Commit new files + fix const eval error

rust-lang/rust#51910
We will have to provide the drop_in_place::<T> ptr upon Arena<T> registration

Author: Avi-D-coder

src/arena.rs

@@ -0,0 +1,37 @@
+use super::auto_traits::*;
+use super::gc::*;
+use super::trace::Trace;
+use super::Mark;
+use std::ptr;
+
+pub struct Arena<T> {
+    // roots: usize,
+    high_ptr: *const T,
+    capacity: u16,
+}
+
+impl<T: Trace> Arena<T> {
+    pub fn new() -> Self {
+        // GC_BUS.with(|type_map| T::TRACE_TYPE_INFOtype_map.entry());
+        Self {
+            high_ptr: ptr::null(),
+            capacity: 1000,
+        }
+    }
+    pub fn gc_alloc<'r>(&'r self, _t: T) -> Gc<'r, T>
+    where
+        T: 'r,
+    {
+        unimplemented!()
+    }
+
+    pub fn advance(&mut self) -> Self {
+        unimplemented!()
+    }
+}
+
+unsafe impl<'o, 'n, T: NoGc + Immutable> Mark<'o, 'n, T, T> for Arena<T> {
+    fn mark(&'n self, o: Gc<'o, T>) -> Gc<'n, T> {
+        unsafe { std::mem::transmute(o) }
+    }
+}

src/auto_traits.rs

@@ -0,0 +1,12 @@
+use std::cell::UnsafeCell;
+use super::gc::*;
+
+pub unsafe auto trait NoGc {}
+impl<'r, T> !NoGc for Gc<'r, T> {}
+unsafe impl<'r, T: NoGc> NoGc for Box<T> {}
+
+/// Shallow immutability
+pub unsafe auto trait Immutable {}
+impl<T> !Immutable for &mut T {}
+impl<T> !Immutable for UnsafeCell<T> {}
+unsafe impl<T> Immutable for Box<T> {}

src/gc.rs

@@ -0,0 +1,36 @@
+use super::auto_traits::*;
+use super::trace::*;
+
+use std::ops::Deref;
+
+#[derive(Debug, Copy, Clone, PartialEq, Eq, PartialOrd, Ord)]
+pub struct Gc<'r, T> {
+    ptr: &'r T,
+}
+
+impl<'r, T: Trace> Deref for Gc<'r, T> {
+    type Target = T;
+    fn deref(&self) -> &T {
+        self.ptr
+    }
+}
+
+unsafe impl<'r, T: 'r + Immutable + Trace> Trace for Gc<'r, T> {
+    fn trace(_: usize) {}
+    // A Gc<Gc<T>> is equvlent to Gc<T>
+    const TRACE_TYPE_INFO: GcTypeInfo = GcTypeInfo::new::<T>();
+    const TRACE_CHILD_TYPE_INFO: [Option<GcTypeInfo>; 8] = [
+        Some(GcTypeInfo::new::<T>()),
+        None,
+        None,
+        None,
+        None,
+        None,
+        None,
+        None,
+    ];
+    fn trace_transitive_type_info(tti: &mut Tti) {
+        tti.add_direct::<Self>();
+        T::trace_transitive_type_info(tti)
+    }
+}

src/lib.rs

@@ -52,7 +52,7 @@ struct List<'r, T> {
 
 // These three impls will be derived with a procedural macro
 unsafe impl<'r, T: 'r + Trace + Immutable> Trace for List<'r, T> {
-    fn trace(_: &List<'r, T>) {}
+    fn trace(_: usize) {}
     const TRACE_TYPE_INFO: GcTypeInfo = GcTypeInfo::new::<Self>();
     const TRACE_CHILD_TYPE_INFO: [Option<GcTypeInfo>; 8] = [
         Some(GcTypeInfo::new::<T>()),
@@ -107,7 +107,7 @@ struct Foo<'r> {
 }
 
 unsafe impl<'r> Trace for Foo<'r> {
-    fn trace(_: &Foo<'r>) {}
+    fn trace(_: usize) {}
     const TRACE_TYPE_INFO: GcTypeInfo = GcTypeInfo::new::<Self>();
     const TRACE_CHILD_TYPE_INFO: [Option<GcTypeInfo>; 8] = GcTypeInfo::one_child::<Gc<'r, usize>>();
     fn trace_transitive_type_info(tti: &mut Tti) {
@@ -180,7 +180,7 @@ fn hidden_lifetime_test() {
 
     // This may not be trivail to implement as a proc macro
     unsafe impl<'a, 'b: 'a> Trace for Foo2<'a, 'b> {
-        fn trace(_: &Foo2<'a, 'b>) {}
+        fn trace(_: usize) {}
         const TRACE_TYPE_INFO: GcTypeInfo = GcTypeInfo::new::<Self>();
         const TRACE_CHILD_TYPE_INFO: [Option<GcTypeInfo>; 8] =
             GcTypeInfo::one_child::<Gc<'a, Bar<'b>>>();

src/mark.rs

@@ -0,0 +1,13 @@
+use super::Gc;
+
+pub unsafe trait Mark<'o, 'n, O, N> {
+    fn mark(&'n self, o: Gc<'o, O>) -> Gc<'n, N>;
+}
+
+// GAT Mark
+// pub unsafe trait Mark<'o, 'n, O> {
+//     type Struct<'l>;
+//     fn mark(&'n self, o: Gc<'o, Self::Struct<'o>>) -> Gc<'n, Self::Struct<'n>>;
+// }
+
+// Blanket Arena<T> impl is in src/arena.rs

