type parameter `V/#2` (V/2) out of range when substituting with MIR inlining enabled

[tmiasko]

env RUSTFLAGS=-Zmir-opt-level=2 cargo check -Zbuild-std --target x86_64-unknown-linux-gnu

Error output

error: internal compiler error: compiler/rustc_middle/src/ty/subst.rs:528:17: type parameter `V/#2` (V/2) out of range when substituting, substs=[fn() -> collections::btree::node::Root<K, V> {collections::btree::node::Root::<K, V>::new_leaf}, ()]

thread 'rustc' panicked at 'Box<Any>', /rustc/0da6d42f297642a60f2640ec313b879b376b9ad8/compiler/rustc_errors/src/lib.rs:891:9
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace

note: the compiler unexpectedly panicked. this is a bug.

note: we would appreciate a bug report: https://github.com/rust-lang/rust/issues/new?labels=C-bug%2C+I-ICE%2C+T-compiler&template=ice.md

note: rustc 1.49.0-nightly (0da6d42f2 2020-10-26) running on x86_64-unknown-linux-gnu

note: compiler flags: -Z force-unstable-if-unmarked -Z mir-opt-level=2 -C embed-bitcode=no -C debuginfo=2 --crate-type lib

note: some of the compiler flags provided by cargo are hidden

query stack during panic:
#0 [optimized_mir] optimizing MIR for `<collections::btree::map::BTreeMap<K, V> as core::clone::Clone>::clone::clone_subtree`
#1 [optimized_mir] optimizing MIR for `<collections::btree::map::BTreeMap<K, V> as core::clone::Clone>::clone`

Regressed in #68965, cc @eddyb.

[tmiasko]

Inlining now uses instance_mir instead of optimized_mir and attempts to inline things it didn't inline before, but as far as I can see some of those require a different treatment of substs, i.e., substs_for_mir_body.

pub struct D<A, B> {
    a: *mut Option<A>,
    b: *mut Vec<B>,
}

impl<A, B> Drop for D<A, B> {
    fn drop(&mut self) {
        unsafe {
            std::ptr::drop_in_place(self.a);
            std::ptr::drop_in_place(self.b);
        }
    }
}

$ rustc --crate-type=lib -Zmir-opt-level=2 a.rs
error: internal compiler error: compiler/rustc_middle/src/ty/subst.rs:528:17: type parameter `B/#1` (B/1) out of range when substituting, substs=[std::vec::Vec<B>]
...
query stack during panic:
#0 [optimized_mir] optimizing MIR for `<D<A, B> as std::ops::Drop>::drop`

[chengniansun]

Not sure whether the following is a duplicate to this bug. If not I will file another one.

trait CollectionFamily {
    type Member<T>;
}
fn floatify() {
    Family as CollectionFamily
}

error[E0425]: cannot find value `Family` in this scope
 --> reduced_mutant.rs:5:5
  |
5 |     Family as CollectionFamily
  |     ^^^^^^ not found in this scope

error[E0658]: generic associated types are unstable
 --> reduced_mutant.rs:2:5
  |
2 |     type Member<T>;
  |     ^^^^^^^^^^^^^^^
  |
  = note: see issue #44265 <https://github.com/rust-lang/rust/issues/44265> for more information
  = help: add `#![feature(generic_associated_types)]` to the crate attributes to enable

warning: trait objects without an explicit `dyn` are deprecated
 --> reduced_mutant.rs:5:15
  |
5 |     Family as CollectionFamily
  |               ^^^^^^^^^^^^^^^^ help: use `dyn`: `dyn CollectionFamily`
  |
  = note: `#[warn(bare_trait_objects)]` on by default

error[E0601]: `main` function not found in crate `reduced_mutant`
 --> reduced_mutant.rs:1:1
  |
1 | / trait CollectionFamily {
2 | |     type Member<T>;
3 | | }
4 | | fn floatify() {
5 | |     Family as CollectionFamily
6 | | }
  | |_^ consider adding a `main` function to `reduced_mutant.rs`

error[E0191]: the value of the associated type `Member` (from trait `CollectionFamily`) must be specified
 --> reduced_mutant.rs:5:15
  |
2 |     type Member<T>;
  |     --------------- `Member` defined here
...
5 |     Family as CollectionFamily
  |               ^^^^^^^^^^^^^^^^ help: specify the associated type: `CollectionFamily<Member = Type>`

error: internal compiler error: compiler/rustc_middle/src/ty/subst.rs:529:17: type parameter `T/#1` (T/1) out of range when substituting, substs=[Self]

thread 'rustc' panicked at 'Box<Any>', /rustc/4f7612ac1499258025077f1fd05d2f429f9accfb/compiler/rustc_errors/src/lib.rs:888:9
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace

note: the compiler unexpectedly panicked. this is a bug.

note: we would appreciate a bug report: https://github.com/rust-lang/rust/issues/new?labels=C-bug%2C+I-ICE%2C+T-compiler&template=ice.md

note: rustc 1.49.0-nightly (4f7612ac1 2020-10-31) running on x86_64-unknown-linux-gnu

query stack during panic:
#0 [object_safety_violations] determine object safety of trait `CollectionFamily`
#1 [typeck] type-checking `floatify`
end of query stack
error: aborting due to 5 previous errors; 1 warning emitted

Some errors have detailed explanations: E0191, E0425, E0601, E0658.
For more information about an error, try `rustc --explain E0191`.

NOTE: The bug is found by our work-in-progress compiler testing tool Kira, and the test program is reduced/minimized by Perses

[tmiasko]

@chengniansun that would be a different issue.