cmNinjaTargetGenerator: ensure that the object output directory exists

If a target has no object compilations within it, nothing ensures that
the directory exists yet it is still mentioned as an order-only
dependency within the build files. While `ninja` is OK with this,
`samu`, an alternate `ninja` implementation, is not. Make sure the
directory always exists for consistency.

Fixes: #25526

1 files changed, 9 insertions, 0 deletions

diff --git a/Source/cmNinjaTargetGenerator.cxx b/Source/cmNinjaTargetGenerator.cxx
index 1f7aaaf..016705e 100644
--- a/Source/cmNinjaTargetGenerator.cxx
+++ b/Source/cmNinjaTargetGenerator.cxx
@@ -1024,6 +1024,15 @@ void cmNinjaTargetGenerator::WriteObjectBuildStatements(
   }
 
   {
+    // Ensure that the object directory exists. If there are no objects in the
+    // target (e.g., an empty `OBJECT` library), the directory is still listed
+    // as an order-only depends in the build files. Alternate `ninja`
+    // implementations may not allow this (such as `samu`). See #25526.
+    auto const objectDir = this->GetObjectFileDir(config);
+    this->EnsureDirectoryExists(objectDir);
+  }
+
+  {
     cmNinjaBuild build("phony");
     build.Comment =
       cmStrCat("Order-only phony target for ", this->GetTargetName());