[3.14] gh-127146: Emscripten: Make os.umask() actually work (GH-136706) (#136711)

Provide a stub implementation of umask that is enough to get some tests passing.
More work is needed upstream in Emscripten to make all umask tests to pass.
(cherry picked from commit 12e52ca)

Co-authored-by: Hood Chatham <[email protected]>

Author: miss-islington

Lib/test/test_os.py

@@ -1918,11 +1918,9 @@ def test_makedir(self):
         support.is_wasi,
         "WASI's umask is a stub."
     )
-    @unittest.skipIf(
-        support.is_emscripten,
-        "TODO: Fails in buildbot; see #135783"
-    )
     def test_mode(self):
+        # Note: in some cases, the umask might already be 2 in which case this
+        # will pass even if os.umask is actually broken.
         with os_helper.temp_umask(0o002):
             base = os_helper.TESTFN
             parent = os.path.join(base, 'dir1')

Python/emscripten_syscalls.c

@@ -7,7 +7,7 @@
 // defined with weak linkage so we can override it.
 EM_JS(int, __syscall_getuid32_js, (void), {
     // If we're in node and we can, report the native uid
-    if (typeof process !== "undefined" && typeof process.getuid === "function") {
+    if (ENVIRONMENT_IS_NODE) {
         return process.getuid();
     }
     // Fall back to the stub case of returning 0.
@@ -17,3 +17,23 @@ EM_JS(int, __syscall_getuid32_js, (void), {
 int __syscall_getuid32(void) {
     return __syscall_getuid32_js();
 }
+
+EM_JS(int, __syscall_umask_js, (int mask), {
+    // If we're in node and we can, call native process.umask()
+    if (ENVIRONMENT_IS_NODE) {
+        try {
+            return process.umask(mask);
+        } catch(e) {
+            // oops...
+            // NodeJS docs: "In Worker threads, process.umask(mask) will throw an exception."
+            // umask docs: "This system call always succeeds"
+            return 0;
+        }
+    }
+    // Fall back to the stub case of returning 0.
+    return 0;
+})
+
+int __syscall_umask(int mask) {
+    return __syscall_umask_js(mask);
+}