Compiler crash with circular reference, redundant conformance requirements

[karwa]

Description

No response

Reproduction

public protocol P: P.T {
    typealias T = X
}
public protocol X {}

Stack dump

<source>:1:22: error: circular reference
1 │ public protocol P: P.T {
  │                 │    ╰─ error: circular reference
  │                 ├─ note: protocol 'P' declared here
  │                 ╰─ note: through reference here
2 │     typealias T = X
3 │ }

<source>:1:22: error: circular reference
1 │ public protocol P: P.T {
  │                 │    ╰─ error: circular reference
  │                 ├─ note: through reference here
  │                 ╰─ note: through reference here
2 │     typealias T = X
3 │ }

Redundant conformance requirements in signature <Self where Self : P>:
Ours:
- Copyable
- Escapable
- X
Theirs:
- X
All requirements:
(requirement "Self" conforms_to "Copyable")
(requirement "Self" conforms_to "Escapable")
(requirement "Self" conforms_to "X")
Requirement machine for <τ_0_0 where τ_0_0 : P>
Rewrite system: {
- [P].[P] => [P] [permanent]
- [P].[X] => [P] [explicit]
- [P].T.[concrete: X] => [P].T [explicit]
- [P].[Copyable] => [P] [explicit]
- [P].[Escapable] => [P] [explicit]
- [X].[X] => [X] [permanent]
- [X].[Copyable] => [X] [explicit]
- [X].[Escapable] => [X] [explicit]
- [Copyable].[Copyable] => [Copyable] [permanent]
- [Escapable].[Escapable] => [Escapable] [permanent]
- τ_0_0.[P] => τ_0_0 [explicit]
- τ_0_0.[X] => τ_0_0
- τ_0_0.T.[concrete: X] => τ_0_0.T
- τ_0_0.[Copyable] => τ_0_0
- τ_0_0.[Escapable] => τ_0_0
}
Property map: {
  [P] => { conforms_to: [P X Copyable Escapable] }
  [X] => { conforms_to: [X Copyable Escapable] }
  [Copyable] => { conforms_to: [Copyable] }
  [Escapable] => { conforms_to: [Escapable] }
  τ_0_0 => { conforms_to: [P X Copyable Escapable] }
  [P].T => { concrete_type: [concrete: X] }
  τ_0_0.T => { concrete_type: [concrete: X] }
}
Conformance paths: {
}
Please submit a bug report (https://swift.org/contributing/#reporting-bugs) and include the crash backtrace.
Stack dump:
0.	Program arguments: /opt/compiler-explorer/swift-nightly/usr/bin/swift-frontend -frontend -S -primary-file <source> -target x86_64-unknown-linux-gnu -disable-objc-interop -g -debug-info-format=dwarf -dwarf-version=4 -empty-abi-descriptor -resource-dir /opt/compiler-explorer/swift-nightly/usr/lib/swift -enable-anonymous-context-mangled-names -file-compilation-dir /app -Xllvm --x86-asm-syntax=intel -module-name output -plugin-path /opt/compiler-explorer/swift-nightly/usr/lib/swift/host/plugins -plugin-path /opt/compiler-explorer/swift-nightly/usr/local/lib/swift/host/plugins -o /app/output.s
1.	Swift version 6.0-dev (LLVM 87789f04c6598f1, Swift 52e8fbc115ca18f)
2.	Compiling with effective version 5.10
3.	While evaluating request TypeCheckSourceFileRequest(source_file "<source>")
4.	While type-checking 'P' (at <source>:1:8)
5.	While checking generic signature <τ_0_0 where τ_0_0 : P>
Stack dump without symbol names (ensure you have llvm-symbolizer in your PATH or set the environment var `LLVM_SYMBOLIZER_PATH` to point to it):
0  swift-frontend 0x000055dda016e357
1  swift-frontend 0x000055dda016c05e
2  swift-frontend 0x000055dda016e9cf
3  libc.so.6      0x00007fc83e442520
4  libc.so.6      0x00007fc83e4969fc pthread_kill + 300
5  libc.so.6      0x00007fc83e442476 raise + 22
6  libc.so.6      0x00007fc83e4287f3 abort + 211
7  swift-frontend 0x000055dd9b16d343
8  swift-frontend 0x000055dd9b16d288
9  swift-frontend 0x000055dd9aa3d0d8
10 swift-frontend 0x000055dd9aa3a194
11 swift-frontend 0x000055dd9ab33598
12 swift-frontend 0x000055dd9ab35d37
13 swift-frontend 0x000055dd9ab334b5
14 swift-frontend 0x000055dd997ddd79
15 swift-frontend 0x000055dd997d582a
16 swift-frontend 0x000055dd997d57c7
17 swift-frontend 0x000055dd994c4d8e
18 swift-frontend 0x000055dd994b1e85
19 swift-frontend 0x000055dd994b01e3
20 swift-frontend 0x000055dd9926fe64
21 libc.so.6      0x00007fc83e429d90
22 libc.so.6      0x00007fc83e429e40 __libc_start_main + 128
23 swift-frontend 0x000055dd9926ed0e

