Revert "[clang][modules-driver] Add scanner to detect C++20 module presence"

[cor3ntin]

Reverts #145220

This breaks CI when building the documentation

Included from /home/runner/work/llvm-project/llvm-project/clang/docs/../include/clang/Basic/Diagnostic.td:74:
/home/runner/work/llvm-project/llvm-project/clang/docs/../include/clang/Basic/DiagnosticGroups.td:628:5: error: Diagnostic group contains both remark and non-remark diagnostics
def ModulesDriver : DiagGroup<"modules-driver">;
    ^

https://github.com/llvm/llvm-project/actions/runs/16116118496/job/45470268367

[llvmbot]

@llvm/pr-subscribers-clang-driver

@llvm/pr-subscribers-clang

Author: Corentin Jabot (cor3ntin)

Changes

Reverts llvm/llvm-project#145220

This breaks CI when building the documentation

Included from /home/runner/work/llvm-project/llvm-project/clang/docs/../include/clang/Basic/Diagnostic.td:74:
/home/runner/work/llvm-project/llvm-project/clang/docs/../include/clang/Basic/DiagnosticGroups.td:628:5: error: Diagnostic group contains both remark and non-remark diagnostics
def ModulesDriver : DiagGroup<"modules-driver">;
    ^

https://github.com/llvm/llvm-project/actions/runs/16116118496/job/45470268367

---

Patch is 21.51 KiB, truncated to 20.00 KiB below, full version: https://github.com/llvm/llvm-project/pull/147286.diff

7 Files Affected:

• (modified) clang/include/clang/Basic/DiagnosticDriverKinds.td (-10)
• (modified) clang/include/clang/Basic/DiagnosticGroups.td (-1)
• (modified) clang/include/clang/Driver/Driver.h (-32)
• (modified) clang/include/clang/Driver/Options.td (-7)
• (modified) clang/lib/Driver/Driver.cpp (-210)
• (removed) clang/test/Driver/modules-driver-cxx20-module-usage-scanner.cpp (-192)
• (modified) clang/test/Frontend/warning-options.cpp (+1-1)

diff --git a/clang/include/clang/Basic/DiagnosticDriverKinds.td b/clang/include/clang/Basic/DiagnosticDriverKinds.td
index efba09dc140f6..34b6c0d7a8acd 100644
--- a/clang/include/clang/Basic/DiagnosticDriverKinds.td
+++ b/clang/include/clang/Basic/DiagnosticDriverKinds.td
@@ -577,16 +577,6 @@ def err_drv_reduced_module_output_overrided : Warning<
   "please consider use '-fmodule-output=' to specify the output file for reduced BMI explicitly">,
   InGroup<DiagGroup<"reduced-bmi-output-overrided">>;
 
