Add -enable-experimental-dependencies and push it through.

Author: David Ungar

include/swift/AST/Decl.h

@@ -958,6 +958,10 @@ class alignas(1 << DeclAlignInBits) Decl {
     assert(Mem); 
     return Mem; 
   }
+
+  /// Scaffolding to permit experimentation with finer-grained dependencies and
+  /// faster rebuilds.
+  bool getEnableExperimentalDependencies() const;
 };
 
 /// \brief Use RAII to track Decl validation progress and non-reentrancy.

include/swift/AST/DeclContext.h

@@ -524,6 +524,10 @@ class alignas(1 << DeclContextAlignInBits) DeclContext {
   LLVM_READONLY
   ASTContext &getASTContext() const;
 
+  /// Scaffolding to permit experimentation with finer-grained dependencies and
+  /// faster rebuilds.
+  bool getEnableExperimentalDependencies() const;
+
   /// Retrieve the set of protocols whose conformances will be
   /// associated with this declaration context.
   ///

include/swift/Basic/LangOptions.h

@@ -288,6 +288,10 @@ namespace swift {
     /// Whether to verify the parsed syntax tree and emit related diagnostics.
     bool VerifySyntaxTree = false;
 
+    /// Scaffolding to permit experimentation with finer-grained dependencies
+    /// and faster rebuilds.
+    bool EnableExperimentalDependencies = false;
+
     /// Sets the target we are building for and updates platform conditions
     /// to match.
     ///

include/swift/Driver/Compilation.h

@@ -206,6 +206,10 @@ class Compilation {
   /// limit filelists will be used.
   size_t FilelistThreshold;
 
+  /// Scaffolding to permit experimentation with finer-grained dependencies and
+  /// faster rebuilds.
+  const bool EnableExperimentalDependencies;
+
   template <typename T>
   static T *unwrap(const std::unique_ptr<T> &p) {
     return p.get();
@@ -234,7 +238,8 @@ class Compilation {
               Optional<unsigned> BatchSizeLimit = None,
               bool SaveTemps = false,
               bool ShowDriverTimeCompilation = false,
-              std::unique_ptr<UnifiedStatsReporter> Stats = nullptr);
+              std::unique_ptr<UnifiedStatsReporter> Stats = nullptr,
+              bool EnableExperimentalDependencies = false);
   ~Compilation();
 
   ToolChain const &getToolChain() const {
@@ -289,6 +294,10 @@ class Compilation {
     EnableIncrementalBuild = false;
   }
 
+  bool getEnableExperimentalDependencies() const {
+    return EnableExperimentalDependencies;
+  }
+
   bool getBatchModeEnabled() const {
     return EnableBatchMode;
   }

include/swift/Driver/DependencyGraph.h

@@ -141,11 +141,13 @@ class DependencyGraphImpl {
   /// \sa SourceFile::getInterfaceHash
   llvm::DenseMap<const void *, std::string> InterfaceHashes;
 
-  LoadResult loadFromBuffer(const void *node, llvm::MemoryBuffer &buffer);
+  LoadResult loadFromBuffer(const void *node, llvm::MemoryBuffer &buffer,
+                            const bool EnableExperimentalDependencies);
 
 protected:
   LoadResult loadFromString(const void *node, StringRef data);
-  LoadResult loadFromPath(const void *node, StringRef path);
+  LoadResult loadFromPath(const void *node, StringRef path,
+                          const bool EnableExperimentalDependencies);
 
   void addIndependentNode(const void *node) {
     bool newlyInserted = Provides.insert({node, {}}).second;
@@ -228,9 +230,10 @@ class DependencyGraph : public DependencyGraphImpl {
   /// ("depends") are not cleared; new dependencies are considered additive.
   ///
   /// If \p node has already been marked, only its outgoing edges are updated.
-  LoadResult loadFromPath(T node, StringRef path) {
-    return DependencyGraphImpl::loadFromPath(Traits::getAsVoidPointer(node),
-                                             path);
+  LoadResult loadFromPath(T node, StringRef path,
+                          const bool EnableExperimentalDependencies) {
+    return DependencyGraphImpl::loadFromPath(
+        Traits::getAsVoidPointer(node), path, EnableExperimentalDependencies);
   }
 
   /// Load "depends" and "provides" data for \p node from a plain string.

include/swift/Option/Options.td

@@ -129,6 +129,10 @@ def driver_always_rebuild_dependents :
   Flag<["-"], "driver-always-rebuild-dependents">, InternalDebugOpt,
   HelpText<"Always rebuild dependents of files that have been modified">;
 
