Get rid of check_opaque_type_well_formed

[compiler-errors]

Instead, replicate it by improving the span of the opaque in check_opaque_meets_bounds.

This has two consequences:

1. We now prefer "concrete type differs" errors, since we'll hit those first before we check the opaque is WF.
2. Spans have gotten slightly worse.

Specifically, (2.) could be improved by adding a new obligation cause that explains that the definition's environment has stronger assumptions than the declaration.

r? lcnr

[compiler-errors]

This is as bad as outlives errors we get within a defining scope, like:

fn foo<'a, T>(t: T) -> impl Sized + 'a { t }

error[E0309]: the parameter type `T` may not live long enough
 --> src/lib.rs:1:42
  |
1 | fn foo<'a, T>(t: T) -> impl Sized + 'a { t }
  |        --                                ^ ...so that the type `T` will meet its required lifetime bounds
  |        |
  |        the parameter type `T` must be valid for the lifetime `'a` as defined here...

[lcnr]

can we also emit the "this definition site has more where clauses than the opaque type" note for region errors, I feel like it's even more useful there

[compiler-errors]

really annoying to do that given the way that region error reporting is handled with a totally different error path :/

[compiler-errors]

This is kinda annoyingly duplicated w/ the TAIT visitor, but also I could not find a way to genericize that without making it a mess, since it has a lot of responsibilities.

[lcnr]

cc @oli-obk

r=me after suggestion

[oli-obk]

I remember we added the duplicate check in borrowck because the wf check failed to handle lifetimes in all cases.

[compiler-errors]

@oli-obk: #96736 does not seem to suggest that this extra well-formedness check is necessary for correctness, and instead is used for improving diagnostics.

I remember we added the duplicate check in borrowck because the wf check failed to handle lifetimes in all cases.

We don't even check lifetimes in the borrowck copy of the well-formedness check, so I'm not totally sure what you mean.... As far as I can tell, the checks in check_opaque_meets_bounds are a strict subset of what we're checking in check_opaque_type_well_formed.

[oli-obk]

Ah, I misremembered. Thanks for investigating.

[compiler-errors]

I spent an hour on this and could not get the lifetime error reporting machinery to work correctly, so I won't do anything else to this PR.

@bors r=lcnr

[bors]

📌 Commit 97dfe8b has been approved by lcnr

It is now in the queue for this repository.

[bors]

⌛ Testing commit 97dfe8b with merge 2a120f8...

[rust-log-analyzer]

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

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

---- [run-make] tests\run-make\avr-rjmp-offset stdout ----

error: rmake recipe failed to complete
status: exit code: 1
command: "C:\\a\\rust\\rust\\build\\x86_64-pc-windows-gnu\\test\\run-make\\avr-rjmp-offset\\rmake.exe"
--- stderr -------------------------------
command failed at line 29
command failed at line 29
Command { cmd: "C:\\a\\rust\\rust\\build\\x86_64-pc-windows-gnu\\stage2\\bin\\rustc.exe" "-L" "C:\\a\\rust\\rust\\build\\x86_64-pc-windows-gnu\\test\\run-make\\avr-rjmp-offset\\rmake_out" "avr-rjmp-offsets.rs" "-Copt-level=s" "-Cpanic=abort" "--target=avr-unknown-gnu-atmega328" "-Clinker=rust-lld" "-Clink-arg=--entry=main" "-o" "compiled", stdin_buf: None, stdin: None, stdout: None, stderr: None, drop_bomb: DropBomb { command: "C:\\a\\rust\\rust\\build\\x86_64-pc-windows-gnu\\stage2\\bin\\rustc.exe", defused: true, armed_location: Location { file: "C:\\a\\rust\\rust\\tests\\run-make\\avr-rjmp-offset\\rmake.rs", line: 16, col: 5 } }, already_executed: true }
output status: `exit code: 1`
=== STDOUT ===


=== STDERR ===
error: linking with `rust-lld` failed: exit code: 0xc0000005
error: linking with `rust-lld` failed: exit code: 0xc0000005
  |
  = note: "rust-lld" "-flavor" "gnu" "C:\\a\\_temp\\msys64\\tmp\\rustcHzwA2Q\\symbols.o" "compiled.avr_rjmp_offsets.ab053966543a1f9f-cgu.0.rcgu.o" "--as-needed" "-Bdynamic" "-z" "noexecstack" "-L" "C:\\a\\rust\\rust\\build\\x86_64-pc-windows-gnu\\test\\run-make\\avr-rjmp-offset\\rmake_out" "-o" "compiled" "--gc-sections" "--entry=main"
  = note: PLEASE submit a bug report to https://github.com/llvm/llvm-project/issues/ and include the crash backtrace.␍
          Stack dump:␍
          0.    Program arguments: rust-lld -flavor gnu C:\\a\\_temp\\msys64\\tmp\\rustcHzwA2Q\\symbols.o compiled.avr_rjmp_offsets.ab053966543a1f9f-cgu.0.rcgu.o --as-needed -Bdynamic -z noexecstack -L C:\\a\\rust\\rust\\build\\x86_64-pc-windows-gnu\\test\\run-make\\avr-rjmp-offset\\rmake_out -o compiled --gc-sections --entry=main␍
          Exception Code: 0xC0000005␍
          0x00007FFB23E97A05, C:\Windows\SYSTEM32\ntdll.dll(0x00007FFB23E80000) + 0x17A05 byte(s), RtlEnterCriticalSection() + 0x585 byte(s)␍
          0x00007FFB23E9B550, C:\Windows\SYSTEM32\ntdll.dll(0x00007FFB23E80000) + 0x1B550 byte(s), RtlGetCurrentServiceSessionId() + 0xBF0 byte(s)␍
          0x00007FFB23E9A8C1, C:\Windows\SYSTEM32\ntdll.dll(0x00007FFB23E80000) + 0x1A8C1 byte(s), RtlFreeHeap() + 0x51 byte(s)␍
          0x00007FFB2299C69C, C:\Windows\System32\msvcrt.dll(0x00007FFB22980000) + 0x1C69C byte(s), free() + 0x1C byte(s)␍
          0x00007FFB2299BD46, C:\Windows\System32\msvcrt.dll(0x00007FFB22980000) + 0x1BD46 byte(s), _aligned_free() + 0x16 byte(s)␍
          0x00007FF737072F1A, C:\a\rust\rust\build\x86_64-pc-windows-gnu\stage2\lib\rustlib\x86_64-pc-windows-gnu\bin\rust-lld.exe(0x00007FF732D30000) + 0x4342F1A byte(s)
error: aborting due to 1 previous error
------------------------------------------

[bors]

💔 Test failed - checks-actions

[compiler-errors]

lol that definitely has nothing to do with opaques

@bors retry