WIP: eliminate DefineOpaqueTypes by using Yes across the compiler

[oli-obk]

Opening this PR because

1. I'm stuck
2. 48cb487 is quite a major change (but unblocks the follow-up commits, which otherwise set the hidden type of the opaque type as anything from the param env that has matching bounds, so a T: Trait will match an -> impl Trait whenver select_where_possible tries to solve some available bounds. This all happens before actually matching the opaque type to the returned value, at which point everything would work correctly, but obviously have issues with ordering). The next solver does not have this issue because it just converts opaque types to inference vars. Tho how it handles the send bounds in that case I do not know, will investigate.

cc @lcnr @compiler-errors I'll open individual issues for things so we can keep separate things separate instead of talking about everything in this one big PR that I'll move out of WIP status when I can add a commit to that removes DefineOpaqueTypes.

Related:

• Do not use global caches if opaque types can be defined #126024

[oli-obk]

Let's discuss these in #127035

[oli-obk]

This is used in selection (behind a probe) and confirmation. Without the previous commit skipping assemble_candidates_from_caller_bounds for opaque types in their defining scope, this will cause functions like

rust/library/core/src/iter/adapters/filter.rs

Lines 73 to 78 in 127fa22

	fn filter_fold<T, Acc>(
	mut predicate: impl FnMut(&T) -> bool,
	mut fold: impl FnMut(Acc, T) -> Acc,
	) -> impl FnMut(Acc, T) -> Acc {
	move |acc, item| if predicate(&item) { fold(acc, item) } else { acc }
	}

to immediately match the opaque type against the APIT with the same bounds.

[oli-obk]

I've looked into it a bit. Do you know of any fundamental issues with moving the old solver to a similar normalization scheme for opaques as the new solver uses? Or is that just a bad version of lazy norm?

[oli-obk]

I guess we need to fix this issue for the new solver and the current one before we can land this commit

[bors]

☔ The latest upstream changes (presumably #127172) made this pull request unmergeable. Please resolve the merge conflicts.

[rust-log-analyzer]

The job x86_64-gnu-llvm-17 failed! Check out the build log: (web) (plain)

Click to see the possible cause of the failure (guessed by this bot)

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 > importing cache manifest from ghcr.io/rust-lang/rust-ci-cache:3aacb9c90579defe09351ac5e8ee504359f8054da6326ff19038f1b7c90e3cb2aafe33685c6d9b76ee8d2ccbd187ca80c46ab5380485abdd8c0ce7d69cd8d8fd:
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##[endgroup]
Setting extra environment values for docker:  --env ENABLE_GCC_CODEGEN=1 --env GCC_EXEC_PREFIX=/usr/lib/gcc/
[CI_JOB_NAME=x86_64-gnu-llvm-17]
---
sccache: Starting the server...
##[group]Configure the build
configure: processing command line
configure: 
configure: build.configure-args := ['--build=x86_64-unknown-linux-gnu', '--llvm-root=/usr/lib/llvm-17', '--enable-llvm-link-shared', '--set', 'rust.thin-lto-import-instr-limit=10', '--set', 'change-id=99999999', '--enable-verbose-configure', '--enable-sccache', '--disable-manage-submodules', '--enable-locked-deps', '--enable-cargo-native-static', '--set', 'rust.codegen-units-std=1', '--set', 'dist.compression-profile=balanced', '--dist-compression-formats=xz', '--set', 'rust.lld=false', '--disable-dist-src', '--release-channel=nightly', '--enable-debug-assertions', '--enable-overflow-checks', '--enable-llvm-assertions', '--set', 'rust.verify-llvm-ir', '--set', 'rust.codegen-backends=llvm,cranelift,gcc', '--set', 'llvm.static-libstdcpp', '--enable-new-symbol-mangling']
configure: target.x86_64-unknown-linux-gnu.llvm-config := /usr/lib/llvm-17/bin/llvm-config
configure: llvm.link-shared     := True
configure: rust.thin-lto-import-instr-limit := 10
configure: change-id            := 99999999
---
---- [ui] tests/ui/auto-traits/opaque_type_candidate_selection.rs stdout ----

