From 7d3c724665943fac539bc76381a937f4a6adec84 Mon Sep 17 00:00:00 2001
From: Kyle Cutler <67761731+kycutler@users.noreply.github.com>
Date: Thu, 19 May 2022 11:02:52 -0700
Subject: [PATCH] Export PATH and ERRNO_CODES from Emscripten (#2582)

BrowserFS can mount custom filesystems into Emscripten.
However it requires the PATH and ERRNO_CODES exports from
Emscripten in addition to FS.

This exports `PATH` and `ERRNO_CODES` from `Module` into the `pyodide`
Javascript API so they can be used with BrowserFS.
---
 Makefile.envs                              |  3 ++-
 docs/project/changelog.md                  |  3 +++
 src/core/main.c                            |  7 -------
 src/core/post.js                           |  5 +++++
 src/js/api.ts                              | 20 ++++++++++++++++++++
 src/js/test/integration/filesystem.test.js | 21 +++++++++++++++++++++
 6 files changed, 51 insertions(+), 8 deletions(-)
 create mode 100644 src/core/post.js

diff --git a/Makefile.envs b/Makefile.envs
index f0241b915..8346e8b14 100644
--- a/Makefile.envs
+++ b/Makefile.envs
@@ -113,7 +113,8 @@ export MAIN_MODULE_LDFLAGS= $(LDFLAGS_BASE) \
 	--exclude-file "*/tests/*" \
 	--exclude-file "*/distutils/*" \
 	--pre-js src/core/pre.js \
-	--pre-js src/js/_pyodide.out.js
+	--pre-js src/js/_pyodide.out.js \
+	--post-js src/core/post.js
 
 
 export SIDE_MODULE_CXXFLAGS = $(CXXFLAGS_BASE)
diff --git a/docs/project/changelog.md b/docs/project/changelog.md
index 964d8faaa..1e45e939a 100644
--- a/docs/project/changelog.md
+++ b/docs/project/changelog.md
@@ -86,6 +86,9 @@ substitutions:
   `clear_interval`, `add_event_listener` and `remove_event_listener` for the corresponding JavaScript functions.
   {pr}`2456`
 
+- {{ Enhancement }} Pyodide now directly exposes the Emscripten `PATH` and `ERRNO_CODES` APIs.
+  {pr}`2582`
+
 ### micropip
 
 - {{ Fix }} micropip now correctly handles package names that include dashes
diff --git a/src/core/main.c b/src/core/main.c
index b3fc51c62..e42bd350a 100644
--- a/src/core/main.c
+++ b/src/core/main.c
@@ -90,13 +90,6 @@ static struct PyModuleDef core_module_def = {
 int
 main(int argc, char** argv)
 {
-  EM_ASM({
-    // For some reason emscripten doesn't make UTF8ToString available on Module
-    // by default...
-    Module.UTF8ToString = UTF8ToString;
-    Module.wasmTable = wasmTable;
-  });
-
   // This exits and prints a message to stderr on failure,
   // no status code to check.
   initialize_python();
diff --git a/src/core/post.js b/src/core/post.js
new file mode 100644
index 000000000..021555cfd
--- /dev/null
+++ b/src/core/post.js
@@ -0,0 +1,5 @@
+// Emscripten doesn't make UTF8ToString or wasmTable available on Module by default...
+Module.UTF8ToString = UTF8ToString;
+Module.wasmTable = wasmTable;
+// Emscripten has a bug where it accidentally exposes an empty object as Module.ERRNO_CODES
+Module.ERRNO_CODES = ERRNO_CODES;
diff --git a/src/js/api.ts b/src/js/api.ts
index 000510104..f549e598a 100644
--- a/src/js/api.ts
+++ b/src/js/api.ts
@@ -449,6 +449,8 @@ export function checkInterrupt() {
 export type PyodideInterface = {
   globals: typeof globals;
   FS: typeof FS;
+  PATH: typeof PATH;
+  ERRNO_CODES: typeof ERRNO_CODES;
   pyodide_py: typeof pyodide_py;
   version: typeof version;
   loadPackage: typeof loadPackage;
@@ -486,14 +488,32 @@ export type PyodideInterface = {
  */
 export let FS: any;
 
+/**
+ * An alias to the `Emscripten Path API
+ * <https://github.com/emscripten-core/emscripten/blob/main/src/library_path.js>`_.
+ *
+ * This provides a variety of operations for working with file system paths, such as
+ * ``dirname``, ``normalize``, and ``splitPath``.
+ */
+export let PATH: any;
+
+/**
+ * An alias to the Emscripten ERRNO_CODES map of standard error codes.
+ */
+export let ERRNO_CODES: any;
+
 /**
  * @private
  */
 API.makePublicAPI = function (): PyodideInterface {
   FS = Module.FS;
+  PATH = Module.PATH;
+  ERRNO_CODES = Module.ERRNO_CODES;
   let namespace = {
     globals,
     FS,
+    PATH,
+    ERRNO_CODES,
     pyodide_py,
     version,
     loadPackage,
diff --git a/src/js/test/integration/filesystem.test.js b/src/js/test/integration/filesystem.test.js
index 50a97c6be..a0c82218a 100644
--- a/src/js/test/integration/filesystem.test.js
+++ b/src/js/test/integration/filesystem.test.js
@@ -25,3 +25,24 @@ describe("FS", () => {
     chai.assert.isTrue(result);
   });
 });
+
+describe("PATH", () => {
+  it("exists", async () => {
+    chai.assert.exists(pyodide.PATH);
+  });
+  it("has expected keys", async () => {
+    chai.assert.exists(pyodide.PATH.dirname);
+    chai.assert.exists(pyodide.PATH.normalize);
+  });
+});
+
+describe("ERRNO_CODES", () => {
+  it("exists", async () => {
+    chai.assert.exists(pyodide.ERRNO_CODES);
+  });
+  it("has expected keys", async () => {
+    chai.assert.exists(pyodide.ERRNO_CODES.ENOENT);
+    chai.assert.exists(pyodide.ERRNO_CODES.EPERM);
+    chai.assert.exists(pyodide.ERRNO_CODES.EEXIST);
+  });
+});