make variable name consistent in ScalaSettings

Options with syntax "-Y" should NOT be named with a variable beginning with `X`.

Author: liufengyun

src/dotty/tools/dotc/config/ScalaSettings.scala

@@ -105,10 +105,10 @@ class ScalaSettings extends Settings.SettingGroup {
   val YcheckMods = BooleanSetting("-Ycheck-mods", "Check that symbols and their defining trees have modifiers in sync")
   val YcheckTypedTrees = BooleanSetting("-YcheckTypedTrees", "Check all constructured typed trees for type correctness")
   val Yshow = PhasesSetting("-Yshow", "(Requires -Xshow-class or -Xshow-object) Show after")
-  val Xcloselim = BooleanSetting("-Yclosure-elim", "Perform closure elimination.")
+  val Ycloselim = BooleanSetting("-Yclosure-elim", "Perform closure elimination.")
   val Ycompacttrees = BooleanSetting("-Ycompact-trees", "Use compact tree printer when displaying trees.")
   val noCompletion = BooleanSetting("-Yno-completion", "Disable tab-completion in the REPL.")
-  val Xdce = BooleanSetting("-Ydead-code", "Perform dead code elimination.")
+  val Ydce = BooleanSetting("-Ydead-code", "Perform dead code elimination.")
   val debug = BooleanSetting("-Ydebug", "Increase the quantity of debugging output.")
   val debugNames = BooleanSetting("-YdebugNames", "Show name-space indicators when printing names")
   val debugTrace = BooleanSetting("-Ydebug-trace", "Trace core operations")
@@ -119,17 +119,17 @@ class ScalaSettings extends Settings.SettingGroup {
   val inline = BooleanSetting("-Yinline", "Perform inlining when possible.")
   val inlineHandlers = BooleanSetting("-Yinline-handlers", "Perform exception handler inlining when possible.")
   val YinlinerWarnings = BooleanSetting("-Yinline-warnings", "Emit inlining warnings. (Normally surpressed due to high volume)")
-  val Xlinearizer = ChoiceSetting("-Ylinearizer", "which", "Linearizer to use", List("normal", "dfs", "rpo", "dump"), "rpo")
+  val Ylinearizer = ChoiceSetting("-Ylinearizer", "which", "Linearizer to use", List("normal", "dfs", "rpo", "dump"), "rpo")
   val log = PhasesSetting("-Ylog", "Log operations during")
   val Ylogcp = BooleanSetting("-Ylog-classpath", "Output information about what classpath is being applied.")
   val Ynogenericsig = BooleanSetting("-Yno-generic-signatures", "Suppress generation of generic signatures for Java.")
   val YnoImports = BooleanSetting("-Yno-imports", "Compile without importing scala.*, java.lang.*, or Predef.")
   val nopredef = BooleanSetting("-Yno-predef", "Compile without importing Predef.")
   val noAdaptedArgs = BooleanSetting("-Yno-adapted-args", "Do not adapt an argument list (either by inserting () or creating a tuple) to match the receiver.")
   val selfInAnnots = BooleanSetting("-Yself-in-annots", "Include a \"self\" identifier inside of annotations.")
-  val Xshowtrees = BooleanSetting("-Yshow-trees", "(Requires -Xprint:) Print detailed ASTs in formatted form.")
-  val XshowtreesCompact = BooleanSetting("-Yshow-trees-compact", "(Requires -Xprint:) Print detailed ASTs in compact form.")
-  val XshowtreesStringified = BooleanSetting("-Yshow-trees-stringified", "(Requires -Xprint:) Print stringifications along with detailed ASTs.")
+  val Yshowtrees = BooleanSetting("-Yshow-trees", "(Requires -Xprint:) Print detailed ASTs in formatted form.")
+  val YshowtreesCompact = BooleanSetting("-Yshow-trees-compact", "(Requires -Xprint:) Print detailed ASTs in compact form.")
+  val YshowtreesStringified = BooleanSetting("-Yshow-trees-stringified", "(Requires -Xprint:) Print stringifications along with detailed ASTs.")
   val Yshowsyms = BooleanSetting("-Yshow-syms", "Print the AST symbol hierarchy after each phase.")
   val Yshowsymkinds = BooleanSetting("-Yshow-symkinds", "Print abbreviated symbol kinds next to symbol names.")
   val Yskip = PhasesSetting("-Yskip", "Skip")