How to unit test VBA code?

So Rubberduck lets you write unit tests for your VBA code. If you’re learning VBA, or if you’re a seasoned VBA developer but have never written a unit test before, this can sound like a crazy useless idea. I know, because before I started working on Rubberduck, that’s how I was seeing unit tests: annoying, redundant code that tells you nothing F5/debugging doesn’t already tell you.

Right? What’s the point anyway?

First, it changes how you think about code. Things like the Single Responsibility Principle start becoming freakishly important, and you begin to break that monolithic macro procedure into smaller, more focused chunks. Future you, or whoever inherits your code, will be extremely thankful for that.

But not all VBA code should be unit-tested. Let’s see why.

Know what NOT to test

All code has dependencies. Some of these dependencies we can’t really do without, and don’t really affect anything – global-scope functions in the VBA Standard Library, for example. Other dependencies affect global state, require user input (MsgBox, InputBox, forms, dialogs, etc.) or access external resources – like a database, the file system, …or a worksheet.

For the sake of this article, say you have a simple procedure like this:

Public Sub DoSomething()
    Dim conn As ADODB.Connection
    Set conn = New ADODB.Connection
    conn.ConnectionString = "{connection string}"
    Dim rs As ADODB.Recordset
    Set rs = conn.Execute("SELECT * FROM dbo.SomeTable")
    Sheet1.Range("A1").CopyFromRecordset rs
End Sub

The problematic dependencies are:

  • conn, an ADODB connection
  • rs, an ADODB recordset
  • Sheet1, an Excel worksheet

Is that procedure doomed and completely untestable? Well, as is, …pretty much: the only way to write a test for this procedure would be to actually run it, and verify that something was dumped into Sheet1. In fact, that’s pretty much automating F5-debug: it’s an integration test, not a unit test – it’s a test, but it’s validating that all components work together. It’s not useless, but that’s not a unit test.


The procedure needs to be parameterless, because it’s invoked from some button: so we have a major problem here – there’s no way to factor out the dependencies!

Or is there? What if we introduced a class, and moved the functionality into there?

Now we’d be looking at this:

Public Sub DoSomething()
    With New MyTestableMacro
    End With
End Sub

At this point we tremendously increased the macro’s abstraction level and that’s awesome, but we didn’t really gain anything. Or did we? Now that we’ve decoupled the macro’s entry point from the implementation, we can pull out the dependencies and unit-test the MyTestableMacro class! But how do we do that?

Think in terms of concerns:

  • Pulling data from a database
  • Writing the data to a worksheet

Now think in terms of objects:

  • We need some data service responsible for pulling data from a database
  • We need some spreadsheet service responsible for writing data to a worksheet

The macro might look like this now:

Public Sub DoSomething()

    Dim dataService As MyDbDataService
    Set dataService = New MyDbDataService

    Dim spreadsheetService As Sheet1Service
    Set spreadsheetService = New Sheet1Service

    With New MyTestableMacro
        .Run dataService, spreadsheetService
    End With

End Sub

Now if we think of MyDbDataService as an interface, we could conceptualize it like this:

Option Explicit
'@Folder "Services.Abstract"
'@Interface IDataService

Public Function GetSomeTable() As Variant
End Function

And if we think of Sheet1Service as an interface, we could conceptualize it like this:

Option Explicit
'@Folder "Services.Abstract"
'@Interface IWorksheetService

Public Sub WriteAllData(ByRef data As Variant)
End Sub

Notice the interfaces don’t know or care about ADODB.Recordset: the last thing we want is to have that dependency in our way, so we’ll be passing a Variant array around instead of a recordset.

Now the Run method’s signature might look like this:

Public Sub Run(ByVal dataService As IDataService, ByVal wsService As IWorksheetService)

Notice it only knows about abstractions, not the concrete implementations. All that’s missing is to make MyDbDataService implement the IDataService interface, and Sheet1Service implement the IWorksheetService interface.

Option Explicit
Implements IDataService
'@Folder "Services.Concrete"

Private Function IDataService_GetSomeTable() As Variant
    Dim conn As ADODB.Connection
    Set conn = New ADODB.Connection
    conn.ConnectionString = "{connection string}"
    Dim rs As ADODB.Recordset
    Set rs = conn.Execute("SELECT * FROM dbo.SomeTable")
    'dump the recordset onto a temp sheet:
    Dim tempSheet As Excel.Worksheet
    Set tempSheet = ThisWorkbook.Worksheets.Add
    tempSheet.Range("A1").CopyFromRecordset rs
    IDataService_GetSomeTable = tempSheet.UsedRange.Value '2D variant array
End Function

Stubbing the interfaces

So here’s where the magic begins: the macro will definitely be using the above implementation, but nothing forces a unit test to use it too. A unit test would be happy to use something like this:

Option Explicit
Implements IDataService
'@Folder "Services.Stubs"

Private Function IDataService_GetSomeTable() As Variant
    Dim result(1 To 50, 1 To 10) As Variant
    IDataService_GetSomeTable = result
End Function

Public Function GetSomeTable() As Variant
    GetSomeTable = IDataService_GetSomeTable
End Function

You could populate the array with some fake results, expose properties and methods to configure the stub in every way your tests require (depending on what logic needs to run against the data after it’s dumped onto the worksheet) – for this example though all we need is for the method to return a 2D variant array, and the above code satisfies that.

Then we need a stub for the IWorksheetService interface, too:

Option Explicit
Implements IWorksheetService
'@Folder "Services.Stubs"

Private written As Boolean
Private arrayPointer As Long

Private Sub IWorksheetService_WriteAllData(ByRef data As Variant)
    written = True
    arrayPointer = VarPtr(data)
End Function

Public Property Get DataWasWritten() As Boolean
    DataWasWritten = written
End Property

Public Property Get WrittenArrayPointer() As Long
    WrittenArrayPointer = arrayPointer
End Property

Writing the tests

That’s all our test needs for now. See where this is going? DoSomething is using concrete implementations of the service interfaces that actually do the work, and a unit test can look like this:

Public Sub GivenData_WritesToWorksheet()
    Dim dataServiceStub As MyDataServiceStub
    Set dataServiceStub = New MyDataServiceStub
    Dim wsServiceStub As MyWorksheetServiceStub
    Set wsServiceStub = New MyWorksheetServiceStub

    With New MyTestableMacro
        .Run dataServiceStub, wsServiceStub
    End With

    Assert.IsTrue wsServiceStub.DataWasWritten
End Sub

If MyTestableMacro.Run invokes IWorksheetService.WriteAllData, this test will pass.

