SIP-53 - Quote pattern explicit type variable syntax #17362

nicolasstucki · 2023-04-28T07:44:29Z

SIP-53: https://github.com/scala/improvement-proposals/blob/main/content/quote-pattern-type-variable-syntax.md

This PR implements the feature under experimental mode.

smarter · 2023-05-02T11:54:17Z

Could you add a test case related to semicolon inference? scala/improvement-proposals#59 (comment)

nicolasstucki · 2023-05-11T09:59:25Z

This is a binary-compatible change. Now that it is also experimental, it seems it no longer needs a minor release.

compiler/src/dotty/tools/dotc/ast/Desugar.scala

smarter · 2023-05-18T19:35:51Z

compiler/src/dotty/tools/dotc/ast/Desugar.scala

+        val untpdTypeVariables = stats.takeWhile {
+          case tdef @ untpd.TypeDef(name, _) => name.isVarPattern
+          case _ => false
+        }.asInstanceOf[List[untpd.TypeDef]]
+        val otherStats = stats.dropWhile {
+          case tdef @ untpd.TypeDef(name, _) => name.isVarPattern
+          case _ => false
+        }


Isn't this equivalent to:

Suggested change

val untpdTypeVariables = stats.takeWhile {

case tdef @ untpd.TypeDef(name, _) => name.isVarPattern

case _ => false

}.asInstanceOf[List[untpd.TypeDef]]

val otherStats = stats.dropWhile {

case tdef @ untpd.TypeDef(name, _) => name.isVarPattern

case _ => false

}

val (untpdTypeVariables, otherStats) = stats.partition:

case tdef @ untpd.TypeDef(name, _) => name.isVarPattern

case _ => false

In the case of quoted type patterns, it might be equivalent. But this might not be the case with expression quote patterns. Consider this ill-formed pattern '{ type t; $x; type u; $y }, in this case we only want to desugar type t as a type variable. When checking the pattern tpye u will chase an error. Changing the way we partition would the way we emit errors in those ill-formed patterns.

in this case we only want to desugar type t as a type variable.

Right, this should be achievable by using .span instead of .partition.

smarter · 2023-05-18T19:39:32Z

compiler/src/dotty/tools/dotc/parsing/Parsers.scala

+      if in.token == SEMI then in.nextToken()
+      if in.isNewLine then in.nextToken()


Could this be:

Suggested change

if in.token == SEMI then in.nextToken()

if in.isNewLine then in.nextToken()

acceptStatSep()

That does not work.

docs/_docs/reference/metaprogramming/macros.md

smarter · 2023-05-18T19:49:24Z

compiler/src/dotty/tools/dotc/typer/QuotesAndSplices.scala

+    for untpdTypeVariable <- untpdTypeVariables do untpdTypeVariable.rhs match
+      case _: TypeBoundsTree => // ok
+      case LambdaTypeTree(_, body: TypeBoundsTree) => // ok
+      case _ => report.error("Quote type variable definition cannot be an alias", untpdTypeVariable.srcPos)


If we declare a type variable with the same as an alias, then we know the type of that variable. It would be useless to solve the type of that type variable at runtime when pattern matching. This could also be seen as a missed optimization.

smarter · 2023-05-18T19:49:54Z

compiler/src/dotty/tools/dotc/typer/QuotesAndSplices.scala

+        if !(typeSymInfo =:= TypeBounds.empty) && !(typeSym.info <:< typeSymInfo) then
+          report.warning(em"Ignored bound$typeSymInfo\n\nConsider defining bounds explicitly `'{ $typeSym$typeSymInfo; ... }`", tree.srcPos)


What's an example where this warning triggers?

import scala.quoted.* type F[x <: Int, y <: Double] def test(x: Type[?])(using Quotes) = x match case '[ F[t, t] ] => // warn // error

-- Warning: t/Test.scala:5:17 -------------------------------------------------- 5 | case '[ F[t, t] ] => // warn // error | ^ | Ignored bound <: Double | | Consider defining bounds explicitly `'{ type t <: Int & Double; ... }` -- [E057] Type Mismatch Error: t/Test.scala:5:15 ------------------------------- 5 | case '[ F[t, t] ] => // warn // error | ^ | Type argument t does not conform to upper bound Double | | longer explanation available when compiling with `-explain`

The winning serves as extra information for the failure that will happen afterward. The warning complements the error message. We could make it an error, but I am not sure how to re-phrase the message in that case. This version seemed to be the simplest with the clearest hint.

I added a test case for this in tests/neg-macros/quote-type-variable-no-inference.scala.

compiler/src/dotty/tools/dotc/typer/QuotesAndSplices.scala

smarter · 2023-05-18T19:59:50Z

compiler/src/dotty/tools/dotc/parsing/Parsers.scala

+     */
+    def quote(inPattern: Boolean): Tree =
+      atSpan(in.skipToken()) {
+        withinStaged(StageKind.Quoted | (if (inPattern) StageKind.QuotedPattern else 0)) {


Is it possible to be StageKind.QuotedPattern but not StageKind.Quoted?

