[Macros] Make the compiler frontend depend on the macro plugin libraries

The dependency of the Observation library on the observation macro
plugin introduces a direct dependency of a target library on a host
library, (lib -> stdlib) that we'd like to avoid. Instead, make the
Swift frontend binary depend on the macro plugin libraries that we
build, so that it's the complete host-side stack.

Author: DougGregor

lib/CMakeLists.txt

@@ -83,16 +83,26 @@ if (SWIFT_SWIFT_PARSER)
   list(TRANSFORM SWIFT_SYNTAX_MODULES APPEND ".swiftmodule"
        OUTPUT_VARIABLE SWIFT_SYNTAX_MODULE_DIRS)
   foreach(module_dir ${SWIFT_SYNTAX_MODULE_DIRS})
+    # Find all of the source module files.
     file(GLOB module_files
          "${SWIFT_SYNTAX_LIBRARIES_SOURCE_DIR}/${module_dir}/*.swiftinterface")
+
+    # Determine the destination module files.
+    set(dest_module_files)
+    foreach(full_module_file ${module_files})
+        get_filename_component(module_file ${full_module_file} NAME)
+        list(APPEND dest_module_files
+            "${SWIFT_HOST_LIBRARIES_DEST_DIR}/${module_dir}/${module_file}")
+    endforeach()
+
     add_custom_command(
-      OUTPUT ${module_files}
+      OUTPUT ${dest_module_files}
       COMMAND ${CMAKE_COMMAND} -E make_directory ${SWIFT_HOST_LIBRARIES_DEST_DIR}/${module_dir}
       COMMAND ${CMAKE_COMMAND} -E copy_if_different ${module_files} ${SWIFT_HOST_LIBRARIES_DEST_DIR}/${module_dir}/
       COMMENT "Copying ${module_dir}"
     )
 
-    list(APPEND SWIFT_SYNTAX_DEST_FILES ${module_files})
+    list(APPEND SWIFT_SYNTAX_DEST_FILES ${dest_module_files})
   endforeach()
 
   # Add a custom target to copy over the SwiftSyntax build products into

lib/Macros/CMakeLists.txt

@@ -45,6 +45,9 @@ function(add_swift_macro_library name)
     ARCHIVE
       DESTINATION "${SWIFT_HOST_PLUGINS_DEST_DIR}"
       COMPONENT compiler)
+
+  # Export this macro plugin target.
+  set_property(GLOBAL APPEND PROPERTY SWIFT_MACRO_PLUGINS ${name})
 endfunction()
 
 add_subdirectory(Sources/ObservationMacros)

stdlib/public/Observation/Sources/Observation/CMakeLists.txt

@@ -10,20 +10,10 @@
 #
 #===----------------------------------------------------------------------===#
 
-# Linux and windows hosts are disabled for now; it is dependent upon earlyswiftsyntax
-# which does not build in the same way just yet
-if (${SWIFT_HOST_VARIANT_SDK} IN_LIST SWIFT_DARWIN_PLATFORMS)
+# We can only build when earlyswiftsyntax is enabled.
+if (SWIFT_SWIFT_PARSER)
   list(APPEND swift_runtime_library_compile_flags -I${SWIFT_SOURCE_DIR}/stdlib/include -I${SWIFT_SOURCE_DIR}/include)
 
-  set(SWIFT_OBSERVATION_SWIFT_FLAGS)
-  set(SWIFT_OBSERVATION_DEPENDS)
-
-  list(APPEND SWIFT_OBSERVATION_SWIFT_FLAGS
-    "-enable-experimental-feature" "Macros"
-    "-DSWIFT_OBSERVATION_MACROS"
-  )
-  list(APPEND SWIFT_OBSERVATION_DEPENDS ObservationMacros)
-
   add_swift_target_library(swiftObservation ${SWIFT_STDLIB_LIBRARY_BUILD_TYPES} IS_STDLIB
     Locking.cpp
     Locking.swift
@@ -37,15 +27,11 @@ if (${SWIFT_HOST_VARIANT_SDK} IN_LIST SWIFT_DARWIN_PLATFORMS)
     ThreadLocal.swift
     TrackedProperties.swift
 
-    DEPENDS ${SWIFT_OBSERVATION_DEPENDS}
-
     SWIFT_COMPILE_FLAGS
       ${SWIFT_STANDARD_LIBRARY_SWIFT_FLAGS}
-      ${SWIFT_OBSERVATION_SWIFT_FLAGS}
     SWIFT_MODULE_DEPENDS _Concurrency
     INSTALL_IN_COMPONENT stdlib
 
     MACCATALYST_BUILD_FLAVOR "zippered"
   )
-
-endif()
+endif()

tools/driver/CMakeLists.txt

@@ -7,6 +7,11 @@ function(add_swift_parser_link_libraries target)
   if(SWIFT_SWIFT_PARSER)
     target_link_libraries(${target}
                           PRIVATE swiftCore)
+
+    get_property(SWIFT_MACRO_PLUGINS GLOBAL PROPERTY SWIFT_MACRO_PLUGINS)
+    foreach(macrolib ${SWIFT_MACRO_PLUGINS})
+      add_dependencies(${target} ${macrolib})
+    endforeach()
   endif()
 endfunction()