Switch our string interpolators to use Show/Shown

compiler/src/dotty/tools/backend/sjs/JSExportsGen.scala

@@ -119,7 +119,7 @@ final class JSExportsGen(jsCodeGen: JSCodeGen)(using Context) {
       if (kind != overallKind) {
         bad = true
         report.error(
-            em"export overload conflicts with export of $firstSym: they are of different types ($kind / $overallKind)",
+            em"export overload conflicts with export of $firstSym: they are of different types (${kind.tryToShow} / ${overallKind.tryToShow})",
             info.pos)
       }
     }

compiler/src/dotty/tools/dotc/core/Decorators.scala

@@ -2,12 +2,13 @@ package dotty.tools
 package dotc
 package core
 
-import annotation.tailrec
-import Symbols._
-import Contexts._, Names._, Phases._, printing.Texts._
-import collection.mutable.ListBuffer
-import dotty.tools.dotc.transform.MegaPhase
-import printing.Formatting._
+import scala.annotation.tailrec
+import scala.collection.mutable.ListBuffer
+import scala.util.control.NonFatal
+
+import Contexts._, Names._, Phases._, Symbols._
+import printing.{ Printer, Showable }, printing.Formatting._, printing.Texts._
+import transform.MegaPhase
 
 /** This object provides useful implicit decorators for types defined elsewhere */
 object Decorators {
@@ -246,13 +247,29 @@ object Decorators {
       }
 
   extension [T](x: T)
-    def showing(
-        op: WrappedResult[T] ?=> String,
-        printer: config.Printers.Printer = config.Printers.default): T = {
-      printer.println(op(using WrappedResult(x)))
+    def showing[U](
+        op: WrappedResult[U] ?=> String,
+        printer: config.Printers.Printer = config.Printers.default)(using c: Conversion[T, U] | Null = null): T = {
+      // either the use of `$result` was driven by the expected type of `Shown`
+      // which led to the summoning of `Conversion[T, Shown]` (which we'll invoke)
+      // or no such conversion was found so we'll consume the result as it is instead
+      val obj = if c == null then x.asInstanceOf[U] else c(x)
+      printer.println(op(using WrappedResult(obj)))
       x
     }
 
+    /** Instead of `toString` call `show` on `Showable` values, falling back to `toString` if an exception is raised. */
+    def tryToShow(using Context): String = x match
+      case x: Showable =>
+        try x.show
+        catch
+          case ex: CyclicReference => "... (caught cyclic reference) ..."
+          case NonFatal(ex)
+              if !ctx.mode.is(Mode.PrintShowExceptions) && !ctx.settings.YshowPrintErrors.value =>
+            val msg = ex match { case te: TypeError => te.toMessage case _ => ex.getMessage }
+            s"[cannot display due to $msg, raw string = $x]"
+      case _ => String.valueOf(x).nn
+
   extension [T](x: T)
     def assertingErrorsReported(using Context): T = {
       assert(ctx.reporter.errorsReported)
@@ -269,19 +286,19 @@ object Decorators {
 
   extension (sc: StringContext)
     /** General purpose string formatting */
-    def i(args: Any*)(using Context): String =
+    def i(args: Shown*)(using Context): String =
       new StringFormatter(sc).assemble(args)
 
     /** Formatting for error messages: Like `i` but suppress follow-on
      *  error messages after the first one if some of their arguments are "non-sensical".
      */
-    def em(args: Any*)(using Context): String =
+    def em(args: Shown*)(using Context): String =
       new ErrorMessageFormatter(sc).assemble(args)
 