*** Signal 11: Backtracing from 0x7fc83e428898... done ***

*** Program crashed: Bad pointer dereference at 0x0000000000000000 ***

Thread 0 "swift-frontend" crashed:

0  0x00007fc83e428898 <unknown> in libc.so.6


Registers:

rax 0x0000000000000000  0
rdx 0x00007fc83eae5880  80 58 ae 3e c8 7f 00 00 a0 62 ae 3e c8 7f 00 00  ·X®>È··· b®>È···
rcx 0x00007fc83e4969fc  41 89 c5 41 f7 dd 3d 00 f0 ff ff b8 00 00 00 00  A·ÅA÷Ý=·ðÿÿ¸····
rbx 0x0000000000000006  6
rsi 0x0000000000000001  1
rdi 0x0000000000000001  1
rbp 0x00007fc83e61be90  01 00 00 00 01 00 00 00 80 58 ae 3e c8 7f 00 00  ·········X®>È···
rsp 0x00007ffd23821910  20 00 00 00 00 00 00 00 d4 48 51 3e c8 7f 00 00   ·······ÔHQ>È···
 r8 0x0000000000000000  0
 r9 0x0000000000000000  0
r10 0x0000000000000008  8
r11 0x0000000000000246  582
r12 0x00007ffd23821a58  a0 ad 5e a6 dd 55 00 00 50 a1 62 a6 dd 55 00 00   ­^¦ÝU··P¡b¦ÝU··
r13 0x0000000000000030  48
r14 0x000055dda160f145  0a 00 65 72 72 6f 72 3a 20 75 6e 6b 6e 6f 77 6e  ··error: unknown
r15 0x00007ffd23821dd8  10 a1 62 a6 dd 55 00 00 02 00 00 00 05 00 00 00  ·¡b¦ÝU··········
rip 0x00007fc83e428898  f4 83 3d 00 36 1f 00 05 75 14 c7 05 f4 35 1f 00  ô·=·6···u·Ç·ô5··

rflags 0x0000000000010246  ZF PF

cs 0x0033  fs 0x0000  gs 0x0000


Images (27 omitted):

0x00007fc83e400000–0x00007fc83e5bc341 c289da5071a3399de893d2af81d6a30c62646e1e libc.so.6 /lib/x86_64-linux-gnu/libc.so.6

Backtrace took 0.01s

Program terminated with signal: SIGSEGV
Compiler returned: 139

Expected behavior

Not really sure, to be honest. Previous versions of the compiler report a circular reference:

<source>:1:22: error: circular reference
public protocol P: P.T {
                     ^
<source>:1:17: note: protocol 'P' declared here
public protocol P: P.T {
                ^
<source>:1:17: note: through reference here
public protocol P: P.T {
                ^
<source>:1:22: error: circular reference
public protocol P: P.T {
                     ^
<source>:1:17: note: through reference here
public protocol P: P.T {
                ^
<source>:1:17: note: through reference here
public protocol P: P.T {
                ^
<source>:1:17: warning: protocol 'P' should be declared to refine 'X' due to a same-type constraint on 'Self'
public protocol P: P.T {

But is it really a circular reference? I'm not so sure.

Environment

Swift version 6.0-dev (LLVM 87789f04c6598f1, Swift 52e8fbc)
Target: x86_64-unknown-linux-gnu

Additional information

Godbolt