-def remark_found_cxx20_module_usage : Remark<
-  "found C++20 module usage in file '%0'">,
-  InGroup<ModulesDriver>;
-def remark_performing_driver_managed_module_build : Remark<
-  "performing driver managed module build">,
-  InGroup<ModulesDriver>;
-def warn_modules_driver_unsupported_standard : Warning<
-  "'-fmodules-driver' is not supported before C++20">,
-  InGroup<ModulesDriver>;
-
 def warn_drv_delayed_template_parsing_after_cxx20 : Warning<
   "-fdelayed-template-parsing is deprecated after C++20">,
   InGroup<DiagGroup<"delayed-template-parsing-in-cxx20">>;
diff --git a/clang/include/clang/Basic/DiagnosticGroups.td b/clang/include/clang/Basic/DiagnosticGroups.td
index d2aa380f8d73f..36fa3227fd6a6 100644
--- a/clang/include/clang/Basic/DiagnosticGroups.td
+++ b/clang/include/clang/Basic/DiagnosticGroups.td
@@ -625,7 +625,6 @@ def ModuleConflict : DiagGroup<"module-conflict">;
 def ModuleFileExtension : DiagGroup<"module-file-extension">;
 def ModuleIncludeDirectiveTranslation : DiagGroup<"module-include-translation">;
 def ModuleMap : DiagGroup<"module-map">;
-def ModulesDriver : DiagGroup<"modules-driver">;
 def RoundTripCC1Args : DiagGroup<"round-trip-cc1-args">;
 def NewlineEOF : DiagGroup<"newline-eof">;
 def Nullability : DiagGroup<"nullability">;
diff --git a/clang/include/clang/Driver/Driver.h b/clang/include/clang/Driver/Driver.h
index 2a04f6dd27655..d9e328fe918bc 100644
--- a/clang/include/clang/Driver/Driver.h
+++ b/clang/include/clang/Driver/Driver.h
@@ -504,9 +504,6 @@ 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.
@@ -792,35 +789,6 @@ 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>
-  ScanInputsForCXXModuleUsage(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
diff --git a/clang/include/clang/Driver/Options.td b/clang/include/clang/Driver/Options.td
index 4f453aa8b7732..54c71b066f9d4 100644
--- a/clang/include/clang/Driver/Options.td
+++ b/clang/include/clang/Driver/Options.td
@@ -3259,13 +3259,6 @@ def modules_reduced_bmi : Flag<["-"], "fmodules-reduced-bmi">,
   HelpText<"Generate the reduced BMI">,
   MarshallingInfoFlag<FrontendOpts<"GenReducedBMI">>;
 
-def fmodules_driver : Flag<["-"], "fmodules-driver">,
-  Group<f_Group>, Visibility<[ClangOption]>,
-  HelpText<"Enable support for driver managed module builds (experimental)">;
-def fno_modules_driver : Flag<["-"], "fno-modules-driver">,
-  Group<f_Group>, Visibility<[ClangOption]>,
-  HelpText<"Disable support for driver managed module builds (experimental)">;
-
 def experimental_modules_reduced_bmi : Flag<["-"], "fexperimental-modules-reduced-bmi">,
   Group<f_Group>, Visibility<[ClangOption, CC1Option]>, Alias<modules_reduced_bmi>;
 
diff --git a/clang/lib/Driver/Driver.cpp b/clang/lib/Driver/Driver.cpp
index 60c5bda14af2f..55748c0bce918 100644
--- a/clang/lib/Driver/Driver.cpp
+++ b/clang/lib/Driver/Driver.cpp
@@ -53,7 +53,6 @@
 #include "ToolChains/WebAssembly.h"
 #include "ToolChains/XCore.h"
 #include "ToolChains/ZOS.h"
-#include "clang/Basic/CharInfo.h"
 #include "clang/Basic/DiagnosticDriver.h"
 #include "clang/Basic/TargetID.h"
 #include "clang/Basic/Version.h"
@@ -4292,13 +4291,6 @@ void Driver::handleArguments(Compilation &C, DerivedArgList &Args,
     YcArg = nullptr;
   }
 
-  if (Args.hasArgNoClaim(options::OPT_fmodules_driver))
-    // TODO: Check against all incompatible -fmodules-driver arguments
-    if (!ModulesModeCXX20) {
-      Diag(diag::warn_modules_driver_unsupported_standard);
-      Args.eraseArg(options::OPT_fmodules_driver);
-    }
-
   Arg *FinalPhaseArg;
   phases::ID FinalPhase = getFinalPhase(Args, &FinalPhaseArg);
 
@@ -4425,174 +4417,6 @@ void Driver::handleArguments(Compilation &C, DerivedArgList &Args,
   }
 }
 
