Effects: Treat #selector as covering throws/async effects in its operand

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; }
   };
 
@@ -3716,6 +3730,12 @@ class CheckEffectsCoverage : public EffectsHandlingWalker<CheckEffectsCoverage>
       Self.Flags.set(ContextFlags::InAsyncLet);
     }
 
+    /// Enter a subexpression that's never exected.
+    void enterNonExecuting() {
+      Self.Flags.set(ContextFlags::IsTryCovered);
+      Self.Flags.set(ContextFlags::IsAsyncCovered);
+    }
+
     void refineLocalContext(Context newContext) {
       Self.CurContext = newContext;
     }
@@ -3825,6 +3845,13 @@ class CheckEffectsCoverage : public EffectsHandlingWalker<CheckEffectsCoverage>
       OldMaxThrowingKind = std::max(OldMaxThrowingKind, Self.MaxThrowingKind);
     }
 
+    void preserveCoverageFromNonExecutingOperand() {
+      OldFlags.mergeFrom(ContextFlags::asyncAwaitFlags(), Self.Flags);
+      OldFlags.mergeFrom(ContextFlags::throwFlags(), Self.Flags);
+      OldFlags.mergeFrom(ContextFlags::unsafeFlags(), Self.Flags);
+      OldMaxThrowingKind = std::max(OldMaxThrowingKind, Self.MaxThrowingKind);
+    }
+
     void preserveCoverageFromOptionalOrForcedTryOperand() {
       OldFlags.mergeFrom(ContextFlags::asyncAwaitFlags(), Self.Flags);
       OldFlags.mergeFrom(ContextFlags::unsafeFlags(), Self.Flags);
@@ -4026,6 +4053,17 @@ class CheckEffectsCoverage : public EffectsHandlingWalker<CheckEffectsCoverage>
     return ShouldRecurse;
   }
 
+  ShouldRecurse_t checkObjCSelector(ObjCSelectorExpr *E) {
+    // Walk the operand.
+    ContextScope scope(*this, std::nullopt);
+    scope.enterNonExecuting();
+
+    E->getSubExpr()->walk(*this);
+
+    scope.preserveCoverageFromNonExecutingOperand();
+    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:))
+}