One more:

Public Sub WorksheetServiceWorksOffDataFromDataService()
    Dim dataServiceStub As MyDataServiceStub
    Set dataServiceStub = New MyDataServiceStub
    Dim expected As Long
    expected = VarPtr(dataServiceStub.GetSomeTable)

    Dim wsServiceStub As MyWorksheetServiceStub
    Set wsServiceStub = New MyWorksheetServiceStub

    With New MyTestableMacro
        .Run dataServiceStub, wsServiceStub
    End With

    Dim actual As Long
    actual = wsServiceStub.WrittenArrayPointer

    Assert.AreEqual expected, actual
End Sub

If the worksheet service receives the exact same array that the data service returned, this test should pass.

That was a relatively trivial example – the overhead (5 classes, including 2 interfaces and 2 stub implementations) is probably not justified given the simplicity of the task at hand (pull data from a database, dump that data to a worksheet). But hopefully it illustrates a number of things:

  • How to pull dependencies out of the logic that needs to be tested.
  • How to abstract the dependencies as interfaces.
  • How to implement test stubs for these dependencies, and how stubs can expose members that aren’t on the interface, for the tests to consume.
  • How unit tests document what the code is supposed to be doing, through descriptive naming.
  • VBA code can be just as object-oriented as any other code, with full-blown polymorphism and dependency injection.

Next tutorial should be about MSForms.UserForm, how not to use it, and how to test code that needs to pop a dialog. I didn’t mention anything about Rubberduck’s Fakes framework here either, but know that if one of your dependencies is a MsgBox and you have different code paths depending on whether the user clicked [Ok] or [Cancel], you can use Rubberduck’s Fakes API to literally configure how the MsgBox statement is going to behave when it’s invoked by a Rubberduck test.


Rubberduck 2.1.x

The release was going to include a number of important fixes for the missing annotation/attribute inspection and quick-fix, but instead we disabled it, along with a few other buggy inspections, and pushed the release – 7 months after 2.0.13, the last release was now over 1,300 commits behind, and we were reaching a point where we knew a “green release” was imminent, but also a point where we were going to have to make some more changes to parts of the core – notably in order to implement the fixes for these broken annotation/attribute inspections.

So we shipped what we had, because we wouldn’t jeopardize the 2.1 release with parser logic changes at that point.


By Hillebrand Steve, U.S. Fish and Wildlife Service [Public domain], via Wikimedia Commons
So here we are, at the crossroads: with v2.1.0 released, things are going to snowball – there’s a lot on our plates, but we now have a solid base to build upon. Here’s what’s coming:

  • Castle Windsor IoC: hopefully-zero user-facing changes, we’re replacing good old Ninject with a new dependency injection framework in order to gain finer control over object destruction – we will end up correctly unloading!

That’s actually priority one: the port is currently under review on GitHub, and pays a fair amount of long-standing technical debt, especially with everything involving menus.

  • Annotation/Attributes: fixing these inspection, and the quick-fix that synchronizes annotations with module attributes and vice-versa, will finally expose VB module and member attributes to VBA code panes, using Rubberduck’s annotation syntax.

For example,  adding '@Description("This procedure does XYZ") on top of a procedure will tell Rubberduck that you mean that procedure to have a VB_Description attribute; when Rubberduck parses that module after you synchronize, it will be able to use that description in the context status bar, or as tooltips in the Code Explorer.

This is considered a serious issue, because it affects pretty much every single inspection. Luckily there’s a [rather annoying and not exactly acceptable] work-around (apply the fix bottom-to-top in a module), but still.

But there’s a Greater Picture, too.

The 2.1.x Cycle

At the end of this development cycle, Rubberduck will:

  • Work in the VB6 IDE;
  • Have formalized the notion of an experimental feature;
  • Have a working Extract Method refactoring;
  • Make you never want to use the VBE’s Project References dialog ever again;
  • Compute and report various code metrics, including cyclomatic complexity and nesting levels, and others (and yes, line count too);
  • Maybe analyze a number of execution paths and implement some of the coolest code inspections we could think of;
  • Be ready to get really, really serious about a tear-tab AvalonEdit code pane.

If all you’re seeing is Rubberduck’s version check, the next version you’ll be notified about will be 2.1.2, for which we’re shooting for 2017-11-13. If you want to try every build until then (or just a few), then you’ll want to keep an eye on our releases page!

Contributor Swag!

Rubberduck is free, and always will be.

But shipping “thank you” packages to the project’s contributors isn’t. I need your help!

You use Rubberduck? You like what we’re doing? Over the few years the project has been running we’ve received extremely motivating positive feedback, tons of feature requests, and over 420 virtual hugs GitHub stars. And we still get that warm fuzzy every time.

Without Rubberduck’s contributors, we wouldn’t be anywhere near where we are today. There wouldn’t be over 50 implemented code inspections, the parser/resolver core would still be terribly slow and approximate, the Smart Indenter port wouldn’t be completed, there would be nobody to work on and fix the source control integration feature; there wouldn’t be a German translation, a regular expression analyzer tool, and so on: the project’s contributors are the real wizards shaping a dream into a reality… and I want to thank them for that, on behalf of all our users, stargazers and followers.

I can’t do this alone, so I started a GoFundMe campaign to collect enough funds to get some Rubberduck swag made and shipped to the project’s contributors.


