Require an explicit drop call on a gc allocation

.gitignore

@@ -1 +1 @@
-/target
+target

Cargo.lock

@@ -45,9 +45,9 @@ checksum = "d468802bab17cbc0cc575e9b053f41e72aa36bfa6b7f55e3529ffa43161b97fa"
 
 [[package]]
 name = "backtrace"
-version = "0.3.64"
+version = "0.3.65"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "5e121dee8023ce33ab248d9ce1493df03c3b38a659b240096fcbd7048ff9c31f"
+checksum = "11a17d453482a265fd5f8479f2a3f405566e6ca627837aaddb85af8b1ab8ef61"
 dependencies = [
  "addr2line",
  "cc",
@@ -78,9 +78,9 @@ checksum = "baf1de4339761588bc0619e3cbc0120ee582ebb74b53b4efbf79117bd2da40fd"
 
 [[package]]
 name = "clap"
-version = "3.1.9"
+version = "3.1.18"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "6aad2534fad53df1cc12519c5cda696dd3e20e6118a027e24054aea14a0bdcbe"
+checksum = "d2dbdf4bdacb33466e854ce889eee8dfd5729abf7ccd7664d0a2d60cd384440b"
 dependencies = [
  "atty",
  "bitflags",
@@ -95,9 +95,9 @@ dependencies = [
 
 [[package]]
 name = "clap_derive"
-version = "3.1.7"
+version = "3.1.18"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "a3aab4734e083b809aaf5794e14e756d1c798d2c69c7f7de7a09a2f5214993c1"
+checksum = "25320346e922cffe59c0bbc5410c8d8784509efb321488971081313cb1e1a33c"
 dependencies = [
  "heck",
  "proc-macro-error",
@@ -108,9 +108,9 @@ dependencies = [
 
 [[package]]
 name = "clap_lex"
-version = "0.1.1"
+version = "0.2.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "189ddd3b5d32a70b35e7686054371742a937b0d99128e76dde6340210e966669"
+checksum = "a37c35f1112dad5e6e0b1adaff798507497a18fceeb30cceb3bae7d1427b9213"
 dependencies = [
  "os_str_bytes",
 ]
@@ -150,6 +150,7 @@ dependencies = [
  "color-eyre",
  "dotenv",
  "from_variants",
+ "gc",
  "itertools",
  "match_any",
  "tracing",
@@ -158,9 +159,9 @@ dependencies = [
 
 [[package]]
 name = "darling"
-version = "0.13.1"
+version = "0.13.4"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "d0d720b8683f8dd83c65155f0530560cba68cd2bf395f6513a483caee57ff7f4"
+checksum = "a01d95850c592940db9b8194bc39f4bc0e89dee5c4265e4b1807c34a9aba453c"
 dependencies = [
  "darling_core",
  "darling_macro",
@@ -168,9 +169,9 @@ dependencies = [
 
 [[package]]
 name = "darling_core"
-version = "0.13.1"
+version = "0.13.4"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "7a340f241d2ceed1deb47ae36c4144b2707ec7dd0b649f894cb39bb595986324"
+checksum = "859d65a907b6852c9361e3185c862aae7fafd2887876799fa55f5f99dc40d610"
 dependencies = [
  "fnv",
  "ident_case",
@@ -182,9 +183,9 @@ dependencies = [
 
 [[package]]
 name = "darling_macro"
-version = "0.13.1"
+version = "0.13.4"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "72c41b3b7352feb3211a0d743dc5700a4e3b60f51bd2b368892d1e0f9a95f44b"
+checksum = "9c972679f83bdf9c42bd905396b6c3588a843a17f0f16dfcfa3e2c5d57441835"
 dependencies = [
  "darling_core",
  "quote",
@@ -205,9 +206,9 @@ checksum = "e78d4f1cc4ae33bbfc157ed5d5a5ef3bc29227303d595861deb238fcec4e9457"
 
 [[package]]
 name = "eyre"
-version = "0.6.7"
+version = "0.6.8"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "9289ed2c0440a6536e65119725cf91fc2c6b5e513bfd2e36e1134d7cca6ca12f"
+checksum = "4c2b6b5a29c02cdc822728b7d7b8ae1bab3e3b05d44522770ddd49722eeac7eb"
 dependencies = [
  "indenter",
  "once_cell",
@@ -240,6 +241,22 @@ dependencies = [
  "syn",
 ]
 
+[[package]]
+name = "gc"
+version = "0.1.0"
+dependencies = [
+ "gctrace-derive",
+]
+
+[[package]]
+name = "gctrace-derive"
+version = "0.1.0"
+dependencies = [
+ "proc-macro2",
+ "quote",
+ "syn",
+]
+
 [[package]]
 name = "gimli"
 version = "0.26.1"
@@ -306,15 +323,15 @@ checksum = "e2abad23fbc42b3700f2f279844dc832adb2b2eb069b2df918f455c4e18cc646"
 
 [[package]]
 name = "libc"
-version = "0.2.121"
+version = "0.2.126"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "efaa7b300f3b5fe8eb6bf21ce3895e1751d9665086af2d64b42f19701015ff4f"
+checksum = "349d5a591cd28b49e1d1037471617a32ddcda5731b99419008085f72d5a53836"
 
 [[package]]
 name = "log"
-version = "0.4.14"
+version = "0.4.17"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "51b9bbe6c47d51fc3e1a9b945965946b4c44142ab8792c50835a980d362c2710"
+checksum = "abb12e687cfb44aa40f41fc3978ef76448f9b6038cad6aef4259d3c095a2382e"
 dependencies = [
  "cfg-if",
 ]
@@ -336,52 +353,51 @@ dependencies = [
 
 [[package]]
 name = "memchr"
-version = "2.4.1"
+version = "2.5.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "308cc39be01b73d0d18f82a0e7b2a3df85245f84af96fdddc5d202d27e47b86a"
+checksum = "2dffe52ecf27772e601905b7522cb4ef790d2cc203488bbd0e2fe85fcb74566d"
 
