Deprecation of case class elements (#17911)

Synthetic members of case classes should not incur deprecation warnings
when a case element is deprecated.

Fixes #17908

Also when message in Java deprecation is empty, improve
```
-- Deprecation Warning: ------------------------------------------------------------------------------------------------
1 |f
  |^
  |method f is deprecated since :
val res0: Int = 42
```
to
```
-- Deprecation Warning: ------------------------------------------------------------------------------------------------
1 |f
  |^
  |method f is deprecated
val res0: Int = 42
```

Author: hamzaremmal

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

@@ -3,6 +3,7 @@ package dotc
 package transform
 
 import core.*
+import Annotations.Annotation
 import Symbols.*, Types.*, Contexts.*, Flags.*, Decorators.*, reporting.*
 import util.SrcPos
 import config.{ScalaVersion, NoScalaVersion, Feature, ScalaRelease}
@@ -161,29 +162,42 @@ object CrossVersionChecks:
 
   /** 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.
+   *
+   *  Also check for deprecation of the companion class for synthetic methods in the companion module.
    */
   private[CrossVersionChecks] def checkDeprecatedRef(sym: Symbol, pos: SrcPos)(using Context): Unit =
-
-    // Also check for deprecation of the companion class for synthetic methods
-    val toCheck = sym :: (if sym.isAllOf(SyntheticMethod) then sym.owner.companionClass :: Nil else Nil)
-    for sym <- toCheck; annot <- sym.getAnnotation(defn.DeprecatedAnnot) do
-      if !skipWarning(sym) then
-        val msg = annot.argumentConstant(0).map(": " + _.stringValue).getOrElse("")
-        val since = annot.argumentConstant(1).map(" since " + _.stringValue).getOrElse("")
-        report.deprecationWarning(em"${sym.showLocated} is deprecated${since}${msg}", pos)
-
-  /** Skip warnings for synthetic members of case classes during declaration and
-   *  scan the chain of outer declaring scopes from the current context
-   *  a deprecation warning will be skipped if one the following holds
-   *  for a given declaring scope:
-   *  - the symbol associated with the scope is also deprecated.
-   *  - if and only if `sym` is an enum case, the scope is either
-   *    a module that declares `sym`, or the companion class of the
-   *    module that declares `sym`.
+    def maybeWarn(annotee: Symbol, annot: Annotation) = if !skipWarning(sym) then
+      val message = annot.argumentConstantString(0).filter(!_.isEmpty).map(": " + _).getOrElse("")
+      val since = annot.argumentConstantString(1).filter(!_.isEmpty).map(" since " + _).getOrElse("")
+      report.deprecationWarning(em"${annotee.showLocated} is deprecated${since}${message}", pos)
+    sym.getAnnotation(defn.DeprecatedAnnot) match
+      case Some(annot) => maybeWarn(sym, annot)
+      case _ =>
+        if sym.isAllOf(SyntheticMethod) then
+          val companion = sym.owner.companionClass
+          if companion.is(CaseClass) then companion.getAnnotation(defn.DeprecatedAnnot).foreach(maybeWarn(companion, _))
+
+  /** Decide whether the deprecation of `sym` should be ignored in this context.
+   *
+   *  The warning is skipped if any symbol in the context owner chain is deprecated,
+   *  that is, an enclosing scope is associated with a deprecated symbol.
+   *
+   *  Further exclusions are needed for enums and case classes,
+   *  since they typically need to refer to deprecated members
+   *  even if the enclosing enum or case class is not deprecated.
+   *
+   *  If and only if `sym` is an enum case, the warning is skipped
+   *  if an enclosing scope is either a module that declares `sym`,
+   *  or the companion class of the module that declares `sym`.
+   *
+   *  For a deprecated case class or case class element,
+   *  the warning is skipped for synthetic sites where the enclosing
+   *  class (or its companion) is either the deprecated case class
+   *  or the case class of the deprecated element.
    */
   private def skipWarning(sym: Symbol)(using Context): Boolean =
 
-    /** is the owner an enum or its companion and also the owner of sym */
+    // is the owner an enum or its companion and also the owner of sym
     def isEnumOwner(owner: Symbol)(using Context) =
       // pre: sym is an enumcase
       if owner.isEnumClass then owner.companionClass eq sym.owner
@@ -194,6 +208,19 @@ object CrossVersionChecks:
       // pre: sym is an enumcase
       owner.isDeprecated || isEnumOwner(owner)
 