During the first 24 hours of the campaign, $365 were donated by only 5 contributors – so I decided to match that amount (little bit more actually) and proceeded to order some of the stuff – as of now the campaign is only 30% raised though.

So what’s the actual swag?

The Rubberduck tee has the project’s name and website on the front, and the GitHub repository URL on the back:

The Rubberduck mug has the same assets, on white and black backgrounds. Both the tees and the mugs are ordered from SpreadShirt:

There’s more to the thank you packages, but I’d like to try to keep the rest a surprise… so I’m not saying anything else about it!

Nice! Can I haz a mug?

Simple: contribute to Rubberduck, and help us bring the VBE into this century! …actually, once I have the packages ready to ship (and the funds to ship them!), I’ll know how much overstock I’m left with (if any). Expect the biggest donators to get a little something too, and if there’s still some left I might run a little contest among Rubberduck users and supporters, so… stay tuned!

Inside Rubberduck (pt.2)
“Rubber Duck” – Voronoi Style Free 3D print model

Last time I went over the startup and initialization of Rubberduck, and I said I was going to follow it up with how the parser and resolver work.

Just so happens that Max Dörner, who has pretty much owned the parser and resolver parts of Rubberduck since he joined the project (that’s right – jumped head-first into some of the toughest, most complicated code in the project!), has nicely documented the highlights of how parsing and resolving works.

So yeah, all I did here was type up an intro. Buckle up, you’re in for a ride!

Part 2: Parsing & Resolving

Rubberduck processes the code in all unprotected modules in a five-step process. First, in the parser state Pending, the projects and modules to parse are determined. Then, in the parser state LoadingReferences, the references currently used by the projects, e.g. the Excel object model, and some built-in declarations are loaded into Rubberduck. Following this, the actual processing of the code begins. Between the parser states Parsing and Parsed the code gets parsed into parse trees with the help of Antlr4. Following this, between the states ResolvingDeclarations and ResolvedDeclarations the module, method and variable declarations are generated based on the parse tree. Finally, between the states ResolvingReferences and Ready the parse trees are walked a second time to determine the references to the declarations within the code.

At each state change, an event is fired which can be handled by any feature subscribing to it, e.g. the CodeExplorer, which listens for the state change to ResolvedDeclarations.

A More Detailed Story

The entry point for the parsing process is the ParseCoordinator inside the Rubberduck.Parsingassembly. It coordinates the parsing process and is responsible for triggering the appropriate state changes at the right time, for which it uses a IParserStateManager passed to it. To trigger the different stages of the parsing process, the ParseCoordinator uses a IParsingStageService. This is a facade passed to it providing a unified interface for calling the individual stages, which are all implemented in an individual set of classes. Each has a concurrent version for production and a synchronous one for testing. The latter was needed because of concurrency problems of the mocking framework.

General Logistics

Every parsing run gets executed in fresh background task. Moreover, to always be in a consistent state, we allow only one parsing run to execute at a time. This is achieved by acquiring a lock in a top level method. This top level method is also the point at which any cancellation or unexpected exception will be caught and logged.

The first step of the actual parsing process is to set the overall parser state to Pending. This signals to all components of Rubberduck that we left a fully usable state. Afterwards, we refresh the projects cache on the RubberduckParserState asking the VBE for the loaded projects and then acquire a collection of the modules currenlty present.

Loading References

After setting the overall parser state to LoadingReferences, the declarations for the project references, i.e. the references selected in Tools –> References... , get loaded into Rubberduck. This is done using the ReferencedDeclarationsCollector in the Rubberduck.Parsing.ComReflectionnamespace, which reads the appropriate type libraries and generates the corresponding declarations.

Note that the order in the References dialog determines what procedure or field an identifier resolves to in VBA if two or more references define a procedure or field of the same name. This prioritization is taken into account when loading the references.

Unfortunately, we are currently not able to load all built-in declarations from the type libraries: there are some hidden members of the MSForms library, some special syntax declarations like LBound and everything related to Debug, and aliases for built-in functions like Left, where Leftis the alias for the actual hidden function defined in the VBA type library. These get loaded as a set of hand-crafted declarations defined in the Rubberduck.Parsing.Symbols.DeclarationLoadersnamespace.

Parsing the Code

At the start of the processing of the actual code, the parser state is set to Parsing. However, this time this is achieved by setting the individual modules states of the modules to be parsed and then evaluating the overall state.

Each module gets parsed separately using an individual ComponentParseTask from the Rubberduck.Parsing.VBA namespace, which is powered by the Antlr4 parser generator. The end result is a pair of two parse trees providing a structured representation of the code one time as seen in the VBE and one time as exported to file.

The general process using Antlr is to provide the code to a lexer that turns the code into a stream of tokens based on lexer rules. (The lexer rules used in Rubberduck can be found in the file VBALexer.g4 in the Rubberduck.Parsing.Grammar namespace.) Then this token stream gets processed by a parser that generates a parse tree based on the stream and a set of parser rules describing the syntactic rules of the language. (The VBA parser rules used in Rubberduck can be found in the file VBAParser.g4 in the Rubberduck.Parsing.Grammar namespace. However, there are more specialized rules in the project). The parse tree then consists of nodes of various types corresponding to the rules in the parser rules.

Even when counting the Antlr workflow described above as one step, the actual parsing process in the ComponentParseTask is a multi stage process in itself. This has two reasons: there are precompiler directives in VBA and some information regarding modules is hidden from the user inside the VBE, namely attributes.

The precompiler directives in VBA allow to conditionally select which code is alive. This allows to write code that would only be legal VBA after evaluating the conditional compilation directives. Accordingly, this has to be done before the code reaches the parser. To achieve this, we parse each module first with a specialized grammar for the precompiler directives and then hide all tokens that are dead after the evaluation from the VBA parser, including the precompiler directives themselves, by sending the tokens to a hidden channel in the tokenstream. Afterwards, the dead code is still part of the text representation of the tokenstream by disregarded by the parser.

