diff options
| -rw-r--r-- | tvix/eval/src/value/attrs.rs | 47 | ||||
| -rw-r--r-- | tvix/eval/src/vm.rs | 12 |
2 files changed, 36 insertions, 23 deletions
diff --git a/tvix/eval/src/value/attrs.rs b/tvix/eval/src/value/attrs.rs index 922aa0c0d3..62fb9b710c 100644 --- a/tvix/eval/src/value/attrs.rs +++ b/tvix/eval/src/value/attrs.rs @@ -151,28 +151,34 @@ impl PartialEq for NixAttrs { impl NixAttrs { // Update one attribute set with the values of the other. - pub fn update(&self, other: &Self) -> Self { + pub fn update(self, other: Self) -> Self { + // Short-circuit on some optimal cases: match (&self.0, &other.0) { - // Short-circuit on some optimal cases: - (AttrsRep::Empty, AttrsRep::Empty) => NixAttrs(AttrsRep::Empty), - (AttrsRep::Empty, _) => other.clone(), - (_, AttrsRep::Empty) => self.clone(), - (AttrsRep::KV { .. }, AttrsRep::KV { .. }) => other.clone(), - - // Slightly more advanced, but still optimised updates - (AttrsRep::Map(m), AttrsRep::KV { name, value }) => { - let mut m = m.clone(); - m.insert(NixString::NAME, name.clone()); - m.insert(NixString::VALUE, value.clone()); + (AttrsRep::Empty, AttrsRep::Empty) => return self, + (AttrsRep::Empty, _) => return other, + (_, AttrsRep::Empty) => return self, + (AttrsRep::KV { .. }, AttrsRep::KV { .. }) => return other, + + // Explicitly handle all branches instead of falling + // through, to ensure that we get at least some compiler + // errors if variants are modified. + (AttrsRep::Map(_), AttrsRep::Map(_)) + | (AttrsRep::Map(_), AttrsRep::KV { .. }) + | (AttrsRep::KV { .. }, AttrsRep::Map(_)) => {} + }; + + // Slightly more advanced, but still optimised updates + match (self.0, other.0) { + (AttrsRep::Map(mut m), AttrsRep::KV { name, value }) => { + m.insert(NixString::NAME, name); + m.insert(NixString::VALUE, value); NixAttrs(AttrsRep::Map(m)) } - (AttrsRep::KV { name, value }, AttrsRep::Map(m)) => { - let mut m = m.clone(); - + (AttrsRep::KV { name, value }, AttrsRep::Map(mut m)) => { match m.entry(NixString::NAME) { btree_map::Entry::Vacant(e) => { - e.insert(name.clone()); + e.insert(name); } btree_map::Entry::Occupied(_) => { /* name from `m` has precedence */ } @@ -180,7 +186,7 @@ impl NixAttrs { match m.entry(NixString::VALUE) { btree_map::Entry::Vacant(e) => { - e.insert(value.clone()); + e.insert(value); } btree_map::Entry::Occupied(_) => { /* value from `m` has precedence */ } @@ -190,12 +196,13 @@ impl NixAttrs { } // Plain merge of maps. - (AttrsRep::Map(m1), AttrsRep::Map(m2)) => { - let mut m1 = m1.clone(); - let mut m2 = m2.clone(); + (AttrsRep::Map(mut m1), AttrsRep::Map(mut m2)) => { m1.append(&mut m2); NixAttrs(AttrsRep::Map(m1)) } + + // Cases handled above by the borrowing match: + _ => unreachable!(), } } diff --git a/tvix/eval/src/vm.rs b/tvix/eval/src/vm.rs index 65534006d0..6de9cd03c4 100644 --- a/tvix/eval/src/vm.rs +++ b/tvix/eval/src/vm.rs @@ -203,10 +203,10 @@ impl VM { OpCode::OpAttrPath(count) => self.run_attr_path(count)?, OpCode::OpAttrsUpdate => { - let rhs = self.pop().to_attrs()?; - let lhs = self.pop().to_attrs()?; + let rhs = unwrap_or_clone_rc(self.pop().to_attrs()?); + let lhs = unwrap_or_clone_rc(self.pop().to_attrs()?); - self.push(Value::Attrs(Rc::new(lhs.update(&rhs)))) + self.push(Value::Attrs(Rc::new(lhs.update(rhs)))) } OpCode::OpAttrsSelect => { @@ -414,6 +414,12 @@ impl VM { } } +// TODO: use Rc::unwrap_or_clone once it is stabilised. +// https://doc.rust-lang.org/std/rc/struct.Rc.html#method.unwrap_or_clone +fn unwrap_or_clone_rc<T: Clone>(rc: Rc<T>) -> T { + Rc::try_unwrap(rc).unwrap_or_else(|rc| (*rc).clone()) +} + pub fn run_lambda(lambda: Lambda) -> EvalResult<Value> { let mut vm = VM { frames: vec![], |