Don't implicitly return assignments.

Corrected a number of diagnostic regressions.

Author: nate-chandler

lib/Parse/ParseDecl.cpp

@@ -5684,6 +5684,13 @@ void Parser::parseAbstractFunctionBody(AbstractFunctionDecl *AFD) {
           }
         }
       } else if (auto *E = Element.dyn_cast<Expr *>()) {
+        if (auto SE = dyn_cast<SequenceExpr>(E->getSemanticsProvidingExpr())) {
+          if (SE->getNumElements() > 0 && isa<AssignExpr>(SE->getElement(1))) {
+            // This is an assignment.  We don't want to implicitly return 
+            // it.
+            return;
+          }
+        }
         if (auto F = dyn_cast<FuncDecl>(AFD)) {
           auto RS = new (Context) ReturnStmt(SourceLoc(), E);
           BS->setElement(0, RS); 

test/PrintAsObjC/extensions.swift

@@ -138,9 +138,9 @@ extension NSString {
 // CHECK-NEXT: - (T _Nullable)extract2 SWIFT_WARN_UNUSED_RESULT;
 // CHECK-NEXT: @end
 extension PettableContainer {
-  @objc func duplicate() -> PettableContainer { _ = 0; fatalError() }
-  @objc func duplicate2() -> PettableContainer<T> { _ = 0; fatalError() }
-  @objc func duplicate3() -> PettableContainer<PettableOverextendedMetaphor> { _ = 0; fatalError() }
-  @objc func extract() -> T { _ = 0; fatalError() }
-  @objc func extract2() -> T? { _ = 0; fatalError() }
+  @objc func duplicate() -> PettableContainer { fatalError() }
+  @objc func duplicate2() -> PettableContainer<T> { fatalError() }
+  @objc func duplicate3() -> PettableContainer<PettableOverextendedMetaphor> { fatalError() }
+  @objc func extract() -> T { fatalError() }
+  @objc func extract2() -> T? { fatalError() }
 }

test/SILGen/closures.swift

@@ -20,7 +20,6 @@ func return_local_generic_function_without_captures<A, R>() -> (A) -> R {
 
 func return_local_generic_function_with_captures<A, R>(_ a: A) -> (A) -> R {
   func f(_: A) -> R {
-    _ = 0
     _ = a
   }
 

test/SILGen/keypath_application.swift

@@ -219,6 +219,5 @@ func writebackNesting(x: inout Int,
   // -- set 'b'
   // CHECK: function_ref @$sSi19keypath_applicationE1bSivs
 
-  _ = 0
   x.b[keyPath: y].u[keyPath: z].tt = w
 }

test/SILGen/objc_blocks_bridging.swift

@@ -74,7 +74,6 @@ import Foundation
   // CHECK:         end_borrow [[BORROWED_SELF_COPY]]
   // CHECK:         destroy_value [[SELF_COPY]]
   @objc dynamic func cFunctionPointer(_ fp: @convention(c) (Int) -> Int, x: Int) -> Int {
-    _ = 0
     _ = fp(x)
   }
 

test/SILGen/objc_bridging_any.swift

@@ -413,7 +413,7 @@ protocol Anyable {
 // Make sure we generate correct bridging thunks
 class SwiftIdLover : NSObject, Anyable {
 
-  @objc func methodReturningAny() -> Any { _ = 0; fatalError() }
+  @objc func methodReturningAny() -> Any { fatalError() }
   // SEMANTIC ARC TODO: This is another case of pattern matching the body of one
   // function in a different function... Just pattern match the unreachable case
   // to preserve behavior. We should check if it is correct.

test/SILOptimizer/return.swift

@@ -1,8 +1,8 @@
 // RUN: %target-swift-frontend %s -emit-sil -verify
 
-func singleBlock() -> () {
+func singleBlock() -> Int {
   _ = 0
-}
+} // expected-error {{missing return in a function expected to return 'Int'}}
 
 func singleBlock2() -> Int {
   var y = 0 

test/expr/capture/order.swift

@@ -34,13 +34,11 @@ func transitiveForwardCapture() {
 
 func transitiveForwardCapture2() {
   func ping() -> Int {
-    _ = 0
     _ = pong() // expected-error{{cannot capture 'pong', which would use 'x' before it is declared}}
   }
   _ = ping()
   var x = 1 // expected-note{{'x' declared here}}
   func pong() -> Int { // expected-note{{'pong', declared here, captures 'pung'}}
-    _ = 0
     _ = pung()
   }
   func pung() -> Int { // expected-note{{'pung', declared here, captures 'x'}}
@@ -52,7 +50,6 @@ func transitiveForwardCapture2() {
 func transitiveForwardCapture3() {
   var y = 2
   func ping() -> Int {
-    _ = 0
     _ = pong() // expected-error{{cannot capture 'pong', which would use 'x' before it is declared}}
   }
   _ = ping()

validation-test/stdlib/AssertDiagnosticsSIL.swift

@@ -1,7 +1,7 @@
 // RUN: %target-swift-frontend %s -emit-sil -verify
 
 func assertionFailure_isNotNoreturn() -> Int {
-  _ = 0
+  _ = 0 // Don't implicitly return the assertionFailure call.
   assertionFailure("")
 } // expected-error {{missing return in a function expected to return 'Int'}}