Add ability to create standalone binaries with qjs

Ref: quickjs-ng/quickjs#438
Closes: quickjs-ng/quickjs#441

Author: saghul

.github/workflows/ci.yml

@@ -160,6 +160,11 @@ jobs:
           git submodule update --init --checkout --depth 1
           time make test262
 
+      - name: test standalone
+        run: |
+          ./build/qjs -c examples/hello.js -o hello
+          ./hello
+
   windows-msvc:
     runs-on: windows-latest
     strategy:
@@ -184,6 +189,10 @@ jobs:
           build\${{matrix.buildType}}\qjs.exe examples\test_point.js
           build\${{matrix.buildType}}\run-test262.exe -c tests.conf
           build\${{matrix.buildType}}\function_source.exe
+      - name: test standalone
+        run: |
+          build\${{matrix.buildType}}\qjs.exe -c examples\hello.js -o hello.exe
+          .\hello.exe
       - name: Set up Visual Studio shell
         uses: egor-tensin/vs-shell@v2
         with:
@@ -351,6 +360,10 @@ jobs:
     - name: test
       run: |
         make test
+    - name: test standalone
+      run: |
+        ./build/qjs -c examples/hello.js -o hello.exe
+        ./hello
   windows-mingw-shared:
     runs-on: windows-latest
     defaults:

CMakeLists.txt

@@ -259,6 +259,7 @@ target_link_libraries(qjsc qjs)
 
 add_executable(qjs_exe
     gen/repl.c
+    gen/standalone.c
     qjs.c
 )
 add_qjs_libc_if_needed(qjs_exe)

Makefile

@@ -70,6 +70,7 @@ clean:
 
 codegen: $(QJSC)
 	$(QJSC) -ss -o gen/repl.c -m repl.js
+	$(QJSC) -ss -o gen/standalone.c -m standalone.js
 	$(QJSC) -e -o gen/function_source.c tests/function_source.js
 	$(QJSC) -e -o gen/hello.c examples/hello.js
 	$(QJSC) -e -o gen/hello_module.c -m examples/hello_module.js

docs/docs/cli.md

@@ -18,10 +18,13 @@ usage: qjs [options] [file [args]]
 -m  --module       load as ES6 module (default=autodetect)
     --script       load as ES6 script (default=autodetect)
 -I  --include file include an additional file
-    --std          make 'std' and 'os' available to the loaded script
+    --std          make 'std', 'os' and 'bjson' available to script
 -T  --trace        trace memory allocation
 -d  --dump         dump the memory usage stats
 -D  --dump-flags   flags for dumping debug data (see DUMP_* defines)
+-c  --compile FILE compile the given JS file as a standalone executable
+-o  --out FILE     output file for standalone executables
+    --exe          select the executable to use as the base, defaults to the current one
     --memory-limit n       limit the memory usage to 'n' Kbytes
     --stack-size n         limit the stack size to 'n' Kbytes
     --unhandled-rejection  dump unhandled promise rejections
@@ -52,6 +55,37 @@ DUMP_ATOMS         0x40000  /* dump atoms in JS_FreeRuntime */
 DUMP_SHAPES        0x80000  /* dump shapes in JS_FreeRuntime */
 ```
 
+### Creating standalone executables
+
+With the `qjs` CLI it's possible to create standalone executables that will bundle the given JavaScript file
+alongside the binary.
+
+```
+$ qjs -c app.js -o app --exe qjs
+```
+
+The resulting `app` binary will have the same runtime dependencies as the `qjs` binary. This is acomplished
+by compiling the target JavaScript file to bytecode and adding it a copy of the executable, with a little
+trailer to help locate it.
+
+Rather than using the current executable, it's possible to use the `--exe` switch to create standalone
+executables for other platforms.
+
+No JavaScript bundling is performed, the specified JS file cannot depend on other files. A bundler such
+as `esbuild` can be used to generate an app bundle which can then be turned into the executable.
+
+```
+npx esbuild my-app/index.js \
+    --bundle \
+    --outfile=app.js \
+    --external:qjs:* \
+    --minify \
+    --target=es2023 \
+    --platform=neutral \
+    --format=esm \
+    --main-fields=main,module
+```
+
 ## `qjsc` - The QuickJS JavaScript compiler
 
 The `qjsc` executable runs the JavaScript compiler, it can generate bytecode from