Auto merge of #88499 - eddyb:layout-off, r=nagisa

Provide `layout_of` automatically (given tcx + param_env + error handling).

After #88337, there's no longer any uses of `LayoutOf` within `rustc_target` itself, so I realized I could move the trait to `rustc_middle::ty::layout` and redesign it a bit.

This is similar to #88338 (and supersedes it), but at no ergonomic loss, since there's no funky `C: LayoutOf<Ty = Ty>` -> `Ty: TyAbiInterface<C>` generic `impl` chain, and each `LayoutOf` still corresponds to one `impl` (of `LayoutOfHelpers`) for the specific context.

After this PR, this is what's needed to get `trait LayoutOf` (with the `layout_of` method) implemented on some context type:
* `TyCtxt`, via `HasTyCtxt`
* `ParamEnv`, via `HasParamEnv`
* a way to transform `LayoutError`s into the desired error type
  * an error type of `!` can be paired with having `cx.layout_of(...)` return `TyAndLayout` *without* `Result<...>` around it, such as used by codegen
  * this is done through a new `LayoutOfHelpers` trait (and so is specifying the type of `cx.layout_of(...)`)

When going through this path (and not bypassing it with a manual `impl` of `LayoutOf`), the end result is that only the error case can be customized, the query itself and the success paths are guaranteed to be uniform.

(**EDIT**: just noticed that because of the supertrait relationship, you cannot actually implement `LayoutOf` yourself, the blanket `impl` fully covers all possible context types that could ever implement it)

Part of the motivation for this shape of API is that I've been working on querifying `FnAbi::of_*`, and what I want/need to introduce for that looks a lot like the setup in this PR - in particular, it's harder to express the `FnAbi` methods in `rustc_target`, since they're much more tied to `rustc` concepts.

r? `@nagisa` cc `@oli-obk` `@bjorn3`

8 files changed, 16 insertions, 24 deletions

diff --git a/compiler/rustc_codegen_ssa/src/base.rs b/compiler/rustc_codegen_ssa/src/base.rs
index f427dd76693..a6bf1d8d1e5 100644
--- a/compiler/rustc_codegen_ssa/src/base.rs
+++ b/compiler/rustc_codegen_ssa/src/base.rs
@@ -22,14 +22,14 @@ use rustc_middle::middle::codegen_fn_attrs::CodegenFnAttrs;
 use rustc_middle::middle::cstore::EncodedMetadata;
 use rustc_middle::middle::lang_items;
 use rustc_middle::mir::mono::{CodegenUnit, CodegenUnitNameBuilder, MonoItem};
-use rustc_middle::ty::layout::{HasTyCtxt, TyAndLayout};
+use rustc_middle::ty::layout::{HasTyCtxt, LayoutOf, TyAndLayout};
 use rustc_middle::ty::query::Providers;
 use rustc_middle::ty::{self, Instance, Ty, TyCtxt};
 use rustc_session::cgu_reuse_tracker::CguReuse;
 use rustc_session::config::{self, EntryFnType};
 use rustc_session::Session;
 use rustc_span::symbol::sym;
-use rustc_target::abi::{Align, LayoutOf, VariantIdx};
+use rustc_target::abi::{Align, VariantIdx};
 
 use std::convert::TryFrom;
 use std::ops::{Deref, DerefMut};
diff --git a/compiler/rustc_codegen_ssa/src/mir/analyze.rs b/compiler/rustc_codegen_ssa/src/mir/analyze.rs
index b6def164fac..8d75b2e7a3d 100644
--- a/compiler/rustc_codegen_ssa/src/mir/analyze.rs
+++ b/compiler/rustc_codegen_ssa/src/mir/analyze.rs
@@ -9,8 +9,7 @@ use rustc_index::vec::IndexVec;
 use rustc_middle::mir::traversal;
 use rustc_middle::mir::visit::{MutatingUseContext, NonMutatingUseContext, PlaceContext, Visitor};
 use rustc_middle::mir::{self, Location, TerminatorKind};
-use rustc_middle::ty::layout::HasTyCtxt;
-use rustc_target::abi::LayoutOf;
+use rustc_middle::ty::layout::{HasTyCtxt, LayoutOf};
 