 [[package]]
 name = "miniz_oxide"
-version = "0.4.4"
+version = "0.5.1"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "a92518e98c078586bc6c934028adcca4c92a53d6a958196de835170a01d84e4b"
+checksum = "d2b29bd4bc3f33391105ebee3589c19197c4271e3e5a9ec9bfe8127eeff8f082"
 dependencies = [
  "adler",
- "autocfg",
 ]
 
 [[package]]
 name = "object"
-version = "0.27.1"
+version = "0.28.4"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "67ac1d3f9a1d3616fd9a60c8d74296f22406a238b6a72f5cc1e6f314df4ffbf9"
+checksum = "e42c982f2d955fac81dd7e1d0e1426a7d702acd9c98d19ab01083a6a0328c424"
 dependencies = [
  "memchr",
 ]
 
 [[package]]
 name = "once_cell"
-version = "1.10.0"
+version = "1.11.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "87f3e037eac156d1775da914196f0f37741a274155e34a0b7e427c35d2a2ecb9"
+checksum = "7b10983b38c53aebdf33f542c6275b0f58a238129d00c4ae0e6fb59738d783ca"
 
 [[package]]
 name = "os_str_bytes"
-version = "6.0.0"
+version = "6.0.1"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "8e22443d1643a904602595ba1cd8f7d896afe56d26712531c5ff73a15b2fbf64"
+checksum = "029d8d0b2f198229de29dca79676f2738ff952edf3fde542eb8bf94d8c21b435"
 
 [[package]]
 name = "owo-colors"
-version = "3.3.0"
+version = "3.4.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "5e72e30578e0d0993c8ae20823dd9cff2bc5517d2f586a8aef462a581e8a03eb"
+checksum = "decf7381921fea4dcb2549c5667eda59b3ec297ab7e2b5fc33eac69d2e7da87b"
 
 [[package]]
 name = "pin-project-lite"
-version = "0.2.8"
+version = "0.2.9"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "e280fbe77cc62c91527259e9442153f4688736748d24660126286329742b4c6c"
+checksum = "e0a7ae3ac2f1173085d398531c705756c94a4c56843785df85a60c1a0afac116"
 
 [[package]]
 name = "proc-macro-error"
@@ -409,27 +425,27 @@ dependencies = [
 
 [[package]]
 name = "proc-macro2"
-version = "1.0.36"
+version = "1.0.40"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "c7342d5883fbccae1cc37a2353b09c87c9b0f3afd73f5fb9bba687a1f733b029"
+checksum = "dd96a1e8ed2596c337f8eae5f24924ec83f5ad5ab21ea8e455d3566c69fbcaf7"
 dependencies = [
- "unicode-xid",
+ "unicode-ident",
 ]
 
 [[package]]
 name = "quote"
-version = "1.0.16"
+version = "1.0.20"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "b4af2ec4714533fcdf07e886f17025ace8b997b9ce51204ee69b6da831c3da57"
+checksum = "3bcdf212e9776fbcb2d23ab029360416bb1706b1aea2d1a5ba002727cbcab804"
 dependencies = [
  "proc-macro2",
 ]
 
 [[package]]
 name = "regex"
-version = "1.5.5"
+version = "1.5.6"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "1a11647b6b25ff05a515cb92c365cec08801e83423a235b51e231e1808747286"
+checksum = "d83f127d94bdbcda4c8cc2e50f6f84f4b611f69c902699ca385a39c3a75f9ff1"
 dependencies = [
  "regex-syntax",
 ]
@@ -445,9 +461,9 @@ dependencies = [
 
 [[package]]
 name = "regex-syntax"
-version = "0.6.25"
+version = "0.6.26"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "f497285884f3fcff424ffc933e56d7cbca511def0c9831a7f9b5f6153e3cc89b"
+checksum = "49b3de9ec5dc0a3417da371aab17d729997c15010e7fd24ff707773a33bddb64"
 
 [[package]]
 name = "rustc-demangle"
@@ -478,13 +494,13 @@ checksum = "73473c0e59e6d5812c5dfe2a064a6444949f089e20eec9a2e5506596494e4623"
 
 [[package]]
 name = "syn"
-version = "1.0.89"
+version = "1.0.98"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "ea297be220d52398dcc07ce15a209fce436d361735ac1db700cab3b6cdfb9f54"
+checksum = "c50aef8a904de4c23c788f104b7dddc7d6f79c647c7c8ce4cc8f73eb0ca773dd"
 dependencies = [
  "proc-macro2",
  "quote",
- "unicode-xid",
+ "unicode-ident",
 ]
 
 [[package]]
@@ -513,9 +529,9 @@ dependencies = [
 
 [[package]]
 name = "tracing"
-version = "0.1.32"
+version = "0.1.34"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "4a1bdf54a7c28a2bbf701e1d2233f6c77f473486b94bee4f9678da5a148dca7f"
+checksum = "5d0ecdcb44a79f0fe9844f0c4f33a342cbcbb5117de8001e6ba0dc2351327d09"
 dependencies = [
  "cfg-if",
  "pin-project-lite",
@@ -525,9 +541,9 @@ dependencies = [
 
 [[package]]
 name = "tracing-attributes"
-version = "0.1.20"
+version = "0.1.21"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "2e65ce065b4b5c53e73bb28912318cb8c9e9ad3921f1d669eb0e68b4c8143a2b"
+checksum = "cc6b8ad3567499f98a1db7a752b07a7c8c7c7c34c332ec00effb2b0027974b7c"
 dependencies = [
  "proc-macro2",
  "quote",
@@ -536,9 +552,9 @@ dependencies = [
 