     /** Formatting with added explanations: Like `em`, but add explanations to
      *  give more info about type variables and to disambiguate where needed.
      */
-    def ex(args: Any*)(using Context): String =
+    def ex(args: Shown*)(using Context): String =
       explained(em(args: _*))
 
   extension [T <: AnyRef](arr: Array[T])

compiler/src/dotty/tools/dotc/core/TypeComparer.scala

@@ -2713,15 +2713,16 @@ object TypeComparer {
      */
     val Fresh: Repr = 4
 
-    extension (approx: Repr)
-      def low: Boolean = (approx & LoApprox) != 0
-      def high: Boolean = (approx & HiApprox) != 0
-      def addLow: Repr = approx | LoApprox
-      def addHigh: Repr = approx | HiApprox
-      def show: String =
-        val lo = if low then " (left is approximated)" else ""
-        val hi = if high then " (right is approximated)" else ""
-        lo ++ hi
+    object Repr:
+      extension (approx: Repr)
+        def low: Boolean = (approx & LoApprox) != 0
+        def high: Boolean = (approx & HiApprox) != 0
+        def addLow: Repr = approx | LoApprox
+        def addHigh: Repr = approx | HiApprox
+        def show: String =
+          val lo = if low then " (left is approximated)" else ""
+          val hi = if high then " (right is approximated)" else ""
+          lo ++ hi
   end ApproxState
   type ApproxState = ApproxState.Repr
 

compiler/src/dotty/tools/dotc/interactive/Completion.scala

@@ -161,7 +161,7 @@ object Completion {
                           |                prefix  = ${completer.prefix},
                           |                term    = ${completer.mode.is(Mode.Term)},
                           |                type    = ${completer.mode.is(Mode.Type)}
-                          |                results = $backtickCompletions%, %""")
+                          |                results = $backtickedCompletions%, %""")
     (offset, backtickedCompletions)
   }
 

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

@@ -606,7 +606,7 @@ object Parsers {
               if startIndentWidth <= nextIndentWidth then
                 i"""Line is indented too far to the right, or a `{` is missing before:
                    |
-                   |$t"""
+                   |${t.tryToShow}"""
               else
                 in.spaceTabMismatchMsg(startIndentWidth, nextIndentWidth),
               in.next.offset

compiler/src/dotty/tools/dotc/printing/Formatting.scala

@@ -1,47 +1,99 @@
-package dotty.tools.dotc
+package dotty.tools
+package dotc
 package printing
 
 import scala.language.unsafeNulls
 
+import scala.collection.mutable
+
 import core._
 import Texts._, Types._, Flags._, Symbols._, Contexts._
-import collection.mutable
 import Decorators._
-import scala.util.control.NonFatal
 import reporting.Message
 import util.DiffUtil
 import Highlighting._
 
