[AST] Make it possible to find what Swift version was used to build a module

For imported modules the version is empty because they don't carry
this information.

include/swift/AST/FileUnit.h

@@ -17,6 +17,7 @@
 #include "swift/AST/RawComment.h"
 #include "swift/Basic/BasicSourceInfo.h"
 #include "swift/Basic/Debug.h"
+#include "swift/Basic/Version.h"
 
 #include "llvm/ADT/PointerIntPair.h"
 
@@ -417,6 +418,10 @@ protected:
     assert(classof(this) && "invalid kind");
   }
 public:
+  /// Returns the language version that was used to compile the contents of this
+  /// file. An empty `Version` is returned if the information is not available.
+  virtual version::Version getLanguageVersionBuiltWith() const = 0;
+
   /// Returns an arbitrary string representing the storage backing this file.
   ///
   /// This is usually a filesystem path.

include/swift/AST/Module.h

@@ -1147,6 +1147,10 @@ public:
 
   SourceRange getSourceRange() const { return SourceRange(); }
 
+  /// Returns the language version that was used to compile this module.
+  /// An empty `Version` is returned if the information is not available.
+  version::Version getLanguageVersionBuiltWith() const;
+
   static bool classof(const DeclContext *DC) {
     if (auto D = DC->getAsDecl())
       return classof(D);

include/swift/ClangImporter/ClangModule.h

@@ -17,6 +17,7 @@
 #define SWIFT_CLANGIMPORTER_CLANGMODULE_H
 
 #include "swift/AST/FileUnit.h"
+#include "swift/Basic/Version.h"
 #include "swift/ClangImporter/ClangImporter.h"
 #include "clang/AST/ExternalASTSource.h"
 #include "clang/Basic/Module.h"
@@ -109,6 +110,10 @@ public:
     llvm_unreachable("no private decls in Clang modules");
   }
 
+  virtual version::Version getLanguageVersionBuiltWith() const override {
+    return version::Version();
+  }
+
   virtual StringRef getFilename() const override;
 
   virtual StringRef getLoadedFilename() const override;

include/swift/Serialization/SerializedModuleLoader.h

@@ -400,7 +400,7 @@ public:
 
   /// Returns the language version that was used to compile the contents of this
   /// file.
-  const version::Version &getLanguageVersionBuiltWith() const;
+  virtual version::Version getLanguageVersionBuiltWith() const override;
 
   virtual bool hadLoadError() const override;
 

lib/AST/Module.cpp

@@ -3935,3 +3935,17 @@ bool IsNonUserModuleRequest::evaluate(Evaluator &evaluator, ModuleDecl *mod) con
   return (!runtimePath.empty() && pathStartsWith(runtimePath, modulePath)) ||
       (!sdkPath.empty() && pathStartsWith(sdkPath, modulePath));
 }
+
+version::Version ModuleDecl::getLanguageVersionBuiltWith() const {
+  for (auto *F : getFiles()) {
+    auto *LD = dyn_cast<LoadedFile>(F);
+    if (!LD)
+      continue;
+
+    auto version = LD->getLanguageVersionBuiltWith();
+    if (!version.empty())
+      return version;
+  }
+
+  return version::Version();
+}

lib/ClangImporter/DWARFImporter.cpp

@@ -82,6 +82,10 @@ public:
     llvm_unreachable("no private decls in Clang modules");
   }
 
+  virtual version::Version getLanguageVersionBuiltWith() const override {
+    return version::Version();
+  }
+
   virtual StringRef getFilename() const override { return ""; }
 
   virtual const clang::Module *getUnderlyingClangModule() const override {

lib/Serialization/ModuleFile.cpp

@@ -1393,7 +1393,7 @@ ValueDecl *SerializedASTFile::getMainDecl() const {
   return cast_or_null<ValueDecl>(File.getDecl(File.getEntryPointDeclID()));
 }
 
-const version::Version &SerializedASTFile::getLanguageVersionBuiltWith() const {
+version::Version SerializedASTFile::getLanguageVersionBuiltWith() const {
   return File.getCompatibilityVersion();
 }