[Immediate] Add frontend option for lazy compilation

Author: Zak Kent

include/swift/Basic/Features.def

@@ -129,6 +129,9 @@ SUPPRESSIBLE_LANGUAGE_FEATURE(ExtensionMacroAttr, 0, "@attached(extension)", tru
 // Whether to enable @_used and @_section attributes
 EXPERIMENTAL_FEATURE(SymbolLinkageMarkers, true)
 
+// Whether to compile scripts lazily in immediate mode
+EXPERIMENTAL_FEATURE(LazyImmediate, false)
+
 // FIXME: MoveOnlyClasses is not intended to be in production,
 // but our tests currently rely on it, and we want to run those
 // tests in non-asserts builds too.

include/swift/Immediate/SwiftMaterializationUnit.h

@@ -114,7 +114,6 @@ class SwiftJIT {
 /// Lazily JITs a Swift AST using function at a time compilation
 class LazySwiftMaterializationUnit : public llvm::orc::MaterializationUnit {
 public:
-
   /// Create a new `LazySwiftMaterializationUnit` with the associated
   /// JIT stack `JIT` and compiler instance `CI`
   static std::unique_ptr<LazySwiftMaterializationUnit>
@@ -140,7 +139,6 @@ class LazySwiftMaterializationUnit : public llvm::orc::MaterializationUnit {
 /// Eagerly materializes a whole `SILModule`
 class EagerSwiftMaterializationUnit : public llvm::orc::MaterializationUnit {
 public:
-
   /// Create a new `EagerSwiftMaterializationUnit` with the JIT stack `JIT`
   /// and provided compiler options
   EagerSwiftMaterializationUnit(SwiftJIT &JIT, const CompilerInstance &CI,
@@ -153,7 +151,8 @@ class EagerSwiftMaterializationUnit : public llvm::orc::MaterializationUnit {
   void materialize(
       std::unique_ptr<llvm::orc::MaterializationResponsibility> MR) override;
 
-  /// Get the linker-level interface defined by the `SILModule` being materialized
+  /// Get the linker-level interface defined by the `SILModule` being
+  /// materialized
   static MaterializationUnit::Interface
   getInterface(SwiftJIT &JIT, const CompilerInstance &CI);
 

lib/AST/ASTPrinter.cpp

@@ -3336,6 +3336,8 @@ static bool usesFeatureMoveOnly(Decl *decl) {
   return false;
 }
 
+static bool usesFeatureLazyImmediate(Decl *D) { return false; }
+
 static bool usesFeatureMoveOnlyClasses(Decl *decl) {
   return isa<ClassDecl>(decl) && usesFeatureMoveOnly(decl);
 }

lib/FrontendTool/FrontendTool.cpp

@@ -1365,7 +1365,17 @@ static bool performAction(CompilerInstance &Instance,
                                   return Instance.getASTContext().hadError();
                                 });
   case FrontendOptions::ActionType::Immediate: {
-    return RunImmediatelyFromAST(Instance) != -1;
+    const auto &Ctx = Instance.getASTContext();
+    if (Ctx.LangOpts.hasFeature(Feature::LazyImmediate)) {
+      ReturnValue = RunImmediatelyFromAST(Instance);
+      return Ctx.hadError();
+    }
+    return withSemanticAnalysis(
+        Instance, observer, [&](CompilerInstance &Instance) {
+          assert(FrontendOptions::doesActionGenerateSIL(opts.RequestedAction) &&
+                 "All actions not requiring SILGen must have been handled!");
+          return performCompileStepsPostSema(Instance, ReturnValue, observer);
+        });
   }
   case FrontendOptions::ActionType::EmitSILGen:
   case FrontendOptions::ActionType::EmitSIBGen: