@OptionStrict annotation

[retailcoder]

Justification

VBA is very forgiving in terms of implicit type conversions. Late-bound member calls move glaring compile-time errors from compile-time to run-time; variables don't even need a declared type! VB.NET addressed these loose ends with Option Strict, and I think we have everything we need to make VBA do the same.

Description

Microsoft Docs describes Option Strict as follows:

Option Strict Statement
Restricts implicit data type conversions to only widening conversions, disallows late binding, and disallows implicit typing that results in an Object type.

_{https://docs.microsoft.com/en-us/dotnet/visual-basic/language-reference/statements/option-strict-statement}

In a VBA context, "Object" means "Object or Variant".

Let's introduce a new @OptionStrict annotation, a MissingOptionStrictInspection "Rubberduck Opportunity" inspection that finds modules without it, and quickfix to add it in this module... and then another error-level OptionStrictInspection that point to all violations.

Bonus: a checkbox setting to "use 'Option Strict' everywhere", and have the annotation added automatically to every new (& existing?) module.

Additional context These annotations should ideally all be valid (with or without the parentheses):

'@OptionStrict
'@OptionStrict(On)
'@OptionStrict("On")
'@OptionStrict Off
'@OptionStrict "Off"

...but it's completely fine to start with just a single @OptionStrict annotation, and have it support a parameter later: if the annotation is there, it's on, if not, it's off.

When '@OptionStrict is on, the following inspections are in effect:

• Implicit narrowing conversion: locates all instances of narrowing type conversions (the essence of #1585, and side-steps the Variant problem)
• Late binding: a better approach than #4925 I think... the inspection locates all instances of, essentially, resolver errors: member calls against Variant or Object.
• Implicit object type: could be interesting to derive a new inspection from VariableTypeNotDeclaredInspection for this... locates all declarations of variables/parameters/fields without an As clause. That way '@OptionStrict would still make it issue a result even if VariableTypeNotDeclaratedInspection is disabled.

Note that explicit Variant and Object declarations are legal with '@OptionStrict: what's not allowed is to make a member call against it without first casting it to an early-bound interface.

The advantages are:

• IntelliSense everywhere!
• Compile-time validation: pretty much eradicates run-time error 438.
• Better run-time performance: since types are bound at compile-time, no interface lookups need to happen at run-time to locate a member.
• Optimal Rubberduck insight: with every statement early-bound, a lot of tough problems solve themselves: we could have inspections that might require @OptionStrict in a module in order to run in that module.
• VBA code that's just as robust as any VB.NET code, and that can easily convert to it.

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The OptionStrict inspections should be public nested types in an all-encompassing OptionStrictInspection, so that '@Ignore OptionStrict works for all OptionStrict results. Disabling the OptionStrictInspection could fire an OptionStrictDisabledInspection result that flags '@OptionStrict annotations when the OptionStrictInspection is disabled, warning about the option not being enacted. Or (perhaps simpler, and less... recursive "what it that one is disabled?"), we special-case OptionStrictInspection and disable changing/configuring that inspection's severity level (Error).

Wiki should also be updated with a table of Widening Conversions adapted to VBA data types.

[retailcoder]

VBA doesn't have an explicit cast operator: a new @DirectCast annotation could be used to decorate assignments that would otherwise trip implicit object type conversions (linking #3580):

Dim a As Foo
Set a = New Foo
Dim b As Bar
'@DirectCast
Set b = a

[SmileyFtW]

My only issue with enforcing early binding is the problem it causes users with different versions and therefore requiring different references… I’d rather develop in early bound mode and then go late-bound when deploying. Maybe that is what you are suggesting and I am missing the point (which is usually the case… ).

[retailcoder]

@SmileyFtW the version-specific issues of early binding are real, but also wildly overstated. Scripting runtime, for one, has no reason to be late-bound: every single Windows machine built this century is running the same version. Ditto with any XML library, or regex, and several others. That said we can't hook the compiler (that I know of) and enforce it at compile-time; best we can do is trigger inspections, and offer quickfixes where appropriate. The vast majority of VBA code uses only standard libraries, and "late binding" has nothing to do with library references (another widely spread piece of misinformation).

This Range call is late-bound:

Worksheets("Sheet1").Range("A1") = 42

It's late bound because Sheets returns Object. The fix is to cast that object to an early-bound interface:

Dim sh As Worksheet
Set sh = Worksheets("Sheet1")

And now a Range call against sh is compile-time validated. That is mostly what this idea is all about. But yes, late-bound library references would also be "forbidden"... and then, moving such library-specific calls into their own module (without @OptionStrict specified) would only make the code more modular and robust overall.

[SmileyFtW]

This is why I love this RD community… I learn something virtually every time I read a post, and ALWAYS when I post a reply. Thanks to you and all who have moved me way beyond where I was a few months ago.