Add CMAKE_BUILD_INTERFACE_INCLUDES build-variable.

This makes

 set(CMAKE_BUILD_INTERFACE_INCLUDES ON)

add the equivalent of

 set_property(TARGET tgt APPEND PROPERTY
   INTERFACE_INCLUDE_DIRECTORIES
   $<BUILD_INTERFACE:${CMAKE_CURRENT_SOURCE_DIR};${CMAKE_CURRENT_BINARY_DIR}>
 )

to every target.

If the headers are in CMAKE_CURRENT_SOURCE_DIR, and the generated headers
are in CMAKE_CURRENT_BINARY_DIR, this is a convenient way to build a target
bar, which depends on foo, just by using target_link_libraries() and adding
the INTERFACE_INCLUDE_DIRECTORIES to the INCLUDE_DIRECTORIES of the target
being linked. There will be more-convenient porcelain API to consume the
property in the future.

3 files changed, 24 insertions, 0 deletions

diff --git a/Tests/CMakeCommands/target_link_libraries/subdir/CMakeLists.txt b/Tests/CMakeCommands/target_link_libraries/subdir/CMakeLists.txt
new file mode 100644
index 0000000..61a1a59
--- /dev/null
+++ b/Tests/CMakeCommands/target_link_libraries/subdir/CMakeLists.txt
@@ -0,0 +1,5 @@
+
+set(CMAKE_BUILD_INTERFACE_INCLUDES ON)
+
+add_library(subdirlib SHARED subdirlib.cpp)
+generate_export_header(subdirlib)
diff --git a/Tests/CMakeCommands/target_link_libraries/subdir/subdirlib.cpp b/Tests/CMakeCommands/target_link_libraries/subdir/subdirlib.cpp
new file mode 100644
index 0000000..cd2f1a2
--- /dev/null
+++ b/Tests/CMakeCommands/target_link_libraries/subdir/subdirlib.cpp
@@ -0,0 +1,7 @@
+
+#include "subdirlib.h"
+
+int SubDirLibObject::foo() const
+{
+  return 0;
+}
diff --git a/Tests/CMakeCommands/target_link_libraries/subdir/subdirlib.h b/Tests/CMakeCommands/target_link_libraries/subdir/subdirlib.h
new file mode 100644
index 0000000..e386f87
--- /dev/null
+++ b/Tests/CMakeCommands/target_link_libraries/subdir/subdirlib.h
@@ -0,0 +1,12 @@
+
+#ifndef SUBDIRLIB_H
+#define SUBDIRLIB_H
+
+#include "subdirlib_export.h"
+
+struct SUBDIRLIB_EXPORT SubDirLibObject
+{
+  int foo() const;
+};
+
+#endif