Delay overloading priority changes to 3.8

With the warnings about the changes enabled in 3.7 and 3.8-migration

Author: EugeneFlesselle

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

@@ -2226,18 +2226,20 @@ trait Applications extends Compatibility {
     record(s"resolveOverloaded1", alts.length)
 
     val sv = Feature.sourceVersion
-    val isOldPriorityVersion: Boolean = sv.isAtMost(SourceVersion.`3.6`)
-    val isWarnPriorityChangeVersion = sv == SourceVersion.`3.6` || sv == SourceVersion.`3.7-migration`
+    val isOldPriorityVersion: Boolean = sv.isAtMost(SourceVersion.`3.7`)
+    val isWarnPriorityChangeVersion = sv == SourceVersion.`3.7` || sv == SourceVersion.`3.8-migration`
 
-    inline def warnOnPriorityChange(oldCands: List[TermRef], newCands: List[TermRef])(f: List[TermRef] => List[TermRef]): List[TermRef] =
+    def warnOnPriorityChange(oldCands: List[TermRef], newCands: List[TermRef])(f: List[TermRef] => List[TermRef]): List[TermRef] =
+      lazy val oldRes = f(oldCands)
+      val newRes = f(newCands)
 
       def doWarn(oldChoice: String, newChoice: String): Unit =
         val (change, whichChoice) =
           if isOldPriorityVersion
           then ("will change", "Current choice ")
           else ("has changed", "Previous choice")
 
-        val msg = // uses oldCands as the list of alternatives since they should be a superset of newCands
+        val msg = // using oldCands to list the alternatives as they should be a superset of newCands
           em"""Overloading resolution for ${err.expectedTypeStr(pt)} between alternatives
               | ${oldCands map (_.info)}%\n %
               |$change.
@@ -2247,9 +2249,6 @@ trait Applications extends Compatibility {
         report.warning(msg, srcPos)
       end doWarn
 
-      lazy val oldRes = f(oldCands)
-      val newRes = f(newCands)
-
       if isWarnPriorityChangeVersion then (oldRes, newRes) match
         case (oldAlt :: Nil, newAlt :: Nil) if oldAlt != newAlt => doWarn(oldAlt.info.show, newAlt.info.show)
         case (oldAlt :: Nil, Nil) => doWarn(oldAlt.info.show, "none")

tests/neg/multiparamlist-overload-3.6.check

@@ -1,12 +1,12 @@
 -- [E007] Type Mismatch Error: tests/neg/multiparamlist-overload-3.6.scala:33:21 ---------------------------------------
-33 |    val r = f(new B)(new A) // error since resolves to R2 in 3.6 (and 3.7) as expected
+33 |    val r = f(new B)(new A) // error since resolves to R2 in 3.7 (and 3.8) as expected
    |                     ^^^^^
    |                     Found:    A
    |                     Required: B
    |
    | longer explanation available when compiling with `-explain`
 -- Warning: tests/neg/multiparamlist-overload-3.6.scala:20:10 ----------------------------------------------------------
-20 |  val r = f(new B)(new C) // resolves to R1 in 3.6
+20 |  val r = f(new B)(new C) // resolves to: R1 in 3.7, R3 in 3.8
    |          ^
    |          Overloading resolution for arguments (B)(C) between alternatives
    |           (x: B)(y: B): R3
@@ -16,7 +16,7 @@
    |          Current choice           : (x: A)(y: C): R1
    |          New choice from Scala 3.7: (x: B)(y: B): R3
 -- Warning: tests/neg/multiparamlist-overload-3.6.scala:40:12 ----------------------------------------------------------
-40 |    val r = f(new B)(new A) // resolves to R1 in 3.6
+40 |    val r = f(new B)(new A) // resolves to: R1 in 3.7, R2 in 3.8 as in Part1
    |            ^
    |            Overloading resolution for arguments (B)(A) between alternatives
    |             (x: B)(y: C): R3

tests/neg/multiparamlist-overload-3.6.scala

@@ -1,4 +1,4 @@
-import scala.language.`3.6`
+import scala.language.`3.7`
 
 class A
 class B extends A
@@ -17,7 +17,7 @@ object Test1:
   def f(x: B)(y: A) = new R2
   def f(x: B)(y: B) = new R3
 
