From a5dcb1d400a8d0d6d341b19d0579e8280c41fdbf Mon Sep 17 00:00:00 2001
From: Robert Widmann <devteam.codafi@gmail.com>
Date: Mon, 11 May 2020 16:44:28 -0700
Subject: [PATCH] [NFC] Add a "Main Module" Bit

The constraint system will need this if it wants to disable debug mode for serialized modules
---
 include/swift/AST/Decl.h   |  7 +++++--
 include/swift/AST/Module.h | 11 +++++++++++
 lib/AST/Module.cpp         | 10 ++++++++++
 lib/Frontend/Frontend.cpp  |  3 ++-
 4 files changed, 28 insertions(+), 3 deletions(-)

diff --git a/include/swift/AST/Decl.h b/include/swift/AST/Decl.h
index 288a6f805ad..eb6af822e7a 100644
--- a/include/swift/AST/Decl.h
+++ b/include/swift/AST/Decl.h
@@ -575,7 +575,7 @@ protected:
     HasAnyUnavailableValues : 1
   );
 
-  SWIFT_INLINE_BITFIELD(ModuleDecl, TypeDecl, 1+1+1+1+1+1+1+1,
+  SWIFT_INLINE_BITFIELD(ModuleDecl, TypeDecl, 1+1+1+1+1+1+1+1+1,
     /// If the module was or is being compiled with `-enable-testing`.
     TestingEnabled : 1,
 
@@ -601,7 +601,10 @@ protected:
 
     /// Whether the module was imported from Clang (or, someday, maybe another
     /// language).
-    IsNonSwiftModule : 1
+    IsNonSwiftModule : 1,
+
+    /// Whether this module is the main module.
+    IsMainModule : 1
   );
 
   SWIFT_INLINE_BITFIELD(PrecedenceGroupDecl, Decl, 1+2,
diff --git a/include/swift/AST/Module.h b/include/swift/AST/Module.h
index 936bf83f5df..c5a70a6e667 100644
--- a/include/swift/AST/Module.h
+++ b/include/swift/AST/Module.h
@@ -347,6 +347,13 @@ public:
     return new (ctx) ModuleDecl(name, ctx, importInfo);
   }
 
+  static ModuleDecl *
+  createMainModule(ASTContext &ctx, Identifier name, ImplicitImportInfo iinfo) {
+    auto *Mod = ModuleDecl::create(name, ctx, iinfo);
+    Mod->Bits.ModuleDecl.IsMainModule = true;
+    return Mod;
+  }
+
   using Decl::getASTContext;
 
   /// Retrieves information about which modules are implicitly imported by
@@ -542,6 +549,10 @@ public:
     Bits.ModuleDecl.IsNonSwiftModule = flag;
   }
 
+  bool isMainModule() const {
+    return Bits.ModuleDecl.IsMainModule;
+  }
+
   /// Retrieve the top-level module. If this module is already top-level, this
   /// returns itself. If this is a submodule such as \c Foo.Bar.Baz, this
   /// returns the module \c Foo.
diff --git a/lib/AST/Module.cpp b/lib/AST/Module.cpp
index a766aafebf3..c8a667ebe38 100644
--- a/lib/AST/Module.cpp
+++ b/lib/AST/Module.cpp
@@ -475,6 +475,16 @@ ModuleDecl::ModuleDecl(Identifier name, ASTContext &ctx,
   setInterfaceType(ModuleType::get(this));
 
   setAccess(AccessLevel::Public);
+
+  Bits.ModuleDecl.TestingEnabled = 0;
+  Bits.ModuleDecl.FailedToLoad = 0;
+  Bits.ModuleDecl.RawResilienceStrategy = 0;
+  Bits.ModuleDecl.HasResolvedImports = 0;
+  Bits.ModuleDecl.PrivateImportsEnabled = 0;
+  Bits.ModuleDecl.ImplicitDynamicEnabled = 0;
+  Bits.ModuleDecl.IsSystemModule = 0;
+  Bits.ModuleDecl.IsNonSwiftModule = 0;
+  Bits.ModuleDecl.IsMainModule = 0;
 }
 
 ArrayRef<ImplicitImport> ModuleDecl::getImplicitImports() const {
diff --git a/lib/Frontend/Frontend.cpp b/lib/Frontend/Frontend.cpp
index ce81e02c40d..b9192a13c45 100644
--- a/lib/Frontend/Frontend.cpp
+++ b/lib/Frontend/Frontend.cpp
@@ -717,7 +717,8 @@ ImplicitImportInfo CompilerInstance::getImplicitImportInfo() const {
 ModuleDecl *CompilerInstance::getMainModule() const {
   if (!MainModule) {
     Identifier ID = Context->getIdentifier(Invocation.getModuleName());
-    MainModule = ModuleDecl::create(ID, *Context, getImplicitImportInfo());
+    MainModule = ModuleDecl::createMainModule(*Context, ID,
+                                              getImplicitImportInfo());
     if (Invocation.getFrontendOptions().EnableTesting)
       MainModule->setTestingEnabled();
     if (Invocation.getFrontendOptions().EnablePrivateImports)