Plugin patterns

Plugin.fs is one recursive module, AST. Its active patterns recognise the pieces of a tag: its constructor, its attributes and its children. Order matters in several places, and the comments say where.

Attributes and properties

The AttributesAndProperties module deals with everything that ends up as an attribute.

• PropertyGetter recognises a read like props.label and returns the property name.
• PropertySetter recognises props.label <- value, in all the shapes Fable produces for it: a setter call, a member val field set, or a [<DefaultValue>] val mutable field set.
• PropsGetterOrSetter combines the two. A getter is recorded with addGetter and rewritten to a plain property read on the self identifier. A setter is recorded with addSetter and removed from the body; it comes back as the merge.

• AttributeExpression recognises one attribute and returns its name and value. It handles the special cases:
  • .style', .class' and ref
  • .data, .attr and .bool, which build data-* and other attribute names from a string
  • .spread, written as {...PARTAS_OTHERS} n$ when you spread the component's own props, or {...x} n$ for any other identifier or field. n$={false} is the marker that closes a spread.
  • polymorphic attributes (as', asChild, or any alias of __PARTAS_POLYMORPHIC__), whose value becomes a function of PARTAS_POLYPROPS that spreads them onto the tag
  • aria setters, renamed to aria-*
• ValueUnroller and MatchValueReplacer flatten the delay/toArray wrappers Fable puts around list and array values in attributes. They only unroll toArray/toList over a delayed sequence; List.toArray xs is a real conversion and stays.
• PropCollector runs over a list of expressions and collects every attribute. Anything it does not recognise is dropped, with debugDisposal.

Tags

TagConstructor recognises the expression that creates a tag, and returns an ElementBuilder. It tries, in order:

1. constructors of types with [<PartasImport>] or [<PartasProxyImport>], which need an import injected. These must come before the local tag case, or they are never reached.
2. a tag declared in this project (a Partas type, matched through its _$ctor)
3. a native element
4. a library import, and then a user-defined import
5. a tag with properties, which Fable writes as a let of the element followed by setters
6. a tag with an extension call such as .spread or .data
7. a tag with children: a call to the builder's Run with the tag as its first argument
8. a context provider, imported or local, which becomes <Context value={...}> (in Solid 2 the context is its own provider)

Children

BuilderCollector walks the expressions inside a tag's computation expression and returns the children. It is the most recursive part of the plugin. It:

• unwraps the builder's let and lambda bindings (PARTAS_ELEMENT, PARTAS_BUILDER, PARTAS_YIELD and the rest)
• turns the lambdas of ChildLambdaProvider types, such as the child function of For.Keyed, into JSX functions with the right number of parameters
• transforms conditionals, and lifts property getters and setters
• keeps field and tuple accessors whole, so a child like item.Title is not thrown away

collectTagInfo does the final clean-up of an ElementBuilder, trimming reserved suffixes off the attribute names.

Other patterns

• SpecialAttributeTransformation.Pojo rewrites a [<Pojo>] constructor and its setters into one object literal. SkipPojoOptimisation turns it off.
• TagValue.TagValue and TagValue.TagRender handle tag values: a tag stored as a value with !@, and rendered later with .render.
• Polymorphism.PolymorphicAttribute decides whether an attribute name is polymorphic.

See Transformation for how these are put together.