error: test compilation failed although it shouldn't!
status: exit status: 1
command: env -u RUSTC_LOG_COLOR RUSTC_ICE="0" RUST_BACKTRACE="short" "/checkout/obj/build/x86_64-unknown-linux-gnu/stage2/bin/rustc" "/checkout/tests/ui/auto-traits/opaque_type_candidate_selection.rs" "-Zthreads=1" "-Zsimulate-remapped-rust-src-base=/rustc/FAKE_PREFIX" "-Ztranslate-remapped-path-to-local-path=no" "-Z" "ignore-directory-in-diagnostics-source-blocks=/cargo" "-Z" "ignore-directory-in-diagnostics-source-blocks=/checkout/vendor" "--sysroot" "/checkout/obj/build/x86_64-unknown-linux-gnu/stage2" "--target=x86_64-unknown-linux-gnu" "--check-cfg" "cfg(FALSE)" "--error-format" "json" "--json" "future-incompat" "-Ccodegen-units=1" "-Zui-testing" "-Zdeduplicate-diagnostics=no" "-Zwrite-long-types-to-disk=no" "-Cstrip=debuginfo" "--emit" "metadata" "-C" "prefer-dynamic" "--out-dir" "/checkout/obj/build/x86_64-unknown-linux-gnu/test/ui/auto-traits/opaque_type_candidate_selection" "-A" "unused" "-A" "internal_features" "-Crpath" "-Cdebuginfo=0" "-Lnative=/checkout/obj/build/x86_64-unknown-linux-gnu/native/rust-test-helpers" "-L" "/checkout/obj/build/x86_64-unknown-linux-gnu/test/ui/auto-traits/opaque_type_candidate_selection/auxiliary"
--- stderr -------------------------------
error[E0284]: type annotations needed
##[error]  --> /checkout/tests/ui/auto-traits/opaque_type_candidate_selection.rs:10:20
   |
   |
LL |     pub fn cast<T>(x: Container<Alias<T>, T>) -> Container<T, T> {
   |                    ^ cannot infer type
   |
   = note: cannot satisfy `<Alias<T> as Trait<T>>::Assoc == _`
note: required because it appears within the type `Container<Alias<T>, T>`
   |
   |
LL | struct Container<T: Trait<U>, U> {
   = help: unsized fn params are gated as an unstable feature
help: function arguments must have a statically known size, borrowed types always have a known size
   |
   |
LL |     pub fn cast<T>(x: &Container<Alias<T>, T>) -> Container<T, T> {

error: aborting due to 1 previous error

For more information about this error, try `rustc --explain E0284`.
For more information about this error, try `rustc --explain E0284`.
------------------------------------------


---- [ui] tests/ui/coherence/occurs-check/opaques.rs#old stdout ----

error in revision `old`: test compilation failed although it shouldn't!
status: exit status: 1
command: env -u RUSTC_LOG_COLOR RUSTC_ICE="0" RUST_BACKTRACE="short" "/checkout/obj/build/x86_64-unknown-linux-gnu/stage2/bin/rustc" "/checkout/tests/ui/coherence/occurs-check/opaques.rs" "-Zthreads=1" "-Zsimulate-remapped-rust-src-base=/rustc/FAKE_PREFIX" "-Ztranslate-remapped-path-to-local-path=no" "-Z" "ignore-directory-in-diagnostics-source-blocks=/cargo" "-Z" "ignore-directory-in-diagnostics-source-blocks=/checkout/vendor" "--sysroot" "/checkout/obj/build/x86_64-unknown-linux-gnu/stage2" "--target=x86_64-unknown-linux-gnu" "--cfg" "old" "--check-cfg" "cfg(FALSE,old,next)" "--error-format" "json" "--json" "future-incompat" "-Ccodegen-units=1" "-Zui-testing" "-Zdeduplicate-diagnostics=no" "-Zwrite-long-types-to-disk=no" "-Cstrip=debuginfo" "--emit" "metadata" "-C" "prefer-dynamic" "--out-dir" "/checkout/obj/build/x86_64-unknown-linux-gnu/test/ui/coherence/occurs-check/opaques.old" "-A" "unused" "-A" "internal_features" "-Crpath" "-Cdebuginfo=0" "-Lnative=/checkout/obj/build/x86_64-unknown-linux-gnu/native/rust-test-helpers" "-L" "/checkout/obj/build/x86_64-unknown-linux-gnu/test/ui/coherence/occurs-check/opaques.old/auxiliary"
--- stderr -------------------------------
error[E0284]: type annotations needed
##[error]  --> /checkout/tests/ui/coherence/occurs-check/opaques.rs:13:20
   |
   |
LL |     pub fn cast<T>(x: Container<Alias<T>, T>) -> Container<T, T> {
   |                    ^ cannot infer type
   |
   = note: cannot satisfy `<Alias<T> as Trait<T>>::Assoc == _`
note: required because it appears within the type `Container<Alias<T>, T>`
   |
   |
LL | struct Container<T: Trait<U>, U> {
   = help: unsized fn params are gated as an unstable feature
help: function arguments must have a statically known size, borrowed types always have a known size
   |
   |
LL |     pub fn cast<T>(x: &Container<Alias<T>, T>) -> Container<T, T> {

