cmImportedCxxModuleInfo: introduce code to parse exported BMI properties

Source/CMakeLists.txt

@@ -298,6 +298,8 @@ add_library(
   cmGraphAdjacencyList.h
   cmGraphVizWriter.cxx
   cmGraphVizWriter.h
+  cmImportedCxxModuleInfo.cxx
+  cmImportedCxxModuleInfo.h
   cmInstallGenerator.h
   cmInstallGenerator.cxx
   cmInstallGetRuntimeDependenciesGenerator.h

Source/cmImportedCxxModuleInfo.cxx

@@ -0,0 +1,76 @@
+/* Distributed under the OSI-approved BSD 3-Clause License.  See accompanying
+   file Copyright.txt or https://cmake.org/licensing for details.  */
+
+#include "cmImportedCxxModuleInfo.h"
+
+#include <cstddef>
+#include <memory>
+#include <string>
+#include <utility>
+#include <vector>
+
+#include "cmCryptoHash.h"
+#include "cmList.h"
+#include "cmStringAlgorithms.h"
+#include "cmSystemTools.h"
+
+bool ImportedCxxModuleLookup::Initialized() const
+{
+  return this->DoneInit;
+}
+
+void ImportedCxxModuleLookup::Initialize(std::string const& importedModules)
+{
+  for (auto const& entry : cmList{ importedModules }) {
+    auto nameSep = entry.find('=');
+    if (nameSep == std::string::npos) {
+      // Invalid entry; ignore.
+      continue;
+    }
+
+    auto name = entry.substr(0, nameSep);
+
+    auto sourceSep = entry.find(',', nameSep);
+    std::string source;
+    if (sourceSep == std::string::npos) {
+      source = entry.substr(nameSep + 1);
+    } else {
+      source = entry.substr(nameSep + 1, sourceSep - nameSep - 1);
+    }
+
+    std::vector<std::string> bmis;
+    if (sourceSep != std::string::npos) {
+      auto bmiPaths = entry.substr(sourceSep + 1);
+      bmis = cmSystemTools::SplitString(bmiPaths, ',');
+    }
+
+    this->ImportedInfo.emplace(source,
+                               ImportedCxxModuleInfo{ name, std::move(bmis) });
+  }
+
+  this->DoneInit = true;
+}
+
+std::string ImportedCxxModuleLookup::BmiNameForSource(std::string const& path)
+{
+  auto genit = this->GeneratorInfo.find(path);
+  if (genit != this->GeneratorInfo.end()) {
+    return genit->second.BmiName;
+  }
+
+  auto importit = this->ImportedInfo.find(path);
+  std::string bmiName;
+  auto hasher = cmCryptoHash::New("SHA3_512");
+  constexpr size_t HASH_TRUNCATION = 12;
+  if (importit != this->ImportedInfo.end()) {
+    auto safename = hasher->HashString(importit->second.Name);
+    bmiName = cmStrCat(safename.substr(0, HASH_TRUNCATION), ".bmi");
+  } else {
+    auto dirhash = hasher->HashString(path);
+    bmiName = cmStrCat(dirhash.substr(0, HASH_TRUNCATION), ".bmi");
+  }
+
+  this->GeneratorInfo.emplace(
+    path, ImportedCxxModuleGeneratorInfo{ &importit->second, bmiName });
+  return bmiName;
+}

Source/cmImportedCxxModuleInfo.h

@@ -0,0 +1,37 @@
+/* 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 <map>
+#include <string>
+#include <vector>
+
+struct ImportedCxxModuleInfo
+{
+  std::string const Name;
+  std::vector<std::string> const AvailableBmis;
+};
+
+struct ImportedCxxModuleGeneratorInfo
+{
+  ImportedCxxModuleInfo const* ImportedInfo;
+  std::string const BmiName;
+};
+
+struct ImportedCxxModuleLookup
+{
+  ImportedCxxModuleLookup() = default;
+  ~ImportedCxxModuleLookup() = default;
+
+  bool Initialized() const;
+  void Initialize(std::string const& importedModules);
+
+  std::string BmiNameForSource(std::string const& path);
+
+private:
+  bool DoneInit = false;
+  std::map<std::string, ImportedCxxModuleInfo> ImportedInfo;
+  std::map<std::string, ImportedCxxModuleGeneratorInfo> GeneratorInfo;
+};

bootstrap

@@ -392,6 +392,7 @@ CMAKE_CXX_SOURCES="\
   cmGlobVerificationManager \
   cmHexFileConverter \
   cmIfCommand \
+  cmImportedCxxModuleInfo \
   cmIncludeCommand \
   cmIncludeGuardCommand \
   cmIncludeDirectoryCommand \