-static void skipWhitespace(const char *&Ptr) {
-  while (isWhitespace(*Ptr))
-    ++Ptr;
-}
-
-// Returns the length of EOL, either 0 (no end-of-line), 1 (\n) or 2 (\r\n).
-static unsigned isEOL(const char *Ptr) {
-  if (*Ptr == '\0')
-    return 0;
-  if (*(Ptr + 1) != '\0' && isVerticalWhitespace(Ptr[0]) &&
-      isVerticalWhitespace(Ptr[1]) && Ptr[0] != Ptr[1])
-    return 2;
-  return !!isVerticalWhitespace(Ptr[0]);
-}
-
-static void skipLine(const char *&Ptr) {
-  for (;;) {
-    char LastNonWhitespace = ' ';
-    while (!isVerticalWhitespace(*Ptr) && *Ptr != '\0') {
-      if (!isHorizontalWhitespace(*Ptr))
-        LastNonWhitespace = *Ptr;
-      ++Ptr;
-    }
-
-    const unsigned Len = isEOL(Ptr);
-    if (!Len)
-      return;
-
-    Ptr += Len;
-    if (LastNonWhitespace != '\\')
-      break;
-  }
-}
-
-// Returns the length of a line splice sequence (including trailing
-// whitespace), or 0 if no line splice is found.
-static unsigned isLineSplice(const char *Start) {
-  if (*Start != '\\')
-    return 0;
-
-  const char *Ptr = Start + 1;
-  while (isHorizontalWhitespace(*Ptr))
-    ++Ptr;
-
-  if (unsigned Len = isEOL(Ptr))
-    return Ptr - Start + Len;
-  return 0;
-}
-
-static bool trySkipLineSplice(const char *&Ptr) {
-  if (unsigned Len = isLineSplice(Ptr); Len) {
-    Ptr += Len;
-    return true;
-  }
-  return false;
-}
-
-static bool trySkipDirective(const char *&Ptr) {
-  if (*Ptr != '#')
-    return false;
-
-  ++Ptr;
-  skipLine(Ptr);
-  return true;
-}
-
-static bool trySkipLineComment(const char *&Ptr) {
-  if (Ptr[0] != '/' || Ptr[1] != '/')
-    return false;
-
-  Ptr += 2;
-  skipLine(Ptr);
-  return true;
-}
-
-static bool trySkipBlockComment(const char *&Ptr) {
-  if (Ptr[0] != '/' || Ptr[1] != '*')
-    return false;
-
-  Ptr += 2;
-  while (*Ptr != '\0') {
-    if (Ptr[0] == '*' && Ptr[1] == '/') {
-      Ptr += 2; // '*/'
-      return true;
-    }
-    ++Ptr;
-  }
-  return true;
-}
-
-static bool trySkipComment(const char *&Ptr) {
-  return trySkipLineComment(Ptr) || trySkipBlockComment(Ptr);
-}
-
-// Skipps over comments and (non-module) directives
-static void skipToRelevantCXXModuleText(const char *&Ptr) {
-  while (*Ptr != '\0') {
-    skipWhitespace(Ptr);
-    if (trySkipComment(Ptr) || trySkipDirective(Ptr) || trySkipLineSplice(Ptr))
-      continue;
-    break; // Found relevant text!
-  }
-}
-
-static bool scanBufferForCXXModuleUsage(const llvm::MemoryBuffer &Buffer) {
-  const char *Ptr = Buffer.getBufferStart();
-  skipToRelevantCXXModuleText(Ptr);
-
-  // Check if the buffer has enough remaining bytes left for any of the
-  // module-related declaration fragments we are checking for, without making
-  // the potentially memory-mapped buffer load unnecessary pages.
-  constexpr int MinKeywordLength = 6;
-  const char *Begin = Ptr;
-  for (int i = 0; i < MinKeywordLength; ++i) {
-    if (*Ptr == '\0')
-      return false;
-    ++Ptr;
-  }
-  StringRef Text(Begin, MinKeywordLength);
-
-  const bool IsGlobalModule = Text.starts_with("module");
