always include Foundation with explicit modules

Summary: When compiling explicit modules unconditionally add the Foundation framework. This is required as Swift generated headers will always export Foundation (and Darwin) regardless of Swift contents.

Reviewed By: milend

fbshipit-source-id: a4d5d74660816637f83b4ccb5493628bed1ca221

Author: rmaz

src/com/facebook/buck/swift/SwiftCompileBase.java

@@ -336,6 +336,7 @@ public ImmutableList<String> constructCompilerArgs(SourcePathResolverAdapter res
       // Import the swiftmodule and pcm output of SDK frameworks and Objc dependencies
       for (ExplicitModuleOutput module : moduleDeps) {
         if (module.getName().equals(moduleName)) {
+          Preconditions.checkState(!module.getIsSwiftmodule());
           // We cannot import the direct path to the underlying module as it will conflict with
           // the exported module of the same name when debugging. Instead we need to import the
           // exported module path, this will be remapped in the VFS overlay to the underlying one.

src/com/facebook/buck/swift/SwiftLibraryDescription.java

@@ -1085,6 +1085,10 @@ private static void collectFrameworkPcmDependencies(
 
     // Always import Darwin, this is required for the C stdlib
     builder.addAll(sdkDepsProvider.getSdkClangModuleDependencies("Darwin", targetTriple));
+
+    // We also need Foundation as this is unconditionally added to exports in Swift generated
+    // headers.
+    builder.addAll(sdkDepsProvider.getSdkClangModuleDependencies("Foundation", targetTriple));
   }
 
   private static ImmutableList<Arg> getModuleCompileSwiftArgs(

test/com/facebook/buck/swift/SwiftLibraryIntegrationTest.java

@@ -457,7 +457,7 @@ public void testExplicitModules() throws IOException {
     Files.createSymbolicLink(
         projectRoot.getPath().resolve("xcode"), Paths.get("/var/db/xcode_select_link"));
 
-    BuildTarget target = workspace.newBuildTarget("//:a#iphonesimulator-x86_64,swift-compile");
+    BuildTarget target = workspace.newBuildTarget("//:a#iphonesimulator-x86_64,static");
     ProcessResult result = workspace.runBuckCommand("build", target.getFullyQualifiedName());
     result.assertSuccess();
   }

test/com/facebook/buck/swift/testdata/swift_explicit_modules/.buckconfig

@@ -1,5 +1,6 @@
 [apple]
 toolchain_set_target = "//:toolchain"
+use_swift_delegate = false
 
 [project]
 read_only_paths = xcode

test/com/facebook/buck/swift/testdata/swift_explicit_modules/BUCK.fixture

@@ -1,7 +1,7 @@
 apple_library(
     name = "a",
     srcs = ["a.swift"],
-    deps = [":b", ":c"],
+    deps = [":b", ":c", ":d"],
     uses_explicit_modules = True,
 )
 
@@ -19,6 +19,14 @@ apple_library(
     libraries = ["$SDKROOT/usr/lib/libz.dylib"],
 )
 
+apple_library(
+    name = "d",
+    exported_headers = ["d.h"],
+    srcs = ["d.swift"],
+    modular = True,
+    uses_explicit_modules = True,
+)
+
 apple_toolchain_set(
     name = "toolchain",
     apple_toolchains = [

test/com/facebook/buck/swift/testdata/swift_explicit_modules/d.h

@@ -0,0 +1,4 @@
+
+public func doStdlibStuff() -> Int {
+    return 123
+}