Auto merge of #117517 - klinvill:smir-projections, r=ouz-a
Add richer structure for Stable MIR Projections Resolves https://github.com/rust-lang/project-stable-mir/issues/49. Projections in Stable MIR are currently just strings. This PR replaces that representation with a richer structure, namely projections become vectors of `ProjectionElem`s, just as in MIR. The `ProjectionElem` enum is heavily based off of the MIR `ProjectionElem`. This PR is a draft since there are several outstanding issues to resolve, including: - How should `UserTypeProjection`s be represented in Stable MIR? In MIR, the projections are just a vector of `ProjectionElem<(),()>`, meaning `ProjectionElem`s that don't have Local or Type arguments (for `Index`, `Field`, etc. objects). Should `UserTypeProjection`s be represented this way in Stable MIR as well? Or is there a more user-friendly representation that wouldn't drag along all the `ProjectionElem` variants that presumably can't appear? - What is the expected behavior of a `Place`'s `ty` function? Should it resolve down the chain of projections so that something like `*_1.f` would return the type referenced by field `f`? - Tests should be added for `UserTypeProjection`
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commit
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4 changed files with 355 additions and 7 deletions
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@ -682,10 +682,44 @@ impl<'tcx> Stable<'tcx> for mir::ConstOperand<'tcx> {
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impl<'tcx> Stable<'tcx> for mir::Place<'tcx> {
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type T = stable_mir::mir::Place;
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fn stable(&self, _: &mut Tables<'tcx>) -> Self::T {
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fn stable(&self, tables: &mut Tables<'tcx>) -> Self::T {
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stable_mir::mir::Place {
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local: self.local.as_usize(),
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projection: format!("{:?}", self.projection),
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projection: self.projection.iter().map(|e| e.stable(tables)).collect(),
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}
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}
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}
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impl<'tcx> Stable<'tcx> for mir::PlaceElem<'tcx> {
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type T = stable_mir::mir::ProjectionElem;
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fn stable(&self, tables: &mut Tables<'tcx>) -> Self::T {
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use mir::ProjectionElem::*;
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match self {
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Deref => stable_mir::mir::ProjectionElem::Deref,
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Field(idx, ty) => {
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stable_mir::mir::ProjectionElem::Field(idx.stable(tables), ty.stable(tables))
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}
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Index(local) => stable_mir::mir::ProjectionElem::Index(local.stable(tables)),
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ConstantIndex { offset, min_length, from_end } => {
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stable_mir::mir::ProjectionElem::ConstantIndex {
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offset: *offset,
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min_length: *min_length,
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from_end: *from_end,
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}
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}
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Subslice { from, to, from_end } => stable_mir::mir::ProjectionElem::Subslice {
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from: *from,
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to: *to,
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from_end: *from_end,
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},
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// MIR includes an `Option<Symbol>` argument for `Downcast` that is the name of the
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// variant, used for printing MIR. However this information should also be accessible
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// via a lookup using the `VariantIdx`. The `Option<Symbol>` argument is therefore
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// dropped when converting to Stable MIR. A brief justification for this decision can be
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// found at https://github.com/rust-lang/rust/pull/117517#issuecomment-1811683486
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Downcast(_, idx) => stable_mir::mir::ProjectionElem::Downcast(idx.stable(tables)),
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OpaqueCast(ty) => stable_mir::mir::ProjectionElem::OpaqueCast(ty.stable(tables)),
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Subtype(ty) => stable_mir::mir::ProjectionElem::Subtype(ty.stable(tables)),
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}
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}
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}
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@ -693,8 +727,8 @@ impl<'tcx> Stable<'tcx> for mir::Place<'tcx> {
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impl<'tcx> Stable<'tcx> for mir::UserTypeProjection {
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type T = stable_mir::mir::UserTypeProjection;
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fn stable(&self, _: &mut Tables<'tcx>) -> Self::T {
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UserTypeProjection { base: self.base.as_usize(), projection: format!("{:?}", self.projs) }
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fn stable(&self, _tables: &mut Tables<'tcx>) -> Self::T {
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UserTypeProjection { base: self.base.as_usize(), projection: opaque(&self.projs) }
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}
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}
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