First step: make capture set propagation shallow

Author: Linyxus

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

@@ -555,7 +555,7 @@ class CheckCaptures extends Recheck, SymTransformer:
           //println(i"Include call or box capture $included from $cs in ${env.owner}/${env.captured}/${env.captured.owner}/${env.kind}")
           checkSubset(included, env.captured, tree.srcPos, provenance(env))
           capt.println(i"Include call or box capture $included from $cs in ${env.owner} --> ${env.captured}")
-          if !isOfNestedMethod(env) then
+          if !isOfNestedMethod(env) && !ccConfig.caplessLike then
             val nextEnv = nextEnvToCharge(env)
             if nextEnv != null && !nextEnv.owner.isStaticOwner then
               recur(included, nextEnv, env)

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

@@ -21,6 +21,12 @@ object ccConfig:
    */
   inline val deferredReaches = false
 
+  /** Use the capless-like scheme for capture checking:
+   * - preciser capture sets for curried function types
+   * - a different rule for handling application captures
+   */
+  inline val caplessLike = true
+
   /** Check that if a type map (which is not a BiTypeMap) maps initial capture
    *  set variable elements to themselves it will not map any elements added in
    *  the future to something else. That is, we can safely use a capture set