Don't ignore params of public methods

Author: som-snytt

compiler/src/dotty/tools/dotc/transform/CheckUnused.scala

@@ -145,8 +145,6 @@ class CheckUnused private (phaseMode: CheckUnused.PhaseMode, suffix: String, _ke
   override def prepareForDefDef(tree: DefDef)(using Context): Context =
     preparing:
       ud.registerTrivial(tree)
-      if !tree.symbol.is(Private) then
-        tree.termParamss.flatten.foreach(p => ud.addIgnoredParam(p.symbol))
       ud.addIgnoredUsage(tree.symbol)
 
   override def transformDefDef(tree: DefDef)(using Context): tree.type =
@@ -571,10 +569,11 @@ object CheckUnused:
     private def isConstructorOfSynth(sym: Symbol)(using Context): Boolean =
       sym.exists && sym.isConstructor && sym.owner.isPackageObject && sym.owner.is(Synthetic)
 
-    /** This is used to avoid reporting the parameters of the synthetic main method generated by `@main`.
+    /** Avoid reporting unused parameter in required main method signature.
+     *  The method may be user-written or generated by `@main`.
      */
     private def isSyntheticMainParam(sym: Symbol)(using Context): Boolean =
-      sym.exists && ctx.platform.isMainMethod(sym.owner) && sym.owner.is(Synthetic)
+      sym.exists && ctx.platform.isMainMethod(sym.owner) //&& sym.owner.is(Synthetic)
 
     /** If -Wunused:strict-no-implicit-warn import and this import selector could potentially import implicit.
      */

tests/warn/i15503e.scala

@@ -1,4 +1,4 @@
-//> using options  -Wunused:explicits
+//> using options -Wunused:explicits
 
 object Foo {
   /* This goes around the "trivial method" detection */
@@ -31,7 +31,7 @@ package scala3main:
 package foo.test.lambda.param:
   val default_val = 1
   val a = (i: Int) => i // OK
-  val b = (i: Int) => default_val // OK
+  val b = (i: Int) => default_val // warn
   val c = (_: Int) => default_val // OK
 
 package foo.test.trivial:
@@ -67,4 +67,4 @@ package foo.test.i16865:
     def fn(a: Int, b: Int): Int = b + 3 // OK
 
   object Ex2 extends Bar:
-    override def fn(a: Int, b: Int): Int = b + 3 // OK
+    override def fn(a: Int, b: Int): Int = b + 3 // OK

tests/warn/i15503h.scala

@@ -1,4 +1,4 @@
-//> using options  -Wunused:linted
+//> using options -Wunused:linted
 
 import collection.mutable.Set // warn
 
@@ -7,14 +7,14 @@ class A {
   val b = 2 // OK
 
   private def c = 2 // warn
-  def d(using x:Int): Int = b // ok
+  def d(using x: Int): Int = b // warn
   def e(x: Int) = 1 // OK
   def f =
     val x = 1 // warn
     def f = 2 // warn
     3
 
   def g(x: Int): Int = x match
-    case x:1 => 0 // OK
+    case x: 1 => 0 // OK
     case _ => 1
-}
+}

tests/warn/i15503i.scala

@@ -17,10 +17,12 @@ class A {
   private def c2 = 2 // OK
   def c3 = c2
 
-  def d1(using x:Int): Int = default_int // ok
-  def d2(using x:Int): Int = x // OK
+  def d1(using x: Int): Int = default_int // warn param
+  def d2(using x: Int): Int = x // OK
+  def d3(using Int): Int = summon[Int] // OK
+  def d4(using Int): Int = default_int // warn
 
-  def e1(x: Int) = default_int // ok
+  def e1(x: Int) = default_int // warn param
   def e2(x: Int) = x // OK
   def f =
     val x = 1 // warn
@@ -44,7 +46,7 @@ package foo.test.scala.annotation:
   val default_int = 12
 
   def a1(a: Int) = a // OK
-  def a2(a: Int) = default_int // ok
+  def a2(a: Int) = default_int // warn
 
   def a3(@unused a: Int) = default_int //OK
 

tests/warn/unused-locals.scala

@@ -0,0 +1,43 @@
+//> using options -Wunused:locals
+
+class Outer {
+  class Inner
+}
+
+trait Locals {
+  def f0 = {
+    var x = 1 // warn
+    var y = 2 // no warn
+    y = 3
+    y + y
+  }
+  def f1 = {
+    val a = new Outer // no warn
+    val b = new Outer // warn
+    new a.Inner
+  }
+  def f2 = {
+    var x = 100 // warn about it being a var
+    x
+  }
+}
+
+object Types {
+  def l1() = {
+    object HiObject { def f = this } // warn
+    class Hi { // warn
+      def f1: Hi = new Hi
+      def f2(x: Hi) = x
+    }
+    class DingDongDoobie // warn
+    class Bippy // no warn
+    type Something = Bippy // no warn
+    type OtherThing = String // warn
+    (new Bippy): Something
+  }
+}
+
+// breakage: local val x$1 in method skolemize is never used
+case class SymbolKind(accurate: String, sanitized: String, abbreviation: String) {
+  def skolemize: SymbolKind = copy(accurate = s"$accurate skolem", abbreviation = s"$abbreviation#SKO")
+}