 object Formatting {
 
+  object ShownDef:
+    /** Represents a value that has been "shown" and can be consumed by StringFormatter.
+     *  Not just a string because it may be a Seq that StringFormatter will intersperse with the trailing separator.
+     *  Also, it's not a `String | Seq[String]` because then we'd need a Context to call `Showable#show`.  We could
+     *  make Context a requirement for a Show instance but then we'd have lots of instances instead of just one ShowAny
+     *  instance.  We could also try to make `Show#show` require the Context, but then that breaks the Conversion. */
+    opaque type Shown = Any
+    object Shown:
+      given [A: Show]: Conversion[A, Shown] = Show[A].show(_)
+
+    sealed abstract class Show[-T]:
+      /** Show a value T by returning a "shown" result. */
+      def show(x: T): Shown
+
+    /** The base implementation, passing the argument to StringFormatter which will try to `.show` it. */
+    object ShowAny extends Show[Any]:
+      def show(x: Any): Shown = x
+
+    class ShowImplicits2:
+      given Show[Product] = ShowAny
+
+    class ShowImplicits1 extends ShowImplicits2:
+      given Show[ImplicitRef]      = ShowAny
+      given Show[Names.Designator] = ShowAny
+      given Show[util.SrcPos]      = ShowAny
+
+    object Show extends ShowImplicits1:
+      inline def apply[A](using inline z: Show[A]): Show[A] = z
+
+      given [X: Show]: Show[Seq[X]] with
+        def show(x: Seq[X]) = x.map(Show[X].show)
+
+      given [A: Show, B: Show]: Show[(A, B)] with
+        def show(x: (A, B)) = (Show[A].show(x._1), Show[B].show(x._2))
+
+      given [X: Show]: Show[X | Null] with
+        def show(x: X | Null) = if x == null then "null" else Show[X].show(x.nn)
+
+      given Show[FlagSet] with
+        def show(x: FlagSet) = x.flagsString
+
+      given Show[TypeComparer.ApproxState] with
+        def show(x: TypeComparer.ApproxState) = TypeComparer.ApproxState.Repr.show(x)
+
+      given Show[Showable]                            = ShowAny
+      given Show[Shown]                               = ShowAny
+      given Show[Int]                                 = ShowAny
+      given Show[Char]                                = ShowAny
+      given Show[Boolean]                             = ShowAny
+      given Show[String]                              = ShowAny
+      given Show[Class[?]]                            = ShowAny
+      given Show[Exception]                           = ShowAny
+      given Show[StringBuffer]                        = ShowAny
+      given Show[CompilationUnit]                     = ShowAny
+      given Show[Phases.Phase]                        = ShowAny
+      given Show[TyperState]                          = ShowAny
+      given Show[config.ScalaVersion]                 = ShowAny
+      given Show[io.AbstractFile]                     = ShowAny
+      given Show[parsing.Scanners.Scanner]            = ShowAny
+      given Show[util.SourceFile]                     = ShowAny
+      given Show[util.Spans.Span]                     = ShowAny
+      given Show[tasty.TreeUnpickler#OwnerTree]       = ShowAny
+    end Show
+  end ShownDef
+  export ShownDef.{ Show, Shown }
+
   /** General purpose string formatter, with the following features:
    *
-   *  1) On all Showables, `show` is called instead of `toString`
-   *  2) Exceptions raised by a `show` are handled by falling back to `toString`.
-   *  3) Sequences can be formatted using the desired separator between two `%` signs,
+   *  1. Invokes the `show` extension method on the interpolated arguments.
+   *  2. Sequences can be formatted using the desired separator between two `%` signs,
    *     eg `i"myList = (${myList}%, %)"`
-   *  4) Safe handling of multi-line margins. Left margins are skipped om the parts
+   *  3. Safe handling of multi-line margins. Left margins are stripped on the parts
    *     of the string context *before* inserting the arguments. That way, we guard
    *     against accidentally treating an interpolated value as a margin.
    */
   class StringFormatter(protected val sc: StringContext) {
-    protected def showArg(arg: Any)(using Context): String = arg match {
-      case arg: Showable =>
-        try arg.show
-        catch {
-          case ex: CyclicReference => "... (caught cyclic reference) ..."
-          case NonFatal(ex)
-          if !ctx.mode.is(Mode.PrintShowExceptions) &&
-             !ctx.settings.YshowPrintErrors.value =>
-            val msg = ex match
-              case te: TypeError => te.toMessage
-              case _ => ex.getMessage
-            s"[cannot display due to $msg, raw string = ${arg.toString}]"
-        }
-      case _ => String.valueOf(arg)
-    }
+    protected def showArg(arg: Any)(using Context): String = arg.tryToShow
 
-    private def treatArg(arg: Any, suffix: String)(using Context): (Any, String) = arg match {
+    private def treatArg(arg: Shown, suffix: String)(using Context): (Any, String) = arg match {
       case arg: Seq[?] if suffix.nonEmpty && suffix.head == '%' =>
         val (rawsep, rest) = suffix.tail.span(_ != '%')
         val sep = StringContext.processEscapes(rawsep)
@@ -51,7 +103,7 @@ object Formatting {
         (showArg(arg), suffix)
     }
 
