[clang][modules-driver] Move logic to enable -fmodules-driver (NFC)

This patch is part of a series to support driver-managed module builds
for C++ named modules and Clang modules.

Commit 9403c2d introduced the entry point for the driver-managed
module build logic and assumed that it would live in the BuildActions
phase of the driver.
That proved unnecessary: the logic can be fully implemented in the
BuildJobs phase.

This reverts changes to BuildActions in preparation for the upcoming
patches.

Author: naveen-seth

clang/include/clang/Driver/Driver.h

@@ -512,9 +512,6 @@ class Driver {
 
   /// BuildActions - Construct the list of actions to perform for the
   /// given arguments, which are only done for a single architecture.
-  /// If the compilation is an explicit module build, delegates to
-  /// BuildDriverManagedModuleBuildActions. Otherwise, BuildDefaultActions is
-  /// used.
   ///
   /// \param C - The compilation that is being built.
   /// \param Args - The input arguments.
@@ -799,35 +796,13 @@ class Driver {
   /// compilation based on which -f(no-)?lto(=.*)? option occurs last.
   void setLTOMode(const llvm::opt::ArgList &Args);
 
-  /// BuildDefaultActions - Constructs the list of actions to perform
-  /// for the provided arguments, which are only done for a single architecture.
-  ///
-  /// \param C - The compilation that is being built.
-  /// \param Args - The input arguments.
-  /// \param Actions - The list to store the resulting actions onto.
-  void BuildDefaultActions(Compilation &C, llvm::opt::DerivedArgList &Args,
-                           const InputList &Inputs, ActionList &Actions) const;
-
-  /// BuildDriverManagedModuleBuildActions - Performs a dependency
-  /// scan and constructs the list of actions to perform for dependency order
-  /// and the provided arguments. This is only done for a single a architecture.
-  ///
-  /// \param C - The compilation that is being built.
-  /// \param Args - The input arguments.
-  /// \param Actions - The list to store the resulting actions onto.
-  void BuildDriverManagedModuleBuildActions(Compilation &C,
-                                            llvm::opt::DerivedArgList &Args,
-                                            const InputList &Inputs,
-                                            ActionList &Actions) const;
-
   /// Scans the leading lines of the C++ source inputs to detect C++20 module
   /// usage.
   ///
   /// \returns True if module usage is detected, false otherwise, or an error on
   /// read failure.
   llvm::ErrorOr<bool>
   ScanInputsForCXX20ModulesUsage(const InputList &Inputs) const;
-
   /// Retrieves a ToolChain for a particular \p Target triple.
   ///
   /// Will cache ToolChains for the life of the driver object, and create them

clang/lib/Driver/Driver.cpp

@@ -1473,6 +1473,33 @@ bool Driver::loadDefaultConfigFiles(llvm::cl::ExpansionContext &ExpCtx) {
   return false;
 }
 
+static bool hasCXXModuleInputType(const Driver::InputList &Inputs) {
+  const auto IsTypeCXXModule = [](const auto &Input) -> bool {
+    const auto TypeID = Input.first;
+    return (TypeID == types::TY_CXXModule);
+  };
+  return llvm::any_of(Inputs, IsTypeCXXModule);
+}
+
+llvm::ErrorOr<bool>
+Driver::ScanInputsForCXX20ModulesUsage(const InputList &Inputs) const {
+  const auto CXXInputs = llvm::make_filter_range(
+      Inputs, [](const auto &Input) { return types::isCXX(Input.first); });
+  for (const auto &Input : CXXInputs) {
+    StringRef Filename = Input.second->getSpelling();
+    auto ErrOrBuffer = VFS->getBufferForFile(Filename);
+    if (!ErrOrBuffer)
+      return ErrOrBuffer.getError();
+    const auto Buffer = std::move(*ErrOrBuffer);
+
+    if (scanInputForCXX20ModulesUsage(Buffer->getBuffer())) {
+      Diags.Report(diag::remark_found_cxx20_module_usage) << Filename;
+      return true;
+    }
+  }
+  return false;
+}
+
 Compilation *Driver::BuildCompilation(ArrayRef<const char *> ArgList) {
   llvm::PrettyStackTraceString CrashInfo("Compilation construction");
 
@@ -1836,6 +1863,26 @@ Compilation *Driver::BuildCompilation(ArrayRef<const char *> ArgList) {
   else
     BuildActions(*C, C->getArgs(), Inputs, C->getActions());
 
