fix #10247: skip deprecation warn if in synthetic def

Author: bishabosha

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

@@ -885,11 +885,11 @@ object RefChecks {
 
 
   /** If @deprecated is present, and the point of reference is not enclosed
-   * in either a deprecated member or a scala bridge method, issue a warning.
+   * in either a deprecated/synthetic member or a scala bridge method, issue a warning.
    */
   private def checkDeprecated(sym: Symbol, pos: SrcPos)(using Context): Unit =
     for annot <- sym.getAnnotation(defn.DeprecatedAnnot) do
-      if !ctx.owner.ownersIterator.exists(_.isDeprecated) then
+      if !ctx.owner.ownersIterator.exists(owner => owner.isDeprecated || owner.is(Synthetic)) then
         val msg = annot.argumentConstant(0).map(": " + _.stringValue).getOrElse("")
         val since = annot.argumentConstant(1).map(" since " + _.stringValue).getOrElse("")
         report.deprecationWarning(s"${sym.showLocated} is deprecated${since}${msg}", pos)

compiler/test/dotty/tools/dotc/CompilationTests.scala

@@ -55,6 +55,7 @@ class CompilationTests {
       compileFile("tests/pos-special/kind-projector.scala", defaultOptions.and("-Ykind-projector")),
       compileFile("tests/run/i5606.scala", defaultOptions.and("-Yretain-trees")),
       compileFile("tests/pos-custom-args/i5498-postfixOps.scala", defaultOptions withoutLanguageFeature "postfixOps"),
+      compileFilesInDir("tests/pos-custom-args/deprecation", defaultOptions.and("-deprecation", "-Xfatal-warnings")),
       compileFile("tests/pos-custom-args/i8875.scala", defaultOptions.and("-Xprint:getters")),
       compileFile("tests/pos-custom-args/i9267.scala", defaultOptions.and("-Ystop-after:erasure")),
       compileFile("tests/pos-special/extend-java-enum.scala", defaultOptions.and("-source", "3.0-migration")),

tests/neg-custom-args/deprecation/i10247.scala

@@ -0,0 +1,7 @@
+object Color {
+  def red = Red // error: Red is deprecated
+}
+
+enum Color {
+  @deprecated("no Red", "0.1") case Red
+}

tests/pos-custom-args/deprecation/i10247.scala

@@ -0,0 +1,4 @@
+// check that deprecation warnings of Red are not caught at its definition
+enum Color {
+  @deprecated("no Red", "0.1") case Red
+}