 [[package]]
 name = "tracing-core"
-version = "0.1.23"
+version = "0.1.26"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "aa31669fa42c09c34d94d8165dd2012e8ff3c66aca50f3bb226b68f216f2706c"
+checksum = "f54c8ca710e81886d498c2fd3331b56c93aa248d49de2222ad2742247c60072f"
 dependencies = [
  "lazy_static",
  "valuable",
@@ -556,9 +572,9 @@ dependencies = [
 
 [[package]]
 name = "tracing-log"
-version = "0.1.2"
+version = "0.1.3"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "a6923477a48e41c1951f1999ef8bb5a3023eb723ceadafe78ffb65dc366761e3"
+checksum = "78ddad33d2d10b1ed7eb9d1f518a5674713876e97e5bb9b7345a7984fbb4f922"
 dependencies = [
  "lazy_static",
  "log",
@@ -567,9 +583,9 @@ dependencies = [
 
 [[package]]
 name = "tracing-subscriber"
-version = "0.3.9"
+version = "0.3.11"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "9e0ab7bdc962035a87fba73f3acca9b8a8d0034c2e6f60b84aeaaddddc155dce"
+checksum = "4bc28f93baff38037f64e6f43d34cfa1605f27a49c34e8a04c5e78b0babf2596"
 dependencies = [
  "ansi_term",
  "lazy_static",
@@ -584,10 +600,10 @@ dependencies = [
 ]
 
 [[package]]
-name = "unicode-xid"
+name = "unicode-ident"
-version = "0.2.2"
+version = "1.0.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "8ccb82d61f80a663efe1f787a51b16b5a51e3314d6ac365b08639f52387b33f3"
+checksum = "d22af068fba1eb5edcb4aea19d382b2a3deb4c8f9d475c589b6ada9e0fd493ee"
 
 [[package]]
 name = "valuable"

Cargo.toml

@@ -3,7 +3,14 @@ name = "crftng-intrprtrs"
 version = "0.1.0"
 edition = "2021"
 
+[workspace]
+members = [
+	"gc",
+	"gc/gctrace-derive"
+]
+
 [dependencies]
+gc = { path = "./gc" }
 clap = { version = "3.1.9", features = ["derive"] }
 color-eyre = "0.6.1"
 dotenv = "0.15.0"

gc/Cargo.toml

@@ -0,0 +1,7 @@
+[package]
+name = "gc"
+version = "0.1.0"
+edition = "2021"
+
+[dependencies]
+gctrace-derive = { version = "0.1.0", path = "gctrace-derive" }

gc/fuzz/.gitignore

@@ -0,0 +1,3 @@
+target
+corpus
+artifacts

gc/fuzz/Cargo.lock

@@ -0,0 +1,105 @@
+# This file is automatically @generated by Cargo.
+# It is not intended for manual editing.
+version = 3
+
+[[package]]
+name = "arbitrary"
+version = "1.1.3"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "5a7924531f38b1970ff630f03eb20a2fde69db5c590c93b0f3482e95dcc5fd60"
+dependencies = [
+ "derive_arbitrary",
+]
+
+[[package]]
+name = "cc"
+version = "1.0.73"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "2fff2a6927b3bb87f9595d67196a70493f627687a71d87a0d692242c33f58c11"
+
+[[package]]
+name = "derive_arbitrary"
+version = "1.1.3"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "c9a577516173adb681466d517d39bd468293bc2c2a16439375ef0f35bba45f3d"
+dependencies = [
+ "proc-macro2",
+ "quote",
+ "syn",
+]
+
+[[package]]
+name = "gc"
+version = "0.1.0"
+dependencies = [
+ "gctrace-derive",
+]
+
+[[package]]
+name = "gc-fuzz"
+version = "0.0.0"
+dependencies = [
+ "gc",
+ "libfuzzer-sys",
+]
+
+[[package]]
+name = "gctrace-derive"
+version = "0.1.0"
+dependencies = [
+ "proc-macro2",
+ "quote",
+ "syn",
+]
+
+[[package]]
+name = "libfuzzer-sys"
+version = "0.4.3"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "336244aaeab6a12df46480dc585802aa743a72d66b11937844c61bbca84c991d"
+dependencies = [
+ "arbitrary",
+ "cc",
+ "once_cell",
+]
+
+[[package]]
+name = "once_cell"
+version = "1.13.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "18a6dbe30758c9f83eb00cbea4ac95966305f5a7772f3f42ebfc7fc7eddbd8e1"
+
+[[package]]
+name = "proc-macro2"
+version = "1.0.40"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "dd96a1e8ed2596c337f8eae5f24924ec83f5ad5ab21ea8e455d3566c69fbcaf7"
+dependencies = [
+ "unicode-ident",
+]
+
+[[package]]
+name = "quote"
+version = "1.0.20"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "3bcdf212e9776fbcb2d23ab029360416bb1706b1aea2d1a5ba002727cbcab804"
+dependencies = [
+ "proc-macro2",
+]
+
+[[package]]
+name = "syn"
+version = "1.0.98"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "c50aef8a904de4c23c788f104b7dddc7d6f79c647c7c8ce4cc8f73eb0ca773dd"
+dependencies = [
+ "proc-macro2",
+ "quote",
+ "unicode-ident",
+]
+
+[[package]]
+name = "unicode-ident"
+version = "1.0.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "5bd2fe26506023ed7b5e1e315add59d6f584c621d037f9368fea9cfb988f368c"

gc/fuzz/Cargo.toml

@@ -0,0 +1,25 @@
+[package]
+name = "gc-fuzz"
+version = "0.0.0"
+authors = ["Automatically generated"]
+publish = false
+edition = "2018"
+
+[package.metadata]
+cargo-fuzz = true
+
+[dependencies]
+libfuzzer-sys = { version = "0.4", features = ["arbitrary-derive"] }
+
+[dependencies.gc]
+path = ".."
+
+# Prevent this from interfering with workspaces
+[workspace]
+members = ["."]
+
+[[bin]]
+name = "fuzz_target_1"
+path = "fuzz_targets/fuzz_target_1.rs"
+test = false
+doc = false

