Effects: do not recurse into #selector effects because the code never runs

Fixes rdar://151968656

Author: DougGregor

lib/Sema/TypeCheckEffects.cpp

@@ -713,6 +713,8 @@ class EffectsHandlingWalker : public ASTWalker {
       }
     } else if (auto TE = dyn_cast<MakeTemporarilyEscapableExpr>(E)) {
       recurse = asImpl().checkTemporarilyEscapable(TE);
+    } else if (auto OSE = dyn_cast<ObjCSelectorExpr>(E)) {
+      recurse = asImpl().checkObjCSelector(OSE);
     }
 
     // Error handling validation (via checkTopLevelEffects) happens after
@@ -2269,6 +2271,10 @@ class ApplyClassifier {
       return ShouldRecurse;
     }
 
+    ShouldRecurse_t checkObjCSelector(ObjCSelectorExpr *E) {
+      return ShouldNotRecurse;
+    }
+        
     ConditionalEffectKind checkExhaustiveDoBody(DoCatchStmt *S) {
       // All errors thrown by the do body are caught, but any errors thrown
       // by the catch bodies are bounded by the throwing kind of the do body.
@@ -2418,6 +2424,10 @@ class ApplyClassifier {
       return ShouldRecurse;
     }
 
+    ShouldRecurse_t checkObjCSelector(ObjCSelectorExpr *E) {
+      return ShouldNotRecurse;
+    }
+
     void visitExprPre(Expr *expr) { return; }
   };
 
@@ -2535,6 +2545,10 @@ class ApplyClassifier {
       return ShouldRecurse;
     }
 
+    ShouldRecurse_t checkObjCSelector(ObjCSelectorExpr *E) {
+      return ShouldNotRecurse;
+    }
+
     void visitExprPre(Expr *expr) { return; }
   };
 
@@ -4026,6 +4040,10 @@ class CheckEffectsCoverage : public EffectsHandlingWalker<CheckEffectsCoverage>
     return ShouldRecurse;
   }
 
+  ShouldRecurse_t checkObjCSelector(ObjCSelectorExpr *E) {
+    return ShouldNotRecurse;
+  }
+
   ConditionalEffectKind checkExhaustiveDoBody(DoCatchStmt *S) {
     // This is a context where errors are handled.
     ContextScope scope(*this, CurContext.withHandlesErrors());

test/expr/primary/selector/selector.swift

@@ -172,3 +172,11 @@ extension SomeProtocol {
 func test() -> Selector {
   #selector(OverloadedFuncAndProperty.f)
 }
+
+@objc protocol HasThrows {
+  @objc optional func doSomething(to object: AnyObject) throws -> Void
+}
+
+func testWithThrowing(obj: AnyObject) {
+  _ = #selector(HasThrows.doSomething(to:))
+}