Fix an issue if user passes a relative path to Python, and some system cache libraries need rebuilding. Emcc tool would spawn sub-emcc tools to rebuild the cache, with different CWD, resulting in the relative path lookups pointing to the wrong relative directories. To fix the issue, normalize the relative tool paths first.

Author: juj

test/test_sanity.py

@@ -846,3 +846,26 @@ def test_bootstrap_without_em_config(self):
 
     # Running bootstrap.py should not fail
     self.run_process([utils.exe_path_from_root('bootstrap')], env=env)
+
+  # Verify that if user specifies a relative path to Python executable, then
+  # Emscripten is still able to build.
+  def test_emcc_with_relative_python_path(self):
+    restore_and_set_up()
+    # Clear the cache, since rebuilding the cache has been observed to fail
+    # if Python path is specified as relative.
+    self.clear_cache()
+
+    try:
+      relative_python = os.path.relpath(os.environ.get('EMSDK_PYTHON'), os.getcwd())
+    except ValueError:
+      self.skipTest('Python and Emscripten are located on different drives, cannot run this test.')
+
+    relative_python_escaped = relative_python.replace("\\", "\\\\")
+    add_to_config(f'PYTHON = "{relative_python_escaped}"')
+
+    env = os.environ.copy()
+    env['EMSDK_PYTHON'] = relative_python
+
+    output = self.do([EMCC, test_file('hello_world.c')], env=env)
+    self.assertNotContained('error', output)
+    self.assertExists('a.out.js')

tools/config.py

@@ -74,6 +74,23 @@ def normalize_config_settings():
     PORTS = os.path.join(CACHE, 'ports')
 
 
+def normalize_relative_environment_variables():
+  # User may have specified environment variables to point to the location
+  # of e.g. Python or Node, like with
+  #
+  #  EMSDK_PYTHON=../../path/to/python emcc test/hello_world.c
+  #
+  # As part of its operation, emcc may spawn sub-emcc tasks when building
+  # libraries to cache. These sub-emcc tasks may run in a different CWD, so
+  # normalize the path directives to current environment here, so that any
+  # sub-tool spawns will see the path to the tool from the parent process.
+  # However, be careful not to normalize e.g. 'python' or other PATH lookups.
+  for env_var in {'EMSDK_PYTHON', 'NODE_JS'}:
+    path = os.environ.get(env_var)
+    if path and ('\\' in path or '/' in path):
+      os.environ[env_var] = os.path.abspath(os.environ[env_var])
+
+
 def set_config_from_tool_location(config_key, tool_binary, f):
   val = globals()[config_key]
   if val is None:
@@ -168,6 +185,7 @@ def read_config():
   set_config_from_tool_location('BINARYEN_ROOT', 'wasm-opt', lambda x: os.path.dirname(os.path.dirname(x)))
 
   normalize_config_settings()
+  normalize_relative_environment_variables()
 
 
 def generate_config(path):