[SR-10562] Imported NS_ERROR_ENUM errors have weird "related decl" description

[lilyball]

Previous ID	SR-10562
Radar	None
Original Reporter	@lilyball
Type	Bug

Environment

Apple Swift version 5.0.1 (swiftlang-1001.0.82.4 clang-1001.0.46.5)
Target: x86_64-apple-darwin18.5.0

Additional Detail from JIRA

Votes	0
Component/s	Compiler
Labels	Bug, Runtime
Assignee	None
Priority	Medium

md5: e29b89b358725c5ca7df0cc90a76c495

Issue Description:

When printing an error created from an Obj-C NS_ERROR_ENUM declaration, the imported error has a bizarre synthesized description that looks like "related decl 'e' for <desc>" (where <desc> is the actual expected description).

For example, with the following Obj-C header:

extern NSErrorDomain const FooErrorDomain;
typedef NS_ERROR_ENUM(FooErrorDomain, FooError) {
    FooErrorOne = 1,
    FooErrorTwo
};

Printing a FooError(.one) from Swift produces the description

related decl 'e' for FooError(_nsError: Error Domain=FooErrorDomain Code=1 "(null)")

And the debug description looks like

__C_Synthesized.related decl 'e' for FooError(_nsError: Error Domain=FooErrorDomain Code=1 "(null)")

[lilyball]

Similar output is obtained by printing FooError.self.

[belkadan]

Yeah, I'm not sure what to do about this one. "FooError" is officially the C enum, not the wrapper struct, but maybe that doesn't matter when doing a demangling that doesn't have to be unique.

[belkadan]

@mikeash, any opinions? (Or Lily, for that matter.) I wrote the original code here but only to fit imported errors into the existing demangling framework, not because I was finessing the output to some spec.

[mikeash]

Seems like it would be pretty decent by just removing the "related decl 'e' for " part.

[lilyball]

Yeah, I'm not thrilled at the _nsError: output but it's at least understandable and clearly a field of the type. The "related decl 'e' for" is just confusing, and if it were removed but everything else left as-is that would be fine (and would match how e.g. CocoaError is printed).

Though I'd also suggest that the __C_Synthesized. prefix on the debug description should go away as well.