Backport "Fix regression: Prioritize tree type over proto type when typing Binds" to 3.8.0 (#24391)

Backports #24175 to the 3.8.0-RC1. PR submitted by the release tooling. [skip ci]

Author: WojciechMazur

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

@@ -2875,7 +2875,7 @@ class Typer(@constructorOnly nestingLevel: Int = 0) extends Namer
  // leave the original tuple type; don't mix with & TupleXXL which would only obscure things
  pt
  case _ =>
- pt & body1.tpe
+ body1.tpe & pt
  val sym = newPatternBoundSymbol(name, symTp, tree.span)
  if (pt == defn.ImplicitScrutineeTypeRef || tree.mods.is(Given)) sym.setFlag(Given)
  if (ctx.mode.is(Mode.InPatternAlternative))

tests/neg/i13780-1.check

@@ -1,7 +1,7 @@
 -- [E007] Type Mismatch Error: tests/neg/i13780-1.scala:38:24 ----------------------------------------------------------
 38 | case x: (h *: t) => x.head // error
  | ^^^^^^
- | Found: Tuple.Head[VS & h *: t]
+ | Found: Tuple.Head[h *: t & VS]
  | Required: h
  | Note that implicit conversions were not tried because the result of an implicit conversion
  | must be more specific than h
@@ -13,8 +13,8 @@
  |
  | Note: a match type could not be fully reduced:
  |
- | trying to reduce Tuple.Head[VS & h *: t]
- | failed since selector VS & h *: t
+ | trying to reduce Tuple.Head[h *: t & VS]
+ | failed since selector h *: t & VS
  | does not uniquely determine parameter x in
  | case x *: _ => x
  | The computed bounds for the parameter are:

tests/neg/i24096.check

@@ -1,7 +1,7 @@
 -- [E007] Type Mismatch Error: tests/neg/i24096.scala:8:31 -------------------------------------------------------------
 8 | case r: Terminal[?] => r // error
  | ^
- | Found: (r : Pull[F, O, Unit] & Pull.Terminal[_])
+ | Found: (r : Pull.Terminal[_] & Pull[F, O, Unit])
  | Required: Pull[F2, O2, Unit]
  |
  | where: F is a type in class StreamPullOps with bounds <: [_²] =>> Any

tests/pos/i24038a.scala

@@ -0,0 +1,31 @@
+final class MBufferLong:
+ final def +=(elem: Long): this.type = ???
+
+type M[Tup <: Tuple] <: Tuple = Tup match
+ case EmptyTuple => EmptyTuple
+ case h *: t => BufferOf[h] *: M[t]
+
+type M2[T <: Tuple] <: Tuple = (T, M[T]) match
+ case (h *: t, a *: b) => BufferOf[h] *: M2[t]
+ case (EmptyTuple, EmptyTuple) => EmptyTuple
+ case (_, EmptyTuple) => EmptyTuple
+ case (EmptyTuple, _) => EmptyTuple
+
+type BufferOf[T] = T match
+ case Long => MBufferLong
+
+inline def append[T](t: T, buffer: BufferOf[T]): BufferOf[T] =
+ inline (t, buffer) match
+ case (x: Long, y: BufferOf[Long]) => y.+=(x)
+ buffer
+
+transparent inline def appendBuffers[T <: Tuple](t: T, buffers: M[T]): M2[T] = {
+ inline (t, buffers) match
+ case abcd: ((h *: t), bh *: bt) =>
+ val (hh *: tt, bh *: bt) = abcd
+ val x: BufferOf[h] = append[h](hh, bh.asInstanceOf[BufferOf[h]])
+ x *: appendBuffers[t](tt, bt.asInstanceOf[M[t]])
+ case _: (EmptyTuple, EmptyTuple) => EmptyTuple
+ case _: (_, EmptyTuple) => EmptyTuple
+ case _: (EmptyTuple, _) => EmptyTuple
+}

tests/pos/i24038b.scala

@@ -0,0 +1,12 @@
+final class MBufferLong
+
+type M[Tup <: Tuple] <: Tuple = Tup match
+ case EmptyTuple => EmptyTuple
+ case h *: t => MBufferLong *: M[t]
+
+def appendBuffers[T <: Tuple](t: T, buffers: M[T]): Unit = {
+ (t, buffers) match
+ case abcd: (h *: t, bh *: bt) =>
+ val (hh *: tt, bh *: bt) = abcd
+ summon[hh.type <:< h]
+}

tests/semanticdb/metac.expect

@@ -4991,8 +4991,8 @@ _empty_/Txn# => trait Txn [typeparam T <: Txn[T]] extends Object { self: Txn[T]
 _empty_/Txn#[T] => typeparam T <: Txn[T]
 _empty_/Txn#`<init>`(). => primary ctor <init> [typeparam T <: Txn[T]](): Txn[T]
 local0 => val local out: Repr[Out]
-local1 => val local inObj: Repr[In] & Obj[In]
-local2 => val local outObj: Repr[Out] & Obj[Out]
+local1 => val local inObj: Obj[In] & Repr[In]
+local2 => val local outObj: Obj[Out] & Repr[Out]
 
 Occurrences:
 [1:6..1:9): Txn <- _empty_/Txn#