+def enable_experimental_dependencies :
+Flag<["-"], "enable-experimental-dependencies">, Flags<[FrontendOption, HelpHidden]>,
+HelpText<"When interface changes, be more selective">;
+
 def driver_mode : Joined<["--"], "driver-mode=">, Flags<[HelpHidden]>,
   HelpText<"Set the driver mode to either 'swift' or 'swiftc'">;
 

lib/AST/Decl.cpp

@@ -6220,6 +6220,10 @@ void Decl::setClangNode(ClangNode Node) {
   *(ptr - 1) = Node.getOpaqueValue();
 }
 
+bool Decl::getEnableExperimentalDependencies() const {
+  return getASTContext().LangOpts.EnableExperimentalDependencies;
+}
+
 // See swift/Basic/Statistic.h for declaration: this enables tracing Decls, is
 // defined here to avoid too much layering violation / circular linkage
 // dependency.

lib/AST/DeclContext.cpp

@@ -624,6 +624,10 @@ unsigned DeclContext::printContext(raw_ostream &OS, unsigned indent) const {
   return Depth + 1;
 }
 
+bool DeclContext::getEnableExperimentalDependencies() const {
+  return getASTContext().LangOpts.EnableExperimentalDependencies;
+}
+
 const Decl *
 IterableDeclContext::getDecl() const {
   switch (getIterableContextKind()) {

lib/Driver/Compilation.cpp

@@ -117,7 +117,8 @@ Compilation::Compilation(DiagnosticEngine &Diags,
                          Optional<unsigned> BatchSizeLimit,
                          bool SaveTemps,
                          bool ShowDriverTimeCompilation,
-                         std::unique_ptr<UnifiedStatsReporter> StatsReporter)
+                         std::unique_ptr<UnifiedStatsReporter> StatsReporter,
+                         bool EnableExperimentalDependencies)
   : Diags(Diags), TheToolChain(TC),
     TheOutputInfo(OI),
     Level(Level),
@@ -138,7 +139,9 @@ Compilation::Compilation(DiagnosticEngine &Diags,
     SaveTemps(SaveTemps),
     ShowDriverTimeCompilation(ShowDriverTimeCompilation),
     Stats(std::move(StatsReporter)),
-    FilelistThreshold(FilelistThreshold) {
+    FilelistThreshold(FilelistThreshold),
+    EnableExperimentalDependencies(EnableExperimentalDependencies) {
+        
 };
 
 static bool writeFilelistIfNecessary(const Job *job, const ArgList &args,
@@ -405,7 +408,9 @@ namespace driver {
         if (ReturnCode == EXIT_SUCCESS || ReturnCode == EXIT_FAILURE) {
           bool wasCascading = DepGraph.isMarked(FinishedCmd);
 
-          switch (DepGraph.loadFromPath(FinishedCmd, DependenciesFile)) {
+          switch (
+              DepGraph.loadFromPath(FinishedCmd, DependenciesFile,
+                                    Comp.getEnableExperimentalDependencies())) {
           case DependencyGraphImpl::LoadResult::HadError:
             if (ReturnCode == EXIT_SUCCESS) {
               dependencyLoadFailed(DependenciesFile);
@@ -696,7 +701,9 @@ namespace driver {
           if (Cmd->getCondition() == Job::Condition::NewlyAdded) {
             DepGraph.addIndependentNode(Cmd);
           } else {
-            switch (DepGraph.loadFromPath(Cmd, DependenciesFile)) {
+            switch (DepGraph.loadFromPath(
+                Cmd, DependenciesFile,
+                Comp.getEnableExperimentalDependencies())) {
             case DependencyGraphImpl::LoadResult::HadError:
               dependencyLoadFailed(DependenciesFile, /*Warn=*/false);
               break;

lib/Driver/DependencyGraph.cpp

@@ -52,11 +52,12 @@ using DependencyKind = DependencyGraphImpl::DependencyKind;
 using DependencyCallbackTy = LoadResult(StringRef, DependencyKind, bool);
 using InterfaceHashCallbackTy = LoadResult(StringRef);
 
