Improve SourceCode string printing

Author: som-snytt

compiler/src/scala/quoted/runtime/impl/printers/SourceCode.scala

@@ -1,8 +1,12 @@
 package scala.quoted
 package runtime.impl.printers
 
+import dotty.tools.dotc.util.Chars
+
 import scala.annotation.switch
 
+import java.lang.StringBuilder
+
 /** Printer for fully elaborated representation of the source code */
 object SourceCode {
 
@@ -97,7 +101,7 @@ object SourceCode {
       this += lineBreak() += "}"
     }
 
-    def result(): String = sb.result()
+    def result(): String = sb.toString
 
     private def lineBreak(): String = "\n" + ("  " * indent)
     private def doubleLineBreak(): String = "\n\n" + ("  " * indent)
@@ -438,7 +442,7 @@ object SourceCode {
           case _ =>
             inParens {
               printTree(term)
-              this += (if (dotty.tools.dotc.util.Chars.isOperatorPart(sb.last)) " : " else ": ")
+              this += (if Chars.isOperatorPart(sb.charAt(sb.length - 1)) then " : " else ": ")
               def printTypeOrAnnots(tpe: TypeRepr): Unit = tpe match {
                 case AnnotatedType(tp, annot) if tp == term.tpe =>
                   printAnnotation(annot)
@@ -957,8 +961,8 @@ object SourceCode {
 
     }
 
-    inline private val qc  = '\''
-    inline private val qSc = '"'
+    inline private val qc  = "\'"
+    inline private val qSc = "\""
 
     def printConstant(const: Constant): this.type = const match {
       case UnitConstant() => this += highlightLiteral("()")
@@ -970,8 +974,8 @@ object SourceCode {
       case LongConstant(v) => this += highlightLiteral(v.toString + "L")
       case FloatConstant(v) => this += highlightLiteral(v.toString + "f")
       case DoubleConstant(v) => this += highlightLiteral(v.toString)
-      case CharConstant(v) => this += highlightString(s"${qc}${escapedChar(v)}${qc}")
-      case StringConstant(v) => this += highlightString(s"${qSc}${escapedString(v)}${qSc}")
+      case CharConstant(v) => this += highlightString(escapedChar(v))
+      case StringConstant(v) => this += highlightString(escapedString(v))
       case ClassOfConstant(v) =>
         this += "classOf"
         inSquare(printType(v))
@@ -1445,19 +1449,61 @@ object SourceCode {
     private def +=(x: Char): this.type = { sb.append(x); this }
     private def +=(x: String): this.type = { sb.append(x); this }
 
-    private def escapedChar(ch: Char): String = (ch: @switch) match {
-      case '\b' => "\\b"
-      case '\t' => "\\t"
-      case '\n' => "\\n"
-      case '\f' => "\\f"
-      case '\r' => "\\r"
-      case '"' => "\\\""
-      case '\'' => "\\\'"
-      case '\\' => "\\\\"
-      case _ => if ch.isControl then f"${"\\"}u${ch.toInt}%04x" else String.valueOf(ch)
-    }
-
-    private def escapedString(str: String): String = str flatMap escapedChar
+    private def escapedChar(ch: Char): String =
+      if requiresFormat(ch) then
+        val b = StringBuilder().append(qc)
+        escapedChar(b, ch)
+        b.append(qc).toString
+      else
+        qc + ch + qc
+
+    private def escapedChar(b: StringBuilder, c: Char): Unit =
+      def quadNibble(b: StringBuilder, x: Int, i: Int): Unit =
+        if i < 4 then
+          quadNibble(b, x >> 4, i + 1)
+          val n = x & 0xF
+          val c = if (n < 10) '0' + n else 'a' + (n - 10)
+          b.append(c.toChar)
+      val replace = (c: @switch) match
+        case '\b' => "\\b"
+        case '\t' => "\\t"
+        case '\n' => "\\n"
+        case '\f' => "\\f"
+        case '\r' => "\\r"
+        case '"'  => "\\\""
+        case '\'' => "\\\'"
+        case '\\' => "\\\\"
+        case c =>
+          if c.isControl then
+            b.append("\\u")
+            quadNibble(b, c.toInt, 0)
+          else
+            b.append(c)
+          return
+      b.append(replace)
+
+    private def requiresFormat(c: Char): Boolean = (c: @switch) match
+      case '\b' | '\t' | '\n' | '\f' | '\r' | '"' | '\'' | '\\' => true
+      case c => c.isControl
+
+    private def escapedString(text: String): String =
+      def mustBuild: Boolean =
+        var i = 0
+        while i < text.length do
+          if requiresFormat(text.charAt(i)) then return true
+          i += 1
+        false
+      if mustBuild then
+        val b = StringBuilder(text.length + 16)
+        b.append(qSc)
+        var i = 0
+        while i < text.length do
+          escapedChar(b, text.charAt(i))
+          i += 1
+        b.append(qSc)
+        b.toString
+      else
+        qSc + text + qSc
 
     private val names = collection.mutable.Map.empty[Symbol, String]
     private val namesIndex = collection.mutable.Map.empty[String, Int]