build: add Swift dynamic linking support

this is in preparation for the upcoming swift 5 transition, where static
linking was replaced by dynamic linking the swift libraries as the
preferred way, by Apple. furthermore Apple removed the static swift libs
from their dev Tools starting with xcode 10.2/swift 5.

because of ABI incompatibility dynamic linking for swift versions prior
to 5 doesn't use the system lib path for the dynamic swift libs.

for now static linking is still the default, but that will be changed
when swift 5 support is added and swift 3 support is dropped.

Fixes #6232

2 files changed, 26 insertions, 2 deletions

diff --git a/waftools/detections/compiler_swift.py b/waftools/detections/compiler_swift.py
index 3dffcdedd2..4ff6d20119 100644
--- a/waftools/detections/compiler_swift.py
+++ b/waftools/detections/compiler_swift.py
@@ -30,12 +30,25 @@ def __add_swift_flags(ctx):
     if ctx.is_optimization():
         ctx.env.SWIFT_FLAGS.append("-O")
 
-def __add_swift_library_linking_flags(ctx, swift_library):
+def __add_static_swift_library_linking_flags(ctx, swift_library):
     ctx.env.append_value('LINKFLAGS', [
         '-L%s' % swift_library,
         '-Xlinker', '-force_load_swift_libs', '-lc++',
     ])
 
+def __add_dynamic_swift_library_linking_flags(ctx, swift_library):
+    ctx.env.append_value('LINKFLAGS', [ '-L%s' % swift_library ])
+
+    #ABI compatibility
+    if StrictVersion(ctx.env.SWIFT_VERSION) >= StrictVersion("5.0"):
+        ctx.env.append_value('LINKFLAGS', [
+            '-Xlinker', '-rpath', '-Xlinker', '/usr/lib/swift',
+        ])
+
+    ctx.env.append_value('LINKFLAGS', [
+        '-Xlinker', '-rpath', '-Xlinker', swift_library,
+    ])
+
 def __find_swift_library(ctx):
     swift_libraries = {}
     #look for set lib paths in passed environment variables
@@ -90,10 +103,16 @@ def __find_swift_library(ctx):
     ctx.start_msg('Checking for static Swift Library')
     if 'SWIFT_LIB_STATIC' in swift_libraries:
         ctx.end_msg(swift_libraries['SWIFT_LIB_STATIC'])
-        __add_swift_library_linking_flags(ctx, swift_libraries['SWIFT_LIB_STATIC'])
+        ctx.env['SWIFT_LIB_STATIC'] = swift_libraries['SWIFT_LIB_STATIC']
     else:
         ctx.end_msg(False)
 
+    enableStatic = getattr(ctx.options, 'enable_swift-static')
+    if (enableStatic or enableStatic == None) and 'SWIFT_LIB_STATIC' in swift_libraries:
+        __add_static_swift_library_linking_flags(ctx, swift_libraries['SWIFT_LIB_STATIC'])
+    else:
+        __add_dynamic_swift_library_linking_flags(ctx, swift_libraries['SWIFT_LIB_DYNAMIC'])
+
 def __find_macos_sdk(ctx):
     ctx.start_msg('Checking for macOS SDK')
     sdk = __run(['xcrun', '--sdk', 'macosx', '--show-sdk-path'])
diff --git a/wscript b/wscript
index 121f3613af..76cfe1ddd3 100644
--- a/wscript
+++ b/wscript
@@ -125,6 +125,11 @@ build_options = [
         'desc': 'generate a clang compilation database',
         'func': check_true,
         'default': 'disable',
+    } , {
+        'name': '--swift-static',
+        'desc': 'static Swift linking',
+        'deps': 'os-darwin',
+        'func': check_ctx_vars('SWIFT_LIB_STATIC')
     }
 ]