To cover both the attributes, which are only present in the exported modules, and provide meaningful line numbers in inspection results, errors and the command bar, we parse both the attributes and the code as seen in the VBE code pane into a separate parse tree and save both on the ModuleState belonging to the module on the RubberduckParserState.

One thing of note is that Antlr provides two different kinds of parsers: the LL parser that basically parses all valid input for every not indirectly left-recursive grammar (our VBA grammar satisfies this) and the SLL parser, which is considerably faster but cannot necessarily parse all valid input for all such grammars. Both parsers are guaranteed to yield the same result whenever the parse succeeds at all. Since the SLL parser works for next to all commonly encountered code, we first parse using it and fall back to the LL parser if there is a parser error.

Following the parse, the state of the module is set to Parsed on a successful parse and to ParserError, otherwise. After all modules have finished parsing, the overall parser state is evaluated. If there has been any parser error, the parsing process ends here.

Resolving Declarations

After parsing the code into parse trees, it is time to generate the declarations for the procedures, functions, properties, variables and arguments in the code.

First, the state of all modules gets set to ResolvingDeclarations, analogous to the start of parsing the code. Then the tree walker and listener infrastructure of Antlr is used to traverse the parse trees and generate declarations whenever the appropriate grammar constructs are encountered. This is done inside the implementations of IDeclarationResolveRunner in the Rubberduck.Parsing.VBAnamespace.

Note that there is still some information missing on the declarations at this point that cannot be determined in this first pass over the parse trees. E.g. the supertypes of classes implementing the interface of another class are not known yet and, although the name of the type of each declaration is already known, the actual type might not be known yet. For both cases we first have to know all declarations.

After the parse trees of all modules have been walked, the overall parser state gets set to ResolvedDeclarations, unless there has been an error, which would result in the state ResolverError and an immediate stop of the parsing run.

Resolving References

After all declarations are known, it is possible to resolve all references to these declarations within the code, beit as types, supertypes or in expressions. This is done using the implementations of IReferenceResolveRunner in the Rubberduck.Parsing.VBA namespace.

First, the state of the modules for which to resolve the references gets set to ResolvingReferencesand the overall state gets evaluated. Then the CompilationPasses run. In these the type names found when resolving the declarations get resolved to the actual types. Moreover, the type hierarchy gets determined, i.e. super- and and subtypes get added to the declarations based on the implements statements in the code.

After that, the parse trees get walked again to find all references to the declarations. This is a slightly complicated process because of the various language constructs in VBA. As a side effect, the variables not resolving to any declaration get collected. Based on these, new declarations get created, which get marked as undeclared. These form the basis for the inspection for undeclared variables.

After all references in a module got resolved, the module state gets set to Ready. If there is some error, the module state gets set to ResolverError. Finally, the overall state gets evaluated and the parsing run ends.

Handling State Changes

On each change of the overall state, an event is raised to which other features can subscribe. Examples are the CodeExplorer, which refreshes on the change to ResolvedDeclarations, and the inspections, which run on the change to Ready.

Handling any state change but the two above is discouraged, except maybe for the change to Pending or the error states if done to disable things. The problem with the other states is that they may never be encountered during a parsing run due to optimizations. Moreover, Rubberduck is generally not in a stable state between Pending and ResolvedDeclarations. Features requiring access to references should generally only handle the Ready state.

Events also get raised for changes of individual module states. However, it should be preferred to handle overall state changes because module states change a lot, especially in large projects.

IMPORTANT: Never request a parse from a state change handler! That will cancel the current parse right after the handlers for this state in favor of the newly requested one.

Doing Only What Is Necessary

When parsing again after a successful parsing run, the easiest way to proceed is to throw away all information you got from the last parsing run and start from scratch. However, this is quite wasteful since typically only a few modules change between parsing runs. So, we try to reuse as much information as possible from prior parsing runs. Since our VBA grammar is build for parsing entire modules the smallest unit of reuse of information we can work with is a module.

We only reparse modules that satisfy one of three conditions: they are new, modified, or not in the state Ready. For the first two conditions it should be obvious why we have to reparse such modules. The question is rather how we evaluate these conditions.

To be able to determine whether a module has changed, we save a hash of the code contained in the module whenever the module gets parsed successfully. At the start of the parsing run, we compare the saved hash with the hash of the corresponding freshly loaded component to find those modules with modified content. In addition we save a flag on the module telling us whether the content hash has ever been saved. If this is not the case, the module is regarded as new.

For the third condition the question is rather why we also reparse such modules. The reason is that such modules might be in an invalid state although the content hash had been written in the last parsing run. E.g. they might have encountered a resolver error or they got parsed successfully in the last parsing run, but the parsing run got cancelled before the declarations got resolved. In these cases the content hash has already been saved so that the module is neither considered to be new nor modified. Consequently, it would not be considered for parsing and resolving if only modules satisfying one of the first two conditions were considered. Because of the possibility of such problems, we rather err on the save side and reparse every module that has not reached the success state Ready.

Since reparsing makes all information we previously acquired about the module invalid, we have to resolve the declarations anew for the modules we reparse. Fortunately, the base characteristics of a declaration only depend on the module it is defined in. So, we only have to resolve declarations for those modules that get reparsed. For references the situation is more complicated.

Since all declarations from the modules we reparse get replaced with new ones, all references to them, all super- and subtypes involving the reparsed modules and all variable and method types involving the reparsed modules are invalid. So, we have to re-resolve the references for all modules that reference the reparsed modules. To allow us to know which modules these are we save the information which module references which other modules in an implementation of IModuleToModuleReferenceManager accessed in the ParseCoordinator via the IParsingCacheService facade. This information gets saved whenever the references for all modules have been resolved successfully, even before evaluating the overall parser state.

In addition to the modules that reference modules that got reparsed, we also re-resolve those modules that referenced modules or project references having just been removed. This is necessary because the references might now point to different declarations. In particular, a renamed module is treated as unrelated to the old one. This means that renaming a module looks to Rubberduck like the removal of the old module and the addition of a new module with a new name.

