Resolver crash

[erniecohen]

The following crashes for me in 3.5.0.40314:

type St = s:St_ | (forall o | o in s :: o.i(this))
type St_ = map<nat,Ob>
type Ob {
    predicate i(s:St_)
}

[robin-aws]

The exception this triggers:

Unhandled exception. System.AggregateException: One or more errors occurred. (Object reference not set to an instance of an object.)
 ---> System.NullReferenceException: Object reference not set to an instance of an object.
   at Microsoft.Dafny.Resolver.GetThisType(IToken tok, TopLevelDeclWithMembers cl) in /Users/salkeldr/Documents/GitHub/dafny/Source/Dafny/Resolver.cs:line 14514
   at Microsoft.Dafny.Resolver.ResolveExpression(Expression expr, ResolveOpts opts) in /Users/salkeldr/Documents/GitHub/dafny/Source/Dafny/Resolver.cs:line 14636
   at Microsoft.Dafny.Resolver.ResolveActualParameters(ActualBindings bindings, List`1 formals, IToken callTok, Object context, ResolveOpts opts, Dictionary`2 typeMap, Expression receiver) in /Users/salkeldr/Documents/GitHub/dafny/Source/Dafny/Resolver.cs:line 16871
   at Microsoft.Dafny.Resolver.ResolveApplySuffix(ApplySuffix e, ResolveOpts opts, Boolean allowMethodCall) in /Users/salkeldr/Documents/GitHub/dafny/Source/Dafny/Resolver.cs:line 16731
   at Microsoft.Dafny.Resolver.ResolveExpression(Expression expr, ResolveOpts opts) in /Users/salkeldr/Documents/GitHub/dafny/Source/Dafny/Resolver.cs:line 14716
   at Microsoft.Dafny.Resolver.ResolveExpression(Expression expr, ResolveOpts opts) in /Users/salkeldr/Documents/GitHub/dafny/Source/Dafny/Resolver.cs:line 15203
   at Microsoft.Dafny.Resolver.ResolveExpression(Expression expr, ResolveOpts opts) in /Users/salkeldr/Documents/GitHub/dafny/Source/Dafny/Resolver.cs:line 14582
   at Microsoft.Dafny.Resolver.ResolveTopLevelDecls_Core(List`1 declarations, Graph`1 datatypeDependencies, Graph`1 codatatypeDependencies, Boolean isAnExport) in /Users/salkeldr/Documents/GitHub/dafny/Source/Dafny/Resolver.cs:line 2703
   at Microsoft.Dafny.Resolver.ResolveModuleDefinition(ModuleDefinition m, ModuleSignature sig, Boolean isAnExport) in /Users/salkeldr/Documents/GitHub/dafny/Source/Dafny/Resolver.cs:line 1032
   at Microsoft.Dafny.Resolver.ResolveProgram(Program prog) in /Users/salkeldr/Documents/GitHub/dafny/Source/Dafny/Resolver.cs:line 507
   at Microsoft.Dafny.Main.Resolve(Program program, ErrorReporter reporter) in /Users/salkeldr/Documents/GitHub/dafny/Source/Dafny/DafnyMain.cs:line 162
   at Microsoft.Dafny.Main.ParseCheck(IList`1 files, String programName, ErrorReporter reporter, Program& program) in /Users/salkeldr/Documents/GitHub/dafny/Source/Dafny/DafnyMain.cs:line 113
   at Microsoft.Dafny.DafnyDriver.ProcessFiles(IList`1 dafnyFiles, ReadOnlyCollection`1 otherFileNames, ErrorReporter reporter, Boolean lookForSnapshots, String programId) in /Users/salkeldr/Documents/GitHub/dafny/Source/DafnyDriver/DafnyDriver.cs:line 249

Note the original example also has an explicit error: Scratch.dfy(1,42): Error: type int does not have a member i. This is because o in s is the same as o in s.Keys rather than o in s.Values, so o gets the type int rather than Ob. But fixing that doesn't change the crash so it doesn't seem relevant.