gc/fuzz/fuzz_targets/fuzz_target_1.rs

@@ -0,0 +1,83 @@
+#![no_main]
+use gc::{self, gc_ref::GcRef, test_utils::GotDropped, trace::GCTrace};
+use libfuzzer_sys::fuzz_target;
+use std::cell::RefCell;
+
+use libfuzzer_sys::arbitrary;
+
+#[derive(arbitrary::Arbitrary, Debug)]
+struct ChildIDx(usize);
+
+impl ChildIDx {
+	fn choose<'a, T>(&self, choices: &'a [T]) -> Option<&'a T> {
+		let idx = self.choose_index(choices.len())?;
+		Some(choices.get(idx).unwrap())
+	}
+
+	fn choose_index(&self, len: usize) -> Option<usize> {
+		(len != 0).then(|| self.0 % len)
+	}
+}
+
+#[derive(arbitrary::Arbitrary, Debug)]
+enum GraphExplore {
+	ExploreChild(ChildIDx, Box<GraphExplore>),
+	Stop,
+}
+
+#[derive(arbitrary::Arbitrary, Debug)]
+enum Op {
+	AddLink(GraphExplore, Option<GraphExplore>),
+	RemoveChild(GraphExplore, ChildIDx),
+	CollectGarbage,
+}
+
+#[derive(GCTrace, Default)]
+struct Node {
+	children: Vec<GCNode>,
+}
+
+type GCNode = GcRef<RefCell<Node>>;
+
+impl Node {
+	fn explore(node: GCNode, instructions: GraphExplore) -> GCNode {
+		match instructions {
+			GraphExplore::ExploreChild(child_idx, child_instructions) => {
+				let child = child_idx
+					.choose(&*node.borrow().children)
+					.map(|v| v.clone());
+				child
+					.map(|c| Node::explore(c, *child_instructions))
+					.unwrap_or(node)
+			}
+			GraphExplore::Stop => node,
+		}
+	}
+}
+
+fuzz_target!(|ops: Vec<Op>| {
+	let mut allocator = gc::allocator::GCAllocator::default();
+	let root: GCNode = allocator.alloc(RefCell::default());
+	for op in ops {
+		match op {
+			Op::AddLink(parent_path, child_path) => {
+				let child = child_path
+					.map(|c| Node::explore(root.clone(), c))
+					.unwrap_or_else(|| allocator.alloc(RefCell::default()));
+
+				let parent = Node::explore(root.clone(), parent_path);
+				parent.borrow_mut().children.push(child);
+			}
+			Op::RemoveChild(parent_path, child_idx) => {
+				let parent = Node::explore(root.clone(), parent_path);
+				let children = &mut parent.borrow_mut().children;
+				let idx = child_idx.choose_index(children.len());
+				if let Some(idx) = idx {
+					children.remove(idx);
+				}
+			}
+			Op::CollectGarbage => unsafe { allocator.gc(&root) },
+		}
+	}
+	unsafe { allocator.gc(&()) };
+});

gc/gctrace-derive/Cargo.toml

@@ -0,0 +1,12 @@
+[package]
+name = "gctrace-derive"
+version = "0.1.0"
+edition = "2021"
+
+[lib]
+proc-macro = true
+
+[dependencies]
+proc-macro2 = "1.0.40"
+quote = "1.0.20"
+syn = "1.0.98"

gc/gctrace-derive/src/lib.rs

@@ -0,0 +1,75 @@
+use proc_macro::TokenStream;
+use proc_macro2::TokenStream as TokenStream2;
+use quote::{quote, quote_spanned};
+use syn::spanned::Spanned;
+use syn::{
+	parse_macro_input, parse_quote, Data, DeriveInput, Fields, GenericParam, Generics, Index,
+};
+
+// Add a bound `T: GcTrace` to every type parameter T.
+fn add_trait_bounds(mut generics: Generics) -> Generics {
+	for param in &mut generics.params {
+		if let GenericParam::Type(ref mut type_param) = *param {
+			type_param.bounds.push(parse_quote!(gc::trace::GcTrace));
+		}
+	}
+	generics
+}
+
+// Generate an expression to call trace on every gc field recursively.
+fn gctrace_fields(data: &Data) -> TokenStream2 {
+	match *data {
+		Data::Struct(ref data) => match data.fields {
+			Fields::Named(ref fields) => {
+				let recurse = fields.named.iter().map(|f| {
+					let name = &f.ident;
+					quote_spanned! {f.span()=>
+						gc::trace::GCTrace::trace(&self.#name, tracer)
+					}
+				});
+				quote! {
+					#(#recurse;)*
+				}
+			}
+			Fields::Unnamed(ref fields) => {
+				let recurse = fields.unnamed.iter().enumerate().map(|(i, f)| {
+					let index = Index::from(i);
+					quote_spanned! {f.span()=>
+						gc::trace::GCTrace::trace(&self.#index, tracer)
+					}
+				});
+				quote! {
+					#(#recurse;)*
+				}
+			}
+			Fields::Unit => TokenStream2::default(),
+		},
+		Data::Enum(_) | Data::Union(_) => unimplemented!(),
+	}
+}
+
+#[proc_macro_derive(GCTrace)]
+pub fn gctrace_derive(input: TokenStream) -> TokenStream {
+	// Parse the input tokens into a syntax tree
+	let input = parse_macro_input!(input as DeriveInput);
+
+	let name = input.ident;
+
+	let generics = add_trait_bounds(input.generics);
+
+	let (impl_generics, ty_generics, where_clause) = generics.split_for_impl();
+	let trace_fields = gctrace_fields(&input.data);
+
+	// Build the output, possibly using quasi-quotation
+	//
+	let expanded = quote! {
+	unsafe impl #impl_generics gc::trace::GCTrace for #name #ty_generics #where_clause {
+			fn trace(&self, tracer: &mut gc::trace::GCTracer) {
+				#trace_fields
+			}
+	}
+	};
+
+	// Hand the output tokens back to the compiler
+	TokenStream::from(expanded)
+}