-  if (!IsGlobalModule && !Text.starts_with("import") &&
-      !Text.starts_with("export"))
-    return false;
-
-  // Ensure the keyword has a proper ending and isn't part of a identifier
-  // or namespace. For this we might have to skip comments and line
-  // continuations.
-  while (*Ptr != '\0') {
-    if (isWhitespace(*Ptr) || (IsGlobalModule && *Ptr == ';'))
-      return true;
-    if (trySkipBlockComment(Ptr) || trySkipLineSplice(Ptr))
-      continue;
-    return false;
-  }
-
-  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::ScanInputsForCXXModuleUsage(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 (scanBufferForCXXModuleUsage(*Buffer)) {
-      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");
@@ -4604,33 +4428,6 @@ 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 = ScanInputsForCXXModuleUsage(Inputs);
-      if (!ErrOrScanResult) {
-        Diags.Report(diag::err_cannot_open_file)
-            << ErrOrScanResult.getError().message();
-        return;
-      }
-      UsesCXXModules = *ErrOrScanResult;
-    }
-    if (UsesCXXModules)
-      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) ||
@@ -4914,13 +4711,6 @@ 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);
-  return;
-}
-
 /// Returns the canonical name for the offloading architecture when using a HIP
 /// or CUDA architecture.
 static StringRef getCanonicalArchString(Compilation &C,
diff --git a/clang/test/Driver/modules-driver-cxx20-module-usage-scanner.cpp b/clang/test/Driver/modules-driver-cxx20-module-usage-scanner.cpp
deleted file mode 100644
index a434587a78759..0000000000000
--- a/clang/test/Driver/modules-driver-cxx20-module-usage-scanner.cpp
+++ /dev/null
@@ -1,192 +0,0 @@
-// The driver never checks to implicitly enable the explicit module build 
-// support unless at least two input files are provided.
-// To trigger the C++20 module usage check, we always pass a second dummy file
-// as input.
-// TODO: Remove -fmodules everywhere once implicitly enabled explicit module 
-// builds are supported.
-
-// RUN: split-file %s %t
-//--- empty.cpp
-// Nothing here
-
-//--- only-global.cpp
-// RUN: %clang -std=c++20 -ccc-print-phases -fmodules-driver -Rmodules-driver \
-// RUN:   %t/only-global.cpp %t/empty.cpp 2>&1 \
-// RUN:   | FileCheck %s --check-prefix=CHECK1
-// CHECK1: remark: found C++20 module usage in file '{{.*}}' [-Rmodules-driver]
-module;
-
-//--- only-import.cpp
-// RUN: %clang -std=c++20 -ccc-print-phases -fmodules-driver -Rmodules-driver \
-// RUN:   %t/only-import.cpp %t/empty.cpp 2>&1 \
-// RUN:   | FileCheck %s --check-prefix=CHECK2
-// CHECK2: remark: found C++20 module usage in file '{{.*}}' [-Rmodules-driver]
-import A;
-
-//--- only-export.cpp
-// RUN: %clang -std=c++20 -ccc-print-phases -fmodules-driver -Rmodules-driver \
-// RUN:   %t/only-export.cpp %t/empty.cpp 2>&1 \
-// RUN:   | FileCheck %s --check-prefix=CHECK3
-// CHECK3: remark: found C++20 module usage in file '{{.*}}' [-Rmodules-driver]
-export module A;
-
-//--- leading-line-comment.cpp
