DebuggerDisplay: six rendering defects

[hexbinoct]

Built from source at 293d77f (0.1.17), net10.0, Windows x64, compared against netcoredbg 3.2.0-1092.

SharpDbg is the only one of the two that honours [DebuggerDisplay] at all, so all of this is ahead of netcoredbg, which renders {Ns.Type} for every annotated type. Six things in the rendering look wrong. Separate fixes, but one attribute, so one issue.

Types, one local of each:

[DebuggerDisplay("{Amount} {Currency,nq}")]
sealed class Money { public decimal Amount; public string Currency; }        // 12.5m, "USD"

[DebuggerDisplay("{Amount} {Currency}")]
sealed class QuotedMoney { public decimal Amount; public string Currency; }  // same values

[DebuggerDisplay("\\{{Value}\\}")]
sealed class Braced { public int Value = 3; }

[DebuggerDisplay("{NoSuchMember}")]
sealed class Missing { public int Value = 2; }

[DebuggerDisplay("{_name,nq} -> {Next._name,nq}")]
sealed class Link { string _name; public Link? Next; }                       // "head" -> "tail", tail.Next is null

[DebuggerDisplay("{Value}", Name = "renamed", Type = "RetypedThing")]
sealed class Labelled { public int Value = 11; }

[DebuggerDisplay("base {Tag,nq}")]
class Base { public string Tag = "b"; }
sealed class Derived : Base { public int Extra = 9; }                        // declares no display of its own

local	SharpDbg	expected
money	12.5 USD	12.5 USD
quoted	12.5 USD	12.5 "USD"
braced	error: A '{' character may only be escaped by doubling	{3}
missing	error: The name 'NoSuchMember' does not exist...	value keeps the parts that resolved
link head	head -> tail	head -> tail
link tail	error: CIL execution failed ... NullReferenceException	tail -> <error> in that fragment only
labelled	renamed = 11	value 11, name column renamed, type column RetypedThing
derived	{Display.Derived}	base b

1. A string fragment is never quoted. money and quoted render identically, so ,nq is a no-op and a quoted string cannot be asked for. ,nq means "no quotes", which implies quotes are the default.

2. \{ and \} are not implemented. These are the documented escape for a literal brace. It looks like the display string is compiled as a C# interpolated string, so the backslash fails the whole value. {{ and }} are the interpolated-string escape, not the DebuggerDisplay one.

3. A fragment that cannot be resolved replaces the whole value. Name={Name} Bad={Nope} loses the half that worked. The error belongs in that fragment's place.

4. A null anywhere on a fragment's member path throws out of the IL interpreter. tail has Next == null, and the whole display becomes a NullReferenceException text. The head of the same list renders fine. A linked structure whose last node has a null link is ordinary, and the same fix as 3 covers it: put the error in the fragment, keep the rest.

5. Name = is folded into the value and Type = is dropped. labelled renders as renamed = 11. Both name columns rather than the value: Name names the variable, Type the type column, and neither belongs in the value text.

6. Attribute inheritance is not honoured, though DebuggerDisplayAttribute is Inherited = true. Derived declares no display and should get base b from Base. This one is only visible if you compare implementations, since a debugger that has no DebuggerDisplay at all produces the same output for it.

Happy to test a branch against these if useful, I have all eight shapes as locals in one program.