More seamless SwiftPM implementation (#567)

This update allows clients to share common syntax for nanopb imports/includes between CocoaPods and Swift Package Manager.

See example at firebase/firebase-ios-sdk#6165

Package.swift

@@ -12,6 +12,13 @@ let package = Package(
         .watchOS(.v2)
     ],
 
+  products: [
+    .library(
+      name: "nanopb",
+      targets: ["nanopb"]
+    )
+  ],
+
   targets: [
     .target(
       name: "nanopb",
@@ -25,7 +32,7 @@ let package = Package(
         "pb_encode.h",
         "pb_encode.c"
       ],
-      publicHeadersPath: "SwiftPackage",
+      publicHeadersPath: "spm_headers",
       cSettings: [
         .define("PB_FIELD_32BIT", to: "1"),
         .define("PB_NO_PACKED_STRUCTS", to: "1"),

SwiftPackage/module.modulemap

@@ -1,5 +0,0 @@
-module nanopb {
-    umbrella header "nanopb.h"
-
-    export *
-}

SwiftPackage/nanopb.h

@@ -1,4 +0,0 @@
-#import "../pb.h"
-#import "../pb_common.h"
-#import "../pb_decode.h"
-#import "../pb_encode.h"

spm-test/objc/c-header.c

@@ -1 +1,3 @@
-#include "nanopb.h"
+#include "pb.h"
+#include "pb_common.h"
+#include "pb_decode.h"

spm-test/objc/objc-header.m

@@ -1 +1,3 @@
-#import "nanopb.h"
+#import "pb.h"
+#import <pb_common.h>
+#include "pb_decode.h"

spm-test/objc/objc-qualified.m

@@ -0,0 +1,3 @@
+#import "nanopb/pb.h"
+#import <nanopb/pb_common.h>
+#include "nanopb/pb_decode.h"

spm_headers/nanopb/pb.h

@@ -0,0 +1 @@
+../../pb.h

spm_headers/nanopb/pb_common.h

@@ -0,0 +1 @@
+../../pb_common.h

spm_headers/nanopb/pb_decode.h

@@ -0,0 +1 @@
+../../pb_decode.h

spm_headers/nanopb/pb_encode.h

@@ -0,0 +1 @@
+../../pb_encode.h

spm_headers/pb.h

@@ -0,0 +1 @@
+#include "nanopb/pb.h"

spm_headers/pb_common.h

@@ -0,0 +1 @@
+#include "nanopb/pb_common.h"

spm_headers/pb_decode.h

@@ -0,0 +1 @@
+#include "nanopb/pb_decode.h"

spm_headers/pb_encode.h

@@ -0,0 +1 @@
+#include "nanopb/pb_encode.h"