The final optimization in place on a reparse is that we do not reload the referenced type libraries or the special built-in declarations every time. We just reload those we have not loaded before.

Caching and Cache Invalidation

If you have read the previous paragraph, you might have already realized that the additional speed due to only doing what is necessary comes at a cost: various types of cached data get invalid after parsing and resolving only some modules. So we have to remove the data at a suitable place in the parsing process. To achieve this the ParseCoordinator primarily calls different methods from the IParsingCacheService facade handed to it.

In the next sections we will work our way up from cache data for which you would probably seldom realize that we forgot to remove it to data for which forgetting to remove it sends the parser down in flames. After that, we will finish with a few words about refreshing the DeclarationFinder on the RubberduckParserState.

Invalid Type Declarations

The kind of cache invalidation problem you would probably not realize is that the type as which a variable is defined has to be replaced in case it is a user defined class and the class module gets reparsed; it now has a different declaration. This would probably just cause some issues with some inspections because the actual IdentifierReference tying the identifier to the class declaration is not related to the type declaration we save. Fortunately, the TypeAnnotationPass works by replacing the type declaration anyway. So, we just have to do that for all modules for which we resolve references.

Invalid Super- and Subtypes

As mentioned in the section about resolving references, we run a TypeHierarchyPass to determine the super- and subtypes of each class module (and built-in library). After reparsing a module, we have to re-resolve its supertypes. However, we also have to remove the old declaration of the module itself from the supertypes of its subtypes and from the subtypes of its supertypes, which has some further data invalidation consequences. Otherwise, the “Find all Implementations” dialog or the rename refactoring might produce …interesting results for the affected modules.

The removal of the super- and subtypes is performed via an implementation of ISupertypeCleareron all modules we re-resolve, including the modules we reparse, before clearing the state of the modules to be reparsed. Here, a removal of the supertypes is sufficient because everything is wired up such that manipulating the supertypes automatically triggers the corresponding change on the subtypes.

Invalid Module-To-Module References

As with all other reference caches, part of our cache saving which module references which other modules can become invalid when we re-resolve a module; it might just be that the the part referencing another module is gone. Fortunately, the way these references are saved does not depend on the actual declarations. So reparsing alone does not cause problems. This allows us to defer the removal of the module-to-module references to the reference resolver.

Being able to postpone the removal until we resolve references is fortunate because of potential problems with cancellations. We use the module-to-module references to determine which modules need to be re-resolved. If they got removed and the parsing run got cancelled before they got filled again in the reference resolver, we would potentially miss modules we have to re-resolve. Then the user would need to modify the affected modules in order to force Rubberduck to re-resolve them.

To handle this problem, the reference resolver itself has a cache of the modules to resolve, which is only cleared at the very end of its work. This is safe because the reference resolver only ever processes modules for which it can find a parse tree on the RupperduckParserState.

Invalid References

Invalid IndentifierReferences to declarations from previous parsing runs can cause any number of strange behaviors. This can range from selections referring to references that have once been at that line and column but having been removed in the meantime to refactorings changing things they really should not change.

It is rather clear that the references from all modules to be re-resolved should be removed. However, this is not as straightforward as it seems. The problem is that the references live in a collection on the referenced declaration and not in a collection attached to the module whose code is referencing the declaration. In particular, this makes it easy to forget to remove references from built-in declarations. To avoid such issues, we extracted the logic for removing references by a module into implementations of IReferenceRemover, which is hidden behind the IParsingCacheService facade.

Modules And Projects That No Longer Exist

Now we come to the piece where everything falls to pieces if we are not doing our job, modules and projects that get removed from the VBE. The problem is that some functionality like the CodeExplorer has to query information from the components in the VBE via COM Interop. If a component does no longer exist when the information gets queried, the parsing run will die with a COMException and there is little we can do about that. So we have to be careful to remove all declarations for no longer existing components right at the start of the parsing run.

To find out which modules no longer exist, we simply collect all the modules on the declarations we have cached and compare these to the modules we get from the VBE. More precisely, we compare the identifiers we use for modules, the QualifiedModuleNames. This will also find modules that got renamed. Projects are bit more tricky since they are usually treated as equal if their ProjectIds are the same; we save these in the project help file. Thus, we have to take special care for renamed projects. Knowing the removed projects, their modules get added to the removed modules as well.

Removing the data for removed modules and projects is a bit more complicated than for modules that still exist. After their declarations got removed, there is no sign anymore that they ever existed. So, we have to take special care to remove everything in the right order to guarantee that all information is gone already when we erase the declaration; after each step, the parsing run might be cancelled.

The final effect of removing modules is that the modules referencing the removed modules need to be re-resolved. Intuitively one might think that this will always result in a resolver error. However, keep in mind that renaming is handled as removing a module and adding another. Then the references will simply point to the new renamed module. Because of possible cancellations on the way to resolving the references, we immediately set the state of the modules to be re-resolved to ResolvingReferences. This has the effect that they will be reparsed in case of a cancellation.

Note that basically the same procedure is also necessary whenever we reload project references. Accordingly, we do this right after unloading the references, without allowing cancellations in between.

Refreshing the DeclarationFinder

Since declarations and references change in nearly all steps of the parsing process, we have to refresh our primary cached source of declarations, the DeclarationFinder, quite regularly when parsing. Unfortunately, this is a rather computation intensive thing to do; a lot of dictionaries get populated. So, we refresh only if we need to. E.g. we do not refresh after loading and unloading project references in case nothing changed. However, there are two points in each parsing run where we always have to refresh it: before setting the state to ResolvedDeclarations and before evaluating the overall state at the end of the parsing run, which results in the Ready state in the success path.

Refreshing before the change to ResolvedDeclarations is necessary to ensure that removed modules vanish from the DeclarationFinder before the handlers of this state change event run, including the CodeExplorer. We have to refresh again at the end because, from inside the ParseCoordinator, we can never be sure that the reference resolver did not do anything; it has its own cache of modules that need to be resolved.