gc/src/allocator.rs

@@ -0,0 +1,86 @@
+use std::ptr::NonNull;
+
+use super::gc_ref::GcRef;
+use super::trace;
+use crate::trace::GCTrace;
+
+#[derive(Default)]
+pub struct GCAllocator {
+	allocations: Vec<Allocation>,
+}
+
+impl GCAllocator {
+	#[inline(always)]
+	/// Allocate a value on the heap
+	pub fn alloc<T: trace::GCTrace>(&mut self, x: T) -> GcRef<T> {
+		let alloc = Allocation::new(x);
+		let ptr = alloc.ptr as *mut T;
+		self.allocations.push(alloc);
+		unsafe { GcRef::new(NonNull::new(ptr).unwrap()) }
+	}
+
+	/// # Safety
+	/// Root needs to contain all the accessible gc allocated references
+	/// In case root itself is gc allocated use [`gc_ref_root`]
+	///
+	/// [`gc_ref_root`]: GCAllocator::gc_ref_root
+	pub unsafe fn gc<T: trace::GCTrace>(&mut self, root: &T) {
+		// Mark
+		let mut tracer = trace::GCTracer::with_capacity(self.allocations.len());
+		root.trace(&mut tracer);
+
+		// And sweep
+		let inaccessible = self
+			.allocations
+			.drain_filter(|a| !tracer.is_accessible(a.ptr));
+
+		// And sweep
+		for mut to_free in inaccessible {
+			to_free.drop();
+		}
+	}
+
+	// Specialization when ;-;
+	/// [`gc`] but for roots that are allocated on the heap
+	/// # Safety
+	/// See [`gc`]
+	///
+	/// [`gc`]: GCAllocator::gc
+	pub unsafe fn gc_ref_root<T: trace::GCTrace>(&mut self, root: &GcRef<T>) {
+		// Mark
+		let mut tracer = trace::GCTracer::with_capacity(self.allocations.len());
+		tracer.mark_reachable_rec(root);
+		root.trace(&mut tracer);
+
+		let inaccessible = self
+			.allocations
+			.drain_filter(|a| !tracer.is_accessible(a.ptr));
+
+		// And sweep
+		for mut to_free in inaccessible {
+			to_free.drop();
+		}
+	}
+}
+
+struct Allocation {
+	ptr: *mut (),
+	drop: unsafe fn(*mut ()),
+}
+
+impl Allocation {
+	fn new<T>(x: T) -> Self {
+		let alloc = Box::new(x);
+		let ptr = Box::into_raw(alloc) as *mut ();
+
+		let drop = |ptr| unsafe {
+			std::mem::drop(Box::from_raw(ptr as *mut T));
+		};
+
+		Self { ptr, drop }
+	}
+
+	fn drop(&mut self) {
+		unsafe { (self.drop)(self.ptr) };
+	}
+}

gc/src/gc_ref.rs

@@ -0,0 +1,44 @@
+use std::{marker::PhantomData, ptr::NonNull};
+
+use crate::trace::GCTrace;
+
+pub struct GcRef<T: GCTrace>(pub(crate) NonNull<T>, PhantomData<T>);
+
+impl<T: GCTrace> Clone for GcRef<T> {
+	fn clone(&self) -> Self {
+		Self(self.0, self.1)
+	}
+}
+
+impl<T: GCTrace> GcRef<T> {
+	pub(crate) unsafe fn new(ptr: NonNull<T>) -> Self {
+		Self(ptr, PhantomData)
+	}
+
+	/// # Safety
+	/// The caller needs to ensure that the underlying pointer hasn't been garbage collected.
+	/// Since the drop order for garbage collected structs is undefined that means it is never
+	/// safe to call this function in a [Drop::drop].
+	///
+	/// Do note that this doesn't mean that any particular instance of GcRef has to be marked
+	/// as reachable during a call to [GCAllocator::gc][`crate::allocator::GCAllocator::gc`]
+	/// but instead any GcRef instance referring to the same underlying pointer has to be reachable
+	pub unsafe fn get(&self) -> &T {
+		unsafe { self.0.as_ref() }
+	}
+
+	/// # Safety
+	/// The caller needs to ensure that the underlying pointer hasn't been garbage collected.
+	/// See [GcRef::get] for more details
+	///
+	/// The caller needs to ensure that this is the only instance of a pointer to the underlying value
+	/// (in other words that [Clone] hasn't been called, or that all other clones of the pointer have
+	/// already been dropped).
+	///
+	/// This function is hard(but not impossible) to use without causing UB. Unless you have a
+	/// really special use case you might want to instead use one of various [cell][`std::cell`]
+	/// types as the allocated type.
+	pub unsafe fn get_mut(this: &mut Self) -> &mut T {
+		this.0.as_mut()
+	}
+}

gc/src/lib.rs

@@ -0,0 +1,36 @@
+#![feature(drain_filter)]
+#![feature(negative_impls)]
+
+pub mod allocator;
+pub mod gc_ref;
+pub mod trace;
+mod trace_impl;
+
+// make the test_utils mod pub to use it in fuzzing
+pub mod test_utils;
+
+#[cfg(test)]
+pub(crate) mod tests {
+
+	use super::allocator::GCAllocator;
+	use super::test_utils::GotDropped;
+
+	#[test]
+	fn gc_allocates_and_frees_structs() {
+		let got_dropped = GotDropped::default();
+
+		let mut gc = GCAllocator::default();
+		gc.alloc(got_dropped.make_drop_checker());
+
+		unsafe { gc.gc(&()) };
+		assert!(got_dropped.was_dropped());
+
+		let got_dropped = GotDropped::default();
+		let drop_checker = gc.alloc(got_dropped.make_drop_checker());
+
+		unsafe { gc.gc(&(drop_checker,)) };
+		assert!(!got_dropped.was_dropped());
+		unsafe { gc.gc(&()) };
+		assert!(got_dropped.was_dropped());
+	}
+}

