Generate extern variable declarations

Due to scala-native/scala-native#202 it is not possible to use `var` so
for now `val`s are used although not semantically correct.

References #70

bindgen/ir/IR.cpp

@@ -88,6 +88,10 @@ llvm::raw_ostream &operator<<(llvm::raw_ostream &s, const IR &ir) {
             s << *typeDef;
         }
 
+        for (const auto &variable : ir.variables) {
+            s << *variable;
+        }
+
         for (const auto &varDefine : ir.varDefines) {
             s << *varDefine;
         }

bindgen/ir/VarDefine.h

@@ -3,7 +3,6 @@
 
 #include "Define.h"
 #include "Variable.h"
-#include <llvm/Support/raw_ostream.h>
 
 /**
  * Stores a pointer to Variable instance from IR

bindgen/ir/Variable.cpp

@@ -2,3 +2,10 @@
 
 Variable::Variable(const std::string &name, Type *type)
     : TypeAndName(name, type) {}
+
+llvm::raw_ostream &operator<<(llvm::raw_ostream &s,
+                              const Variable &variable) {
+    s << "  val " << variable.getName() << ": "
+      << variable.getType()->str() << " = native.extern\n";
+    return s;
+}

bindgen/ir/Variable.h

@@ -2,10 +2,14 @@
 #define SCALA_NATIVE_BINDGEN_VARIABLE_H
 
 #include "TypeAndName.h"
+#include <llvm/Support/raw_ostream.h>
 
 class Variable : public TypeAndName {
   public:
     Variable(const std::string &name, Type *type);
+
+    friend llvm::raw_ostream &operator<<(llvm::raw_ostream &s,
+                                         const Variable &variable);
 };
 
 #endif // SCALA_NATIVE_BINDGEN_VARIABLE_H

tests/samples/Extern.c

@@ -0,0 +1,9 @@
+#include "Extern.h"
+
+int forty_two = 42;
+const char version[] = "0.1.0";
+
+enum mode mode = USER;
+
+struct version semver_instance = { .major = 1, .minor = 2, .patch = 3 };
+struct version *semver = &semver_instance;

tests/samples/Extern.h

@@ -0,0 +1,12 @@
+extern int forty_two;
+extern const char version[];
+
+enum mode { SYSTEM, USER };
+extern enum mode mode;
+
+struct version {
+    int major;
+    int minor;
+    int patch;
+};
+extern struct version *semver;

tests/samples/Extern.scala

@@ -0,0 +1,36 @@
+package org.scalanative.bindgen.samples
+
+import scala.scalanative._
+import scala.scalanative.native._
+
+@native.link("bindgentests")
+@native.extern
+object Extern {
+  type enum_mode = native.CUnsignedInt
+  type struct_version = native.CStruct3[native.CInt, native.CInt, native.CInt]
+  val forty_two: native.CInt = native.extern
+  val version: native.CString = native.extern
+  val mode: enum_mode = native.extern
+  val semver: native.Ptr[struct_version] = native.extern
+}
+
+import Extern._
+
+object ExternEnums {
+  final val enum_mode_SYSTEM: enum_mode = 0.toUInt
+  final val enum_mode_USER: enum_mode = 1.toUInt
+}
+
+object ExternHelpers {
+
+  implicit class struct_version_ops(val p: native.Ptr[struct_version]) extends AnyVal {
+    def major: native.CInt = !p._1
+    def major_=(value: native.CInt):Unit = !p._1 = value
+    def minor: native.CInt = !p._2
+    def minor_=(value: native.CInt):Unit = !p._2 = value
+    def patch: native.CInt = !p._3
+    def patch_=(value: native.CInt):Unit = !p._3 = value
+  }
+
+  def struct_version()(implicit z: native.Zone): native.Ptr[struct_version] = native.alloc[struct_version]
+}

tests/samples/VarDefine.scala

@@ -6,6 +6,11 @@ import scala.scalanative.native._
 @native.link("bindgentests")
 @native.extern
 object VarDefine {
+  val a: native.CInt = native.extern
+  val constInt: native.CInt = native.extern
+  val constIntPointer: native.Ptr[native.CInt] = native.extern
+  val c: native.CInt = native.extern
+  val f: native.CFloat = native.extern
   @name("a")
   val A: native.CInt = native.extern
   @name("constInt")

tests/samples/src/test/scala/org/scalanative/bindgen/samples/ExternTests.scala

@@ -0,0 +1,21 @@
+package org.scalanative.bindgen.samples
+
+import utest._
+import scalanative.native._
+
+object ExternTests extends TestSuite {
+  val tests = Tests {
+    'forty_two - {
+      assert(Extern.forty_two == 42)
+    }
+
+    'mode - {
+      assert(Extern.mode == ExternEnums.enum_mode_USER)
+    }
+
+    'semver - {
+      import ExternHelpers._
+      assert(Extern.semver.major == 1 && Extern.semver.minor == 2 && Extern.semver.patch == 3)
+    }
+  }
+}