-static LoadResult
-parseDependencyFile(llvm::MemoryBuffer &buffer,
-                    llvm::function_ref<DependencyCallbackTy> providesCallback,
-                    llvm::function_ref<DependencyCallbackTy> dependsCallback,
-                    llvm::function_ref<InterfaceHashCallbackTy> interfaceHashCallback) {
+static LoadResult parseDependencyFile(
+    llvm::MemoryBuffer &buffer,
+    llvm::function_ref<DependencyCallbackTy> providesCallback,
+    llvm::function_ref<DependencyCallbackTy> dependsCallback,
+    llvm::function_ref<InterfaceHashCallbackTy> interfaceHashCallback,
+    const bool EnableExperimentalDependencies) {
   namespace yaml = llvm::yaml;
 
   // FIXME: Switch to a format other than YAML.
@@ -211,21 +212,25 @@ parseDependencyFile(llvm::MemoryBuffer &buffer,
   return result;
 }
 
-LoadResult DependencyGraphImpl::loadFromPath(const void *node, StringRef path) {
+LoadResult
+DependencyGraphImpl::loadFromPath(const void *node, StringRef path,
+                                  const bool EnableExperimentalDependencies) {
   auto buffer = llvm::MemoryBuffer::getFile(path);
   if (!buffer)
     return LoadResult::HadError;
-  return loadFromBuffer(node, *buffer.get());
+  return loadFromBuffer(node, *buffer.get(), EnableExperimentalDependencies);
 }
 
 LoadResult
 DependencyGraphImpl::loadFromString(const void *node, StringRef data) {
   auto buffer = llvm::MemoryBuffer::getMemBuffer(data);
-  return loadFromBuffer(node, *buffer);
+  return loadFromBuffer(node, *buffer, false);
 }
 
-LoadResult DependencyGraphImpl::loadFromBuffer(const void *node,
-                                               llvm::MemoryBuffer &buffer) {
+LoadResult
+DependencyGraphImpl::loadFromBuffer(const void *node,
+                                    llvm::MemoryBuffer &buffer,
+                                    const bool EnableExperimentalDependencies) {
   auto &provides = Provides[node];
 
   auto dependsCallback = [this, node](StringRef name, DependencyKind kind,
@@ -291,7 +296,8 @@ LoadResult DependencyGraphImpl::loadFromBuffer(const void *node,
   };
 
   return parseDependencyFile(buffer, providesCallback, dependsCallback,
-                             interfaceHashCallback);
+                             interfaceHashCallback,
+                             EnableExperimentalDependencies);
 }
 
 void DependencyGraphImpl::markExternal(SmallVectorImpl<const void *> &visited,

lib/Driver/Driver.cpp

@@ -920,7 +920,9 @@ Driver::buildCompilation(const ToolChain &TC,
         ArgList->hasArg(options::OPT_driver_time_compilation);
     std::unique_ptr<UnifiedStatsReporter> StatsReporter =
         createStatsReporter(ArgList.get(), Inputs, OI, DefaultTargetTriple);
-    
+    const bool EnableExperimentalDependencies =
+        ArgList->hasArg(options::OPT_enable_experimental_dependencies);
+
     C = llvm::make_unique<Compilation>(
         Diags, TC, OI, Level,
         std::move(ArgList),
@@ -939,7 +941,8 @@ Driver::buildCompilation(const ToolChain &TC,
         DriverBatchSizeLimit,
         SaveTemps,
         ShowDriverTimeCompilation,
-        std::move(StatsReporter));
+        std::move(StatsReporter),
+        EnableExperimentalDependencies);
   }
 
   // Construct the graph of Actions.

lib/Driver/ToolChains.cpp

@@ -218,6 +218,8 @@ static void addCommonFrontendArgs(const ToolChain &TC, const OutputInfo &OI,
   inputArgs.AddLastArg(arguments, options::OPT_O_Group);
   inputArgs.AddLastArg(arguments, options::OPT_RemoveRuntimeAsserts);
   inputArgs.AddLastArg(arguments, options::OPT_AssumeSingleThreaded);
+  inputArgs.AddLastArg(arguments,
+                       options::OPT_enable_experimental_dependencies);
 
   // Pass on any build config options
   inputArgs.AddAllArgs(arguments, options::OPT_D);

lib/Frontend/CompilerInvocation.cpp

@@ -273,6 +273,9 @@ static bool ParseLangArgs(LangOptions &Opts, ArgList &Args,
     Opts.BuildSyntaxTree = true;
     Opts.VerifySyntaxTree = true;
   }
+  
+  if (Args.hasArg(OPT_enable_experimental_dependencies))
+    Opts.EnableExperimentalDependencies = true;
 
   Opts.DebuggerSupport |= Args.hasArg(OPT_debugger_support);
   if (Opts.DebuggerSupport)