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Consider rendering prefix when pretty printing values in the REPL #24118

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Consider rendering prefix when pretty printing values in the REPL #24118

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dc166dd
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lihaoyi Oct 1, 2025
4e017e3
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lihaoyi Oct 1, 2025
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23 changes: 18 additions & 5 deletions compiler/src/dotty/tools/repl/Rendering.scala
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Original file line number Diff line number Diff line change
Expand Up @@ -53,16 +53,23 @@ private[repl] class Rendering(parentClassLoader: Option[ClassLoader] = None):
else str.substring(0, str.offsetByCodePoints(0, maxPrintCharacters - 1))

/** Return a String representation of a value we got from `classLoader()`. */
private[repl] def replStringOf(sym: Symbol, value: Object)(using Context): String = {
private[repl] def replStringOf(value: Object, prefixLength: Int)(using Context): String = {
// pretty-print things with 100 cols 50 rows by default,
dotty.shaded.pprint.PPrinter.BlackWhite.apply(value, width = 100, height = 50).plainText
dotty.shaded.pprint.PPrinter.BlackWhite
.apply(
value,
width = 100,
height = 50,
initialOffset = prefixLength
)
.plainText
}

/** Load the value of the symbol using reflection.
*
* Calling this method evaluates the expression using reflection
*/
private def valueOf(sym: Symbol)(using Context): Option[String] =
private def valueOf(sym: Symbol, prefixLength: Int)(using Context): Option[String] =
val objectName = sym.owner.fullName.encode.toString.stripSuffix("$")
val resObj: Class[?] = Class.forName(objectName, true, classLoader())
val symValue = resObj
Expand All @@ -71,7 +78,7 @@ private[repl] class Rendering(parentClassLoader: Option[ClassLoader] = None):
.flatMap(result => rewrapValueClass(sym.info.classSymbol, result.invoke(null)))
symValue
.filter(_ => sym.is(Flags.Method) || sym.info != defn.UnitType)
.map(value => stripReplPrefix(replStringOf(sym, value)))
.map(value => stripReplPrefix(replStringOf(value, prefixLength)))

private def stripReplPrefix(s: String): String =
if (s.startsWith(REPL_WRAPPER_NAME_PREFIX))
Expand Down Expand Up @@ -108,7 +115,13 @@ private[repl] class Rendering(parentClassLoader: Option[ClassLoader] = None):
try
Right(
if d.symbol.is(Flags.Lazy) then Some(msg(dcl))
else valueOf(d.symbol).map(value => msg(s"$dcl = $value"))
else {
val prefix = s"$dcl = "
// Prefix can have multiple lines, only consider the last one
// when determining the initial column offset for pretty-printing
val prefixLength = prefix.linesIterator.toSeq.lastOption.getOrElse("").length
valueOf(d.symbol, prefixLength).map(value => msg(s"$prefix$value"))
}
)
catch case e: ReflectiveOperationException => Left(e)
end renderVal
Expand Down
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