From 1f7789f71aea94c38aa53b4f9505c825d3c9a2d6 Mon Sep 17 00:00:00 2001
From: Hamza REMMAL <hamza@remmal.net>
Date: Tue, 27 Feb 2024 18:25:51 +0100
Subject: [PATCH] Improve error reporting for missing members

Co-Authored-By: valentin2.schneeberger@gmail.com
Co-Authored-By: sana.carlo@gmail.com
Co-Authored-By: mehdi.ala03@gmail.com
---
 .../dotty/tools/dotc/typer/RefChecks.scala    | 12 ++++-----
 tests/neg/i19731.check                        | 27 +++++++++++++++++++
 tests/neg/i19731.scala                        | 17 ++++++++++++
 3 files changed, 50 insertions(+), 6 deletions(-)
 create mode 100644 tests/neg/i19731.check
 create mode 100644 tests/neg/i19731.scala

diff --git a/compiler/src/dotty/tools/dotc/typer/RefChecks.scala b/compiler/src/dotty/tools/dotc/typer/RefChecks.scala
index cf30945a7751..ff44ba6d010d 100644
--- a/compiler/src/dotty/tools/dotc/typer/RefChecks.scala
+++ b/compiler/src/dotty/tools/dotc/typer/RefChecks.scala
@@ -654,8 +654,8 @@ object RefChecks {
 
         val missingMethods = grouped.toList flatMap {
           case (name, syms) =>
-            val withoutSetters = syms filterNot (_.isSetter)
-            if (withoutSetters.nonEmpty) withoutSetters else syms
+            syms.filterConserve(!_.isSetter)
+              .distinctBy(_.signature) // Avoid duplication for similar definitions (#19731)
         }
 
         def stubImplementations: List[String] = {
@@ -666,7 +666,7 @@ object RefChecks {
 
           if (regrouped.tail.isEmpty)
             membersStrings(regrouped.head._2)
-          else (regrouped.sortBy("" + _._1.name) flatMap {
+          else (regrouped.sortBy(_._1.name.toString()) flatMap {
             case (owner, members) =>
               ("// Members declared in " + owner.fullName) +: membersStrings(members) :+ ""
           }).init
@@ -685,7 +685,7 @@ object RefChecks {
           return
         }
 
-        for (member <- missing) {
+        for (member <- missingMethods) {
           def showDclAndLocation(sym: Symbol) =
             s"${sym.showDcl} in ${sym.owner.showLocated}"
           def undefined(msg: String) =
@@ -1002,9 +1002,9 @@ object RefChecks {
   end checkNoPrivateOverrides
 
   def checkVolatile(sym: Symbol)(using Context): Unit =
-    if sym.isVolatile && !sym.is(Mutable) then 
+    if sym.isVolatile && !sym.is(Mutable) then
       report.warning(VolatileOnVal(), sym.srcPos)
-  
+
   /** Check that unary method definition do not receive parameters.
    *  They can only receive inferred parameters such as type parameters and implicit parameters.
    */
diff --git a/tests/neg/i19731.check b/tests/neg/i19731.check
new file mode 100644
index 000000000000..eebfb924d199
--- /dev/null
+++ b/tests/neg/i19731.check
@@ -0,0 +1,27 @@
+-- Error: tests/neg/i19731.scala:4:6 -----------------------------------------------------------------------------------
+4 |class F1 extends Foo: // error
+  |      ^
+  |      class F1 needs to be abstract, since def foo(): Unit in class F1 is not defined 
+-- Error: tests/neg/i19731.scala:7:6 -----------------------------------------------------------------------------------
+7 |class F2 extends Foo: // error
+  |      ^
+  |      class F2 needs to be abstract, since:
+  |      it has 2 unimplemented members.
+  |      /** As seen from class F2, the missing signatures are as follows.
+  |       *  For convenience, these are usable as stub implementations.
+  |       */
+  |        def foo(): Unit = ???
+  |        def foo(x: Int): Unit = ???
+-- Error: tests/neg/i19731.scala:16:6 ----------------------------------------------------------------------------------
+16 |class B1 extends Bar: // error
+   |      ^
+   |      class B1 needs to be abstract, since:
+   |      it has 2 unimplemented members.
+   |      /** As seen from class B1, the missing signatures are as follows.
+   |       *  For convenience, these are usable as stub implementations.
+   |       */
+   |        // Members declared in B1
+   |        def foo(x: Int): Unit = ???
+   |        
+   |        // Members declared in Bar
+   |        def foo(): Unit = ???
diff --git a/tests/neg/i19731.scala b/tests/neg/i19731.scala
new file mode 100644
index 000000000000..75fff0e53872
--- /dev/null
+++ b/tests/neg/i19731.scala
@@ -0,0 +1,17 @@
+trait Foo:
+  def foo(): Unit
+
+class F1 extends Foo: // error
+  def foo(): Unit
+
+class F2 extends Foo: // error
+  def foo(): Unit
+  def foo(x: Int): Unit
+
+
+trait Bar:
+  def foo(): Unit
+  def foo(x: Int): Unit
+
+class B1 extends Bar: // error
+  def foo(x: Int): Unit