 pub fn non_ssa_locals<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>>(
     fx: &FunctionCx<'a, 'tcx, Bx>,
diff --git a/compiler/rustc_codegen_ssa/src/mir/block.rs b/compiler/rustc_codegen_ssa/src/mir/block.rs
index 2a76ad0fb13..2ca7e8fd7e8 100644
--- a/compiler/rustc_codegen_ssa/src/mir/block.rs
+++ b/compiler/rustc_codegen_ssa/src/mir/block.rs
@@ -14,13 +14,13 @@ use rustc_hir::lang_items::LangItem;
 use rustc_index::vec::Idx;
 use rustc_middle::mir::AssertKind;
 use rustc_middle::mir::{self, SwitchTargets};
-use rustc_middle::ty::layout::{FnAbiExt, HasTyCtxt};
+use rustc_middle::ty::layout::{FnAbiExt, HasTyCtxt, LayoutOf};
 use rustc_middle::ty::print::with_no_trimmed_paths;
 use rustc_middle::ty::{self, Instance, Ty, TypeFoldable};
 use rustc_span::source_map::Span;
 use rustc_span::{sym, Symbol};
 use rustc_target::abi::call::{ArgAbi, FnAbi, PassMode};
-use rustc_target::abi::{self, HasDataLayout, LayoutOf};
+use rustc_target::abi::{self, HasDataLayout};
 use rustc_target::spec::abi::Abi;
 
 /// Used by `FunctionCx::codegen_terminator` for emitting common patterns
diff --git a/compiler/rustc_codegen_ssa/src/mir/operand.rs b/compiler/rustc_codegen_ssa/src/mir/operand.rs
index cfb2befdf91..5cee25b5cca 100644
--- a/compiler/rustc_codegen_ssa/src/mir/operand.rs
+++ b/compiler/rustc_codegen_ssa/src/mir/operand.rs
@@ -8,9 +8,9 @@ use crate::MemFlags;
 
 use rustc_middle::mir;
 use rustc_middle::mir::interpret::{ConstValue, Pointer, Scalar};
-use rustc_middle::ty::layout::TyAndLayout;
+use rustc_middle::ty::layout::{LayoutOf, TyAndLayout};
 use rustc_middle::ty::Ty;
-use rustc_target::abi::{Abi, Align, LayoutOf, Size};
+use rustc_target::abi::{Abi, Align, Size};
 
 use std::fmt;
 
diff --git a/compiler/rustc_codegen_ssa/src/mir/place.rs b/compiler/rustc_codegen_ssa/src/mir/place.rs
index 20be46606a0..b48d6d42b43 100644
--- a/compiler/rustc_codegen_ssa/src/mir/place.rs
+++ b/compiler/rustc_codegen_ssa/src/mir/place.rs
@@ -8,10 +8,10 @@ use crate::MemFlags;
 
 use rustc_middle::mir;
 use rustc_middle::mir::tcx::PlaceTy;
-use rustc_middle::ty::layout::{HasTyCtxt, TyAndLayout};
+use rustc_middle::ty::layout::{HasTyCtxt, LayoutOf, TyAndLayout};
 use rustc_middle::ty::{self, Ty};
 use rustc_target::abi::{Abi, Align, FieldsShape, Int, TagEncoding};
-use rustc_target::abi::{LayoutOf, VariantIdx, Variants};
+use rustc_target::abi::{VariantIdx, Variants};
 
