Loosen the "does not match previously inferred" criterion (#23067)

The expected type here is still the one using cap, not fresh. So it's OK
if the actual
type uses fresh where the expected uses cap.

Also: fix hasCap test to establish PrintFresh criterion. This was
missing a case, it seems.

Author: bracevac

compiler/src/dotty/tools/dotc/cc/CheckCaptures.scala

@@ -1081,9 +1081,12 @@ class CheckCaptures extends Recheck, SymTransformer:
       tree.tpt match
         case tpt: InferredTypeTree if !canUseInferred =>
           val expected = tpt.tpe.dropAllRetains
-          todoAtPostCheck += (() => checkConformsExpr(tp, expected, tree.rhs, addenda(expected)))
-            // The check that inferred <: expected is done after recheck so that it
-            // does not interfere with normal rechecking by constraining capture set variables.
+          todoAtPostCheck += { () =>
+            withCapAsRoot:
+              checkConformsExpr(tp, expected, tree.rhs, addenda(expected))
+              // The check that inferred <: expected is done after recheck so that it
+              // does not interfere with normal rechecking by constraining capture set variables.
+          }
         case _ =>
       tp
     end checkInferredResult

compiler/src/dotty/tools/dotc/cc/root.scala

@@ -340,6 +340,7 @@ object root:
         x || t.dealiasKeepAnnots.match
           case Fresh(_) => false
           case t: TermRef => t.isCap || this(x, t.widen)
+          case CapturingType(t1, refs) => refs.containsCap || this(x, t1)
           case x: ThisType => false
           case _ => foldOver(x, t)
 
@@ -349,7 +350,9 @@ object root:
       case refs: CaptureSet =>
         refs.elems.exists(_.stripReadOnly.isCap)
 
-    if refs.exists(containsCap) then ctx.withProperty(PrintFresh, Some(()))
-    else ctx
+    if refs.exists(containsCap) then
+      ctx.withProperty(PrintFresh, Some(()))
+    else
+      ctx
   end printContext
 end root

tests/neg-custom-args/captures/capt-depfun.check

@@ -2,7 +2,7 @@
 11 |  val dc: ((Str^{y, z}) => Str^{y, z}) = ac(g()) // error // error: separatioon
    |                                         ^^^^^^^
    |                                         Found:    Str^{} ->{ac, y, z} Str^{y, z}
-   |                                         Required: Str^{y, z} ->{fresh} Str^{y, z}
+   |                                         Required: Str^{y, z} => Str^{y, z}
    |
    | longer explanation available when compiling with `-explain`
 -- Error: tests/neg-custom-args/captures/capt-depfun.scala:11:24 -------------------------------------------------------

tests/neg-custom-args/captures/cc-existential-conformance.check

@@ -1,8 +1,8 @@
 -- [E007] Type Mismatch Error: tests/neg-custom-args/captures/cc-existential-conformance.scala:8:24 --------------------
 8 |  val y: A -> Fun[B^] = x // error
   |                        ^
-  |                        Found:    (x : A -> (x²: A) -> B^{localcap})
-  |                        Required: A -> A -> B^{fresh}
+  |                        Found:    (x : A -> (x²: A) -> B^)
+  |                        Required: A -> A -> B^
   |
   |                        where:    x  is a value in method test
   |                                  x² is a reference to a value parameter
@@ -21,8 +21,8 @@
 -- [E007] Type Mismatch Error: tests/neg-custom-args/captures/cc-existential-conformance.scala:13:19 -------------------
 13 |  val y: Fun[B^] = x // error
    |                   ^
-   |                   Found:    (x : (x²: A) -> B^{localcap})
-   |                   Required: A -> B^{fresh}
+   |                   Found:    (x : (x²: A) -> B^)
+   |                   Required: A -> B^
    |
    |                   where:    x  is a value in method test2
    |                             x² is a reference to a value parameter

tests/neg-custom-args/captures/i19330.check

@@ -14,7 +14,7 @@
 22 |  val bad: bar.T = foo(bar) // error
    |                   ^^^^^^^^
    |                   Found:    bar.T
-   |                   Required: () => Logger^
+   |                   Required: () ->{fresh} Logger^{fresh}
    |
    | longer explanation available when compiling with `-explain`
 -- Error: tests/neg-custom-args/captures/i19330.scala:16:14 ------------------------------------------------------------

tests/neg-custom-args/captures/i21614.check

@@ -8,8 +8,8 @@
 -- [E007] Type Mismatch Error: tests/neg-custom-args/captures/i21614.scala:15:12 ---------------------------------------
 15 |  files.map(new Logger(_)) // error, Q: can we improve the error message?
    |            ^^^^^^^^^^^^^
-   |            Found:    (_$1: box File^{files*}) ->{files*} box Logger{val f: File^{_$1}}^{localcap.rd, _$1}
-   |            Required: (_$1: box File^{files*}) ->{fresh} box Logger{val f: File^?}^?
+   |            Found:    (_$1: box File^{files*}) ->{files*} box Logger{val f: File^{_$1}}^{cap.rd, _$1}
+   |            Required: (_$1: box File^{files*}) => box Logger{val f: File^?}^?
    |
    |            Note that reference <cap of (_$1: box File^{files*}): box Logger{val f: File^?}^?>.rd
    |            cannot be included in outer capture set ?

tests/pos-custom-args/captures/i23027.scala

@@ -0,0 +1,12 @@
+import language.experimental.captureChecking
+
+trait Test {
+    def foo(x: Test): Test =
+        Test.bar
+        ???
+}
+
+object Test {
+    val _bar: Any => Any = identity
+    def bar[T] = _bar.asInstanceOf[T => T] // error
+}