-    def assemble(args: Seq[Any])(using Context): String = {
+    def assemble(args: Seq[Shown])(using Context): String = {
       def isLineBreak(c: Char) = c == '\n' || c == '\f' // compatible with StringLike#isLineBreak
       def stripTrailingPart(s: String) = {
         val (pre, post) = s.span(c => !isLineBreak(c))
@@ -77,18 +129,6 @@ object Formatting {
     override protected def showArg(arg: Any)(using Context): String =
       wrapNonSensical(arg, super.showArg(arg)(using errorMessageCtx))
 
-  class SyntaxFormatter(sc: StringContext) extends StringFormatter(sc) {
-    override protected def showArg(arg: Any)(using Context): String =
-      arg match {
-        case hl: Highlight =>
-          hl.show
-        case hb: HighlightBuffer =>
-          hb.toString
-        case _ =>
-          SyntaxHighlighting.highlight(super.showArg(arg))
-      }
-  }
-
   private def wrapNonSensical(arg: Any, str: String)(using Context): String = {
     import Message._
     def isSensical(arg: Any): Boolean = arg match {

compiler/src/dotty/tools/dotc/reporting/messages.scala

@@ -1759,7 +1759,9 @@ import transform.SymUtils._
 
   class ClassAndCompanionNameClash(cls: Symbol, other: Symbol)(using Context)
     extends NamingMsg(ClassAndCompanionNameClashID) {
-    def msg = em"Name clash: both ${cls.owner} and its companion object defines ${cls.name.stripModuleClassSuffix}"
+    def msg =
+      val name = cls.name.stripModuleClassSuffix
+      em"Name clash: both ${cls.owner} and its companion object defines $name"
     def explain =
       em"""|A ${cls.kindString} and its companion object cannot both define a ${hl("class")}, ${hl("trait")} or ${hl("object")} with the same name:
            |  - ${cls.owner} defines ${cls}

compiler/src/dotty/tools/dotc/sbt/ExtractAPI.scala

@@ -776,7 +776,7 @@ private class ExtractAPICollector(using Context) extends ThunkHolder {
           case n: Name =>
             h = nameHash(n, h)
           case elem =>
-            cannotHash(what = i"`$elem` of unknown class ${elem.getClass}", elem, tree)
+            cannotHash(what = i"`${elem.tryToShow}` of unknown class ${elem.getClass}", elem, tree)
       h
     end iteratorHash
 

compiler/src/dotty/tools/dotc/transform/AccessProxies.scala

@@ -58,7 +58,7 @@ abstract class AccessProxies {
 
   /** Add all needed accessors to the `body` of class `cls` */
   def addAccessorDefs(cls: Symbol, body: List[Tree])(using Context): List[Tree] = {
-    val accDefs = accessorDefs(cls)
+    val accDefs = accessorDefs(cls).toList
     transforms.println(i"add accessors for $cls: $accDefs%, %")
     if (accDefs.isEmpty) body else body ++ accDefs
   }

compiler/src/dotty/tools/dotc/transform/DropOuterAccessors.scala

@@ -80,7 +80,7 @@ class DropOuterAccessors extends MiniPhase with IdentityDenotTransformer:
             cpy.Block(rhs)(inits.filterNot(dropOuterInit), expr)
         })
     assert(droppedParamAccessors.isEmpty,
-      i"""Failed to eliminate: $droppedParamAccessors
+      i"""Failed to eliminate: ${droppedParamAccessors.toList}
           when dropping outer accessors for ${ctx.owner} with
           $impl""")
     cpy.Template(impl)(constr = constr1, body = body1)

compiler/src/dotty/tools/dotc/transform/Erasure.scala

@@ -266,7 +266,7 @@ object Erasure {
     def constant(tree: Tree, const: Tree)(using Context): Tree =
       (if (isPureExpr(tree)) const else Block(tree :: Nil, const)).withSpan(tree.span)
 