gc/src/test_utils.rs

@@ -0,0 +1,28 @@
+use std::sync::atomic::{AtomicBool, Ordering};
+
+use crate::trace::GCTrace;
+
+#[derive(Default)]
+pub struct GotDropped(AtomicBool);
+
+impl GotDropped {
+	pub fn make_drop_checker(&self) -> DropChecker {
+		DropChecker(self)
+	}
+
+	pub fn was_dropped(&self) -> bool {
+		self.0.load(Ordering::SeqCst)
+	}
+}
+
+pub struct DropChecker<'a>(pub &'a GotDropped);
+
+impl<'a> Drop for DropChecker<'a> {
+	fn drop(&mut self) {
+		self.0 .0.store(true, Ordering::SeqCst);
+	}
+}
+
+unsafe impl<'a> GCTrace for DropChecker<'a> {
+	fn trace(&self, _tracer: &mut crate::trace::GCTracer) {}
+}

gc/src/trace.rs

@@ -0,0 +1,45 @@
+use std::{collections::HashSet, ops::Deref};
+
+use crate::gc_ref::GcRef;
+
+pub struct GCTracer {
+	accessible: HashSet<*const ()>,
+	explored: HashSet<*const ()>,
+}
+
+impl GCTracer {
+	pub(super) fn with_capacity(cap: usize) -> Self {
+		Self {
+			accessible: HashSet::with_capacity(cap),
+			explored: HashSet::with_capacity(cap),
+		}
+	}
+
+	pub fn is_accessible(&self, ptr: *const ()) -> bool {
+		self.accessible.contains(&ptr)
+	}
+
+	pub fn mark_reachable_rec<T: GCTrace>(&mut self, obj: &T) {
+		let ptr = obj as *const T as *const ();
+		if self.explored.insert(ptr) {
+			obj.trace(self);
+		}
+	}
+}
+
+pub use gctrace_derive::GCTrace;
+
+///
+/// # Safety
+/// Implementors of the trait *need* to ensure that every reachable reference gets marked as
+/// reachable by callign trace on it
+pub unsafe trait GCTrace {
+	fn trace(&self, _tracer: &mut GCTracer) {}
+}
+
+unsafe impl<T: GCTrace> GCTrace for GcRef<T> {
+	fn trace(&self, tracer: &mut GCTracer) {
+		tracer.accessible.insert(self.0.as_ptr() as *const ());
+		tracer.mark_reachable_rec(self.deref());
+	}
+}

gc/src/trace_impl.rs

@@ -0,0 +1,51 @@
+use super::trace::{GCTrace, GCTracer};
+use std::{cell::RefCell, collections::HashMap, ops::Deref};
+unsafe impl GCTrace for () {}
+unsafe impl GCTrace for i32 {}
+unsafe impl GCTrace for u32 {}
+unsafe impl GCTrace for i64 {}
+unsafe impl GCTrace for u64 {}
+unsafe impl GCTrace for f32 {}
+unsafe impl GCTrace for f64 {}
+unsafe impl GCTrace for bool {}
+unsafe impl GCTrace for isize {}
+unsafe impl GCTrace for usize {}
+unsafe impl GCTrace for String {}
+
+unsafe impl<T: GCTrace> GCTrace for (T,) {
+	fn trace(&self, tracer: &mut GCTracer) {
+		tracer.mark_reachable_rec(&self.0)
+	}
+}
+
+unsafe impl<T: GCTrace> GCTrace for RefCell<T> {
+	fn trace(&self, tracer: &mut GCTracer) {
+		let borrow = self.borrow();
+		tracer.mark_reachable_rec(borrow.deref())
+	}
+}
+
+unsafe impl<T: GCTrace> GCTrace for Option<T> {
+	fn trace(&self, tracer: &mut GCTracer) {
+		if let Some(ref v) = self {
+			tracer.mark_reachable_rec(v)
+		}
+	}
+}
+
+unsafe impl<K: GCTrace, V: GCTrace> GCTrace for HashMap<K, V> {
+	fn trace(&self, tracer: &mut GCTracer) {
+		for (k, v) in self.iter() {
+			tracer.mark_reachable_rec(k);
+			tracer.mark_reachable_rec(v);
+		}
+	}
+}
+
+unsafe impl<T: GCTrace> GCTrace for Vec<T> {
+	fn trace(&self, tracer: &mut GCTracer) {
+		for val in self.iter() {
+			tracer.mark_reachable_rec(val)
+		}
+	}
+}

pre-commit-hook.sh

@@ -5,20 +5,20 @@
 
 set -eu
 
-if ! cargo fmt -- --check
+if ! cargo fmt --all -- --check 
 then
     echo "There are some code style issues."
     echo "Run cargo fmt first."
     exit 1
 fi
 
-if ! cargo clippy --all-targets -- -D warnings
+if ! cargo clippy --all-targets --workspace -- -D warnings 
 then
     echo "There are some clippy issues."
     exit 1
 fi
 
