Disable special treatment of eta expansions in recheckClosure

Author: odersky

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

@@ -33,6 +33,13 @@ object ccConfig:
    */
   inline val optimizedRefinements = false
 
+  /** If enabled, use a special path in recheckClosure for closures
+   *  that are eta expansions. This can improve some error messages but
+   *  currently leads to unsoundess for handlng reach capabilities.
+   *  TODO: The unsoundness needs followin up.
+   */
+  inline val handleEtaExpansionsSpecially = false
+
   /** If true, use existential capture set variables */
   def useExistentials(using Context) =
     Feature.sourceVersion.stable.isAtLeast(SourceVersion.`3.5`)

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

@@ -628,7 +628,7 @@ class CheckCaptures extends Recheck, SymTransformer:
         // Constrain closure's parameters and result from the expected type before
         // rechecking the body.
         val res = recheckClosure(expr, pt, forceDependent = true)
-        if !isEtaExpansion(mdef) then
+        if !(isEtaExpansion(mdef) && ccConfig.handleEtaExpansionsSpecially) then
           // If closure is an eta expanded method reference it's better to not constrain
           // its internals early since that would give error messages in generated code
           // which are less intelligible.

tests/neg-custom-args/captures/effect-swaps-explicit.check

@@ -25,5 +25,5 @@
 -- Error: tests/neg-custom-args/captures/effect-swaps-explicit.scala:68:15 ---------------------------------------------
 68 |        Result.make: //lbl ?=> // error, escaping label from Result
    |        ^^^^^^^^^^^
-   |local reference contextual$9 from (using contextual$9: boundary.Label[Result[box Future[box T^?]^{fr, contextual$9}, box E^?]]^):
-   |  box Future[box T^?]^{fr, contextual$9} leaks into outer capture set of type parameter T of method make in object Result
+   |local reference contextual$9 from (using contextual$9: boundary.Label[Result[box Future[box T^?]^{fr, contextual$9, contextual$9}, box E^?]]^):
+   |  box Future[box T^?]^{fr, contextual$9, contextual$9} leaks into outer capture set of type parameter T of method make in object Result

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

@@ -5,13 +5,10 @@
    |          that type captures the root capability `cap`.
    |          This is often caused by a local capability in an argument of constructor Ref
    |          leaking as part of its result.
--- [E007] Type Mismatch Error: tests/neg-custom-args/captures/levels.scala:24:11 ---------------------------------------
+-- Error: tests/neg-custom-args/captures/levels.scala:24:11 ------------------------------------------------------------
 24 |    r.setV(g) // error
    |           ^
-   |           Found:    box (x: String) ->{cap3} String
-   |           Required: box (x$0: String) ->? String
+   |           reference (cap3 : CC^) is not included in the allowed capture set ? of value r
    |
    |           Note that reference (cap3 : CC^), defined in method scope
    |           cannot be included in outer capture set ? of value r
-   |
-   | longer explanation available when compiling with `-explain`

tests/neg-custom-args/captures/vars-simple.check

@@ -8,13 +8,11 @@
    |         since at least one of their capture sets contains the root capability `cap`
    |
    | longer explanation available when compiling with `-explain`
--- [E007] Type Mismatch Error: tests/neg-custom-args/captures/vars-simple.scala:16:8 -----------------------------------
+-- Error: tests/neg-custom-args/captures/vars-simple.scala:16:8 --------------------------------------------------------
 16 |    a = g  // error
    |        ^
-   |        Found:    box (x: String) ->{cap3} String
-   |        Required: box (x: String) ->{cap1, cap2} String
-   |
-   | longer explanation available when compiling with `-explain`
+   |        reference (cap3 : Cap) is not included in the allowed capture set {cap1, cap2}
+   |        of an enclosing function literal with expected type box String ->{cap1, cap2} String
 -- [E007] Type Mismatch Error: tests/neg-custom-args/captures/vars-simple.scala:17:12 ----------------------------------
 17 |    b = List(g) // error
    |        ^^^^^^^

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

@@ -5,16 +5,13 @@
    |
    |             Note that reference (cap3 : Cap), defined in method scope
    |             cannot be included in outer capture set {cap1} of variable a
--- [E007] Type Mismatch Error: tests/neg-custom-args/captures/vars.scala:25:8 ------------------------------------------
+-- Error: tests/neg-custom-args/captures/vars.scala:25:8 ---------------------------------------------------------------
 25 |    a = g      // error
    |        ^
-   |        Found:    (x: String) ->{cap3} String
-   |        Required: (x$0: String) ->{cap1} String
+   |        reference (cap3 : Cap) is not included in the allowed capture set {cap1} of variable a
    |
    |        Note that reference (cap3 : Cap), defined in method scope
    |        cannot be included in outer capture set {cap1} of variable a
-   |
-   | longer explanation available when compiling with `-explain`
 -- [E007] Type Mismatch Error: tests/neg-custom-args/captures/vars.scala:27:12 -----------------------------------------
 27 |    b = List(g) // error
    |        ^^^^^^^