[SR-13148] Add special-case diagnostic when detecting request for Comparable synthesis for structs

[typesanitizer]

Previous ID	SR-13148
Radar	rdar://problem/65116465
Original Reporter	@typesanitizer
Type	Improvement
Status	Closed
Resolution	Done

Additional Detail from JIRA

Votes	0
Component/s	Compiler
Labels	Improvement, DiagnosticsQoI, TypeChecker
Assignee	@theblixguy
Priority	Medium

md5: 4bb991b5e9e2dccaaee344947a743120

Issue Description:

struct S : Comparable { // error: type 'S' does not conform to protocol 'Comparable'
  var x: Int
} 

Maybe it should look something like (straw-man suggestion):

synthesizing Comparable conformances is not supported for structs

Bit of a tangent but... this limitation is just plain weird, given that we support Comparable derivation for enums with associated fields:

enum E : Comparable {
  case e(Int, Int) // Just Works
} 

Should one use single-case enums instead of structgs to get the sweet, sweet conformance synthesis? �

[typesanitizer]

@swift-ci create

[theblixguy]

#32797

[theblixguy]

Fixed on master. theindigamer (JIRA User) please verify using the next available snapshot

[typesanitizer]

Confirming that this has been fixed on master. Cheers!