One optimization done in the DeclarationFinder itself is that some collections are populated lazily, in particular those dealing only with built-in declarations. This saves the time to rebuild the collections multiple times on each parsing run. However, there is a price to pay. The primary users of the DeclarationFinder are the reference resolver and the inspections, both of which are parallelized. Accordingly, it can happen that multiple threads race to populate the collections. This is bad for the performance of the corresponding features. So, we make compromises by immediately populating the most commonly used collections.

Inside Rubberduck (pt.1)
“Rubber Duck” – Voronoi Style Free 3D print model

Maybe you’ve browsed Rubberduck’s repository, or forked it to get a closer look at the source code. Or maybe you didn’t but you’re still curious about how it might all work.

I haven’t written a blog post in quite a long while (been busy!), so I thought I’d start a series that describes Rubberduck’s internals, starting at the beginning.

Part I: Starting up

Rubberduck embraces the Dependency Injection principle: depend on abstractions, not concrete implementations. Hand-in-hand with DI, the Inversion of Control principle describes how all the decoupled pieces come together. This decoupling enables testable code, which is fundamental when your add-in has a unit testing framework feature in any project of that size.

Because RD is a rather large project, instead of injecting the dependencies (and their dependencies, and these dependencies’ dependencies, and so on…) “by hand”, we use Ninject to do it for us.

We configure Ninject in the Rubberduck.Root namespace, more specifically in the complete mess of a class, RubberduckModule. I say complete mess because, well, a couple of things are wrong in that file. How it steals someone else’s job by constructing the menus, for example. Or how it’s completely under-using the conventions Ninject extension. The abstract factory convention is nice though: Ninject will automatically inject a generated proxy type that implements the factory interface – you never need a concrete implementation of a factory class!

The add-in’s entry point is located in Rubberdcuk._Extension, the class that the VBE discovers in the Windows Registry as an add-in to load. This class implements the IDTExtensibility2 interface, which looks essentially like this:

public interface IDTExtensibility2
    void OnAddInsUpdate(ref Array custom);
    void OnConnection(object Application, ext_ConnectMode ConnectMode, object AddInInst, ref Array custom);
    void OnStartupComplete(ref Array custom);
    void OnBeginShutdown(ref Array custom);
    void OnDisconnection(ext_DisconnectMode RemoveMode, ref Array custom);

The Application object is the VBE itself – the very same VBE object you’d get in VBA from the host application’s Application.VBE property, and there are a number of things to consider in how these methods are implemented, but everything essentially starts in OnConnection and ends in OnDisconnection.

So we first get hold a reference to the precious Application and AddInInst objects that we receive here, but because we don’t want a direct dependency on the VBIDE API throughout Rubberduck, we wrap it with a wrapper type that implements our IVBE interface – same for the IAddIn(yes, we wrapped every single type in the VBIDE API type library; that way we can at least try to make Rubberduck work in VB6):

 var vbe = (VBE) Application; 
 _ide = new VBEditor.SafeComWrappers.VBA.VBE(vbe);
 var addin = (AddIn)AddInInst;
 _addin = new VBEditor.SafeComWrappers.VBA.AddIn(addin) { Object = this };

Then InitializeAddIn is called. That method looks for the configuration settings file, and sets the Thread.CurrentUICulture accordingly. When we know that the settings aren’t disabling the startup splash, we get our build number from the running assembly and bring up the splash screen. Only then do we call the Startup method; when Startup returns (or throws), the splash screen is disposed.

The method is pretty simple:

private void Startup()
    var currentDomain = AppDomain.CurrentDomain;
    currentDomain.AssemblyResolve += LoadFromSameFolder;

    _kernel = new StandardKernel(
        new NinjectSettings {LoadExtensions = true}, 
        new FuncModule(), 
        new DynamicProxyModule());
    _kernel.Load(new RubberduckModule(_ide, _addin));

    _app = _kernel.Get<App>();

    _isInitialized = true;

We initialize a Ninject StandardKernel, load our module (give it our IVBE and IAddIn object references), get an App object and call its Startup method, where the fun stuff begins:

public void Startup()
    _hooks.HookHotkeys(); // need to hook hotkeys before we localize menus, to correctly display ShortcutTexts


    if (_config.UserSettings.GeneralSettings.CheckVersion)

The method names speak for themselves: we conditionally hit the registry looking for a legacy Smart Indenter key to import indenter settings from, and run the asynchronous “version check” command, which sends an HTTP request to, a URL that merely returns the version number of the build that’s running on the website: by comparing that version with the running version, Rubberduck can let you know when a new version is available.

That’s literally all there is to it: just with that, we have a backbone to build with. If we want a new command, we just implement an ICommand, and if that command goes into a menu we hook it up to a CommandMenuItem class. Commands often delegate their work to more specialized objects, e.g. a refactoring, or a presenter of some sort.

Next post will dive into how Rubberduck’s parser and resolver work.

to be continued…

Inspections 2.1

The Project

With the planned features and project design for 2.1/3.0, we needed to give our inspections some thought. The basic inspection design had not really changed since the initial conception, except we allowed constructor parameters in 2.0 after we moved to Ninject DI instead of using reflection to create them. This post describes how quick fixes are being made independent of a inspection results.


The reason why this was so important has many sides. First, we want to make Rubberduck extensible. If you want to write an add-in for our add-in, we want you to be able to do that. We cannot provide every feature, and we especially cannot provide every inspection you would want. Part of this reason is that not every inspection is in scope for this project—you could write an inspection and quick fix using Rubberduck’s parse trees and declarations to safely correct some bad behavior that is specific to your project, or perhaps you just want to write a custom quick fix for one of our inspections, maybe you want to write an inspection that uses one of our quick fixes. This would be somewhat difficult under our previous design of:

Inspection -> IEnumerable GetInspectionResults()
IInspectionResult -> IEnumerable QuickFixes { get }

If any inspection wanted to offer a specific set of quick fixes, it had to have its own inspection result. An existing inspection could not gain more quick fixes without changing its inspection result, which required us to completely redeploy the solution.

