f-interpolator parity

[som-snytt]

Minimized code

scala> f"${3.14}%.2f rounds to ${3}%d"
1 |f"${3.14}%.2f rounds to ${3}%d"
  |                          ^
  |                          type mismatch;
  |                           found   : Double
  |                           required: Int
  | This location contains code that was inlined from rs$line$2:1

scala> f"${java.lang.Boolean.valueOf(false)}%b"   // any boxed value
1 |f"${java.lang.Boolean.valueOf(false)}%b"
  |    ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  |    type mismatch;
  |     found   : Boolean
  |     required: Boolean
  | This location contains code that was inlined from rs$line$17:1

scala> f"${BigInt(120)}%d"
1 |f"${BigInt(120)}%d"
  |    ^^^^^^^^^^^
  |    type mismatch;
  |     found   : math.BigInt
  |     required: Int
  | This location contains code that was inlined from rs$line$27:1

scala> f"${BigDecimal(3.4)}%e"
1 |f"${BigDecimal(3.4)}%e"
  |    ^^^^^^^^^^^^^^^
  |    type mismatch;
  |     found   : math.BigDecimal
  |     required: Double
  | This location contains code that was inlined from rs$line$30:1

scala> f"${3L}%e"
1 |f"${3L}%e"
  |    ^^
  |    type mismatch;
  |     found   : Long
  |     required: Double
  | This location contains code that was inlined from rs$line$31:1

Output

// as shown

Expectation

scala 2.13.3> f"${3.14}%.2f rounds to ${3}%d"
val res0: String = 3.14 rounds to 3

scala 2.13.3> f"${java.lang.Boolean.valueOf(false)}%b"
val res0: String = false

scala 2.13.3> f"${BigInt(120)}%d"
val res5: String = 120

scala 2.13.3> f"${BigDecimal(3.4)}%e"
val res8: String = 3.400000e+00

scala 2.13.3> f"${3L}%e"
val res11: String = 3.000000e+00

[som-snytt]

scala> f"${0}%n"
val res1: String = "
"

[som-snytt]

scala> f"${0}%d"
val res9: String = 0

scala> f"${0}%%d"
val res10: String = %d

scala> f"${0}%%%d"
val res11: String = %0

scala> f"${0}%%%%d"
val res12: String = %%d

scala> f"${0}%%%%%d"
val res13: String = %%0

expected

scala 2.13.3> f"${0}%d"
val res21: String = 0

scala 2.13.3> f"${0}%%d"
val res22: String = 0%d

scala 2.13.3> f"${0}%%%d"
                      ^
              error: conversions must follow a splice; use %% for literal %, %n for newline

scala 2.13.3> f"${0}%%%%d"
val res24: String = 0%%d

scala 2.13.3> f"${0}%%%%%d"
                        ^
              error: conversions must follow a splice; use %% for literal %, %n for newline

[nicolasstucki]

I guess we should just port the implementation from Scala 2. We can port it in StringContextChecker.

[som-snytt]

I took a few minutes to try these examples from the scala 2 tests, and a minute more to look at fixing. I'll try to make time, modulo day job and pandemic sleep schedule. It's not obvious that keeping the old code is desirable. Also, it's tiresome to hear "String.format is slow." It would be nice to have ff or "fast format" interpolator that compiled to pretty printers. The challenge is to support all the format features.

[b-studios]

Thanks @som-snytt for looking into it, I assigned you to the issue.

[som-snytt]

Compare

Starting scala3 REPL...
scala> f"%"
1 |f"%"
  |  ^
  |  Missing conversion operator in '%'; use %% for literal %, %n for newline

scala> val x: Int = 5                                                           
     | val y: Int = 2
val x: Int = 5
val y: Int = 2

scala> f"x % y = ${x % y}%d"
java.util.UnknownFormatConversionException: Conversion = 'y'
  at java.base/java.util.Formatter$FormatSpecifier.conversion(Formatter.java:2839)
  at java.base/java.util.Formatter$FormatSpecifier.<init>(Formatter.java:2865)
  at java.base/java.util.Formatter.parse(Formatter.java:2713)
  at java.base/java.util.Formatter.format(Formatter.java:2655)
  at java.base/java.util.Formatter.format(Formatter.java:2609)
  at java.base/java.lang.String.format(String.java:3292)
  at scala.collection.StringOps$.format$extension(StringOps.scala:968)
  ... 27 elided

scala> f"%y"
1 |f"%y"
  |   ^^
  |   illegal conversion character 'y'

[som-snytt]

Cf #10315