-  val r = f(new B)(new C) // resolves to R1 in 3.6
+  val r = f(new B)(new C) // resolves to: R1 in 3.7, R3 in 3.8
   val _: R1 = r
 end Test1
 
@@ -30,14 +30,14 @@ object Test2:
     def f(x: A)(y: A) = new R1
     def f(x: B)(y: B) = new R2
 
-    val r = f(new B)(new A) // error since resolves to R2 in 3.6 (and 3.7) as expected
+    val r = f(new B)(new A) // error since resolves to R2 in 3.7 (and 3.8) as expected
 
   object Part2:
     def f(x: A)(y: A) = new R1
     def f(x: B)(y: B) = new R2
     def f(x: B)(y: C) = new R3
 
-    val r = f(new B)(new A) // resolves to R1 in 3.6
+    val r = f(new B)(new A) // resolves to: R1 in 3.7, R2 in 3.8 as in Part1
     val _: R1 = r
 
 end Test2

tests/neg/multiparamlist-overload-3.7.check

@@ -1,20 +1,20 @@
 -- [E007] Type Mismatch Error: tests/neg/multiparamlist-overload-3.7.scala:33:21 ---------------------------------------
-33 |    val r = f(new B)(new A) // error since resolves to R2 in 3.7 (and 3.6), as expected
+33 |    val r = f(new B)(new A) // error, since resolves to R2 in both 3.7 and 3.8, as expected
    |                     ^^^^^
    |                     Found:    A
    |                     Required: B
    |
    | longer explanation available when compiling with `-explain`
 -- [E134] Type Error: tests/neg/multiparamlist-overload-3.7.scala:40:12 ------------------------------------------------
-40 |    val r = f(new B)(new A) // error since resolves to R2 in 3.7, as in Part1
+40 |    val r = f(new B)(new A) // error since resolves to R2 in 3.8 as in Part1 (was R1 in 3.7)
    |            ^
    |            None of the overloaded alternatives of method f in object Part2 with types
    |             (x: B)(y: C): R3
    |             (x: B)(y: B): R2
    |             (x: A)(y: A): R1
    |            match arguments (B)(A)
 -- Warning: tests/neg/multiparamlist-overload-3.7.scala:20:10 ----------------------------------------------------------
-20 |  val r = f(new B)(new C) // resolves to R3 in 3.7
+20 |  val r = f(new B)(new C) // resolves to: R1 in 3.7, R3 in 3.8
    |          ^
    |          Overloading resolution for arguments (B)(C) between alternatives
    |           (x: B)(y: B): R3

tests/neg/multiparamlist-overload-3.7.scala

@@ -1,4 +1,4 @@
-import scala.language.`3.7-migration`
+import scala.language.`3.8-migration`
 
 class A
 class B extends A
@@ -17,7 +17,7 @@ object Test1:
   def f(x: B)(y: A) = new R2
   def f(x: B)(y: B) = new R3
 
-  val r = f(new B)(new C) // resolves to R3 in 3.7
+  val r = f(new B)(new C) // resolves to: R1 in 3.7, R3 in 3.8
   val _: R3 = r
 end Test1
 
@@ -30,13 +30,13 @@ object Test2:
     def f(x: A)(y: A) = new R1
     def f(x: B)(y: B) = new R2
 
-    val r = f(new B)(new A) // error since resolves to R2 in 3.7 (and 3.6), as expected
+    val r = f(new B)(new A) // error, since resolves to R2 in both 3.7 and 3.8, as expected
 
   object Part2:
     def f(x: A)(y: A) = new R1
     def f(x: B)(y: B) = new R2
     def f(x: B)(y: C) = new R3
 
-    val r = f(new B)(new A) // error since resolves to R2 in 3.7, as in Part1
+    val r = f(new B)(new A) // error since resolves to R2 in 3.8 as in Part1 (was R1 in 3.7)
 
 end Test2

tests/neg/scalatest-overload-3.7.scala

@@ -1,4 +1,4 @@
-import scala.language.`3.7`
+import scala.language.`3.8`
 
 class TestBody1
 class TestBody2