-if ! cargo test
+if ! cargo test --workspace
 then
     echo "There are some test issues."
     exit 1

src/error.rs

@@ -52,6 +52,7 @@ impl<T: Error> ErrorLocationWrapper<T> {
 
 impl<T: std::error::Error> ErrorWithLocation for ErrorLocationWrapper<T> {
 	fn get_location(&self) -> Location {
+		#[allow(clippy::needless_borrow)]
 		(&self.location).into()
 	}
 }

src/interpreter/ast_walker/expression_interpreter.rs

@@ -1,5 +1,5 @@
 use super::Interpret;
-use super::{types::Value, RuntimeError};
+use super::{types::Primitive, RuntimeError};
 use crate::ast::expression::{
 	self,
 	operator::{Operator, UnaryOperator},
@@ -7,19 +7,19 @@ use crate::ast::expression::{
 use crate::interpreter::world::World;
 
 impl Interpret for expression::ExpressionNode {
-	fn interpret(&self, w: &mut World) -> Result<Value, RuntimeError> {
+	fn interpret(&self, w: &mut World) -> Result<Primitive, RuntimeError> {
 		expression::all_variants!(self, n => n.interpret(w))
 	}
 }
 
 impl Interpret for expression::Literal {
-	fn interpret(&self, _: &mut World) -> Result<Value, RuntimeError> {
+	fn interpret(&self, _: &mut World) -> Result<Primitive, RuntimeError> {
 		Ok(self.clone().into())
 	}
 }
 
 impl Interpret for expression::BinaryExpr {
-	fn interpret(&self, w: &mut World) -> Result<Value, RuntimeError> {
+	fn interpret(&self, w: &mut World) -> Result<Primitive, RuntimeError> {
 		let left_val = self.left.interpret(w).expect("expected lval");
 		let right_val = self.right.interpret(w).expect("expected rval");
 		match self.operator {
@@ -36,13 +36,13 @@ impl Interpret for expression::BinaryExpr {
 }
 
 impl Interpret for expression::UnaryExpr {
-	fn interpret(&self, w: &mut World) -> Result<Value, RuntimeError> {
+	fn interpret(&self, w: &mut World) -> Result<Primitive, RuntimeError> {
 		let val = self.right.interpret(w)?;
 		match self.operator {
-			UnaryOperator::Bang => Ok(Value::Bool(!val.truthy())),
+			UnaryOperator::Bang => Ok(Primitive::Bool(!val.truthy())),
 			UnaryOperator::Minus => match val {
-				Value::Int(i) => Ok(Value::Int(-i)),
+				Primitive::Int(i) => Ok(Primitive::Int(-i)),
-				Value::Float(f) => Ok(Value::Float(-f)),
+				Primitive::Float(f) => Ok(Primitive::Float(-f)),
 				_ => Err(RuntimeError),
 			},
 		}
@@ -50,25 +50,25 @@ impl Interpret for expression::UnaryExpr {
 }
 
 impl Interpret for expression::GroupingExpr {
-	fn interpret(&self, w: &mut World) -> Result<Value, RuntimeError> {
+	fn interpret(&self, w: &mut World) -> Result<Primitive, RuntimeError> {
 		self.0.interpret(w)
 	}
 }
 
 impl Interpret for expression::VariableExpr {
-	fn interpret(&self, world: &mut World) -> Result<Value, RuntimeError> {
+	fn interpret(&self, world: &mut World) -> Result<Primitive, RuntimeError> {
 		match world.get_var(&self.var_name) {
-			Some(v) => Ok(v.clone()),
+			Some(v) => Ok(v),
 			None => Err(RuntimeError),
 		}
 	}
 }
 
 impl Interpret for expression::BlockExpr {
-	fn interpret(&self, world: &mut World) -> Result<Value, RuntimeError> {
+	fn interpret(&self, world: &mut World) -> Result<Primitive, RuntimeError> {
 		for stmnt in self.statements.iter() {
 			stmnt.interpret(world)?;
 		}
-		Ok(Value::Nil)
+		Ok(Primitive::Nil)
 	}
 }

src/interpreter/ast_walker/mod.rs

@@ -1,8 +1,8 @@
 mod expression_interpreter;
 mod statement_interpreter;
 pub use super::{error::RuntimeError, types};
-use super::{types::Value, world::World};
+use super::{types::Primitive, world::World};
 
 pub trait Interpret {
-	fn interpret(&self, world: &mut World) -> Result<Value, RuntimeError>;
+	fn interpret(&self, world: &mut World) -> Result<Primitive, RuntimeError>;
 }

src/interpreter/ast_walker/statement_interpreter.rs

@@ -1,16 +1,16 @@
 use super::Interpret;
-use super::{types::Value, RuntimeError};
+use super::{types::Primitive, RuntimeError};
 use crate::ast::statement;
 use crate::interpreter::world::World;
 
 impl Interpret for statement::Statement {
-	fn interpret(&self, w: &mut World) -> Result<Value, RuntimeError> {
+	fn interpret(&self, w: &mut World) -> Result<Primitive, RuntimeError> {
 		statement::all_variants!(self, n => n.interpret(w))
 	}
 }
 
 impl Interpret for statement::PrintStatement {
-	fn interpret(&self, w: &mut World) -> Result<Value, RuntimeError> {
+	fn interpret(&self, w: &mut World) -> Result<Primitive, RuntimeError> {
 		let res = self.0.interpret(w)?;
 		println!("{:?}", res);
 		Ok(res)
@@ -18,13 +18,13 @@ impl Interpret for statement::PrintStatement {
 }
 
 impl Interpret for statement::ExpressionStatement {
-	fn interpret(&self, w: &mut World) -> Result<Value, RuntimeError> {
+	fn interpret(&self, w: &mut World) -> Result<Primitive, RuntimeError> {
 		self.0.interpret(w)
 	}
 }
 
 impl Interpret for statement::VariableAssignmentStatement {
-	fn interpret(&self, w: &mut World) -> Result<Value, RuntimeError> {
+	fn interpret(&self, w: &mut World) -> Result<Primitive, RuntimeError> {
 		let expr_val = self.node.interpret(w)?;
 		// Clone for now, later this will use a GC and won't need to clone
 		w.set_var(self.var_name.clone(), expr_val.clone());

src/interpreter/types.rs

@@ -1,8 +1,9 @@
 use crate::ast::expression;
 use from_variants::FromVariants;
+use gc::trace::GCTrace;
 