+  if (C->getArgs().hasFlag(options::OPT_fmodules_driver,
+                           options::OPT_fno_modules_driver, false)) {
+    // TODO: When -fmodules-driver is no longer experimental, it should be
+    // enabled by default only if both conditions are met: (1) there are two or
+    // more C++ source inputs; and (2) at least one input uses C++20 named
+    // modules.
+    // The detection logic for this is kept here only for diagnostics until
+    // is enabled by default.
+    bool UsesCXXModules = hasCXXModuleInputType(Inputs);
+    if (!UsesCXXModules) {
+      const auto ErrOrScanResult = ScanInputsForCXX20ModulesUsage(Inputs);
+      if (!ErrOrScanResult) {
+        Diags.Report(diag::err_cannot_open_file)
+            << ErrOrScanResult.getError().message();
+      }
+      UsesCXXModules = *ErrOrScanResult;
+    }
+    Diags.Report(diag::remark_performing_driver_managed_module_build);
+  }
+
   if (CCCPrintPhases) {
     PrintActions(*C);
     return C;
@@ -4320,33 +4367,6 @@ void Driver::handleArguments(Compilation &C, DerivedArgList &Args,
   }
 }
 
-static bool hasCXXModuleInputType(const Driver::InputList &Inputs) {
-  const auto IsTypeCXXModule = [](const auto &Input) -> bool {
-    const auto TypeID = Input.first;
-    return (TypeID == types::TY_CXXModule);
-  };
-  return llvm::any_of(Inputs, IsTypeCXXModule);
-}
-
-llvm::ErrorOr<bool>
-Driver::ScanInputsForCXX20ModulesUsage(const InputList &Inputs) const {
-  const auto CXXInputs = llvm::make_filter_range(
-      Inputs, [](const auto &Input) { return types::isCXX(Input.first); });
-  for (const auto &Input : CXXInputs) {
-    StringRef Filename = Input.second->getSpelling();
-    auto ErrOrBuffer = VFS->getBufferForFile(Filename);
-    if (!ErrOrBuffer)
-      return ErrOrBuffer.getError();
-    const auto Buffer = std::move(*ErrOrBuffer);
-
-    if (scanInputForCXX20ModulesUsage(Buffer->getBuffer())) {
-      Diags.Report(diag::remark_found_cxx20_module_usage) << Filename;
-      return true;
-    }
-  }
-  return false;
-}
-
 void Driver::BuildActions(Compilation &C, DerivedArgList &Args,
                           const InputList &Inputs, ActionList &Actions) const {
   llvm::PrettyStackTraceString CrashInfo("Building compilation actions");
@@ -4358,33 +4378,6 @@ void Driver::BuildActions(Compilation &C, DerivedArgList &Args,
 
   handleArguments(C, Args, Inputs, Actions);
 
-  if (Args.hasFlag(options::OPT_fmodules_driver,
-                   options::OPT_fno_modules_driver, false)) {
-    // TODO: Move the logic for implicitly enabling explicit-module-builds out
-    // of -fmodules-driver once it is no longer experimental.
-    // Currently, this serves diagnostic purposes only.
-    bool UsesCXXModules = hasCXXModuleInputType(Inputs);
-    if (!UsesCXXModules) {
-      const auto ErrOrScanResult = ScanInputsForCXX20ModulesUsage(Inputs);
-      if (!ErrOrScanResult) {
-        Diags.Report(diag::err_cannot_open_file)
-            << ErrOrScanResult.getError().message();
-        return;
-      }
-      UsesCXXModules = *ErrOrScanResult;
-    }
-    if (UsesCXXModules || Args.hasArg(options::OPT_fmodules))
-      BuildDriverManagedModuleBuildActions(C, Args, Inputs, Actions);
-    return;
-  }
-
-  BuildDefaultActions(C, Args, Inputs, Actions);
-}
-
-void Driver::BuildDefaultActions(Compilation &C, DerivedArgList &Args,
-                                 const InputList &Inputs,
-                                 ActionList &Actions) const {
-
   bool UseNewOffloadingDriver =
       C.isOffloadingHostKind(Action::OFK_OpenMP) ||
       C.isOffloadingHostKind(Action::OFK_SYCL) ||
@@ -4680,12 +4673,6 @@ void Driver::BuildDefaultActions(Compilation &C, DerivedArgList &Args,
   Args.ClaimAllArgs(options::OPT_cl_ignored_Group);
 }
 
-void Driver::BuildDriverManagedModuleBuildActions(
-    Compilation &C, llvm::opt::DerivedArgList &Args, const InputList &Inputs,
-    ActionList &Actions) const {
-  Diags.Report(diag::remark_performing_driver_managed_module_build);
-}
-
 /// Returns the canonical name for the offloading architecture when using a HIP
 /// or CUDA architecture.
 static StringRef getCanonicalArchString(Compilation &C,