-// RUN: %clang -std=c++20 -ccc-print-phases -fmodules-driver -Rmodules-driver \
-// RUN:   %t/leading-line-comment.cpp %t/empty.cpp 2>&1 \
-// RUN:   | FileCheck %s --check-prefix=CHECK4
-// CHECK4: remark: found C++20 module usage in file '{{.*}}' [-Rmodules-driver]
-// My line comment
-import A;
-
-//--- leading-block-comment1.cpp
-// RUN: %clang -std=c++20 -ccc-print-phases -fmodules-driver -Rmodules-driver \
-// RUN:   %t/leading-block-comment1.cpp %t/empty.cpp 2>&1 \
-// RUN:   | FileCheck %s --check-prefix=CHECK5
-// CHECK5: remark: found C++20 module usage in file '{{.*}}' [-Rmodules-driver]
-/*My block comment */
-import A;
-
-//--- leading-block-comment2.cpp
-// RUN: %clang -std=c++20 -ccc-print-phases -fmodules-driver -Rmodules-driver \
-// RUN:   %t/leading-block-comment2.cpp %t/empty.cpp 2>&1 \
-// RUN:   | FileCheck %s --check-prefix=CHECK6
-// CHECK6: remark: found C++20 module usage in file '{{.*}}' [-Rmodules-driver]
-/*My line comment */ import A;
-
-//--- inline-block-comment1.cpp
-// RUN: %clang -std=c++20 -ccc-print-phases -fmodules-driver -Rmodules-driver \
-// RUN:   %t/leading-block-comment1.cpp %t/empty.cpp 2>&1 \
-// RUN:   | FileCheck %s --check-prefix=CHECK7
-// CHECK7: remark: found C++20 module usage in file '{{.*}}' [-Rmodules-driver]
-export/*a comment*/module/*another comment*/A;
-
-//--- inline-block-comment2.cpp
-// RUN: %clang -std=c++20 -ccc-print-phases -fmodules-driver -Rmodules-driver \
-// RUN:   %t/leading-block-comment2.cpp %t/empty.cpp 2>&1 \
-// RUN:   | FileCheck %s --check-prefix=CHECK8
-// CHECK8: remark: found C++20 module usage in file '{{.*}}' [-Rmodules-driver]
-module/*a comment*/;
-
-//--- leading-directives.cpp
-// RUN: %clang -std=c++23 -ccc-print-phases -fmodules-driver -Rmodules-driver \
-// RUN:   %t/leading-directives.cpp %t/empty.cpp 2>&1 \
-// RUN:   | FileCheck %s --check-prefix=CHECK9
-// CHECK9: remark: found C++20 module usage in file '{{.*}}' [-Rmodules-driver]
-#define A
-#undef A
-#if A
-#ifdef A
-#elifdef A
-#elifndef A
-#endif
-#ifndef A
-#elif A
-#else
-#endif
-#endif
-#pragma once;
-#include <iostream>
-import m;
-
-//--- multiline-directive.cpp
-// RUN: %clang -std=c++23 -ccc-print-phases -fmodules-driver -Rmodules-driver \
-// RUN:   %t/multiline-directive.cpp %t/empty.cpp 2>&1 \
-// RUN:   | FileCheck %s --check-prefix=CHECK10
-// CHECK10: remark: found C++20 module usage in file '{{.*}}' [-Rmodules-driver]
-#define MACRO(a,  \
-              b)  \
-        call((a), \
-             (b)
-import a;
-
-//--- leading-line-splice.cpp
-// RUN: %clang -std=c++23 -ccc-print-phases -fmodules-driver -Rmodules-driver \
-// RUN:   %t/leading-line-splice.cpp %t/empty.cpp 2>&1 \
-// RUN:   | FileCheck %s --check-prefix=CHECK11
-// CHECK11: remark: found C++20 module usage in file '{{.*}}' [-Rmodules-driver]
-\
-module;
-
-//--- leading-line-splice-trailing-whitespace.cpp
-// RUN: %clang -std=c++23 -ccc-print-phases -fmodules-driver -Rmodules-driver \
-// RUN:   %t/leading-line-splice-trailing-whitespace.cpp %t/empty.cpp 2>&1 \