-    (ctx.owner.is(Synthetic) && sym.is(CaseClass))
-      || ctx.owner.ownersIterator.exists(if sym.isEnumCase then isDeprecatedOrEnum else _.isDeprecated)
+    def siteIsEnclosedByDeprecatedElement =
+      ctx.owner.ownersIterator.exists:
+        if sym.isEnumCase then isDeprecatedOrEnum else _.isDeprecated
+
+    def siteIsSyntheticCaseClassMember =
+      val owner = ctx.owner
+      def symIsCaseOrMember =
+        val enclosing = owner.enclosingClass
+        val companion = enclosing.companionClass
+        // deprecated sym is either enclosing case class or a sibling member
+        def checkSym(k: Symbol) = sym == k || sym.owner == k
+        (enclosing.is(CaseClass) || companion.is(CaseClass)) && (checkSym(enclosing) || checkSym(companion))
+      owner.is(Synthetic) && symIsCaseOrMember
+
+    siteIsSyntheticCaseClassMember || siteIsEnclosedByDeprecatedElement
   end skipWarning

compiler/test-resources/repl/reset-command

@@ -12,7 +12,7 @@ scala> def f(thread: Thread) = thread.stop()
 -- Deprecation Warning: --------------------------------------------------------
 1 | def f(thread: Thread) = thread.stop()
   |                         ^^^^^^^^^^^
-  |method stop in class Thread is deprecated since : see corresponding Javadoc for more information.
+  |method stop in class Thread is deprecated: see corresponding Javadoc for more information.
 def f(thread: Thread): Unit
 
 scala> def resetNoArgsStillWorks = 1

compiler/test-resources/repl/settings-command

@@ -11,7 +11,7 @@ scala> def f(thread: Thread) = thread.stop()
 -- Deprecation Warning: --------------------------------------------------------
 1 | def f(thread: Thread) = thread.stop()
   |                         ^^^^^^^^^^^
-  |method stop in class Thread is deprecated since : see corresponding Javadoc for more information.
+  |method stop in class Thread is deprecated: see corresponding Javadoc for more information.
 def f(thread: Thread): Unit
 
 scala>

tests/pos/i11022.scala

@@ -1,3 +1,5 @@
 //> using options -Werror -deprecation
 @deprecated("no CaseClass")
 case class CaseClass(rgb: Int)
+
+case class K(@deprecated("don't use k, ok?","0.1") k: Int)

tests/warn/i11022.check

@@ -1,3 +1,7 @@
+-- Deprecation Warning: tests/warn/i11022.scala:19:22 ------------------------------------------------------------------
+19 |  def usage(k: K) = k.k   // warn
+   |                    ^^^
+   |                    value k in class K is deprecated since 0.1: don't use k, ok?
 -- Deprecation Warning: tests/warn/i11022.scala:10:7 -------------------------------------------------------------------
 10 |val a: CaseClass = CaseClass(42)        // warn: deprecated type // warn: deprecated apply method
    |       ^^^^^^^^^
@@ -18,3 +22,7 @@
 12 |val c: Unit = CaseClass(42).magic()     // warn: deprecated apply method
    |              ^^^^^^^^^
    |              class CaseClass is deprecated: no CaseClass
+-- Deprecation Warning: tests/warn/i11022.scala:14:4 -------------------------------------------------------------------
+14 |val CaseClass(rgb) = b                  // warn
+   |    ^^^^^^^^^
+   |    class CaseClass is deprecated: no CaseClass

tests/warn/i11022.scala

@@ -10,4 +10,12 @@ object CaseClass:
 val a: CaseClass = CaseClass(42)        // warn: deprecated type // warn: deprecated apply method
 val b: CaseClass = new CaseClass(42)    // warn: deprecated type // warn: deprecated class
 val c: Unit = CaseClass(42).magic()     // warn: deprecated apply method
-val d: Unit = CaseClass.notDeprecated() // compiles
+val d: Unit = CaseClass.notDeprecated() // compiles
+val CaseClass(rgb) = b                  // warn
+
+case class K(@deprecated("don't use k, ok?","0.1") k: Int)
+
+object K:
+  def usage(k: K) = k.k   // warn
+
+val s: String = CaseClass.toString