Skip non-namespaced BUILD_INTERFACE targets in dependency export

Updates the dependency export logic to only process BUILD_INTERFACE targets that are namespaced (external dependencies). Non-namespaced BUILD_INTERFACE targets, which are local build targets, are now skipped to avoid incorrect dependency tracking.

Author: sean-parent

cmake/cpp-library-install.cmake

@@ -60,8 +60,17 @@ function(_cpp_library_generate_dependencies OUTPUT_VAR TARGET_NAME NAMESPACE)
         # When re-exporting dependencies from external packages, they must be wrapped in BUILD_INTERFACE
         # to avoid CMake export errors, but we still want to track them for find_dependency()
         if(LIB MATCHES "^\\$<BUILD_INTERFACE:([^>]+)>$")
-            set(LIB "${CMAKE_MATCH_1}")
-            message(DEBUG "cpp-library: Extracted ${LIB} from BUILD_INTERFACE generator expression")
+            set(EXTRACTED_TARGET "${CMAKE_MATCH_1}")
+            # Only process if it's a namespaced target (external dependency)
+            # Non-namespaced targets in BUILD_INTERFACE are local build targets
+            if(EXTRACTED_TARGET MATCHES "::")
+                set(LIB "${EXTRACTED_TARGET}")
+                message(DEBUG "cpp-library: Extracted ${LIB} from BUILD_INTERFACE generator expression")
+            else()
+                # Skip non-namespaced BUILD_INTERFACE targets (local build targets)
+                message(DEBUG "cpp-library: Skipping non-namespaced BUILD_INTERFACE target: ${EXTRACTED_TARGET}")
+                continue()
+            endif()
         elseif(LIB MATCHES "^\\$<")
             # Skip other generator expressions (INSTALL_INTERFACE, etc.)
             continue()