Remove octal escape literals

Closes #10895
Ref scala/scala#6324

This PR removes octal escape in String literals, which was deprecated
and removed in scala 2.

Author: tanishiking

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

@@ -1146,6 +1146,7 @@ object Scanners {
       if (ch == '\\') {
         nextChar()
         if ('0' <= ch && ch <= '7') {
+          val start = charOffset - 2
           val leadch: Char = ch
           var oct: Int = digit2int(ch, 8)
           nextChar()
@@ -1157,6 +1158,8 @@ object Scanners {
               nextChar()
             }
           }
+          val alt = if oct == LF then raw"\n" else f"\u$oct%04x"
+          error(s"octal escape literals are unsupported: use $alt instead", start)
           putChar(oct.toChar)
         }
         else if (ch == 'u' || ch == 'U') {

tests/neg-custom-args/typeclass-derivation2.scala

@@ -26,8 +26,8 @@ object TypeLevel {
     val label: Array[Array[String]] =
       initLabels(0, 0, new mutable.ArrayBuffer[String], new mutable.ArrayBuffer[Array[String]])
 
-    private final val elemSeparator = '\000'
-    private final val caseSeparator = '\001'
+    private final val elemSeparator = '\u0000'
+    private final val caseSeparator = '\u0001'
 
     private def initLabels(start: Int, cur: Int,
                            elems: mutable.ArrayBuffer[String],
@@ -135,7 +135,7 @@ object Lst {
     Shape.Case[Nil.type, EmptyTuple]
   )]
 
-  val genericClass = new GenericClass("Cons\000hd\000tl\001Nil")
+  val genericClass = new GenericClass("Cons\u0000hd\u0000tl\u0001Nil")
   import genericClass.mirror
 
   val NilMirror = mirror(1)
@@ -165,7 +165,7 @@ object Pair {
 
   type Shape[T] = Shape.Case[Pair[T], (T, T)]
 
-  val genericClass = new GenericClass("Pair\000x\000y")
+  val genericClass = new GenericClass("Pair\u0000x\u0000y")
   import genericClass.mirror
 
   implicit def pairShape[T]: Shaped[Pair[T], Shape[T]] = new {
@@ -189,7 +189,7 @@ object Either {
     Shape.Case[Right[R], R *: EmptyTuple]
   )]
 
-  val genericClass = new GenericClass("Left\000x\001Right\000x")
+  val genericClass = new GenericClass("Left\u0000x\u0001Right\u0000x")
   import genericClass.mirror
 
   implicit def eitherShape[L, R]: Shaped[Either[L, R], Shape[L, R]] = new {

tests/neg/t7292-removal.check

@@ -0,0 +1,12 @@
+-- Error: tests/neg/t7292-removal.scala:2:14 ---------------------------------------------------------------------------
+2 |  val chr1 = '\0' // error
+  |              ^
+  |              octal escape literals are unsupported: use \u0000 instead
+-- Error: tests/neg/t7292-removal.scala:3:17 ---------------------------------------------------------------------------
+3 |  val str1 = "abc\123456" // error
+  |                 ^
+  |                 octal escape literals are unsupported: use \u0053 instead
+-- Error: tests/neg/t7292-removal.scala:4:12 ---------------------------------------------------------------------------
+4 |  val lf = '\012' // error
+  |            ^
+  |            octal escape literals are unsupported: use \n instead

tests/neg/t7292-removal.scala

@@ -0,0 +1,5 @@
+object OctalEscapes {
+  val chr1 = '\0' // error
+  val str1 = "abc\123456" // error
+  val lf = '\012' // error
+}

tests/pending/run/t8266-octal-interp.check

@@ -2,8 +2,6 @@
 RichCharTest1:
 true
 true
-true
-true
 
 RichIntTest:
 10

tests/pending/run/t8266-octal-interp.flags

@@ -18,8 +18,6 @@ trait RichTest {
 object RichCharTest1 extends RichTest {
   def run: Unit = {
     println("\n" + getObjectName + ":")
-    println('\40'.isWhitespace)
-    println('\011'.isWhitespace)
     println('1'.asDigit == 1)
     println('A'.asDigit == 10)
   }

tests/pending/run/t8266-octal-interp.scala

@@ -25,8 +25,8 @@ object TypeLevel {
     def mirror(ordinal: Int): Mirror =
       mirror(ordinal, EmptyProduct)
 
-    private final val elemSeparator = '\000'
-    private final val caseSeparator = '\001'
+    private final val elemSeparator = '\u0000'
+    private final val caseSeparator = '\u0001'
 
     val label: Array[Array[String]] =
       initLabels(0, 0, new mutable.ArrayBuffer[String], new mutable.ArrayBuffer[Array[String]])
@@ -123,7 +123,7 @@ object Lst {
   // common compiler-generated infrastructure
   import TypeLevel._
 
-  val genericClass = new GenericClass("Cons\000hd\000tl\001Nil")
+  val genericClass = new GenericClass("Cons\u0000hd\u0000tl\u0001Nil")
   import genericClass.mirror
 
   private type ShapeOf[T] = Shape.Cases[(
@@ -158,7 +158,7 @@ object Pair {
   // common compiler-generated infrastructure
   import TypeLevel._
 
-  val genericClass = new GenericClass("Pair\000x\000y")
+  val genericClass = new GenericClass("Pair\u0000x\u0000y")
   import genericClass.mirror
 
   private type ShapeOf[T] = Shape.Case[Pair[T], (T, T)]
@@ -186,7 +186,7 @@ case class Right[R](x: R) extends Either[Nothing, R]
 object Either {
   import TypeLevel._
 
-  val genericClass = new GenericClass("Left\000x\001Right\000x")
+  val genericClass = new GenericClass("Left\u0000x\u0001Right\u0000x")
   import genericClass.mirror
 
   private type ShapeOf[L, R] = Shape.Cases[(