Frontend: Introduce -experimental-lazy-typecheck action.

This action is currently just an alias of the `-resolve-imports` action.
However, it's named to more clearly reflect the purpose which is to do the
minimal typechecking needed in order to emit the requested outputs. This mode
is intended to improve performance when emitting `.swiftinterface` and `.tbd`
files.

Author: tshortli

include/swift/Frontend/FrontendOptions.h

@@ -155,6 +155,7 @@ class FrontendOptions {
     NoneAction,        ///< No specific action
     Parse,             ///< Parse only
     ResolveImports,    ///< Parse and resolve imports only
+    LazyTypecheck,     ///< Parse and then do minimal type-checking for outputs
     Typecheck,         ///< Parse and type-check only
     DumpParse,         ///< Parse only and dump AST
     DumpInterfaceHash, ///< Parse and dump the interface token hash.

include/swift/Option/Options.td

@@ -1160,6 +1160,9 @@ def resolve_imports : Flag<["-"], "resolve-imports">,
 def typecheck : Flag<["-"], "typecheck">,
   HelpText<"Parse and type-check input file(s)">, ModeOpt,
   Flags<[FrontendOption, NoInteractiveOption, DoesNotAffectIncrementalBuild]>;
+def experimental_lazy_typecheck : Flag<["-"], "experimental-lazy-typecheck">,
+  HelpText<"Parse input file(s), then type-check lazily as needed to produce requested outputs">, ModeOpt,
+  Flags<[FrontendOption, NoInteractiveOption, HelpHidden, DoesNotAffectIncrementalBuild]>;
 def dump_parse : Flag<["-"], "dump-parse">,
   HelpText<"Parse input file(s) and dump AST(s)">, ModeOpt,
   Flags<[FrontendOption, NoInteractiveOption, DoesNotAffectIncrementalBuild]>;

lib/Driver/Driver.cpp

@@ -1607,6 +1607,7 @@ void Driver::buildOutputInfo(const ToolChain &TC, const DerivedArgList &Args,
 
     case options::OPT_parse:
     case options::OPT_resolve_imports:
+    case options::OPT_experimental_lazy_typecheck:
     case options::OPT_typecheck:
     case options::OPT_dump_parse:
     case options::OPT_print_ast:

lib/Frontend/ArgsToFrontendOptionsConverter.cpp

@@ -552,6 +552,8 @@ ArgsToFrontendOptionsConverter::determineRequestedAction(const ArgList &args) {
     return FrontendOptions::ActionType::Parse;
   if (Opt.matches(OPT_resolve_imports))
     return FrontendOptions::ActionType::ResolveImports;
+  if (Opt.matches(OPT_experimental_lazy_typecheck))
+    return FrontendOptions::ActionType::LazyTypecheck;
   if (Opt.matches(OPT_typecheck))
     return FrontendOptions::ActionType::Typecheck;
   if (Opt.matches(OPT_dump_parse))

lib/Frontend/FrontendOptions.cpp

@@ -33,6 +33,7 @@ bool FrontendOptions::needsProperModuleName(ActionType action) {
   case ActionType::NoneAction:
   case ActionType::Parse:
   case ActionType::ResolveImports:
+  case ActionType::LazyTypecheck:
   case ActionType::Typecheck:
   case ActionType::DumpParse:
   case ActionType::DumpAST:
@@ -104,6 +105,7 @@ bool FrontendOptions::doesActionRequireSwiftStandardLibrary(ActionType action) {
   case ActionType::PrintFeature:
     return false;
   case ActionType::ResolveImports:
+  case ActionType::LazyTypecheck:
   case ActionType::Typecheck:
   case ActionType::DumpAST:
   case ActionType::PrintAST:
@@ -149,6 +151,7 @@ bool FrontendOptions::doesActionRequireInputs(ActionType action) {
   case ActionType::CompileModuleFromInterface:
   case ActionType::TypecheckModuleFromInterface:
   case ActionType::ResolveImports:
+  case ActionType::LazyTypecheck:
   case ActionType::Typecheck:
   case ActionType::DumpAST:
   case ActionType::PrintAST:
@@ -191,6 +194,7 @@ bool FrontendOptions::doesActionPerformEndOfPipelineActions(ActionType action) {
   case ActionType::CompileModuleFromInterface:
   case ActionType::TypecheckModuleFromInterface:
   case ActionType::ResolveImports:
+  case ActionType::LazyTypecheck:
   case ActionType::Typecheck:
   case ActionType::DumpAST:
   case ActionType::PrintAST:
@@ -230,6 +234,7 @@ bool FrontendOptions::supportCompilationCaching(ActionType action) {
   case ActionType::EmitImportedModules:
   case ActionType::ScanDependencies:
   case ActionType::ResolveImports:
+  case ActionType::LazyTypecheck:
   case ActionType::Typecheck:
   case ActionType::DumpAST:
   case ActionType::PrintAST:
@@ -290,6 +295,7 @@ FrontendOptions::formatForPrincipalOutputFileForAction(ActionType action) {
 
