From a52db148203824484caa82a23fe88f0a137274ee Mon Sep 17 00:00:00 2001 From: Vincent Ambo Date: Sat, 27 Aug 2022 17:16:46 +0300 Subject: feat(tvix/eval): detect illegally shadowed variables Nix does not allow things like `let a = 1; a = 2; in a`, but doing it across depths is allowed. Change-Id: I6a259f8b01a254b433b58c736e245c9c764641b6 Reviewed-on: https://cl.tvl.fyi/c/depot/+/6301 Tested-by: BuildkiteCI Reviewed-by: sterni --- tvix/eval/src/compiler/mod.rs | 31 +++++++++++++++++++++++++++++++ 1 file changed, 31 insertions(+) (limited to 'tvix/eval/src/compiler') diff --git a/tvix/eval/src/compiler/mod.rs b/tvix/eval/src/compiler/mod.rs index 38eaddddc16b..eefcbfcd65a0 100644 --- a/tvix/eval/src/compiler/mod.rs +++ b/tvix/eval/src/compiler/mod.rs @@ -54,6 +54,14 @@ impl Depth { Depth::At(ours) => *ours > theirs, } } + + /// Does this variable live below the other given depth? + fn below(&self, theirs: usize) -> bool { + match self { + Depth::Unitialised => false, + Depth::At(ours) => *ours < theirs, + } + } } /// Represents a single local already known to the compiler. @@ -1013,6 +1021,26 @@ impl Compiler { self.scope_mut().poison(global_ident, depth); } + let mut shadowed = false; + for local in self.scope().locals.iter().rev() { + if local.depth.below(self.scope().scope_depth) { + // Shadowing identifiers from higher scopes is allowed. + break; + } + + if local.name == name { + shadowed = true; + break; + } + } + + if shadowed { + self.emit_error( + node.clone(), + ErrorKind::VariableAlreadyDefined(name.clone()), + ); + } + self.scope_mut().locals.push(Local { name, depth: Depth::At(depth), @@ -1022,6 +1050,9 @@ impl Compiler { }); } + /// Declare a local variable that occupies a stack slot and should + /// be accounted for, but is not directly accessible by users + /// (e.g. attribute sets used for `with`). fn declare_phantom(&mut self) { let depth = self.scope().scope_depth; self.scope_mut().locals.push(Local { -- cgit 1.4.1