-    final def box(tree: Tree, target: => String = "")(using Context): Tree = trace(i"boxing ${tree.showSummary}: ${tree.tpe} into $target") {
+    final def box(tree: Tree, target: => String = "")(using Context): Tree = trace(i"boxing ${tree.showSummary()}: ${tree.tpe} into $target") {
       tree.tpe.widen match {
         case ErasedValueType(tycon, _) =>
           New(tycon, cast(tree, underlyingOfValueClass(tycon.symbol.asClass)) :: Nil) // todo: use adaptToType?
@@ -286,7 +286,7 @@ object Erasure {
       }
     }
 
-    def unbox(tree: Tree, pt: Type)(using Context): Tree = trace(i"unboxing ${tree.showSummary}: ${tree.tpe} as a $pt") {
+    def unbox(tree: Tree, pt: Type)(using Context): Tree = trace(i"unboxing ${tree.showSummary()}: ${tree.tpe} as a $pt") {
       pt match {
         case ErasedValueType(tycon, underlying) =>
           def unboxedTree(t: Tree) =
@@ -1031,7 +1031,7 @@ object Erasure {
     }
 
     override def adapt(tree: Tree, pt: Type, locked: TypeVars, tryGadtHealing: Boolean)(using Context): Tree =
-      trace(i"adapting ${tree.showSummary}: ${tree.tpe} to $pt", show = true) {
+      trace(i"adapting ${tree.showSummary()}: ${tree.tpe} to $pt", show = true) {
         if ctx.phase != erasurePhase && ctx.phase != erasurePhase.next then
           // this can happen when reading annotations loaded during erasure,
           // since these are loaded at phase typer.

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

@@ -1197,7 +1197,7 @@ trait Checking {
     case _: TypeTree =>
     case _ =>
       if tree.tpe.typeParams.nonEmpty then
-        val what = if tree.symbol.exists then tree.symbol else i"type $tree"
+        val what = if tree.symbol.exists then tree.symbol.show else i"type $tree"
         report.error(em"$what takes type parameters", tree.srcPos)
 
   /** Check that we are in an inline context (inside an inline method or in inline code) */

compiler/test/dotty/tools/dotc/printing/PrinterTests.scala

@@ -1,9 +1,11 @@
-package dotty.tools.dotc.printing
+package dotty.tools
+package dotc
+package printing
 
-import dotty.tools.DottyTest
-import dotty.tools.dotc.ast.{Trees,tpd}
-import dotty.tools.dotc.core.Names._
-import dotty.tools.dotc.core.Symbols._
+import ast.{ Trees, tpd }
+import core.Names._
+import core.Symbols._
+import core.Decorators._
 import dotty.tools.dotc.core.Contexts.Context
 
 import org.junit.Assert.assertEquals
@@ -49,4 +51,26 @@ class PrinterTests extends DottyTest {
       assertEquals("Int & (Boolean | String)", bar.tpt.show)
     }
   }
+
+  @Test def string: Unit = assertEquals("foo", i"${"foo"}")
+
+  import core.Flags._
+  @Test def flagsSingle: Unit      = assertEquals("final", i"$Final")
+  @Test def flagsSeq: Unit         = assertEquals("<static>, final", i"${Seq(JavaStatic, Final)}%, %")
+  @Test def flagsTuple: Unit       = assertEquals("(<static>,final)", i"${(JavaStatic, Final)}")
+  @Test def flagsSeqOfTuple: Unit  = assertEquals("(final,given), (private,lazy)", i"${Seq((Final, Given), (Private, Lazy))}%, %")
+
+  class StorePrinter extends config.Printers.Printer:
+    var string: String = "<never set>"
+    override def println(msg: => String) = string = msg
+
+  @Test def testShowing: Unit =
+    val store = StorePrinter()
+    (JavaStatic | Final).showing(i"flags=$result", store)
+    assertEquals("flags=final <static>", store.string)
+
+  @Test def TestShowingWithOriginalType: Unit =
+    val store = StorePrinter()
+    (JavaStatic | Final).showing(i"flags=${if result.is(Private) then result &~ Private else result | Private}", store)
+    assertEquals("flags=private final <static>", store.string)
 }