Remove gn, add bazel

Bazel build works so long as you copy the dll, but there's no good way to copy an artifact that I can find in Bazel.

Author: fuzzybinary

Diff for: .gitignore

@@ -1 +1,2 @@
-out/*
+dart-sdk/*
+bazel-*/

Diff for: BUILD.gn

@@ -2,8 +2,6 @@
 
 This is an attempt / POC to build the Dart VM into a dynamic library, importable in any platform Dart supports.
 
-This uses the same build system any style as the Dart SDK, partially so that it can be built from a parallel checkout of the Dart SDK source, and (potentially, maybe one day) be brought into the Dart SDK directly.
-
 ## Eventual support
 
 The hope is that the the dynamic library will eventually support the following targets:
@@ -28,8 +26,28 @@ None. I literally just started.
 
 ## Building
 
-`TODO:`
+* Fetch the Dart SDK into this directory. Follow the instructions from [the dart repo](https://github.com/dart-lang/sdk/wiki/Building#source). Put it in `dart-sdk`. The code and scripts assume that this is where the dart-sdk lives.
+* Build the Dart libraries
+  * There is a Dart script for doing this that will do some checks for you as well:
+  ```
+  dart tools/build/build.dart
+  ```
 
 ## Contributing
 
 `TODO:`
+
+# What I Did
+
+This section is as much for my benefit as for yours.
+
+* Modify the BUILD.gn files to add a `libdart` target. This is done by applying the patch in `./dart_sdk.patch`
+* Make sure all correct environment variables are set
+  * On Windows, these are set with the `setup_env.ps1` script. Specifically, you need to set `GYP_MSVS_OVERRIDE_PATH`, `GYP_MSVS_VERSION`, and `DEPOT_TOOLS_WIN_TOOLCHAIN=0`
+* Builds libdart with:
+  ```bash
+  python ./tools/build.py --no-goma -m release libdart
+  ```
+* Revert the changes made to build files to leave a clean copy of the dart-sdk (this makes updating easier)
+* Build the dynamic library using the Bazel script
+  * This puts the output in `out/lib/platform` and `out/include`. The various examples look for these directories, and these can be copied for use in other projects.

Diff for: README.md

@@ -0,0 +1,13 @@
+cc_binary(
+    name = "simple_example",
+    srcs = ["main.cpp"],
+    data = [
+        "//src:dyndart"
+    ],
+    deps = [
+        "//src:libdyndart"
+    ],
+    dynamic_deps = [ 
+        "//src:dyndart",
+    ],
+)

Diff for: WORKSPACE

@@ -1,8 +1,8 @@
 #include <stdio.h>
 
-int main() {
-    
-    printf("Hello world");
-    
-    return 0;
-}
+#include "src/dart_dll.h"
+
+void main() {
+  DartDll_Initialize();
+  printf("Hello World!");
+}

Diff for: dart_sdk.patch

@@ -0,0 +1,3 @@
+$Env:GYP_MSVS_OVERRIDE_PATH="C:\Program Files\Microsoft Visual Studio\2022\Community\"
+$Env:GYP_MSVS_VERSION=2019
+$Env:DEPOT_TOOLS_WIN_TOOLCHAIN=0

Diff for: examples/simple_example/BUILD

@@ -0,0 +1,13 @@
+cc_shared_library(
+    name = "dyndart",
+    roots = [ ":libdyndart" ],
+    visibility = ["//visibility:public"],
+)
+
+cc_library(
+    name = "libdyndart",
+    hdrs = [ "dart_dll.h" ],
+    srcs = [ "dart_dll.cpp" ],
+    visibility = ["//visibility:public"],
+    copts = [ "/DDART_DLL_EXPORTING" ]
+)

Diff for: examples/simple_example/BUILD.gn

@@ -0,0 +1,7 @@
+#include <iostream>
+
+#include "dart_dll.h"
+
+void DartDll_Initialize() {
+    std::cout << "Hello from DartDll_Initialize()";
+}

Diff for: examples/simple_example/main.cpp

@@ -0,0 +1,9 @@
+#pragma once
+
+#ifdef DART_DLL_EXPORTING
+    #define DART_DLL_EXPORT __declspec(dllexport)
+#else
+    #define DART_DLL_EXPORT __declspec(dllimport)
+#endif
+
+DART_DLL_EXPORT void DartDll_Initialize();