Use presence of 'await' to make top-level async

To help maintain source-compatibility, the presence of an `await` in
top-level code to kick the top-level code over to being a concurrent
context.

This, of course, means that in the test cases that exist today, they
will go back to behaving identically to how they did before I added all
of this because they don't have any awaits in the top-level. I'll be
adding new tests to verify the differences in behavior between swift 5,
swift 6, with and without async top level enabled in the next commit.

Author: etcwilde

include/swift/AST/SourceFile.h

@@ -582,6 +582,9 @@ class SourceFile final : public FileUnit {
 
   ArrayRef<OpaqueTypeDecl *> getOpaqueReturnTypeDecls();
 
+  /// Returns true if the source file contains concurrency in the top-level
+  bool isAsyncTopLevelSourceFile() const;
+
 private:
 
   /// If not \c None, the underlying vector contains the parsed tokens of this

include/swift/AST/TypeCheckRequests.h

@@ -3246,6 +3246,21 @@ class ClosureEffectsRequest
   bool isCached() const { return true; }
 };
 
+class GetSourceFileAsyncNode
+    : public SimpleRequest<GetSourceFileAsyncNode, ASTNode(const SourceFile *),
+                           RequestFlags::Cached> {
+public:
+  using SimpleRequest::SimpleRequest;
+
+private:
+  friend SimpleRequest;
+
+  ASTNode evaluate(Evaluator &evaluator, const SourceFile *) const;
+
+public:
+  bool isCached() const { return true; }
+};
+
 void simple_display(llvm::raw_ostream &out, Type value);
 void simple_display(llvm::raw_ostream &out, const TypeRepr *TyR);
 void simple_display(llvm::raw_ostream &out, ImplicitMemberAction action);

include/swift/AST/TypeCheckerTypeIDZone.def

@@ -372,3 +372,6 @@ SWIFT_REQUEST(TypeChecker, RenamedDeclRequest,
 SWIFT_REQUEST(TypeChecker, ClosureEffectsRequest,
               FunctionType::ExtInfo(ClosureExpr *),
               Cached, NoLocationInfo)
+SWIFT_REQUEST(TypeChecker, GetSourceFileAsyncNode,
+              AwaitExpr *(const SourceFile *),
+              Cached, NoLocationInfo)

lib/AST/DeclContext.cpp

@@ -1228,8 +1228,13 @@ bool DeclContext::isAsyncContext() const {
   case DeclContextKind::GenericTypeDecl:
     return false;
   case DeclContextKind::FileUnit:
+    if (const SourceFile *sf = dyn_cast<SourceFile>(this))
+      return getASTContext().LangOpts.EnableExperimentalAsyncTopLevel &&
+             sf->isAsyncTopLevelSourceFile();
+    return false;
   case DeclContextKind::TopLevelCodeDecl:
-    return getASTContext().LangOpts.EnableExperimentalAsyncTopLevel;
+    return getASTContext().LangOpts.EnableExperimentalAsyncTopLevel &&
+           getParent()->isAsyncContext();
   case DeclContextKind::AbstractClosureExpr:
     return cast<AbstractClosureExpr>(this)->isBodyAsync();
   case DeclContextKind::AbstractFunctionDecl: {

lib/AST/Module.cpp

@@ -3038,6 +3038,24 @@ SourceFile::lookupOpaqueResultType(StringRef MangledName) {
   return nullptr;
 }
 
