Runtime error when a single '%' character is specified for a string literal with f interpolator

[kynthus]

Compiler version

3.0.0-M3

Minimized code

val x: Int = 5
val y: Int = 2

println(f"x % y = ${x % y}%d") // java.util.UnknownFormatConversionException

Output

Starting scala3 REPL...
Scala compiler version 3.0.0-M3 -- Copyright 2002-2020, LAMP/EPFL
scala> val x: Int = 5
     | val y: Int = 2
     |
     | println(f"x % y = ${x % y}%d")
java.util.UnknownFormatConversionException: Conversion = 'y'
  at java.util.Formatter$FormatSpecifier.conversion(Unknown Source)
  at java.util.Formatter$FormatSpecifier.<init>(Unknown Source)
  at java.util.Formatter.parse(Unknown Source)
  at java.util.Formatter.format(Unknown Source)
  at java.util.Formatter.format(Unknown Source)
  at java.lang.String.format(Unknown Source)
  at scala.collection.StringOps$.format$extension(StringOps.scala:968)
  ... 27 elided
java.lang.NoClassDefFoundError: Could not initialize class rs$line$1$
  at rs$line$1.y(rs$line$1)
  at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
  at sun.reflect.NativeMethodAccessorImpl.invoke(Unknown Source)
  at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source)
  at java.lang.reflect.Method.invoke(Unknown Source)
  at dotty.tools.repl.Rendering.$anonfun$3(Rendering.scala:84)
  at scala.Option.map(Option.scala:242)
  at dotty.tools.repl.Rendering.valueOf(Rendering.scala:84)
  at dotty.tools.repl.Rendering.renderVal(Rendering.scala:121)
  at dotty.tools.repl.ReplDriver.$anonfun$13(ReplDriver.scala:308)
  at scala.collection.immutable.List.flatMap(List.scala:293)
  at scala.collection.immutable.List.flatMap(List.scala:79)
  at dotty.tools.repl.ReplDriver.extractAndFormatMembers$2(ReplDriver.scala:308)
  at dotty.tools.repl.ReplDriver.renderDefinitions$$anonfun$2(ReplDriver.scala:331)
  at scala.Option.map(Option.scala:242)
  at dotty.tools.repl.ReplDriver.renderDefinitions(ReplDriver.scala:334)
  at dotty.tools.repl.ReplDriver.compile$$anonfun$2(ReplDriver.scala:253)
  at scala.util.Either.fold(Either.scala:189)
  at dotty.tools.repl.ReplDriver.compile(ReplDriver.scala:269)
  at dotty.tools.repl.ReplDriver.interpret(ReplDriver.scala:197)
  at dotty.tools.repl.ReplDriver.loop$1(ReplDriver.scala:130)
  at dotty.tools.repl.ReplDriver.runUntilQuit$$anonfun$1(ReplDriver.scala:133)
  at dotty.tools.repl.ReplDriver.withRedirectedOutput(ReplDriver.scala:152)
  at dotty.tools.repl.ReplDriver.runUntilQuit(ReplDriver.scala:133)
  at dotty.tools.repl.Main$.main(Main.scala:6)
  at dotty.tools.repl.Main.main(Main.scala)
java.lang.NoClassDefFoundError: Could not initialize class rs$line$1$
  at rs$line$1.res0(rs$line$1)
  at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
  at sun.reflect.NativeMethodAccessorImpl.invoke(Unknown Source)
  at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source)
  at java.lang.reflect.Method.invoke(Unknown Source)
  at dotty.tools.repl.Rendering.$anonfun$3(Rendering.scala:84)
  at scala.Option.map(Option.scala:242)
  at dotty.tools.repl.Rendering.valueOf(Rendering.scala:84)
  at dotty.tools.repl.Rendering.renderVal(Rendering.scala:121)
  at dotty.tools.repl.ReplDriver.$anonfun$13(ReplDriver.scala:308)
  at scala.collection.immutable.List.flatMap(List.scala:293)
  at scala.collection.immutable.List.flatMap(List.scala:79)
  at dotty.tools.repl.ReplDriver.extractAndFormatMembers$2(ReplDriver.scala:308)
  at dotty.tools.repl.ReplDriver.renderDefinitions$$anonfun$2(ReplDriver.scala:331)
  at scala.Option.map(Option.scala:242)
  at dotty.tools.repl.ReplDriver.renderDefinitions(ReplDriver.scala:334)
  at dotty.tools.repl.ReplDriver.compile$$anonfun$2(ReplDriver.scala:253)
  at scala.util.Either.fold(Either.scala:189)
  at dotty.tools.repl.ReplDriver.compile(ReplDriver.scala:269)
  at dotty.tools.repl.ReplDriver.interpret(ReplDriver.scala:197)
  at dotty.tools.repl.ReplDriver.loop$1(ReplDriver.scala:130)
  at dotty.tools.repl.ReplDriver.runUntilQuit$$anonfun$1(ReplDriver.scala:133)
  at dotty.tools.repl.ReplDriver.withRedirectedOutput(ReplDriver.scala:152)
  at dotty.tools.repl.ReplDriver.runUntilQuit(ReplDriver.scala:133)
  at dotty.tools.repl.Main$.main(Main.scala:6)
  at dotty.tools.repl.Main.main(Main.scala)

Expectation

On Scala 2.10.2 to the current stable version,
I get a compile error when specifying a single '%' character.

Welcome to Scala version 2.10.2 (Java HotSpot(TM) 64-Bit Server VM, Java 1.6.0_45).
Type in expressions to have them evaluated.
Type :help for more information.

scala> val x: Int = 5
x: Int = 5

scala> val y: Int = 2
y: Int = 2

scala>

scala> println(f"x % y = ${x % y}%d")
<console>:10: error: percent signs not directly following splicees must be escaped
              println(f"x % y = ${x % y}%d")
                          ^

Welcome to Scala 2.13.4 (Java HotSpot(TM) 64-Bit Server VM, Java 1.8.0_202).
Type in expressions for evaluation. Or try :help.

scala> val x: Int = 5
     | val y: Int = 2
     |
     | println(f"x % y = ${x % y}%d")
       println(f"x % y = ${x % y}%d")
                     ^
On line 4: error: illegal conversion character 'y'

So I expected it to be the same in Scala 3.

[som-snytt]

Added to #9939

[kynthus]

@som-snytt Thanks for the addition as a related issue!

[som-snytt]

Worth noting "% y" looks like a format conversion because space char is a legal flag ("leading space for positive values").