cmCxxModuleMapper: add source to handle module mapper contents

This will allow all generators to share an implementation for actually
writing out the module map formats.

Source/CMakeLists.txt

@@ -197,6 +197,8 @@ set(SRCS
   cmCustomCommandLines.cxx
   cmCustomCommandLines.h
   cmCustomCommandTypes.h
+  cmCxxModuleMapper.cxx
+  cmCxxModuleMapper.h
   cmDefinitions.cxx
   cmDefinitions.h
   cmDependencyProvider.h

Source/cmCxxModuleMapper.cxx

@@ -0,0 +1,30 @@
+/* Distributed under the OSI-approved BSD 3-Clause License.  See accompanying
+   file Copyright.txt or https://cmake.org/licensing for details.  */
+#include "cmCxxModuleMapper.h"
+
+#include <cassert>
+
+#include "cmScanDepFormat.h"
+
+cm::optional<std::string> CxxModuleLocations::BmiGeneratorPathForModule(
+  std::string const& logical_name) const
+{
+  if (auto l = this->BmiLocationForModule(logical_name)) {
+    return this->PathForGenerator(*l);
+  }
+  return {};
+}
+
+cm::static_string_view CxxModuleMapExtension(
+  cm::optional<CxxModuleMapFormat> format)
+{
+  return ".bmi"_s;
+}
+
+std::string CxxModuleMapContent(CxxModuleMapFormat format,
+                                CxxModuleLocations const& loc,
+                                cmScanDepInfo const& obj)
+{
+  assert(false);
+  return {};
+}

Source/cmCxxModuleMapper.h

@@ -0,0 +1,47 @@
+/* Distributed under the OSI-approved BSD 3-Clause License.  See accompanying
+   file Copyright.txt or https://cmake.org/licensing for details.  */
+#pragma once
+
+#include "cmConfigure.h" // IWYU pragma: keep
+
+#include <functional>
+#include <string>
+
+#include <cm/optional>
+#include <cmext/string_view>
+
+struct cmScanDepInfo;
+
+enum class CxxModuleMapFormat
+{
+};
+
+struct CxxModuleLocations
+{
+  // The path from which all relative paths should be computed. If
+  // this is relative, it is relative to the compiler's working
+  // directory.
+  std::string RootDirectory;
+
+  // A function to convert a full path to a path for the generator.
+  std::function<std::string(std::string const&)> PathForGenerator;
+
+  // Lookup the BMI location of a logical module name.
+  std::function<cm::optional<std::string>(std::string const&)>
+    BmiLocationForModule;
+
+  // Returns the generator path (if known) for the BMI given a
+  // logical module name.
+  cm::optional<std::string> BmiGeneratorPathForModule(
+    std::string const& logical_name) const;
+};
+
+// Return the extension to use for a given modulemap format.
+cm::static_string_view CxxModuleMapExtension(
+  cm::optional<CxxModuleMapFormat> format);
+
+// Return the contents of the module map in the given format for the
+// object file.
+std::string CxxModuleMapContent(CxxModuleMapFormat format,
+                                CxxModuleLocations const& loc,
+                                cmScanDepInfo const& obj);

bootstrap

@@ -328,6 +328,7 @@ CMAKE_CXX_SOURCES="\
   cmCustomCommand \
   cmCustomCommandGenerator \
   cmCustomCommandLines \
+  cmCxxModuleMapper \
   cmDefinePropertyCommand \
   cmDefinitions \
   cmDocumentationFormatter \