Remove ExplicitCompletionHandlerIndex flag

Assuming that we don't typecheck a deserialized module, we don't
actually need the ExplicitCompletionHandlerIndex. We used this flag to
determine whether we could trust the number stored in the handler index
or just take the last parameter of the function we're attached to.

Since we only typecheck it before serialization, we can safely check
that the completion handler location is valid before choosing whether we
should trust it or not.

Author: etcwilde

include/swift/AST/Attr.h

@@ -2172,14 +2172,10 @@ class CompletionHandlerAsyncAttr final : public DeclAttribute {
   /// Source location of the completion handler index passed to the index
   const SourceLoc CompletionHandlerIndexLoc;
 
-  /// True when the completion handler was specified explicitly
-  const bool ExplicitCompletionHandlerIndex;
-
   AbstractFunctionDecl *AsyncFunctionDecl = nullptr;
 
   CompletionHandlerAsyncAttr(DeclNameRef asyncFunctionName,
                              SourceLoc asyncFunctionNameLoc,
-                             bool explicitCompletionHandlerIndex,
                              size_t completionHandlerIndex,
                              SourceLoc completionHandlerIndexLoc,
                              SourceLoc atLoc, SourceRange range)
@@ -2188,19 +2184,16 @@ class CompletionHandlerAsyncAttr final : public DeclAttribute {
         AsyncFunctionName(asyncFunctionName),
         AsyncFunctionNameLoc(asyncFunctionNameLoc),
         CompletionHandlerIndex(completionHandlerIndex),
-        CompletionHandlerIndexLoc(completionHandlerIndexLoc),
-        ExplicitCompletionHandlerIndex(explicitCompletionHandlerIndex) {}
+        CompletionHandlerIndexLoc(completionHandlerIndexLoc) {}
 
   CompletionHandlerAsyncAttr(AbstractFunctionDecl &asyncFunctionDecl,
-                             bool explicitCompletionHandlerIndex,
                              size_t completionHandlerIndex,
                              SourceLoc completionHandlerIndexLoc,
                              SourceLoc atLoc, SourceRange range)
       : DeclAttribute(DAK_CompletionHandlerAsync, atLoc, range,
                       /*implicit*/ false),
         CompletionHandlerIndex(completionHandlerIndex),
         CompletionHandlerIndexLoc(completionHandlerIndexLoc),
-        ExplicitCompletionHandlerIndex(explicitCompletionHandlerIndex),
         AsyncFunctionDecl(&asyncFunctionDecl) {}
 
 

lib/Parse/ParseDecl.cpp

@@ -1630,7 +1630,7 @@ parseCompletionHandlerAsyncAttribute(Parser &P, StringRef AttrName,
 
   return new (P.Context) CompletionHandlerAsyncAttr(
       parsedAsyncName.formDeclNameRef(P.Context), nameLoc,
-      handlerIndexLoc.isValid(), handlerIndex, handlerIndexLoc, AtLoc,
+      handlerIndex, handlerIndexLoc, AtLoc,
       AttrRange);
 }
 

lib/Sema/TypeCheckAttr.cpp

@@ -5710,7 +5710,7 @@ void AttributeChecker::visitCompletionHandlerAsyncAttr(
              diag::attr_completion_handler_async_handler_not_func, attr);
     return;
   }
-  size_t completionHandlerIndex = attr->ExplicitCompletionHandlerIndex
+  size_t completionHandlerIndex = attr->CompletionHandlerIndexLoc.isValid()
                                       ? attr->CompletionHandlerIndex
                                       : attachedFunctionParams->size() - 1;
   if (attachedFunctionParams->size() < completionHandlerIndex) {

lib/Serialization/Deserialization.cpp

@@ -4554,17 +4554,14 @@ llvm::Error DeclDeserializer::deserializeDeclCommon() {
 
       case decls_block::CompletionHandlerAsync_DECL_ATTR: {
         uint64_t handlerIndex;
-        bool explicitHandlerIndex;
         uint64_t asyncFunctionDeclID;
         serialization::decls_block::CompletionHandlerAsyncDeclAttrLayout::
-            readRecord(scratch, explicitHandlerIndex, handlerIndex,
-                       asyncFunctionDeclID);
+            readRecord(scratch, handlerIndex, asyncFunctionDeclID);
 
         auto mappedFunctionDecl =
             cast<AbstractFunctionDecl>(MF.getDecl(asyncFunctionDeclID));
         Attr = new (ctx) CompletionHandlerAsyncAttr(
-            *mappedFunctionDecl, explicitHandlerIndex, handlerIndex,
-            /*handlerIndexLoc*/ SourceLoc(),
+            *mappedFunctionDecl, handlerIndex, /*handlerIndexLoc*/ SourceLoc(),
             /*atLoc*/ SourceLoc(), /*range*/ SourceRange());
         break;
       }

lib/Serialization/ModuleFormat.h

@@ -1926,7 +1926,6 @@ namespace decls_block {
 
   using CompletionHandlerAsyncDeclAttrLayout = BCRecordLayout<
     CompletionHandlerAsync_DECL_ATTR,
-    BCFixed<1>,                 // True if explicit handler index
     BCVBR<5>,                   // Completion handler index
     DeclIDField                 // Mapped async function decl
   >;

lib/Serialization/Serialization.cpp

@@ -2632,8 +2632,7 @@ class Serializer::DeclSerializer : public DeclVisitor<DeclSerializer> {
       auto asyncFuncDeclID = S.addDeclRef(attr->AsyncFunctionDecl);
 
       CompletionHandlerAsyncDeclAttrLayout::emitRecord(
-          S.Out, S.ScratchRecord, abbrCode,
-          attr->ExplicitCompletionHandlerIndex, attr->CompletionHandlerIndex,
+          S.Out, S.ScratchRecord, abbrCode, attr->CompletionHandlerIndex,
           asyncFuncDeclID);
       return;
     }