Further consideration reveals that the quick fixes really have their own scope and that our inspections were violating the Single Responsibility Principle (SRP). An inspection’s responsibility is to find issues. An inspection result’s responsibility is to report an issue, and nothing else. A quick fix’s responsibility is to fix the issue—it doesn’t care about anything else. We needed to split these up in a way that

  1. Allows an inspection to have new quick fixes added at runtime
  2. Separates inspections and quick fixes so that
    1. A quick fix knows what inspections it can fix
    2. An inspection and its result knows nothing about which quick fixes support it
  3. Is clean and maintainable

The Solution

Our final solution is to leave the inspections pretty much alone, except move more of them to be IParseTreeInspection’s because we are moving from lists of declarations to making a full AST with our ANTLR parse trees. The inspection-specific result classes are now gone, and we made the following inheritance structure:

IInspectionResult -> InspectionResultBase
InspectionResultBase ->
DeclarationInspectionResult         // works off declaration nodes
IdentifierReferenceInspectionResult // works off identifier references
QualifiedContextInspectionResult    // works off a qualified context, which is a module name and ANTLR node

So, an inspection still reports inspection results, just like previously. However, it no longer needs to inject dependencies only used by the quick fix. Previously, we had to pass these dependencies into the quick fix through the inspection result through the inspection; this was causing some minor problems in the website, as well. Once we get our add-in structure complete, the user will be able to create a class library using Rubberduck’s features, install it to a certain folder, and Ninject will automatically load the types into Rubberduck and the inspections will be treated just like  our “built-in” inspections.
An inspection result also has a simpler constructor, and only takes the information needed to report the inspection result and its scope. This is open to slight changes in the future as we stop reporting lists of results, but rather directly annotate parse trees with them. However, the beauty of it at this point is nothing else is affected—most of the inspection result is consumed by the end user only.
A quick fix now is a standalone feature exposing the following interface:

IQuickFix ->
void Fix(IInspectionResult result)
string Description(IInspectionResult result)
bool CanFixInProcedure { get }
bool CanFixInModule { get }
bool CanFixInProject { get }
IReadOnlyCollection SupportedInspections { get }

Rubberduck exposes the quick fix to the user through the IQuickFixProvider, which returns a set of quick fixes for an inspection result by checking the reported inspection type and allows the user to fix an individual inspection or all inspections of a certain type from a set of results in a certain scope. This provider is incomplete, but will allow the user to add or remove a quick fix for any inspection, other than inspection/quick fix mappings built-in to Rubberduck.

Further Considerations

At this point, one inspection is broken because it did not enable the quick fixes in certain circumstances. The solution for this is still being thought about, but it will likely involve giving the inspection result a dictionary of properties, with a special case for disabling a set of inspections:

{ “DisableInspections”, “FooInspection,BarInspection” }

Other properties can be used by the quick fixes either for performance enhancements, simplifications, or to convey information not allowed by the inspection result API.


Recently I asked on Twitter what the next RD News post should be about.


Seems you want to hear about upcoming new features, so… here it goes!

The current build contains a number of breakthrough features; I mentioned an actual Fakes framework for Rubberduck unit tests in an earlier post. That will be an ongoing project on its own though; as of this writing the following are implemented:

  • Fakes
    • CurDir
    • DoEvents
    • Environ
    • InputBox
    • MsgBox
    • Shell
    • Timer
  • Stubs
    • Beep
    • ChDir
    • ChDrive
    • Kill
    • MkDir
    • RmDir
    • SendKey

As you can see there’s still a lot to add to this list, but we’re not going to wait until it’s complete to release it. So far everything we’re hijacking hooking up is located in VBA7.DLL, but ideally we’ll eventually have fakes/stubs for the scripting runtime (FileSystemObject), ADODB (database access), and perhaps even host applications’ own libraries (stabbing stubbing the Excel object has been a dream of mine) – they’ll probably become available as separate plug-in downloads, as Rubberduck is heading towards a plug-in architecture.

The essential difference between a Fake and a Stub is that a Fake‘s return value can be configured, whereas a Stub doesn’t return a value. As far as the calling VBA code is concerned, that’s nothing to care about though: it’s just another member call:

public interface IStub
    [Description("Gets an interface for verifying invocations performed during the test.")]
    IVerify Verify { get; }

    [Description("Configures the stub such as an invocation assigns the specified value to the specified ByRef argument.")]
    void AssignsByRef(string Parameter, object Value);

    [Description("Configures the stub such as an invocation raises the specified run-time eror.")]
    void RaisesError(int Number = 0, string Description = "");

    [Description("Gets/sets a value that determines whether execution is handled by Rubberduck.")]
    bool PassThrough { get; set; }

So how does this sorcery work? Presently, quite rigidly:

public interface IFakesProvider
    [Description("Configures VBA.Interactions.MsgBox calls.")]
    IFake MsgBox { get; }

    [Description("Configures VBA.Interactions.InputBox calls.")]
    IFake InputBox { get; }

    [Description("Configures VBA.Interaction.Beep calls.")]
    IStub Beep { get; }

    [Description("Configures VBA.Interaction.Environ calls.")]
    IFake Environ { get; }

    [Description("Configures VBA.DateTime.Timer calls.")]
    IFake Timer { get; }

    [Description("Configures VBA.Interaction.DoEvents calls.")]
    IFake DoEvents { get; }

    [Description("Configures VBA.Interaction.Shell calls.")]
    IFake Shell { get; }

    [Description("Configures VBA.Interaction.SendKeys calls.")]
    IStub SendKeys { get; }

    [Description("Configures VBA.FileSystem.Kill calls.")]
    IStub Kill { get; }


Not an ideal solution – the IFakesProvider API needs to change every time a new IFake or IStub implementation needs to be exposed. We’ll think of a better way (ideas welcome)…