error: aborting due to 1 previous error

For more information about this error, try `rustc --explain E0284`.
---

16 LL + use Parser;
17    |
18 
- error[E0391]: cycle detected when computing type of opaque `recursive_fn::{opaque#0}`
-    |
-    |
- LL | pub fn recursive_fn<E>() -> impl Parser<E> {
-    |
-    |
- note: ...which requires type-checking `recursive_fn`...
-    |
-    |
- LL |     move || recursive_fn().parse()
-    |             ^^^^^^^^^^^^^^
-    = note: ...which requires evaluating trait selection obligation `recursive_fn::{opaque#0}: core::marker::Unpin`...
-    = note: ...which again requires computing type of opaque `recursive_fn::{opaque#0}`, completing the cycle
- note: cycle used when computing type of `recursive_fn::{opaque#0}`
-    |
-    |
- LL | pub fn recursive_fn<E>() -> impl Parser<E> {
-    |                             ^^^^^^^^^^^^^^
-    = note: see https://rustc-dev-guide.rust-lang.org/overview.html#queries and https://rustc-dev-guide.rust-lang.org/query.html for more information
38 
- error: aborting due to 3 previous errors
- 
- Some errors have detailed explanations: E0282, E0391, E0599.
---
Actual stderr saved to /checkout/obj/build/x86_64-unknown-linux-gnu/test/ui/impl-trait/recursive-bound-eval.current/recursive-bound-eval.current.stderr
To update references, rerun the tests and pass the `--bless` flag
To only update this specific test, also pass `--test-args impl-trait/recursive-bound-eval.rs`

error in revision `current`: 1 errors occurred comparing output.
status: exit status: 1
command: env -u RUSTC_LOG_COLOR RUSTC_ICE="0" RUST_BACKTRACE="short" "/checkout/obj/build/x86_64-unknown-linux-gnu/stage2/bin/rustc" "/checkout/tests/ui/impl-trait/recursive-bound-eval.rs" "-Zthreads=1" "-Zsimulate-remapped-rust-src-base=/rustc/FAKE_PREFIX" "-Ztranslate-remapped-path-to-local-path=no" "-Z" "ignore-directory-in-diagnostics-source-blocks=/cargo" "-Z" "ignore-directory-in-diagnostics-source-blocks=/checkout/vendor" "--sysroot" "/checkout/obj/build/x86_64-unknown-linux-gnu/stage2" "--target=x86_64-unknown-linux-gnu" "--cfg" "current" "--check-cfg" "cfg(FALSE,next,current)" "--error-format" "json" "--json" "future-incompat" "-Ccodegen-units=1" "-Zui-testing" "-Zdeduplicate-diagnostics=no" "-Zwrite-long-types-to-disk=no" "-Cstrip=debuginfo" "--emit" "metadata" "-C" "prefer-dynamic" "--out-dir" "/checkout/obj/build/x86_64-unknown-linux-gnu/test/ui/impl-trait/recursive-bound-eval.current" "-A" "unused" "-A" "internal_features" "-Crpath" "-Cdebuginfo=0" "-Lnative=/checkout/obj/build/x86_64-unknown-linux-gnu/native/rust-test-helpers" "-L" "/checkout/obj/build/x86_64-unknown-linux-gnu/test/ui/impl-trait/recursive-bound-eval.current/auxiliary"
--- stderr -------------------------------
error[E0282]: type annotations needed
##[error]  --> /checkout/tests/ui/impl-trait/recursive-bound-eval.rs:19:28
   |
   |
LL |     move || recursive_fn().parse()

error[E0599]: no method named `parse` found for opaque type `impl Parser<_>` in the current scope
##[error]  --> /checkout/tests/ui/impl-trait/recursive-bound-eval.rs:19:28
   |
   |
LL |     move || recursive_fn().parse()
   |                            ^^^^^ method not found in `impl Parser<_>`
   = help: items from traits can only be used if the trait is implemented and in scope
help: trait `Parser` which provides `parse` is implemented but not in scope; perhaps you want to import it
   |
LL + use Parser;

[bors]

☔ The latest upstream changes (presumably #125443) made this pull request unmergeable. Please resolve the merge conflicts.