 #[derive(Debug, PartialEq, PartialOrd, Clone, FromVariants)]
-pub enum Value {
+pub enum Primitive {
 	Int(i32),
 	Float(f32),
 	Bool(bool),
@@ -11,7 +12,9 @@ pub enum Value {
 	String(String),
 }
 
-impl From<expression::Literal> for Value {
+unsafe impl GCTrace for Primitive {}
+
+impl From<expression::Literal> for Primitive {
 	fn from(l: expression::Literal) -> Self {
 		match_any::match_any!(l,
 			expression::Literal::Int(v) | expression::Literal::Bool(v) | expression::Literal::Float(v) | expression::Literal::String(v) => v.into(),
@@ -20,13 +23,13 @@ impl From<expression::Literal> for Value {
 	}
 }
 
-impl Default for Value {
+impl Default for Primitive {
 	fn default() -> Self {
 		Self::Nil
 	}
 }
 
-impl Value {
+impl Primitive {
 	pub fn truthy(&self) -> bool {
 		!(matches!(*self, Self::Bool(false)))
 	}

src/interpreter/world.rs

@@ -1,23 +1,59 @@
-use std::collections::HashMap;
+use std::{cell::RefCell, collections::HashMap};
+
+use gc::{allocator::GCAllocator, gc_ref::GcRef, trace::GCTrace};
 
 use crate::ast::statement::Statement;
 
 use super::{
 	ast_walker::{Interpret, RuntimeError},
-	types::Value,
+	types::Primitive,
 };
 
-#[derive(Default)]
+#[derive(Default, GCTrace)]
+pub struct Environment {
+	variables: HashMap<String, Primitive>,
+	parent: Option<GcRef<RefCell<Environment>>>,
+}
+
+impl Environment {
+	// Update an already existing variable in current scope
+	pub fn update_var(&mut self, name: &str, v: Primitive) -> Option<Primitive> {
+		if let Some(cur) = self.variables.get_mut(name) {
+			Some(std::mem::replace(cur, v))
+		} else if let Some(ref parent) = self.parent {
+			unsafe { parent.get().borrow_mut().update_var(name, v) }
+		} else {
+			None
+		}
+	}
+
+	pub fn set_var(&mut self, name: String, v: Primitive) -> Option<Primitive> {
+		self.update_var(&name, v.clone())
+			.or_else(|| self.variables.insert(name, v))
+	}
+
+	pub fn get_var(&self, name: &str) -> Option<Primitive> {
+		self.variables.get(name).cloned().or_else(|| {
+			if let Some(ref parent) = self.parent {
+				unsafe { parent.get().borrow().get_var(name) }
+			} else {
+				None
+			}
+		})
+	}
+}
+
 pub struct World {
-	variables: HashMap<String, Value>,
+	env: GcRef<RefCell<Environment>>,
+	_gc: GCAllocator,
 }
 
 impl World {
-	pub fn set_var(&mut self, name: String, v: Value) -> Option<Value> {
+	pub fn set_var(&mut self, name: String, v: Primitive) -> Option<Primitive> {
-		self.variables.insert(name, v)
+		unsafe { self.env.get().borrow_mut().set_var(name, v) }
 	}
-	pub fn get_var(&mut self, name: &str) -> Option<&Value> {
+	pub fn get_var(&self, name: &str) -> Option<Primitive> {
-		self.variables.get(name)
+		unsafe { self.env.get().borrow().get_var(name) }
 	}
 }
 
@@ -25,11 +61,17 @@ impl World {
 	pub fn new() -> Self {
 		Self::default()
 	}
-	pub fn exec(&mut self, nodes: Vec<Statement>) -> Result<Value, RuntimeError> {
+	pub fn exec(&mut self, nodes: Vec<Statement>) -> Result<Primitive, RuntimeError> {
-		let mut last_res = Value::Nil;
+		nodes
-		for statement in nodes {
+			.into_iter()
-			last_res = statement.interpret(self)?;
+			.try_fold(Primitive::Nil, |_, stmnt| stmnt.interpret(self))
-		}
+	}
-		Ok(last_res)
+}
+
+impl Default for World {
+	fn default() -> Self {
+		let mut gc = GCAllocator::default();
+		let env = gc.alloc(RefCell::default());
+		Self { env, _gc: gc }
 	}
 }

src/lexer/mod.rs

@@ -87,7 +87,7 @@ impl<'a, 'b> Lexer<'a, 'b> {
 						}
 						found_period = true;
 					}
-					c.is_digit(10) || c == '.'
+					c.is_ascii_digit() || c == '.'
 				});
 				let res = if found_period {
 					num_str

src/lib.rs

@@ -7,7 +7,7 @@ pub mod lexer;
 use ast::parser::ParseAllResult;
 use ast::statement::Statement;
 use interpreter::ast_walker::{Interpret, RuntimeError};
-use interpreter::types::Value;
+use interpreter::types::Primitive;
 use interpreter::world::World;
 use lexer::{token::Token, Lexer, LexingError};
 
@@ -24,8 +24,8 @@ pub fn parse(tokens: Vec<Token>) -> ParseAllResult {
 	parser.parse_all()
 }
 
-pub fn exec(nodes: Vec<Statement>) -> Result<Value, RuntimeError> {
+pub fn exec(nodes: Vec<Statement>) -> Result<Primitive, RuntimeError> {
-	let mut last_res = Value::Nil;
+	let mut last_res = Primitive::Nil;
 	let mut world = World::new();
 	for statement in nodes {
 		last_res = statement.interpret(&mut world)?;
@@ -33,7 +33,7 @@ pub fn exec(nodes: Vec<Statement>) -> Result<Value, RuntimeError> {
 	Ok(last_res)
 }
 
-pub fn run(code: &str) -> Result<Value, run::Error> {
+pub fn run(code: &str) -> Result<Primitive, run::Error> {
 	let tokens = lex(code, None)?;
 	let nodes = parse(tokens)?;
 	Ok(exec(nodes)?)