+bool SourceFile::isAsyncTopLevelSourceFile() const {
+  return isScriptMode() &&
+         (bool)evaluateOrDefault(getASTContext().evaluator,
+                                 GetSourceFileAsyncNode{this}, ASTNode());
+}
+
+ASTNode GetSourceFileAsyncNode::evaluate(Evaluator &eval,
+                                         const SourceFile *sf) const {
+  for (Decl *d : sf->getTopLevelDecls()) {
+    TopLevelCodeDecl *tld = dyn_cast<TopLevelCodeDecl>(d);
+    if (tld && tld->getBody()) {
+      if (ASTNode asyncNode = tld->getBody()->findAsyncNode())
+        return asyncNode;
+    }
+  }
+  return ASTNode();
+}
+
 //===----------------------------------------------------------------------===//
 // SynthesizedFileUnit Implementation
 //===----------------------------------------------------------------------===//

test/SILGen/toplevel.swift

@@ -1,5 +1,5 @@
-// RUN: %target-swift-emit-silgen -Xllvm -sil-full-demangle %s | %FileCheck %s --check-prefixes='CHECK,SYNC-CHECK'
-// RUN: %target-swift-emit-silgen -Xllvm -sil-full-demangle -enable-experimental-async-top-level %s | %FileCheck %s --check-prefixes='CHECK,ASYNC-CHECK'
+// RUN: %target-swift-emit-silgen -Xllvm -sil-full-demangle %s | %FileCheck %s
+// RUN: %target-swift-emit-silgen -Xllvm -sil-full-demangle -enable-experimental-async-top-level %s | %FileCheck %s
 
 func markUsed<T>(_ t: T) {}
 
@@ -11,13 +11,7 @@ func trap() -> Never {
 // CHECK-LABEL: sil [ossa] @main
 // CHECK: bb0({{%.*}} : $Int32, {{%.*}} : $UnsafeMutablePointer<Optional<UnsafeMutablePointer<Int8>>>):
 
-// async setup call to @async_Main (this is in @main)
-// ASYNC-CHECK: [[ASYNC_MAIN:%[0-9]+]] = function_ref @async_Main : $@convention(thin) @async () -> ()
-// ASYNC-CHECK: [[THUNK:%[0-9]+]] = function_ref @$sIetH_yts5Error_pIegHrzo_TR
-
-// Actual body of async top-level
-// ASYNC-CHECK-LABEL: sil hidden [ossa] @async_Main
-// ASYNC-CHECK: bb0:
+// CHECK-NOT: @async_Main
 
 
 // -- initialize x
@@ -127,11 +121,7 @@ defer {
 
 
 // CHECK: [[RET:%[0-9]+]] = struct $Int32
-// SYNC-CHECK: return [[RET]]
-
-// ASYNC-CHECK: [[EXITFUNC:%[0-9]+]] = function_ref @exit
-// ASYNC-CHECK: apply [[EXITFUNC]]([[RET]]) : $@convention(c) (Int32) -> Never
-// ASYNC-CHECK: unreachable
+// CHECK: return [[RET]]
 
 // CHECK-LABEL: sil hidden [ossa] @$s8toplevel7print_xyyF
 

test/SILGen/toplevel_errors.swift

@@ -1,5 +1,5 @@
-// RUN: %target-swift-emit-silgen %s | %FileCheck %s --check-prefixes='CHECK,SYNC-CHECK'
-// RUN: %target-swift-emit-silgen -enable-experimental-async-top-level %s | %FileCheck %s --check-prefixes='CHECK,ASYNC-CHECK'
+// RUN: %target-swift-emit-silgen %s | %FileCheck %s
+// RUN: %target-swift-emit-silgen -enable-experimental-async-top-level %s | %FileCheck %s
 
 enum MyError : Error {
   case A, B
@@ -18,10 +18,7 @@ throw MyError.A
 // CHECK: br bb2([[ERR2]] : $Error)
 
 // CHECK: bb1([[T0:%.*]] : $Int32):
-// SYNC-CHECK: return [[T0]] : $Int32
-// ASYNC-CHECK: [[EXITFUNC:%[0-9]+]] = function_ref @exit
-// ASYNC-CHECK: {{[0-9]+}} = apply [[EXITFUNC]]([[T0]])
-// ASYNC-CHECK: unreachable
+// CHECK: return [[T0]] : $Int32
 
 // CHECK: bb2([[T0:%.*]] : @owned $Error):
 // CHECK: builtin "errorInMain"([[T0]] : $Error)