Don't use dispatch if we can't build it

external/dispatch/CMakeLists.txt

@@ -4,59 +4,66 @@
 # For license and copyright information please follow this link:
 # https://github.com/desktop-app/legal/blob/master/LEGAL
 
-add_library(external_dispatch INTERFACE IMPORTED GLOBAL)
-add_library(desktop-app::external_dispatch ALIAS external_dispatch)
+set(dispatch_loc ${third_party_loc}/dispatch)
+set(dispatch_prefix ${CMAKE_CURRENT_BINARY_DIR}/dispatch-prefix)
+set(dispatch_binary_dir ${dispatch_prefix}/src/dispatch-build)
 
 if (DESKTOP_APP_USE_PACKAGED)
     find_library(DISPATCH_LIBRARIES dispatch)
     find_path(DISPATCH_INCLUDE_DIRS dispatch/dispatch.h)
+endif()
 
-    if (DISPATCH_LIBRARIES AND DISPATCH_INCLUDE_DIRS)
-        target_include_directories(external_dispatch SYSTEM INTERFACE ${DISPATCH_INCLUDE_DIRS})
-        target_link_libraries(external_dispatch INTERFACE ${DISPATCH_LIBRARIES})
-        return()
+if (NOT DISPATCH_LIBRARIES OR NOT DISPATCH_INCLUDE_DIRS)
+    execute_process(
+        COMMAND ${CMAKE_COMMAND} ${dispatch_loc}
+            -B ${dispatch_binary_dir}
+            -GNinja
+            -DCMAKE_BUILD_TYPE=Release
+            -DCMAKE_C_COMPILER=clang
+            -DCMAKE_CXX_COMPILER=clang++
+            -DBUILD_SHARED_LIBS=OFF
+            -DBUILD_TESTING=OFF
+    )
+
+    execute_process(
+        COMMAND ${CMAKE_COMMAND} --build ${dispatch_binary_dir}
+    )
+
+    if (NOT EXISTS ${dispatch_binary_dir}/src/libdispatch.a)
+        if (DESKTOP_APP_SPECIAL_TARGET)
+            message(FATAL_ERROR "Dispatch build failed")
+        else()
+            return()
+        endif()
     endif()
 endif()
 
+add_library(external_dispatch INTERFACE IMPORTED GLOBAL)
+add_library(desktop-app::external_dispatch ALIAS external_dispatch)
+
+if (DESKTOP_APP_USE_PACKAGED AND DISPATCH_LIBRARIES AND DISPATCH_INCLUDE_DIRS)
+    target_include_directories(external_dispatch SYSTEM INTERFACE ${DISPATCH_INCLUDE_DIRS})
+    target_link_libraries(external_dispatch INTERFACE ${DISPATCH_LIBRARIES})
+    return()
+endif()
+
 add_library(external_dispatch_bundled STATIC IMPORTED)
 
-include(ExternalProject)
-ExternalProject_Add(dispatch
-    URL ${third_party_loc}/dispatch
-    CMAKE_GENERATOR Ninja
-    CMAKE_ARGS
-        -DCMAKE_BUILD_TYPE=Release
-        -DCMAKE_C_COMPILER=clang
-        -DCMAKE_CXX_COMPILER=clang++
-        -DBUILD_SHARED_LIBS=OFF
-        -DBUILD_TESTING=OFF
-    STEP_TARGETS build
-    EXCLUDE_FROM_ALL TRUE
-    BUILD_BYPRODUCTS
-        <BINARY_DIR>/src/libdispatch.a
-        <BINARY_DIR>/src/BlocksRuntime/libBlocksRuntime.a
-)
-
-ExternalProject_Get_property(dispatch SOURCE_DIR)
-ExternalProject_Get_property(dispatch BINARY_DIR)
-
 set_target_properties(external_dispatch_bundled PROPERTIES
-    IMPORTED_LOCATION "${BINARY_DIR}/src/libdispatch.a"
+    IMPORTED_LOCATION "${dispatch_binary_dir}/src/libdispatch.a"
 )
 
 target_include_directories(external_dispatch_bundled SYSTEM
 INTERFACE
-    ${SOURCE_DIR}
+    ${dispatch_loc}
 )
 
 target_link_libraries(external_dispatch_bundled
 INTERFACE
-    ${BINARY_DIR}/src/BlocksRuntime/libBlocksRuntime.a
+    ${dispatch_binary_dir}/src/BlocksRuntime/libBlocksRuntime.a
     pthread
 )
 
-add_dependencies(external_dispatch_bundled dispatch-build)
-
 target_link_libraries(external_dispatch
 INTERFACE
     external_dispatch_bundled