Ninja: Support embedding of CMake as subninja project

Add a `CMAKE_NINJA_OUTPUT_PATH_PREFIX` variable.  When it is set, CMake
generates a `build.ninja` file suitable for embedding into another ninja
project potentially generated by an alien generator.

4 files changed, 70 insertions, 7 deletions

diff --git a/Source/cmAlgorithms.h b/Source/cmAlgorithms.h
index 76acaca..ee803c8 100644
--- a/Source/cmAlgorithms.h
+++ b/Source/cmAlgorithms.h
@@ -379,4 +379,19 @@ std::reverse_iterator<Iter> cmMakeReverseIterator(Iter it)
   return std::reverse_iterator<Iter>(it);
 }
 
+inline bool cmHasSuffix(const std::string& str, const std::string& suffix)
+{
+  if (str.size() < suffix.size()) {
+    return false;
+  }
+  return str.compare(str.size() - suffix.size(), suffix.size(), suffix) == 0;
+}
+
+inline void cmStripSuffixIfExists(std::string& str, const std::string& suffix)
+{
+  if (cmHasSuffix(str, suffix)) {
+    str.resize(str.size() - suffix.size());
+  }
+}
+
 #endif
diff --git a/Source/cmGlobalNinjaGenerator.cxx b/Source/cmGlobalNinjaGenerator.cxx
index 3c5a8e3..d65b463 100644
--- a/Source/cmGlobalNinjaGenerator.cxx
+++ b/Source/cmGlobalNinjaGenerator.cxx
@@ -488,6 +488,7 @@ void cmGlobalNinjaGenerator::Generate()
   this->OpenBuildFileStream();
   this->OpenRulesFileStream();
 
+  this->InitOutputPathPrefix();
   this->TargetAll = this->NinjaOutputPath("all");
   this->CMakeCacheFile = this->NinjaOutputPath("CMakeCache.txt");
 
@@ -717,6 +718,23 @@ void cmGlobalNinjaGenerator::CloseRulesFileStream()
   }
 }
 
+static void EnsureTrailingSlash(std::string& path)
+{
+  if (path.empty()) {
+    return;
+  }
+  std::string::value_type last = path[path.size() - 1];
+#ifdef _WIN32
+  if (last != '\\') {
+    path += '\\';
+  }
+#else
+  if (last != '/') {
+    path += '/';
+  }
+#endif
+}
+
 std::string cmGlobalNinjaGenerator::ConvertToNinjaPath(const std::string& path)
 {
   cmLocalNinjaGenerator* ng =
@@ -1136,8 +1154,10 @@ void cmGlobalNinjaGenerator::WriteTargetAll(std::ostream& os)
   this->WritePhonyBuild(os, "The main all target.", outputs,
                         this->AllDependencies);
 
-  cmGlobalNinjaGenerator::WriteDefault(os, outputs,
-                                       "Make the all target the default.");
+  if (!this->HasOutputPathPrefix()) {
+    cmGlobalNinjaGenerator::WriteDefault(os, outputs,
+                                         "Make the all target the default.");
+  }
 }
 
 void cmGlobalNinjaGenerator::WriteTargetRebuildManifest(std::ostream& os)
@@ -1251,7 +1271,28 @@ void cmGlobalNinjaGenerator::WriteTargetHelp(std::ostream& os)
              /*variables=*/cmNinjaVars());
 }
 
+void cmGlobalNinjaGenerator::InitOutputPathPrefix()
+{
+  this->OutputPathPrefix =
+    this->LocalGenerators[0]->GetMakefile()->GetSafeDefinition(
+      "CMAKE_NINJA_OUTPUT_PATH_PREFIX");
+  EnsureTrailingSlash(this->OutputPathPrefix);
+}
+
 std::string cmGlobalNinjaGenerator::NinjaOutputPath(std::string const& path)
 {
-  return path;
+  if (!this->HasOutputPathPrefix() || cmSystemTools::FileIsFullPath(path)) {
+    return path;
+  }
+  return this->OutputPathPrefix + path;
+}
+
+void cmGlobalNinjaGenerator::StripNinjaOutputPathPrefixAsSuffix(
+  std::string& path)
+{
+  if (path.empty()) {
+    return;
+  }
+  EnsureTrailingSlash(path);
+  cmStripSuffixIfExists(path, this->OutputPathPrefix);
 }
diff --git a/Source/cmGlobalNinjaGenerator.h b/Source/cmGlobalNinjaGenerator.h
index 15c0f34..6d9bfe8 100644
--- a/Source/cmGlobalNinjaGenerator.h
+++ b/Source/cmGlobalNinjaGenerator.h
@@ -315,6 +315,8 @@ public:
   bool SupportsConsolePool() const;
 
   std::string NinjaOutputPath(std::string const& path);
+  bool HasOutputPathPrefix() const { return !this->OutputPathPrefix.empty(); }
+  void StripNinjaOutputPathPrefixAsSuffix(std::string& path);
 
 protected:
   virtual void Generate();
@@ -401,6 +403,9 @@ private:
   std::string NinjaVersion;
 
 private:
+  void InitOutputPathPrefix();
+
+  std::string OutputPathPrefix;
   std::string TargetAll;
   std::string CMakeCacheFile;
 };
diff --git a/Source/cmNinjaTargetGenerator.cxx b/Source/cmNinjaTargetGenerator.cxx
index 994daea..4d58242 100644
--- a/Source/cmNinjaTargetGenerator.cxx
+++ b/Source/cmNinjaTargetGenerator.cxx
@@ -669,10 +669,12 @@ void cmNinjaTargetGenerator::EnsureDirectoryExists(
   if (cmSystemTools::FileIsFullPath(path.c_str())) {
     cmSystemTools::MakeDirectory(path.c_str());
   } else {
-    const std::string fullPath = std::string(this->GetGlobalGenerator()
-                                               ->GetCMakeInstance()
-                                               ->GetHomeOutputDirectory()) +
-      "/" + path;
+    cmGlobalNinjaGenerator* gg = this->GetGlobalGenerator();
+    std::string fullPath =
+      std::string(gg->GetCMakeInstance()->GetHomeOutputDirectory());
+    // Also ensures their is a trailing slash.
+    gg->StripNinjaOutputPathPrefixAsSuffix(fullPath);
+    fullPath += path;
     cmSystemTools::MakeDirectory(fullPath.c_str());
   }
 }