tests/warn/unused-params.scala

@@ -0,0 +1,153 @@
+//> using options -Wunused:params -Werror
+//
+
+import Answers._
+
+trait InterFace {
+  /** Call something. */
+  def call(a: Int, b: String, c: Double): Int
+}
+
+trait BadAPI extends InterFace {
+  def f(a: Int,
+        b: String,               // warn
+        c: Double): Int = {
+    println(c)
+    a
+  }
+  @deprecated("no warn in deprecated API", since="yesterday")
+  def g(a: Int,
+        b: String,               // no warn
+        c: Double): Int = {
+    println(c)
+    a
+  }
+  override def call(a: Int,
+                    b: String,               // no warn, required by superclass
+                    c: Double): Int = {
+    println(c)
+    a
+  }
+
+  def meth(x: Int) = x
+
+  override def equals(other: Any): Boolean = true  // no warn
+
+  def i(implicit s: String) = answer           // yes, warn
+
+  /*
+  def future(x: Int): Int = {
+    val y = 42
+    val x = y               // maybe option to warn only if shadowed
+    x
+  }
+  */
+}
+
+// mustn't alter warnings in super
+trait PoorClient extends BadAPI {
+  override def meth(x: Int) = ???       // no warn
+  override def f(a: Int, b: String, c: Double): Int = a + b.toInt + c.toInt
+}
+
+class Unusing(u: Int) {       // warn
+  def f = ???
+}
+
+class Valuing(val u: Int)        // no warn
+
+class Revaluing(u: Int) { def f = u } // no warn
+
+case class CaseyKasem(k: Int)        // no warn
+
+case class CaseyAtTheBat(k: Int)(s: String)        // warn
+
+trait Ignorance {
+  def f(readResolve: Int) = answer           // warn
+}
+
+class Reusing(u: Int) extends Unusing(u)   // no warn
+
+class Main {
+  def main(args: Array[String]): Unit = println("hello, args")  // no warn
+}
+
+trait Unimplementation {
+  def f(u: Int): Int = ???        // no warn for param in unimplementation
+}
+
+trait DumbStuff {
+  def f(implicit dummy: DummyImplicit) = answer
+  def g(dummy: DummyImplicit) = answer
+}
+trait Proofs {
+  def f[A, B](implicit ev: A =:= B) = answer
+  def g[A, B](implicit ev: A <:< B) = answer
+  def f2[A, B](ev: A =:= B) = answer
+  def g2[A, B](ev: A <:< B) = answer
+}
+
+trait Anonymous {
+  def f = (i: Int) => answer      // warn
+
+  def f1 = (_: Int) => answer     // no warn underscore parameter (a fresh name)
+
+  def f2: Int => Int = _ + 1  // no warn placeholder syntax (a fresh name and synthetic parameter)
+
+  def g = for (i <- List(1)) yield answer    // no warn patvar elaborated as map.(i => 42)
+}
+trait Context[A] { def m(a: A): A = a }
+trait Implicits {
+  def f[A](implicit ctx: Context[A]) = answer
+  def g[A: Context] = answer
+}
+class Bound[A: Context]
+object Answers {
+  def answer: Int = 42
+}
+
+trait BadMix { _: InterFace =>
+  def f(a: Int,
+        b: String,               // warn
+        c: Double): Int = {
+    println(c)
+    a
+  }
+  @deprecated("no warn in deprecated API", since="yesterday")
+  def g(a: Int,
+        b: String,               // no warn
+        c: Double): Int = {
+    println(c)
+    a
+  }
+  override def call(a: Int,
+                    b: String,               // no warn, required by superclass
+                    c: Double): Int = {
+    println(c)
+    a
+  }
+
+  def meth(x: Int) = x
+
+  override def equals(other: Any): Boolean = true  // no warn
+
+  def i(implicit s: String) = answer           // yes, warn
+}
+
+class Unequal {
+  override def equals(other: Any) = toString.nonEmpty   // no warn non-trivial RHS, required by universal method
+}
+
+class Seriously {
+  def f(s: Serializable) = toString.nonEmpty  // warn explicit param of marker trait
+}
+
+class TryStart(start: String) {
+  def FINALLY(end: END.type) = start
+}
+
+object END
+
+class Nested {
+  @annotation.unused private def actuallyNotUsed(fresh: Int, stale: Int) = fresh
+}