Creating Power Fx from Classic Workflows (XAML)

[filcole]

I am experimenting with the possibility of creating a utility to convert simple classic workflows to Power Fx suitable for use in low code plugins. Starting from a point of total ignorance I have:

• Attempted parsing the XAML of classic workflows using the WWF libraries (failed)
• Realised that I needed an internal representation of a WF XAML. Learned that this is known as a AST (Abstract Syntax Tree)
• Found ANTLR (lexer/parser generator) and attempted to create a grammar for WWF XAML - realised that this was quite a task.
• Consumed some of the Language Implementation Patterns book by Terence Parr (ANTLR author)
• Found that there exists a nice parser and executor of XAML (workflows, BR, rollups) already created by Delegate A/S here (https://github.com/delegateas/XrmMockup/blob/master/src/XrmMockupWorkflow/WorkflowTree.cs) by @magesoe et al, which creates a 'compressed' AST for the XAML. I had a futile attempt to create Power-Fx directly from this AST.
• Found that there is a lexer/parser that generates an AST for Power Fx within this repo. See
  

  Power-Fx/src/libraries/Microsoft.PowerFx.Core/Parser/TexlParser.cs

  Line 599 in caa821f

  private TexlNode Parse(ref List<TexlError> errors)

I think the next steps are to:

1. Determine if there is anything in the Power Fx repo/library that will allow an external application to create an AST for Power Fx and then generate the source code (serialised Power Fx) from the AST. @MikeStall is this currently possible, and exposed by the Power-Fx nuget packages?
2. Find a way to transform the XAML/WF AST to a Power Fx AST. Need to review chapters 11 to 13 of 'Language Implementation Patterns'.

Is this a sane approach? Are there any thoughts on the approach, or things that should be done differently?

The following nodes in XAML WF need to be converted:

XAML Activity	Power Fx equivalent (thoughts)
CreateVariable	Suspect this will be eliminated because this is mostly temporary variables used in XAML
SelectFirstNonNull	maps to Coalesce()
Arithmetic	maps to + - / *
Aggregate	Think not needed for classic workflows
Concat	maps to Concatenate()
AddTime	maps to DateAdd()
SubtractTime	maps to DateAdd()
DiffInTime	maps to DateDiff()
Trim	maps to TrimEnds()
Skip	??? only used in Waiting workflows? If so, abort conversion, and recommend using cloud flow.
GetEntityProperty	Have to work this one out. Could be Lookup(), could be dot notation
ConditionExp	Maps to an expression within an If() statement
Condition	Maps to If(conditionexpr, thenstatement, ..., defaultstatement)
LogicalComparison	Suspect this will be eliminated and mapped into ConditionExp
SetEntityProperty	Sets a value (in memory) for use later in CreateEntity or UpdateEntity
SetAttributeValue	???
CreateEntity	Maps to Patch() when creating a new entity for any SetAttributeValue
UpdateEntity	Maps to Set() when updating the current record otherwise maps to Patch(). Uses in memory values set by SetEntityProperty
Assign	??? think used internally to set a value to a variable. Should disappear - or maybe need to convert using With()
AssignEntity	Think maps to Set(Owner, xxx) or Patch(table, createdrecord, { Owner: xxx})
ActivityList	???? only used with SendEmail?
TerminateWorkflow	Likely needs to be remapped to if(not(condition), XXX). Also need to roll-back any earlier CreateEntity/UpdateEntity if termination is 'Cancelled' instead of 'Successful'. Use Error() if termination is 'Cancelled' to expose message to user. Probably the most difficult to handle??
RollUp	Think not needed for classic workflows
CallCodeActivity	Terminate conversion if encountering a CWA
ConvertType	Unsure - may map to Value() or Text()
SendEmail	Unsure, perhaps Patch(email, { contents})

[MikeStall]

Re 1 - we don't have any programmatic support for ASTs (although it is definitely something we're interested in).
Just generate the power fx as a string.

[filcole]

Thanks @MikeStall. Yes, I noticed that all the AST classes have internal constructors. I'm currently got a few classes which create a cut down AST of the necessary PowerFx functions, If, Coalesce, Set, etc, and outputting a Power Fx string from that. Long statements aren't currently broken over multiple lines :/ I noticed there's PrettyPrinting functions in the repo, but it's not exposed externally.

[MikeStall]

Also - re AddTime, etc.... PowerFx has a DateAdd() method.
https://learn.microsoft.com/en-us/power-platform/power-fx/reference/function-dateadd-datediff

[MikeStall]

Also note that PrettyPrinting shows up in TexlNode.ToString(), which is public :)

[rnwood]

Sharing my attempt at the same thing:
https://github.com/rnwood/workflow-moderniser

Interesting to read the conversation above having figured out some of this out independently.

Parsing the XAML is quite straightforward using the System.Xaml and System.Activities namespaces along with Microsoft.Xrm.Sdk.Workflow.Activities from the SDK.

The hairy bit currently is the VB expressions that are embedded. I could not figure out how to successfully parse those despite the above libraries supporting it on paper. So currently, those bits are just parsing out specifics with regex/split/etc.