Figured out a way to override the MEMFS object through --js-library linking, and wrapped the Emscripten module in a function that can take arguments

Author: CMCDragonkai

README.md

@@ -28,19 +28,16 @@ emcc \
   -O2 \
   --bind \
   --memory-init-file 0 \
-  --pre-js ./prejs.js \
+  --pre-js ./pre.js \
+  --post-js ./post.js \
+  --js-library ./library_virtualfs.js \
   -s "EXTRA_EXPORTED_RUNTIME_METHODS=['FS']" \
-  -s FORCE_FILESYSTEM=1 \
   -s PRECISE_I64_MATH=1 \
   -s PRECISE_F32=1 \
   -s ASSERTIONS=2 \
-  libgit2_wrapper.bc \
-  libgit2.bc \
-  -o libgit2.js
+  ./libgit2_wrapper.bc \
+  ./libgit2.bc \
+  -o ./libgit2.js
 
-# require libgit2.js into VirtualGit.js module
-# expose a JS wrapper around functions and JS semantics
-# moduralize and export name may not actually work
-# the --memory-init-file=0 makes sure not to have a separate memory file
-# since this is not designed for browser usage, or well it's geared towards system usage anyway
-# libgit2.js would eventually be required by VirtualGit.js and then a proper cjs module and es6 module exposed here, which has to allow the insertion of the VirtualFS as a parameter from the outside
+// if the resulting js uses es6 modules
+// you need to use babel and rollup to use it

emscripten/build.sh

@@ -0,0 +1,19 @@
+// suppose this a thing to be linked over the MEMFS
+// so it overrides the MEMFS implementation
+// OH I GET IT
+// the resulting system evals this
+// modules.js EVALS this code
+// the mergeInto function is evaluated at compile time
+// this is evaluated at compile time
+// we can pass in JS code to be evaluated at program load time
+// or in this case LibGit call time
+// this will set the correct item?
+// but if staticInit is called first, then you have a problem, since that will try to initialise the fs with no memfs available?
+// ok this won't work cause the staticInit is called first before the $MEMFS__postset
+// so we cannot acquire the Module.libgit.virtualfs here
+
+mergeInto(LibraryManager.library, {
+  $MEMFS__deps: ['$FS'],
+  $MEMFS__postset: 'console.log("MEMFS POSTSET");',
+  $MEMFS: null
+});

emscripten/library_virtualfs.js

@@ -0,0 +1,8 @@
+  return Module;
+
+} // LibGit function footer
+
+module.exports = LibGit;
+
+// use this once we have babel + rollup working
+// exports default LibGit;

emscripten/post.js

@@ -0,0 +1,27 @@
+// vfs: VirtualFS instance
+// there may be other parameters to add in the future
+// like socket implementation (to deal with different underlying engine)
+function LibGit (vfs) { // LibGit function header
+
+  // this prevents explicit cjs exporting at shell.js
+  let module = undefined;
+
+  // we'll use a libgit namespace to avoid conflicts
+  var Module = {
+    thisProgram: 'virtualgit',
+    libgit: {
+      virtualfs: vfs
+    }
+  };
+
+  // things that change according to environment:
+  // so if we set environment to shell, which is the most generic environment
+  // these methods will need to be set
+  // print, printErr
+  // read
+  // readBinary
+  // arguments
+  // load
+  // readAsync
+  // thisProgram
+  // inspect