 #[derive(Copy, Clone, Debug)]
 pub struct PlaceRef<'tcx, V> {
diff --git a/compiler/rustc_codegen_ssa/src/mir/rvalue.rs b/compiler/rustc_codegen_ssa/src/mir/rvalue.rs
index 02e2db54e74..3d8ea29160b 100644
--- a/compiler/rustc_codegen_ssa/src/mir/rvalue.rs
+++ b/compiler/rustc_codegen_ssa/src/mir/rvalue.rs
@@ -11,10 +11,10 @@ use rustc_apfloat::{ieee, Float, Round, Status};
 use rustc_hir::lang_items::LangItem;
 use rustc_middle::mir;
 use rustc_middle::ty::cast::{CastTy, IntTy};
-use rustc_middle::ty::layout::HasTyCtxt;
+use rustc_middle::ty::layout::{HasTyCtxt, LayoutOf};
 use rustc_middle::ty::{self, adjustment::PointerCast, Instance, Ty, TyCtxt};
 use rustc_span::source_map::{Span, DUMMY_SP};
-use rustc_target::abi::{Abi, Int, LayoutOf, Variants};
+use rustc_target::abi::{Abi, Int, Variants};
 
 impl<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>> FunctionCx<'a, 'tcx, Bx> {
     pub fn codegen_rvalue(
diff --git a/compiler/rustc_codegen_ssa/src/mono_item.rs b/compiler/rustc_codegen_ssa/src/mono_item.rs
index 48d753e0d84..5f0f50ae2df 100644
--- a/compiler/rustc_codegen_ssa/src/mono_item.rs
+++ b/compiler/rustc_codegen_ssa/src/mono_item.rs
@@ -4,8 +4,7 @@ use crate::traits::*;
 use rustc_hir as hir;
 use rustc_middle::mir::mono::MonoItem;
 use rustc_middle::mir::mono::{Linkage, Visibility};
-use rustc_middle::ty::layout::HasTyCtxt;
-use rustc_target::abi::LayoutOf;
+use rustc_middle::ty::layout::{HasTyCtxt, LayoutOf};
 
 pub trait MonoItemExt<'a, 'tcx> {
     fn define<Bx: BuilderMethods<'a, 'tcx>>(&self, cx: &'a Bx::CodegenCx);
diff --git a/compiler/rustc_codegen_ssa/src/traits/backend.rs b/compiler/rustc_codegen_ssa/src/traits/backend.rs
index 96e53f51dac..dbb7e1ee8b1 100644
--- a/compiler/rustc_codegen_ssa/src/traits/backend.rs
+++ b/compiler/rustc_codegen_ssa/src/traits/backend.rs
@@ -8,15 +8,14 @@ use rustc_data_structures::fx::FxHashMap;
 use rustc_errors::ErrorReported;
 use rustc_middle::dep_graph::{WorkProduct, WorkProductId};
 use rustc_middle::middle::cstore::{EncodedMetadata, MetadataLoaderDyn};
-use rustc_middle::ty::layout::{HasTyCtxt, TyAndLayout};
+use rustc_middle::ty::layout::{HasTyCtxt, LayoutOf, TyAndLayout};
 use rustc_middle::ty::query::Providers;
-use rustc_middle::ty::{Ty, TyCtxt};
+use rustc_middle::ty::TyCtxt;
 use rustc_session::{
     config::{self, OutputFilenames, PrintRequest},
     Session,
 };
 use rustc_span::symbol::Symbol;
-use rustc_target::abi::LayoutOf;
 use rustc_target::spec::Target;
 
 pub use rustc_data_structures::sync::MetadataRef;
@@ -39,17 +38,12 @@ pub trait BackendTypes {
 }
 
 pub trait Backend<'tcx>:
-    Sized
-    + BackendTypes
-    + HasTyCtxt<'tcx>
-    + LayoutOf<'tcx, Ty = Ty<'tcx>, TyAndLayout = TyAndLayout<'tcx>>
+    Sized + BackendTypes + HasTyCtxt<'tcx> + LayoutOf<'tcx, LayoutOfResult = TyAndLayout<'tcx>>
 {
 }
 
 impl<'tcx, T> Backend<'tcx> for T where
-    Self: BackendTypes
-        + HasTyCtxt<'tcx>
-        + LayoutOf<'tcx, Ty = Ty<'tcx>, TyAndLayout = TyAndLayout<'tcx>>
+    Self: BackendTypes + HasTyCtxt<'tcx> + LayoutOf<'tcx, LayoutOfResult = TyAndLayout<'tcx>>
 {
 }