Macro annotations class modifications (part 2) #16454

nicolasstucki · 2022-12-01T16:23:07Z

Enable modification of classes with MacroAnnotation:

Can annotate class to transform it
Can annotate object to transform the companion class

Supported class modifications:

Modify the implementations of def, val, var, lazy val, class, object in the class
Add new def, val, var, lazy val, class, object members to the class
Add a new override for a def, val, var, lazy val members in the class

Restrictions:

An annotation on a top-level class cannot return a top-level def, val, var, lazy val.

Related PRs:

Includes Fix macro annotations spliceOwner #16513
Follows Macro annotation (part 1) #16392
Followed by Enable returning classes from MacroAnnotations (part 3) #16534

Fixes #16266

@memoize

#### Add basic support for macro annotations * Introduce experimental `scala.annotations.MacroAnnotation` * Macro annotations can analyze or modify definitions * Macro annotation can add definition around the annotated definition * Added members are not visible while typing * Added members are not visible to other macro annotations * Added definition must have the same owner * Implement macro annotation expansion * Implemented at `Inlining` phase * Can use macro annotations in staged expressions (expanded when at stage 0) * Can use staged expression to implement macro annotations * Can insert calls to inline methods in macro annotations * Current limitations (to be loosened in following PRs) * Can only be used on `def`, `val`, `lazy val` and `var` * Can only add `def`, `val`, `lazy val` and `var` definitions #### Example ```scala class memoize extends MacroAnnotation: def transform(using Quotes)(tree: quotes.reflect.Definition): List[quotes.reflect.Definition] = import quotes.reflect._ tree match case DefDef(name, TermParamClause(param :: Nil) :: Nil, tpt, Some(rhsTree)) => (Ref(param.symbol).asExpr, rhsTree.asExpr) match case ('{ $paramRefExpr: t }, '{ $rhsExpr: u }) => val cacheTpe = TypeRepr.of[Map[t, u]] val cacheSymbol = Symbol.newVal(tree.symbol.owner, name + "Cache", cacheTpe, Flags.Private, Symbol.noSymbol) val cacheRhs = '{ Map.empty[t, u] }.asTerm val cacheVal = ValDef(cacheSymbol, Some(cacheRhs)) val cacheRefExpr = Ref(cacheSymbol).asExprOf[Map[t, u]] val newRhs = '{ $cacheRefExpr.getOrElseUpdate($paramRefExpr, $rhsExpr) }.asTerm val newTree = DefDef.copy(tree)(name, TermParamClause(param :: Nil) :: Nil, tpt, Some(newRhs)) List(cacheVal, newTree) case _ => report.error("Annotation only supported on `def` with a single argument are supported") List(tree) ``` with this macro annotation a user can write ```scala @memoize def fib(n: Int): Int = println(s"compute fib of $n") if n <= 1 then n else fib(n - 1) + fib(n - 2) ``` and the macro will modify the definition to create ```scala val fibCache = mutable.Map.empty[Int, Int] def fib(n: Int): Int = fibCache.getOrElseUpdate( n, { println(s"compute fib of $n") if n <= 1 then n else fib(n - 1) + fib(n - 2) } ) ``` #### Based on * #15626 * https://infoscience.epfl.ch/record/294615?ln=en #### Followed by * #16454

Enable the addition of classes from a `MacroAnnotation`: * Can add new `class` definitions next to the annotated definition Special cases: * A top-level `def`, `val`, `var`, `lazy val` can return a `class` definition that is owned by the package or package object. Related PRs: * Follows scala#16454

Enable the addition of classes from a `MacroAnnotation`: * Can add new `class` definitions next to the annotated definition Special cases: * An annotated top-level `def`, `val`, `var`, `lazy val` can return a `class` definition that is owned by the package or package object. Related PRs: * Follows scala#16454

* Add `Symbol.freshName` * Remove `Symbol.newUniqueMethod` * Remove `Symbol.newUniqueVal` This API is necessary to be able to create new class members without having name clashes. It should also be usable to create new top level definitions that have names that do not clash. This version of unique name can be used for `val`, `def` and `class` symbols.

