From 776120de05fc9f26d1af5da92d8b25ec26648365 Mon Sep 17 00:00:00 2001 From: Vincent Ambo Date: Sun, 28 Aug 2022 06:07:20 +0300 Subject: fix(tvix/eval): instantiate *new* closures from blueprints each time The previous closure refactoring introduced a bug in which the same closure object would get mutated constantly for each instance of a closure, which is incorrect behaviour. This commit instead introduces an explicit new Value variant for the internal "blueprint" that the compiler generates (essentially just the lambda) and uses this variant to construct the closure at runtime. If the blueprint ever leaks out to a user somehow that is a critical bug and tvix-eval will panic. As a ~treat~ test for this, the fibonacci function is being used as it is a self-recursive closure (i.e. different instantiations of the same "blueprint") getting called with different values and it's good to have it around. Change-Id: I485de675e9bb0c599ed7d5dc0f001eb34ab4c15f Reviewed-on: https://cl.tvl.fyi/c/depot/+/6323 Tested-by: BuildkiteCI Reviewed-by: sterni --- tvix/eval/src/compiler/mod.rs | 7 ++++--- tvix/eval/src/tests/tvix_tests/eval-okay-fib.exp | 1 + tvix/eval/src/tests/tvix_tests/eval-okay-fib.nix | 7 +++++++ tvix/eval/src/value/function.rs | 4 ++-- tvix/eval/src/value/mod.rs | 9 ++++++--- tvix/eval/src/vm.rs | 22 +++++++++++++--------- 6 files changed, 33 insertions(+), 17 deletions(-) create mode 100644 tvix/eval/src/tests/tvix_tests/eval-okay-fib.exp create mode 100644 tvix/eval/src/tests/tvix_tests/eval-okay-fib.nix (limited to 'tvix') diff --git a/tvix/eval/src/compiler/mod.rs b/tvix/eval/src/compiler/mod.rs index 78fe76ca01a9..0d2ed66f5bf5 100644 --- a/tvix/eval/src/compiler/mod.rs +++ b/tvix/eval/src/compiler/mod.rs @@ -805,16 +805,17 @@ impl Compiler { // If the function is not a closure, just emit it directly and // move on. if compiled.lambda.upvalue_count == 0 { - self.emit_constant(Value::Closure(Closure::new(compiled.lambda))); + self.emit_constant(Value::Closure(Closure::new(Rc::new(compiled.lambda)))); return; } // If the function is a closure, we need to emit the variable // number of operands that allow the runtime to close over the - // upvalues. + // upvalues and leave a blueprint in the constant index from + // which the runtime closure can be constructed. let closure_idx = self .chunk() - .push_constant(Value::Closure(Closure::new(compiled.lambda))); + .push_constant(Value::Blueprint(Rc::new(compiled.lambda))); self.chunk().push_op(OpCode::OpClosure(closure_idx)); for upvalue in compiled.scope.upvalues { diff --git a/tvix/eval/src/tests/tvix_tests/eval-okay-fib.exp b/tvix/eval/src/tests/tvix_tests/eval-okay-fib.exp new file mode 100644 index 000000000000..8643cf6debac --- /dev/null +++ b/tvix/eval/src/tests/tvix_tests/eval-okay-fib.exp @@ -0,0 +1 @@ +89 diff --git a/tvix/eval/src/tests/tvix_tests/eval-okay-fib.nix b/tvix/eval/src/tests/tvix_tests/eval-okay-fib.nix new file mode 100644 index 000000000000..9a22d85ac5f1 --- /dev/null +++ b/tvix/eval/src/tests/tvix_tests/eval-okay-fib.nix @@ -0,0 +1,7 @@ +let + fib' = i: n: m: if i == 0 + then n + else fib' (i - 1) m (n + m); + + fib = n: fib' n 1 1; +in fib 10 diff --git a/tvix/eval/src/value/function.rs b/tvix/eval/src/value/function.rs index d0209cc50725..e5db43d58ace 100644 --- a/tvix/eval/src/value/function.rs +++ b/tvix/eval/src/value/function.rs @@ -29,7 +29,7 @@ impl Lambda { #[derive(Clone, Debug)] pub struct InnerClosure { - pub lambda: Lambda, + pub lambda: Rc, pub upvalues: Vec, } @@ -38,7 +38,7 @@ pub struct InnerClosure { pub struct Closure(Rc>); impl Closure { - pub fn new(lambda: Lambda) -> Self { + pub fn new(lambda: Rc) -> Self { Closure(Rc::new(RefCell::new(InnerClosure { upvalues: Vec::with_capacity(lambda.upvalue_count), lambda, diff --git a/tvix/eval/src/value/mod.rs b/tvix/eval/src/value/mod.rs index 54211e8ba313..911af9d6ae12 100644 --- a/tvix/eval/src/value/mod.rs +++ b/tvix/eval/src/value/mod.rs @@ -35,6 +35,7 @@ pub enum Value { AttrPath(Vec), AttrNotFound, DynamicUpvalueMissing(NixString), + Blueprint(Rc), } impl Value { @@ -55,9 +56,10 @@ impl Value { Value::Closure(_) | Value::Builtin(_) => "lambda", // Internal types - Value::AttrPath(_) | Value::AttrNotFound | Value::DynamicUpvalueMissing(_) => { - "internal" - } + Value::AttrPath(_) + | Value::AttrNotFound + | Value::DynamicUpvalueMissing(_) + | Value::Blueprint(_) => "internal", } } @@ -166,6 +168,7 @@ impl Display for Value { // internal types Value::AttrPath(path) => write!(f, "internal[attrpath({})]", path.len()), Value::AttrNotFound => f.write_str("internal[not found]"), + Value::Blueprint(_) => f.write_str("internal[blueprint]"), Value::DynamicUpvalueMissing(name) => { write!(f, "internal[no_dyn_upvalue({name})]") } diff --git a/tvix/eval/src/vm.rs b/tvix/eval/src/vm.rs index 5d5cb57dbabf..7b3de6406549 100644 --- a/tvix/eval/src/vm.rs +++ b/tvix/eval/src/vm.rs @@ -385,15 +385,19 @@ impl VM { } OpCode::OpClosure(idx) => { - let value = self.chunk().constant(idx).clone(); - self.push(value.clone()); + let blueprint = match self.chunk().constant(idx) { + Value::Blueprint(lambda) => lambda.clone(), + _ => panic!("compiler bug: non-blueprint in blueprint slot"), + }; + + let closure = Closure::new(blueprint); + self.push(Value::Closure(closure.clone())); - // This refers to the same Rc, and from this point - // on internally mutates the closure objects - // upvalues. The closure is already in its stack - // slot, which means that it can capture itself as - // an upvalue for self-recursion. - let closure = value.to_closure()?; + // From this point on we internally mutate the + // closure object's upvalues. The closure is + // already in its stack slot, which means that it + // can capture itself as an upvalue for + // self-recursion. debug_assert!( closure.upvalue_count() > 0, @@ -536,6 +540,6 @@ pub fn run_lambda(lambda: Lambda) -> EvalResult { with_stack: vec![], }; - vm.call(Closure::new(lambda), 0); + vm.call(Closure::new(Rc::new(lambda)), 0); vm.run() } -- cgit 1.4.1