Fix sysroot installation when emscripten itself is read-only

test/test_sanity.py

@@ -7,6 +7,7 @@
 import os
 import platform
 import shutil
+import stat
 import time
 import re
 import tempfile
@@ -35,6 +36,14 @@ def restore():
   shutil.copyfile(EM_CONFIG + '_backup', EM_CONFIG)
 
 
+def for_all_files(dir, callback):
+  for root, dirs, files in os.walk(dir):
+    for d in dirs:
+      callback(os.path.join(dir, root, d))
+    for f in files:
+      callback(os.path.join(dir, root, f))
+
+
 # restore the config file and set it up for our uses
 def restore_and_set_up():
   restore()
@@ -460,6 +469,23 @@ def test_emcc_multiprocess_cache_access(self):
     # Exactly one child process should have triggered libc build!
     self.assertEqual(num_times_libc_was_built, 1)
 
+  # Test that sysroot headers can be installed from a read-only
+  # emscripten tree.
+  def test_readonly_sysroot_install(self):
+    restore_and_set_up()
+
+    def make_readonly(filename):
+      old_mode = stat.S_IMODE(os.stat(filename).st_mode)
+      os.chmod(filename, old_mode & ~(stat.S_IWUSR | stat.S_IWGRP | stat.S_IWOTH))
+
+    try:
+      for_all_files(path_from_root('system/include'), make_readonly)
+
+      with env_modify({'EM_CACHE': self.in_dir('test_cache')}):
+        self.run_process([EMCC, test_file('hello_world.c'), '-c'])
+    finally:
+      for_all_files(path_from_root('system/include'), shared.make_writable)
+
   @parameterized({
     '': [False, False],
     'response_files': [True, False],

tools/shared.py

@@ -694,7 +694,7 @@ def get_file_suffix(filename):
 
 
 def make_writable(filename):
-  assert os.path.isfile(filename)
+  assert os.path.exists(filename)
   old_mode = stat.S_IMODE(os.stat(filename).st_mode)
   os.chmod(filename, old_mode | stat.S_IWUSR)
 

tools/system_libs.py

@@ -2453,8 +2453,21 @@ def calculate(options):
   return ret
 
 
-def copytree_exist_ok(src, dst):
-  shutil.copytree(src, dst, dirs_exist_ok=True)
+def safe_copytree(src, dst):
+  # We cannot use `shutil.copytree` there because we need to ensure the
+  # output tree is writable, and in some cases the emscripten tree
+  # itself is readonly (e.g. NixOS).
+  # Even if we pass copy_function=safe_copy python's `shutil.copytree`
+  # will use its internal logic for copying directories and it will
+  # unconditionally copy the source directory's mode bits.
+  os.makedirs(dst, exist_ok=True)
+  for entry in os.scandir(src):
+    srcname = os.path.join(src, entry.name)
+    dstname = os.path.join(dst, entry.name)
+    if entry.is_dir():
+      safe_copytree(srcname, dstname)
+    else:
+      shared.safe_copy(srcname, dstname)
 
 
 def install_system_headers(stamp):
@@ -2477,15 +2490,15 @@ def install_system_headers(stamp):
   for src, dest in install_dirs.items():
     src = utils.path_from_root('system', *src)
     dest = os.path.join(target_include_dir, dest)
-    copytree_exist_ok(src, dest)
+    safe_copytree(src, dest)
 
   pkgconfig_src = utils.path_from_root('system/lib/pkgconfig')
   pkgconfig_dest = cache.get_sysroot_dir('lib/pkgconfig')
-  copytree_exist_ok(pkgconfig_src, pkgconfig_dest)
+  safe_copytree(pkgconfig_src, pkgconfig_dest)
 
   bin_src = utils.path_from_root('system/bin')
   bin_dest = cache.get_sysroot_dir('bin')
-  copytree_exist_ok(bin_src, bin_dest)
+  safe_copytree(bin_src, bin_dest)
 
   # Create a version header based on the emscripten-version.txt
   version_file = cache.get_include_dir('emscripten/version.h')