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.

1 files changed, 6 insertions, 4 deletions

diff --git a/Source/cmNinjaTargetGenerator.cxx b/Source/cmNinjaTargetGenerator.cxx
index 994daeae2a..4d58242a5f 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());
   }
 }