src/trace.rs

@@ -0,0 +1,123 @@
+use super::auto_traits::*;
+
+use std::collections::HashSet;
+use std::mem::*;
+use std::ops::Deref;
+
+pub unsafe trait Trace {
+    fn trace(t: usize);
+    const TRACE_TYPE_INFO: GcTypeInfo;
+    const TRACE_CHILD_TYPE_INFO: [Option<GcTypeInfo>; 8];
+    fn trace_transitive_type_info(tti: &mut Tti);
+}
+
+// Ideally would use negative impls
+// Blanket impl seems to be safe, since Mark's blanket requires NoGc
+// If you only implement Mark and not Trace CHILD_TYPE_INFO will all be const None
+unsafe impl<T: Immutable> Trace for T {
+    default fn trace(_: usize) {}
+    default const TRACE_TYPE_INFO: GcTypeInfo = GcTypeInfo::new::<Self>();
+    default const TRACE_CHILD_TYPE_INFO: [Option<GcTypeInfo>; 8] = [None; 8];
+    default fn trace_transitive_type_info(_: &mut Tti) {}
+}
+
+#[derive(Debug, Copy, Clone, PartialEq, Eq, PartialOrd, Ord, Hash)]
+pub struct GcTypeInfo {
+    trace_ptr: fn(usize),
+    needs_drop: bool,
+    byte_size: u16,
+    alignment: u16,
+}
+
+impl GcTypeInfo {
+    pub const fn new<T: Trace>() -> Self {
+        Self {
+            trace_ptr: T::trace,
+            needs_drop: needs_drop::<T>(),
+            byte_size: size_of::<T>() as u16,
+            alignment: align_of::<T>() as u16,
+        }
+    }
+
+    pub(crate) const fn one_child<T: Trace>() -> [Option<GcTypeInfo>; 8] {
+        [
+            Some(GcTypeInfo::new::<T>()),
+            None,
+            None,
+            None,
+            None,
+            None,
+            None,
+            None,
+        ]
+    }
+}
+
+pub struct Tti {
+    /// Holds fn ptr of trace_transitive_type_info calls
+    parrents: HashSet<usize>,
+    type_info: HashSet<GcTypeInfo>,
+}
+
+impl Tti {
+    pub fn new() -> Self {
+        Self {
+            parrents: HashSet::new(),
+            type_info: HashSet::new(),
+        }
+    }
+
+    pub fn add_direct<T: Trace>(&mut self) {
+        self.type_info
+            .extend(T::TRACE_CHILD_TYPE_INFO.iter().filter_map(|o| *o));
+    }
+
+    pub fn add_trans(&mut self, tti: fn(&mut Tti)) {
+        if self.parrents.insert(tti as *const fn(&mut Tti) as usize) {
+            tti(self)
+        }
+    }
+}
+
+/// # std impls
+
+unsafe impl<'r, T: Immutable + Trace> Trace for Option<T> {
+    default fn trace(o: usize) {
+        if let Some(t) = unsafe { &*(o as *const Self) } {
+            T::trace(t as *const T as usize)
+        }
+    }
+    default const TRACE_TYPE_INFO: GcTypeInfo = GcTypeInfo::new::<Self>();
+    default const TRACE_CHILD_TYPE_INFO: [Option<GcTypeInfo>; 8] = GcTypeInfo::one_child::<T>();
+    default fn trace_transitive_type_info(tti: &mut Tti) {
+        tti.add_direct::<Self>();
+        tti.add_trans(T::trace_transitive_type_info);
+    }
+}
+
+unsafe impl<'r, T: Immutable + Trace + NoGc> Trace for Option<T> {
+    fn trace(_: usize) {}
+    const TRACE_TYPE_INFO: GcTypeInfo = GcTypeInfo::new::<Self>();
+    const TRACE_CHILD_TYPE_INFO: [Option<GcTypeInfo>; 8] = [None; 8];
+    fn trace_transitive_type_info(_: &mut Tti) {}
+}
+
+unsafe impl<T: Immutable + Trace> Trace for Box<T> {
+    default fn trace(b: usize) {
+        let t = unsafe { &*(b as *const Self) }.deref();
+        T::trace(t as *const T as usize)
+    }
+    default const TRACE_TYPE_INFO: GcTypeInfo = GcTypeInfo::new::<Self>();
+    default const TRACE_CHILD_TYPE_INFO: [Option<GcTypeInfo>; 8] = [None; 8];
+    default fn trace_transitive_type_info(_: &mut Tti) {}
+}
+
+unsafe impl<T: Immutable + Trace + NoGc> Trace for Box<T> {
+    fn trace(_: usize) {}
+    const TRACE_TYPE_INFO: GcTypeInfo = GcTypeInfo::new::<Self>();
+    const TRACE_CHILD_TYPE_INFO: [Option<GcTypeInfo>; 8] = GcTypeInfo::one_child::<T>();
+    fn trace_transitive_type_info(tti: &mut Tti) {
+        tti.add_direct::<Self>();
+        tti.add_trans(T::trace_transitive_type_info);
+    }
+}