   case ActionType::Parse:
   case ActionType::ResolveImports:
+  case ActionType::LazyTypecheck:
   case ActionType::Typecheck:
   case ActionType::TypecheckModuleFromInterface:
   case ActionType::DumpParse:
@@ -377,6 +383,7 @@ bool FrontendOptions::canActionEmitDependencies(ActionType action) {
   case ActionType::PrintFeature:
     return false;
   case ActionType::ResolveImports:
+  case ActionType::LazyTypecheck:
   case ActionType::Typecheck:
   case ActionType::MergeModules:
   case ActionType::EmitModuleOnly:
@@ -403,6 +410,7 @@ bool FrontendOptions::canActionEmitReferenceDependencies(ActionType action) {
   case ActionType::NoneAction:
   case ActionType::Parse:
   case ActionType::ResolveImports:
+  case ActionType::LazyTypecheck:
   case ActionType::DumpParse:
   case ActionType::DumpInterfaceHash:
   case ActionType::DumpAST:
@@ -445,6 +453,7 @@ bool FrontendOptions::canActionEmitModuleSummary(ActionType action) {
   case ActionType::NoneAction:
   case ActionType::Parse:
   case ActionType::ResolveImports:
+  case ActionType::LazyTypecheck:
   case ActionType::DumpParse:
   case ActionType::DumpInterfaceHash:
   case ActionType::DumpAST:
@@ -506,6 +515,7 @@ bool FrontendOptions::canActionEmitClangHeader(ActionType action) {
   case ActionType::PrintVersion:
   case ActionType::PrintFeature:
     return false;
+  case ActionType::LazyTypecheck:
   case ActionType::Typecheck:
   case ActionType::MergeModules:
   case ActionType::EmitModuleOnly:
@@ -547,6 +557,7 @@ bool FrontendOptions::canActionEmitLoadedModuleTrace(ActionType action) {
   case ActionType::PrintFeature:
     return false;
   case ActionType::ResolveImports:
+  case ActionType::LazyTypecheck:
   case ActionType::Typecheck:
   case ActionType::MergeModules:
   case ActionType::EmitModuleOnly:
@@ -576,6 +587,7 @@ bool FrontendOptions::canActionEmitModuleSemanticInfo(ActionType action) {
   case ActionType::NoneAction:
   case ActionType::Parse:
   case ActionType::ResolveImports:
+  case ActionType::LazyTypecheck:
   case ActionType::DumpParse:
   case ActionType::DumpInterfaceHash:
   case ActionType::DumpAST:
@@ -619,6 +631,7 @@ bool FrontendOptions::canActionEmitConstValues(ActionType action) {
   case ActionType::NoneAction:
   case ActionType::Parse:
   case ActionType::ResolveImports:
+  case ActionType::LazyTypecheck:
   case ActionType::DumpParse:
   case ActionType::DumpInterfaceHash:
   case ActionType::DumpAST:
@@ -660,6 +673,7 @@ bool FrontendOptions::canActionEmitModule(ActionType action) {
   case ActionType::NoneAction:
   case ActionType::Parse:
   case ActionType::ResolveImports:
+  case ActionType::LazyTypecheck:
   case ActionType::Typecheck:
   case ActionType::DumpParse:
   case ActionType::DumpInterfaceHash:
@@ -727,6 +741,7 @@ bool FrontendOptions::canActionEmitInterface(ActionType action) {
   case ActionType::PrintFeature:
     return false;
   case ActionType::ResolveImports:
+  case ActionType::LazyTypecheck:
   case ActionType::Typecheck:
   case ActionType::MergeModules:
   case ActionType::EmitModuleOnly:
@@ -747,6 +762,7 @@ bool FrontendOptions::doesActionProduceOutput(ActionType action) {
   switch (action) {
   case ActionType::Parse:
   case ActionType::ResolveImports:
+  case ActionType::LazyTypecheck:
   case ActionType::Typecheck:
   case ActionType::DumpParse:
   case ActionType::DumpAST:
@@ -805,6 +821,7 @@ bool FrontendOptions::doesActionProduceTextualOutput(ActionType action) {
 
   case ActionType::Parse:
   case ActionType::ResolveImports:
+  case ActionType::LazyTypecheck:
   case ActionType::Typecheck:
   case ActionType::DumpParse:
   case ActionType::DumpInterfaceHash:
@@ -834,6 +851,7 @@ bool FrontendOptions::doesActionGenerateSIL(ActionType action) {
   case ActionType::NoneAction:
   case ActionType::Parse:
   case ActionType::ResolveImports:
+  case ActionType::LazyTypecheck:
   case ActionType::Typecheck:
   case ActionType::DumpParse:
   case ActionType::DumpInterfaceHash:
@@ -885,6 +903,7 @@ bool FrontendOptions::doesActionGenerateIR(ActionType action) {
   case ActionType::DumpTypeInfo:
   case ActionType::CompileModuleFromInterface:
   case ActionType::TypecheckModuleFromInterface:
+  case ActionType::LazyTypecheck:
   case ActionType::Typecheck:
   case ActionType::ResolveImports:
   case ActionType::MergeModules:

lib/FrontendTool/FrontendTool.cpp

@@ -1359,6 +1359,9 @@ static bool performAction(CompilerInstance &Instance,
     return performParseOnly(*Instance.getMainModule());
   case FrontendOptions::ActionType::ResolveImports:
     return Instance.performParseAndResolveImportsOnly();
+  case FrontendOptions::ActionType::LazyTypecheck:
+    // For now, this action is just an alias of ResolveImports.
+    return Instance.performParseAndResolveImportsOnly();
   case FrontendOptions::ActionType::Typecheck:
     return withSemanticAnalysis(Instance, observer,
                                 [](CompilerInstance &Instance) {