Improve bazel example

Author: jinfwhuang

bazel/README.md

@@ -25,13 +25,16 @@ emsdk_emscripten_deps()
 
 Put the following lines into your `.bazelrc`:
 ```
-build:wasm --crosstool_top=//emscripten_toolchain:everything
+build:wasm --crosstool_top=@emsdk//emscripten_toolchain:everything
 build:wasm --cpu=wasm
 build:wasm --host_crosstool_top=@bazel_tools//tools/cpp:toolchain
 ```
 
-Simply pass `--config=wasm` when building a normal `cc_binary`. The result of
-this build will be a tar archive containing any files produced by emscripten.
+Simply pass `--config=wasm` when building a normal `cc_binary`, e.g.
+```
+bazel build --config=wasm :hello-world
+```
+The result of this build will be a tar archive containing any files produced by emscripten.
 
 ### Using wasm_cc_binary
 First, write a new rule wrapping your `cc_binary`.

bazel/test_external/.bazelrc

@@ -0,0 +1,3 @@
+build:wasm --crosstool_top=@emsdk//emscripten_toolchain:everything
+build:wasm --cpu=wasm
+build:wasm --host_crosstool_top=@bazel_tools//tools/cpp:toolchain

bazel/test_external/.gitignore

@@ -0,0 +1,2 @@
+bazel-*
+dist/

bazel/test_external/BUILD

@@ -3,6 +3,9 @@ load("@emsdk//emscripten_toolchain:wasm_rules.bzl", "wasm_cc_binary")
 cc_binary(
     name = "hello-world",
     srcs = ["hello-world.cc"],
+    linkopts = [
+        "--bind",
+    ],
 )
 
 wasm_cc_binary(

bazel/test_external/README.md

@@ -0,0 +1,8 @@
+```bash
+# Native
+bazel run :hello-world
+
+# Build wasm
+bazel build --config=wasm :hello-world
+bazel build :hello-world-wasm
+```

bazel/test_external/hello-world.cc

@@ -1,6 +1,24 @@
+#ifdef __EMSCRIPTEN__
+#include <emscripten.h>
+#include <emscripten/bind.h>
+using namespace emscripten;
+#endif
+
 #include <iostream>
 
+void sayHello() {
+  std::cout << "hello" << std::endl;
+}
+
+#ifdef __EMSCRIPTEN__
+EMSCRIPTEN_BINDINGS(aa) {
+  function("sayHello", &sayHello);
+}
+#else
 int main(int argc, char** argv) {
-  std::cout << "hello world!" << std::endl;
+  std::cout << "start main function" << std::endl;
+  sayHello();
+  std::cout << "end main function" << std::endl;
   return 0;
 }
+#endif