From 9ed667283e0bbe2791b44e62f050262c15040cca Mon Sep 17 00:00:00 2001
From: Som Snytt <som.snytt@gmail.com>
Date: Mon, 20 Jun 2022 04:35:21 -0700
Subject: [PATCH] When reporting unused import, check deprecations

---
 .../tools/nsc/typechecker/Contexts.scala      | 28 +++++++++++++--
 test/files/neg/t11758.check                   | 24 +++++++++++++
 test/files/neg/t11758.scala                   | 35 +++++++++++++++++++
 3 files changed, 84 insertions(+), 3 deletions(-)
 create mode 100644 test/files/neg/t11758.check
 create mode 100644 test/files/neg/t11758.scala

diff --git a/src/compiler/scala/tools/nsc/typechecker/Contexts.scala b/src/compiler/scala/tools/nsc/typechecker/Contexts.scala
index b1b4beec2abd..703824097d96 100644
--- a/src/compiler/scala/tools/nsc/typechecker/Contexts.scala
+++ b/src/compiler/scala/tools/nsc/typechecker/Contexts.scala
@@ -70,8 +70,24 @@ trait Contexts { self: Analyzer =>
     mutable.Map.empty[CompilationUnit, List[(ImportInfo, Symbol)]].withDefaultValue(Nil)
 
   def warnUnusedImports(unit: CompilationUnit) = if (!unit.isJava) {
+    def msg(sym: Symbol) = sym.deprecationMessage.map(": " + _).getOrElse("")
+    def checkDeprecatedElementInPath(selector: ImportSelector, info: ImportInfo): String = {
+      def badName(name: Name) =
+        info.qual.tpe.member(name) match {
+          case m if m.isDeprecated => Some(s" of deprecated $m${msg(m)}")
+          case _ => None
+        }
+      val badSelected =
+        if (!selector.isMask && selector.isSpecific) badName(selector.name).orElse(badName(selector.name.toTypeName))
+        else None
+      def badFrom = {
+        val sym = info.qual.symbol
+        if (sym.isDeprecated) Some(s" from deprecated $sym${msg(sym)}") else None
+      }
+      badSelected.orElse(badFrom).getOrElse("")
+    }
     def warnUnusedSelections(infos0: List[(ImportInfo, Symbol)]): Unit = {
-      type Culled = (Position, Symbol, String)
+      type Culled = (ImportSelector, ImportInfo, Symbol)
       var unused = List.empty[Culled]
       @tailrec def loop(infos: List[(ImportInfo, Symbol)]): Unit =
         infos match {
@@ -82,7 +98,7 @@ trait Contexts { self: Analyzer =>
                 case selector :: rest =>
                   checkSelectors(rest)
                   if (!selector.isMask && !used(selector))
-                    unused ::= ((info.posOf(selector), owner, info.fullSelectorString(selector)))
+                    unused ::= ((selector, info, owner))
                 case _ =>
               }
             checkSelectors(info.tree.selectors)
@@ -90,7 +106,13 @@ trait Contexts { self: Analyzer =>
           case _ =>
         }
       loop(infos0)
-      unused.foreach { case (pos, owner, origin) => runReporting.warning(pos, "Unused import", WarningCategory.UnusedImports, owner, origin) }
+      unused.foreach {
+        case (selector, info, owner) =>
+          val pos = info.posOf(selector)
+          val origin = info.fullSelectorString(selector)
+          val addendum = checkDeprecatedElementInPath(selector, info)
+          runReporting.warning(pos, s"Unused import$addendum", WarningCategory.UnusedImports, owner, origin)
+      }
     }
     allImportInfos.remove(unit).foreach(warnUnusedSelections)
   }
diff --git a/test/files/neg/t11758.check b/test/files/neg/t11758.check
new file mode 100644
index 000000000000..8ddaee35d53a
--- /dev/null
+++ b/test/files/neg/t11758.check
@@ -0,0 +1,24 @@
+t11758.scala:3: warning: Unused import of deprecated lazy value higherKinds: higherKinds no longer needs to be imported explicitly
+import language.higherKinds
+                ^
+t11758.scala:19: warning: Unused import from deprecated object outer: no outer
+  import outer.other
+               ^
+t11758.scala:21: warning: Unused import of deprecated object inner: no inner
+  import outer.{inner => odder}
+                ^
+t11758.scala:25: warning: Unused import of deprecated class C: no see
+  import nest.C
+              ^
+t11758.scala:23: warning: object inner in object outer is deprecated (since 2.0): no inner
+  def f = inner
+          ^
+t11758.scala:23: warning: object outer is deprecated (since 1.0): no outer
+  def f = inner
+          ^
+t11758.scala:30: warning: class C in object nest is deprecated (since 3.0): no see
+  def g = new C
+              ^
+error: No warnings can be incurred under -Werror.
+7 warnings
+1 error
diff --git a/test/files/neg/t11758.scala b/test/files/neg/t11758.scala
new file mode 100644
index 000000000000..c6109ff684fc
--- /dev/null
+++ b/test/files/neg/t11758.scala
@@ -0,0 +1,35 @@
+// scalac: -Xlint:deprecation -Wunused:imports -Werror
+
+import language.higherKinds
+
+@deprecated("no outer", "1.0")
+object outer {
+  @deprecated("no inner", "2.0")
+  object inner
+  object other
+}
+object nest {
+  @deprecated("no see", "3.0")
+  class C
+
+  val status = true
+}
+
+trait T {
+  import outer.other
+  import outer.inner
+  import outer.{inner => odder}
+
+  def f = inner
+
+  import nest.C
+  def g = ()
+}
+trait U {
+  import nest.C
+  def g = new C
+}
+trait OK {
+  import nest.{C => _, _}
+  def ok = status
+}