-// RUN:   | FileCheck %s --check-prefix=CHECK12
-// CHECK12: remark: found C++20 module usage in file '{{.*}}' [-Rmodules-driver]
-// v This backslash has trailing whitespace.
-   \      
-export module A;
-
-//--- comment-line-splice.cpp
-// RUN: %clang -std=c++23 -ccc-print-phases -fmodules-driver -Rmodules-driver \
-// RUN:   %t/comment-line-splice.cpp %t/empty.cpp 2>&1 \
-// RUN:   | FileCheck %s  --allow-empty --check-prefix=CHECK13
-// CHECK13-NOT: remark: found C++20 module usage in file '{{.*}}' [-Rmodules-driver]
-// My comment continues next-line!\
-import A;
-
-//--- comment-line-splice-trailing-whitespace.cpp
-// RUN: %clang -std=c++23 -ccc-print-phases -fmodules-driver -Rmodules-driver \
-// RUN:   %t/comment-line-splice-trailing-whitespace.cpp %t/empty.cpp 2>&1 \
-// RUN:   | FileCheck %s --allow-empty --check-prefix=CHECK14
-// CHECK14-NOT: remark: found C++20 module usage in file '{{.*}}' [-Rmodules-driver]
-// My comment continues next-line! This backslash has trailing whitespace. -> \   
-module;
-
-//--- line-splice-in-directive1.cpp
-// RUN: %clang -std=c++23 -ccc-print-phases -fmodules-driver -Rmodules-driver \
-// RUN:   %t/line-splice-in-directive1.cpp %t/empty.cpp 2>&1 \
-// RUN:   | FileCheck %s --check-prefix=CHECK15
-// CHECK15: remark: found C++20 module usage in file '{{.*}}' [-Rmodules-driver]
-
-module\
-;
-
-//--- line-splice-in-directive2.cpp
-// RUN: %clang -std=c++23 -ccc-print-phases -fmodules-driver -Rmodules-driver \
-// RUN:   %t/line-splice-in-directive2.cpp %t/empty.cpp 2>&1 \
-// RUN:   | FileCheck %s --check-prefix=CHECK16
-// CHECK16: remark: found C++20 module usage in file '{{.*}}' [-Rmodules-driver]
-
-export\
-  module\
-  A;
-
-//--- no-module-usage1.cpp
-// RUN: %clang -std=c++23 -ccc-print-phases -fmodules-driver -Rmodules-driver \
-// RUN:   %t/no-module-usage1.cpp %t/empty.cpp 2>&1 \
-// RUN:   | FileCheck %s  --allow-empty --check-prefix=CHECK17
-// CHECK17-NOT: remark: found C++20 module usage in file '{{.*}}' [-Rmodules-driver]
-auto main() -> int {}
-
-//--- no-module-usage2.cpp
-// RUN: %clang -std=c++23 -ccc-print-phases -fmodules-driver -Rmodules-driver \
-// RUN:   %t/no-module-usage2.cpp %t/empty.cpp 2>&1 \
-// RUN:   | FileCheck %s  --allow-empty --check-prefix=CHECK18
-// CHECK18-NOT: remark: found C++20 module usage in file '{{.*}}' [-Rmodules-driver]
-moduleStruct{};
-
-//--- no-module-usage3.cpp
-// RUN: %clang -std=c++23 -ccc-print-phases -fmodules-driver -Rmodules-driver \
-// RUN:   %t/no-module-usage3.cpp %t/empty.cpp 2>&1 \
-// RUN:   | FileCheck %s  --allow-empty --check-prefix=CHECK19
-// CHECK19-NOT: remark: found C++20 module usage in file '{{.*}}' [-Rmodules-driver]
-export_struct{};
-
-//--- no-module-usage-namespace-import.cpp
-// RUN: %clang -std=c++23 -ccc-print-phases -fmodules-driver -Rmodules-driver \
-// RUN:   %t/no-module-usage-namespace-import.cpp %t/empty.cpp 2>&1 \
-// RUN:   | FileCheck %s  --allow-empty --check-prefix=CHECK20
-// CHECK20-NOT...
[truncated]

[AaronBallman]

LGTM