No. It would be possible to make all StageKind disjoint if we want.

smarter · 2023-05-18T20:01:05Z

compiler/src/dotty/tools/dotc/parsing/Parsers.scala

@@ -1761,6 +1758,20 @@ object Parsers {
      if in.isNewLine then in.nextToken()
      tdef

+    /** Quoted ::=  ‘'’ ‘{’ Block ‘}’
+     *           |  ‘'’ ‘[’ Type ‘]’


Couldn't the grammar be refactored so that we can drop this case and only have Block and TypeBlock?

This should just be TypeBlock. Type is already one of the cases of TypeBlock.

In syntax.md we have the correct one

Quoted ::= ‘'’ ‘{’ Block ‘}’ | ‘'’ ‘[’ TypeBlock ‘]’

nicolasstucki · 2023-06-07T06:43:43Z

Rebased

With this change we can support references to quote pattern type variables without backticks. ```scala case '{ type t; ... : F[t] } ``` SIP: https://github.com/scala/improvement-proposals/blob/main/content/quote-pattern-type-variable-syntax.md?plain=1#L66-L70 ```scala case '{ ... : F[t, t] } ``` SIP: https://github.com/scala/improvement-proposals/blob/main/content/quote-pattern-type-variable-syntax.md?plain=1#L72-L78

Support explicit type variable definition in quoted patterns. This allows users to set explicit bounds or use the binding twice. Previously this was only possible on quoted expression patterns case '{ ... }. ```scala case '[type x; x] => case '[type x; Map[x, x]] => case '[type x <: List[Any]; x] => case '[type f[X]; f] => case '[type f <: AnyKind; f] => ``` Fixes scala#10864 Fixes scala#11738

nicolasstucki · 2023-06-16T09:06:49Z

Rebased

SIP-53: https://docs.scala-lang.org/sips/quote-pattern-type-variable-syntax.html Follow up of #17362 for 3.4

nicolasstucki added the needs-minor-release This PR cannot be merged until the next minor release label Apr 28, 2023

This was referenced Apr 28, 2023

Quoted pattern type variables without backticks #16935

Closed

Support type variable with bounds in quoted pattern #16910

Closed

nicolasstucki force-pushed the sip-53 branch from 2d3136f to 713c246 Compare April 28, 2023 07:54

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SIP-53 - Quote Pattern Explicit Type Variable Syntax scala/improvement-proposals#59

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This was linked to issues May 2, 2023

Quoting type in a pattern doesn't work with higher-kinded types #10864

Closed

Can't patmat to extract type constructor from quoted type #11738

Closed

nicolasstucki mentioned this pull request May 2, 2023

Can't compile quotations matching with HK type arguments involved #9360

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nicolasstucki marked this pull request as ready for review May 2, 2023 11:21

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nicolasstucki force-pushed the sip-53 branch from a726494 to 6932f9e Compare May 3, 2023 10:27

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smarter mentioned this pull request May 3, 2023

transparent macro : Unexpected loss of refinement #17398

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Kordyjan added the release-notes Should be mentioned in the release notes label May 12, 2023

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nicolasstucki added 3 commits June 16, 2023 11:00

Refactor quote parsing

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Stabilize SIP-53 (quote pattern explicit type variable syntax) #18574

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smarter added a commit that referenced this pull request Oct 6, 2023

Stabilize SIP-53 (quote pattern explicit type variable syntax) (#18574)

5d6578d

SIP-53: https://docs.scala-lang.org/sips/quote-pattern-type-variable-syntax.html Follow up of #17362 for 3.4

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SIP-53 - Quote pattern explicit type variable syntax #17362

SIP-53 - Quote pattern explicit type variable syntax #17362

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nicolasstucki commented Jun 7, 2023

nicolasstucki commented Jun 16, 2023

		if in.token == SEMI then in.nextToken()
		if in.isNewLine then in.nextToken()

	if in.token == SEMI then in.nextToken()
	if in.isNewLine then in.nextToken()
	acceptStatSep()

		if !(typeSymInfo =:= TypeBounds.empty) && !(typeSym.info <:< typeSymInfo) then
		report.warning(em"Ignored bound$typeSymInfo\n\nConsider defining bounds explicitly `'{ $typeSym$typeSymInfo; ... }`", tree.srcPos)

SIP-53 - Quote pattern explicit type variable syntax #17362

SIP-53 - Quote pattern explicit type variable syntax #17362

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nicolasstucki commented Jun 7, 2023

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nicolasstucki commented Apr 28, 2023 •

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