Enable modification of classes with `MacroAnnotation`: * Can annotate `class` to transform it * Can annotate `object` to transform the companion class Supported class modifications: * Modify the implementations of `def`, `val`, `var`, `lazy val`, `class`, `object` in the class * Add new `def`, `val`, `var`, `lazy val`, `class`, `object` members to the class * Add a new override for a `def`, `val`, `var`, `lazy val` members in the class Restrictions: * An annotation on a top-level class cannot return a top-level `def`, `val`, `var`, `lazy val`

Enable the addition of classes from a `MacroAnnotation`: * Can add new `class` definitions next to the annotated definition Special cases: * An annotated top-level `def`, `val`, `var`, `lazy val` can return a `class` definition that is owned by the package or package object. Related PRs: * Follows scala#16454

Enable the addition of classes from a `MacroAnnotation`: * Can add new `class`/`object` definitions next to the annotated definition Special cases: * An annotated top-level `def`, `val`, `var`, `lazy val` can return a `class`/`object` definition that is owned by the package or package object. Related PRs: * Follows #16454

Enable the addition of classes from a `MacroAnnotation`: * Can add new `class` definitions next to the annotated definition Special cases: * An annotated top-level `def`, `val`, `var`, `lazy val` can return a `class` definition that is owned by the package or package object. Related PRs: * Follows scala#16454

jilen · 2023-02-17T04:45:58Z

Is it possible to transform companion object while annotate on class ?

alexarchambault · 2023-02-22T10:51:01Z

Is it possible to transform companion object while annotate on class ?

Would love to know this too. In Scala 2 macro annotations, the transform method accepts a list of Trees, like def transform(annottees: Tree*): Tree, that is passed both a ClassDef and a ModuleDef. But it only accepts a single quotes.reflect.Definition in Scala 3.

nicolasstucki · 2023-02-22T11:05:36Z

Is it possible to transform companion object while annotate on class ?

It is not possible with this version. What is the use case?

alexarchambault · 2023-02-22T11:16:39Z

A use case for me would be a macro annotation acting as a more refined derives, or more generally, adding given instances in the companion depending on what's in the class body, like

@IsMapEntry
class Foo {
  @Key
  def id: String = "a"
  @Value
  def value: Int = 2
}

where @IsMapEntry would look at the body of Foo, find the @Key and @Value annotated methods, read their types, and put something like this in the companion of Foo:

given AsMapEntry[Foo, String, Int] = AsMapEntry.derive // String and Int are the @Key and @Value annotated method types

nicolasstucki · 2023-02-22T16:32:11Z

In this version of macro annotations, you cannot generate definitions that will be visible to users. The generated given AsMapEntry could only be accessed from your macro implementation.

Why not use class Foo(val id: String = "a", val value: Int = 2) derives IsMapEntry ?

alexarchambault · 2023-02-22T17:34:23Z

Why not use class Foo(val id: String = "a", val value: Int = 2) derives IsMapEntry ?

Because IsMapEntry has more than one type parameter. Getting an error like Foo cannot be unified with the type argument of IsMapEntry when using derives (and things like derives IsMapEntry[?, String, String] don't seem to work).

alexarchambault · 2023-02-22T17:36:04Z

In more complex cases, I wish I would have been able to use parameters of the annotation in the additional definitions (derives wouldn't cover that case either).

jilen · 2023-02-23T02:06:06Z

Another case is the zio accessor generation.
Also, it would be great for scala2 migration (e.g. JsonCodec in circe.)

kitlangton · 2023-03-07T00:25:51Z

Similar to the accessor macro above, generating lenses on the companion object would also be an example use case.

