.GetValueAsUnsigned()
+        self.weak_count = self.weak.GetValueAsUnsigned() - 1
+
+    def has_children(self):
+        # type: () -> bool
+        return True
+
+
+class StdCellSyntheticProvider:
+    """Pretty-printer for std::cell::Cell"""
+
+    def __init__(self, valobj, dict):
+        # type: (SBValue, dict) -> StdCellSyntheticProvider
+        self.valobj = valobj
+        self.value = valobj.GetChildMemberWithName("value").GetChildAtIndex(0)
+
+    def num_children(self):
+        # type: () -> int
+        return 1
+
+    def get_child_index(self, name):
+        # type: (str) -> int
+        if name == "value":
+            return 0
+        return -1
+
+    def get_child_at_index(self, index):
+        # type: (int) -> SBValue
+        if index == 0:
+            return self.value
+        return None
+
+    def update(self):
+        # type: () -> None
+        pass
+
+    def has_children(self):
+        # type: () -> bool
+        return True
+
+
+def StdRefSummaryProvider(valobj, dict):
+    # type: (SBValue, dict) -> str
+    borrow = valobj.GetChildMemberWithName("borrow").GetValueAsSigned()
+    return "borrow={}".format(borrow) if borrow >= 0 else "borrow_mut={}".format(-borrow)
+
+
+class StdRefSyntheticProvider:
+    """Pretty-printer for std::cell::Ref, std::cell::RefMut, and std::cell::RefCell"""
+
+    def __init__(self, valobj, dict, is_cell=False):
+        # type: (SBValue, dict, bool) -> StdRefSyntheticProvider
+        self.valobj = valobj
+
+        borrow = valobj.GetChildMemberWithName("borrow")
+        value = valobj.GetChildMemberWithName("value")
+        if is_cell:
+            self.borrow = borrow.GetChildMemberWithName("value").GetChildMemberWithName("value")
+            self.value = value.GetChildMemberWithName("value")
+        else:
+            self.borrow = borrow.GetChildMemberWithName("borrow").GetChildMemberWithName(
+                "value").GetChildMemberWithName("value")
+            self.value = value.Dereference()
+
+        self.value_builder = ValueBuilder(valobj)
+
+        self.update()
+
+    def num_children(self):
+        # type: () -> int
+        # Actually there are 2 children, but only the `value` should be shown as a child
+        return 1
+
+    def get_child_index(self, name):
+        if name == "value":
+            return 0
+        if name == "borrow":
+            return 1
+        return -1
+
+    def get_child_at_index(self, index):
+        # type: (int) -> SBValue
+        if index == 0:
+            return self.value
+        if index == 1:
+            return self.value_builder.from_int("borrow", self.borrow_count)
+        return None
+
+    def update(self):
+        # type: () -> None
+        self.borrow_count = self.borrow.GetValueAsSigned()
+
+    def has_children(self):
+        # type: () -> bool
+        return True