So we use the awesomeness of EasyHook to inject a callback that executes whenever the stubbed method gets invoked in the hooked library. Implementing a stub/fake is pretty straightforward… as long as we know which internal function we’re dealing with – for example this is the Beep implementation:

internal class Beep : StubBase
    private static readonly IntPtr ProcessAddress = EasyHook.LocalHook.GetProcAddress(TargetLibrary, "rtcBeep");

    public Beep() 
        InjectDelegate(new BeepDelegate(BeepCallback), ProcessAddress);

    [UnmanagedFunctionPointer(CallingConvention.StdCall, SetLastError = true)]
    private delegate void BeepDelegate();

    [DllImport(TargetLibrary, SetLastError = true)]
    private static extern void rtcBeep();

    public void BeepCallback()

        if (PassThrough)

As you can see the VBA7.DLL (the TargetLibrary) contains a method named rtcBeep which gets invoked whenever the VBA runtime interprets/executes a Beep keyword. The base class StubBase is responsible for telling the Verifier that an usage is being tracked, for tracking the number of invocations, …and disposing all attached hooks.

The FakesProvider disposes all fakes/stubs when a test stops executing, and knows whether a Rubberduck unit test is running: that way, Rubberduck fakes will only ever work during a unit test.

The test module template has been modified accordingly: once this feature is released, every new Rubberduck test module will include the good old Assert As Rubberduck.AssertClass field, but also a new Fakes As Rubberduck.FakesProvider module-level variable that all tests can use to configure their fakes/stubs, so you can write a test for a method that Kills all files in a folder, and verify and validate that the method does indeed invoke VBA.FileSystem.Kill with specific arguments, without worrying about actually deleting anything on disk. Or a test for a method that invokes VBA.Interaction.SendKeys, without actually sending any keys anywhere.

And just so, a new era begins.

Awesome! What else?

One of the oldest dreams in the realm of Rubberduck features, is to be able to add/remove module and member attributes without having to manually export and then re-import the module every time. None of this is merged yet (still very much WIP), but here’s the idea: a bunch of new @Annotations, and a few new inspections:

  • MissingAttributeInspection will compare module/member attributes to module/member annotations, and when an attribute doesn’t have a matching annotation, it will spawn an inspection result. For example if a class has a @PredeclaredId annotation, but no corresponding VB_PredeclaredId attribute, then an inspection result will tell you about it.
  • MissingAnnotationInspection will do the same thing, the other way around: if a member has a VB_Description attribute, but no corresponding @Description annotation, then an inspection result will also tell you about it.
  • IllegalAnnotationInspection will pop a result when an annotation is illegal – e.g. a member annotation at module level, or a duplicate member or module annotation.

These inspections’ quick-fixes will respectively add a missing attribute or annotation, or remove the annotation or attribute, accordingly. The new attributes are:

  • @Description: takes a string parameter that determines a member’s DocString, which appears in the Object Browser‘s bottom panel (and in Rubberduck 3.0’s eventual enhanced IntelliSense… but that one’s quite far down the road). “Add missing attribute” quick-fix will be adding a [MemberName].VB_Description attribute with the specified value.
  • @DefaultMember: a simple parameterless annotation that makes a member be the class’ default member; the quick-fix will be adding a [MemberName].VB_UserMemId attribute with a value of 0. Only one member in a given class can legally have this attribute/annotation.
  • @Enumerator: a simple parameterless annotation that commands a [MemberName].VB_UserMemId attribute with a value of -4, which is required when you’re writing a custom collection class that you want to be able to iterate with a For Each loop construct.
  • @PredeclaredId: a simple parameterless annotation that translates into a VB_PredeclaredId (class) module attribute with a value of True, which is how UserForm objects can be used without Newing them up: the VBA runtime creates a default instance, in global namespace, named after the class itself.
  • @Internal: another parameterless annotation, that controls the VB_Exposed module attribute, which determines if a class is exposed to other, referencing VBA projects. The attribute value will be False when this annotation is specified (it’s True by default).

Because the only way we’ve got to do this (for now) is to export the module, modify the attributes, save the file to disk, and then re-import the module, the quick-fixes will work against all results in that module, and synchronize attributes & annotations in one pass.

Because document modules can’t be imported into the project through the VBE, these attributes will unfortunately not work in document modules. Sad, but on the flip side, this might make [yet] an[other] incentive to implement functionality in dedicated modules, rather than in worksheet/workbook event handler procedures.

Rubberduck command bar addition

The Rubberduck command bar has been used as some kind of status bar from the start, but with context sensitivity, we’re using these VB_Description attributes we’re picking up, and @Description attributes, and DocString metadata in the VBA project’s referenced COM libraries, to display it right there in the toolbar:


Until we get custom IntelliSense, that’s as good as it’s going to get I guess.


As of next release, every single modification to the code is done using Antlr4‘s TokenStreamRewriter – which means we’re no longer rewriting strings and using the VBIDE API to rewrite VBA code (which means a TON of code has just gone “poof!”): we now work with the very tokens that the Antlr-generated parser itself works with. This also means we can now make all the changes we want in a given module, and apply the changes all at once – by rewriting the entire module in one go. This means the VBE’s own native undo feature no longer gets overwhelmed with a rename refactoring, and it means fewer parses, too.

There’s a bit of a problem though. There are things our grammar doesn’t handle:

  • Line numbers
  • Dead code in #If / #Else branches

Rubberduck is kinda cheating, by pre-processing the code such that the parser only sees WS (whitespace) tokens in their place. This worked well… as long as we were using the VBIDE API to rewrite the code. So there’s this part still left to work out: we need the parser’s token stream to determine the “new contents” of a module, but the tokens in there aren’t necessarily the code you had in the VBE before the parse was initiated… and that’s quite a critical issue that needs to be addressed before we can think of releasing.

So we’re not releasing just yet. But when we do, it’s likely not going to be v2.0.14, for everything described above: we’re looking at v2.1 stuff here, and that makes me itch to complete the add/remove project references dialog… and then there’s data-driven testing that’s scheduled for 2.1.x…

To be continued…