Merge #289: cmake: make target_capnp_sources use CURRENT dirs

615a94f cmake: document ONLY_CAPNP option in target_capnp_sources (Ryan Ofsky)
620f297 cmake: make target_capnp_sources use CURRENT dirs (Ryan Ofsky)

Pull request description:

  Tweak `target_capnp_sources` to use `CMAKE_CURRENT_SOURCE_DIR` and `CMAKE_CURRENT_BINARY_DIR` instead of `CMAKE_SOURCE_DIR` and `CMAKE_BINARY_DIR` to compute include directory paths.

  This allows `target_capnp_sources` to work properly inside libmultiprocess when libmultiprocess is used as a subproject and `CMAKE_SOURCE_DIR` point somewhere outside of it, as happens in support branch used by #287.

  This is also a good change to make more generally because `CMAKE_CURRENT_SOURCE_DIR` is a more predictable path than `CMAKE_SOURCE_DIR` and is passed in by all current `target_capnp_sources` callers.

ACKs for top commit:
  hebasto:
    re-ACK 615a94f.

Tree-SHA512: 978a3172dee80cff4dd2afb4858347216c9211a6f182b6b0b9ad71641f30ccaea619d5ddd61484cd08375dd21c290b8fb5b52307baadc8042443b12bd6c3b908

Author: ryanofsky

cmake/TargetCapnpSources.cmake

@@ -27,10 +27,8 @@ Arguments:
 
       #include <schema.capnp.h>
 
-    The specified include_prefix should be ${CMAKE_SOURCE_DIR} or a
-    subdirectory of it to include files relative to the project root. It can
-    be ${CMAKE_CURRENT_SOURCE_DIR} to include files relative to the current
-    source directory.
+    Pass ${CMAKE_CURRENT_SOURCE_DIR} or a subdirectory of it to include files
+    relative to the current source directory (the typical usage).
 
 Additional Unnamed Arguments:
 
@@ -43,12 +41,19 @@ Optional Keyword Arguments:
   IMPORT_PATHS: Specifies additional directories to search for imported
     `.capnp` files.
 
+  ONLY_CAPNP: If specified, only the Cap'n Proto serialization files
+    (`.capnp.h`, `.capnp.c++`) are generated and compiled. The mpgen proxy
+    files (`.capnp.proxy-client.c++`, `.capnp.proxy-server.c++`,
+    `.capnp.proxy-types.c++`, etc.) are skipped. Useful when you need
+    Cap'n Proto serialization without the multiprocess RPC proxy
+    infrastructure.
+
 Example:
   # Assuming `my_library` is a target and `lib/` contains `.capnp` schema
   # files with imports from `include/`.
-  target_capnp_sources(my_library "${CMAKE_SOURCE_DIR}"
+  target_capnp_sources(my_library "${CMAKE_CURRENT_SOURCE_DIR}"
                        lib/schema1.capnp lib/schema2.capnp
-                       IMPORT_PATHS ${CMAKE_SOURCE_DIR}/include)
+                       IMPORT_PATHS ${CMAKE_CURRENT_SOURCE_DIR}/include)
 
 #]=]
 
@@ -98,8 +103,8 @@ function(target_capnp_sources target include_prefix)
 
   # Translate include_prefix from a source path to a binary path and add it as a
   # target include directory.
-  set(build_include_prefix ${CMAKE_BINARY_DIR})
-  file(RELATIVE_PATH relative_path ${CMAKE_SOURCE_DIR} ${include_prefix})
+  set(build_include_prefix ${CMAKE_CURRENT_BINARY_DIR})
+  file(RELATIVE_PATH relative_path ${CMAKE_CURRENT_SOURCE_DIR} ${include_prefix})
   if(relative_path)
     string(APPEND build_include_prefix "/" "${relative_path}")
   endif()