internal error: function call on datatype with updated member

[erniecohen]

Dafny version

nightly (4.6, 4/25)

Code to produce this issue

datatype S  = S(
    n:nat
) {
    function f():S { this }
    function g():S { this.(n := 0).f() }
}

Command to run and resulting output

vscode

What happened?

Dafny encountered an internal error. Please report it at https://github.com/dafny-lang/dafny/issues.
System.NullReferenceException: Object reference not set to an instance of an object.
at Microsoft.Dafny.ExpressionTester.CheckIsCompilable(Expression expr, ICodeContext codeContext, Boolean insideBranchesOnly)
at Microsoft.Dafny.ExpressionTester.CheckIsCompilable(Expression expr, ICodeContext codeContext, Boolean insideBranchesOnly)
at Microsoft.Dafny.ModuleResolver.ResolveClassMembers_Pass1(TopLevelDeclWithMembers cl)
at Microsoft.Dafny.ModuleResolver.ResolveTopLevelDecls_Core(List1 declarations, Graph1 datatypeDependencies, Graph1 codatatypeDependencies, String moduleDescription, Boolean isAnExport) at Microsoft.Dafny.ModuleDefinition.Resolve(ModuleSignature sig, ModuleResolver resolver, String exportSetName) at Microsoft.Dafny.LiteralModuleDecl.Resolve(ModuleResolver resolver, CompilationData compilation) at Microsoft.Dafny.ModuleResolver.ResolveModuleDeclaration(CompilationData compilation, ModuleDecl decl) at Microsoft.Dafny.ProgramResolver.ResolveModuleDeclaration(CompilationData compilation, ModuleDecl decl) at Microsoft.Dafny.LanguageServer.Language.CachingResolver.ResolveModuleDeclaration(CompilationData compilation, ModuleDecl decl) at Microsoft.Dafny.ProgramResolver.Resolve(CancellationToken cancellationToken) at Microsoft.Dafny.LanguageServer.Language.CachingResolver.<>n__0(CancellationToken cancellationToken) at Microsoft.Dafny.LanguageServer.Language.CachingResolver.<>c__DisplayClass5_0.<Resolve>b__0() at Microsoft.Dafny.LanguageServer.Language.CacheExtensions.ProfileAndPruneCache[T,Key,Value](PruneIfNotUsedSinceLastPruneCache2 cache, Func`1 useCache, TelemetryPublisherBase telemetryPublisher, String programName, String activity)
at Microsoft.Dafny.LanguageServer.Language.CachingResolver.Resolve(CancellationToken cancellationToken)
at Microsoft.Dafny.LanguageServer.Language.Symbols.DafnyLangSymbolResolver.RunDafnyResolver(Compilation compilation, Program program, CancellationToken cancellationToken)
at Microsoft.Dafny.LanguageServer.Language.Symbols.DafnyLangSymbolResolver.ResolveSymbols(Compilation compilation, Program program, CancellationToken cancellationToken)
at Microsoft.Dafny.TextDocumentLoader.ResolveInternal(Compilation compilation, Program program, CancellationToken cancellationToken)
at Microsoft.Dafny.TextDocumentLoader.<>c__DisplayClass5_0.<b__0>d.MoveNext()
--- End of stack trace from previous location ---
at Microsoft.Dafny.TextDocumentLoader.ResolveAsync(Compilation compilation, Program program, CancellationToken cancellationToken)
at Microsoft.Dafny.Compilation.ResolveAsync()

What type of operating system are you experiencing the problem on?

Mac