@lenses
case class Person(name: String, age: Int)

// Would expand into

case class Person(name: String, age: Int)

object Person:
  val name: Lens[Person, String] = Lens.make(_.name)
  val age: List[Person, Int] = Lens.make(_.age)

It seems like a trivial thing, but it'd be nice to avoid the boilerplate 😄. I wonder if there's a solution to this that doesn't require full power Scala 2-style pre-type-checked annotations.

smarter · 2023-03-07T12:42:49Z

I wonder if there's a solution to this that doesn't require full power Scala 2-style pre-type-checked annotations.

My best attempt: https://contributors.scala-lang.org/t/scala-3-macro-annotations-and-code-generation/6035

kitlangton · 2023-03-07T13:55:40Z

That seems like a great idea @smarter! I'll give it a try :)

smarter · 2023-03-07T14:00:41Z

Cool! In case you haven't seen it, I have a prototype up at #16545

kitlangton · 2023-03-07T14:01:47Z

I was actually just looking at that! It would appear that it's not yet using the -rewrite mechanism, is that correct? If not, is there anything preventing that at the moment, if I were to try to hook into that ability?

smarter · 2023-03-07T14:17:42Z

If not, is there anything preventing that at the moment

No, it's just a matter of doing the work, so you're more than welcome to take a stab at it :). This ties in with work started by @ckipp01 on structured diagnostics since we want to expose that information to IDEs, but that part should be orthogonal to the API we use in macros hopefully.

nicolasstucki self-assigned this Dec 1, 2022

nicolasstucki force-pushed the macro-annotations-modify-class branch 3 times, most recently from 1dc36c6 to 51c7a41 Compare December 5, 2022 13:57

nicolasstucki changed the title ~~TASTy macro annotations class modifications (part 2)~~ Macro annotations class modifications (part 2) Dec 5, 2022

nicolasstucki mentioned this pull request Dec 5, 2022

Macro annotation (part 1) #16392

Merged

nicolasstucki force-pushed the macro-annotations-modify-class branch 12 times, most recently from bf08d00 to 1599314 Compare December 9, 2022 16:29

Kordyjan added this to the 3.3.0-RC1 milestone Dec 12, 2022

nicolasstucki force-pushed the macro-annotations-modify-class branch 6 times, most recently from e4d781a to 86c6d54 Compare December 14, 2022 10:58

nicolasstucki mentioned this pull request Dec 15, 2022

Fix macro annotations spliceOwner #16513

Merged

nicolasstucki mentioned this pull request Dec 15, 2022

Enable returning classes from MacroAnnotations (part 3) #16534

Merged

nicolasstucki added 2 commits December 19, 2022 16:49

nicolasstucki force-pushed the macro-annotations-modify-class branch from 88c6f14 to 52c9461 Compare December 19, 2022 15:50

nicolasstucki enabled auto-merge December 19, 2022 16:29

nicolasstucki merged commit 0555491 into scala:main Dec 19, 2022

nicolasstucki deleted the macro-annotations-modify-class branch December 19, 2022 17:02

yilinwei mentioned this pull request Dec 19, 2022

Recommended replacement for @Lenses optics-dev/Monocle#1181

Open

nicolasstucki mentioned this pull request Dec 23, 2022

Basic Design of Macro Annotations #15626

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armanbilge mentioned this pull request Mar 11, 2023

Mononcle doesn't support @Lenses in Scala3. optics-dev/Monocle#1337

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ckipp01 mentioned this pull request Jun 5, 2023

Support for macro annotations lampepfl/dotty-feature-requests#278

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Kordyjan modified the milestones: 3.3.0-RC1, 3.3.0 Aug 1, 2023

joroKr21 mentioned this pull request Jul 12, 2024

Scala 3 feature parity typelevel/cats-tagless#170

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Macro annotations class modifications (part 2) #16454

Macro annotations class modifications (part 2) #16454

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Macro annotations class modifications (part 2) #16454

Macro annotations class modifications (part 2) #16454

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