[CSGen/SyntaticElement] Remove logic that connects tap expressions to closures

Both single- and multi-statement closures now use variable reference
collector to identify variables used in the interpolation body, which
means that it's not longer necessary to connect to the closure explicitly
(if interpolation is contained in one).

Author: xedin

lib/Sema/CSGen.cpp

@@ -1305,14 +1305,6 @@ struct VarRefCollector : public ASTWalker {
         SmallVector<TypeVariableType *, 2> referencedVars;
 
         if (auto *tap = getAsExpr<TapExpr>(appendingExpr)) {
-          auto *tapDC = tap->getVar()->getDeclContext();
-          // If tap expression is located in a closure, let's
-          // connect them because interpolation could use parameters.
-          if (auto *closure = dyn_cast<ClosureExpr>(tapDC)) {
-            referencedVars.push_back(
-                CS.getType(closure)->castTo<TypeVariableType>());
-          }
-
           // Collect all of the variable references that appear
           // in the tap body, otherwise tap expression is going
           // to get disconnected from the context.

lib/Sema/CSSyntacticElement.cpp

@@ -360,15 +360,6 @@ static void createConjunction(ConstraintSystem &cs,
   }
 
   if (locator->directlyAt<TapExpr>()) {
-    auto *tap = castToExpr<TapExpr>(locator->getAnchor());
-    auto *tapDC = tap->getVar()->getDeclContext();
-
-    referencedVars.push_back(cs.getType(tap)->castTo<TypeVariableType>());
-
-    if (auto *closure = dyn_cast<ClosureExpr>(tapDC)) {
-      referencedVars.push_back(cs.getType(closure)->castTo<TypeVariableType>());
-    }
-
     // Body of the interpolation is always isolated from its context, only
     // its individual elements are allowed access to type information
     // from the outside e.g. external declaration references.

test/Sema/string_interpolations.swift

@@ -43,3 +43,16 @@ do {
     }
   }
 }
+
+// This case is (currently) interesting because "\(query)" is type-checked
+// separately as part of ~= operator application.
+func test_interpolation_in_case(query: String) {
+  _ = { (request: String) in
+    switch request {
+    case "\(query)": // Ok
+      break
+    default:
+      break
+    }
+  }
+}