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Auto merge of #88337 - eddyb:field-failure-is-not-an-option, r=nagisa

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rustc_target: `TyAndLayout::field` should never error.

This refactor (making `TyAndLayout::field` return `TyAndLayout` without any `Result` around it) is based on a simple observation, regarding `TyAndLayout::field`:

If `cx.layout_of(ty)` succeeds (for some `cx` and `ty`), then `.field(cx, i)` on the resulting `TyAndLayout` should *always* succeed in computing `cx.layout_of(field_ty)` (where `field_ty` is the type of the `i`th field of `ty`).

The reason for this is that no matter which field is chosen, `cx.layout_of(field_ty)` *will have already been computed*, as part of computing `cx.layout_of(ty)`, as we cannot determine the layout of *any* type without considering the layouts of *all* of its fields.

And so it should be fine to turn any errors into ICEs, since they likely indicate a `cx` mismatch, or some other edge case that is due to a compiler bug (as opposed to ever being an user-facing error).

<hr/>

Each commit should probably be reviewed separately, though note that there's some `where` clauses (in `rustc_target::abi::call::*`) that change in most commits.

cc `@nagisa` `@oli-obk`
This commit is contained in:
bors 2021-08-29 22:54:26 +00:00
commit 9556d7a09a
32 changed files with 308 additions and 271 deletions
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25
compiler/rustc_lint/src/context.rs
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@ -41,7 +41,7 @@ use rustc_session::Session;
use rustc_session::SessionLintStore;
use rustc_span::lev_distance::find_best_match_for_name;
use rustc_span::{symbol::Symbol, MultiSpan, Span, DUMMY_SP};
use rustc_target::abi::LayoutOf;
use rustc_target::abi::{self, LayoutOf};
use tracing::debug;
use std::cell::Cell;
@ -1059,7 +1059,28 @@ impl<'tcx> LateContext<'tcx> {
}
}
impl<'tcx> LayoutOf for LateContext<'tcx> {
impl<'tcx> abi::HasDataLayout for LateContext<'tcx> {
#[inline]
fn data_layout(&self) -> &abi::TargetDataLayout {
&self.tcx.data_layout
}
}
impl<'tcx> ty::layout::HasTyCtxt<'tcx> for LateContext<'tcx> {
#[inline]
fn tcx(&self) -> TyCtxt<'tcx> {
self.tcx
}
}
impl<'tcx> ty::layout::HasParamEnv<'tcx> for LateContext<'tcx> {
#[inline]
fn param_env(&self) -> ty::ParamEnv<'tcx> {
self.param_env
}
}
impl<'tcx> LayoutOf<'tcx> for LateContext<'tcx> {
type Ty = Ty<'tcx>;
type TyAndLayout = Result<TyAndLayout<'tcx>, LayoutError<'tcx>>;