Use $CFGDIR in generated .emscripten for emscripten 6.0.4+

For emscripten version 6.0.4 and above, update the generated
`.emscripten` config file to use `$CFGDIR` directly in config
path strings instead of including `import os` and constructing
paths dynamically with `emsdk_path`.

Older versions of emscripten (< 6.0.4) will continue to generate
and use the legacy config format.

emsdk.py

diff --git a/emsdk.py b/emsdk.py
index 512ea3f..71031fd 100644
--- a/emsdk.py
+++ b/emsdk.py
@@ -1784,8 +1784,17 @@
 
 
 def generate_em_config(active_tools, permanently_activate, system):
-  cfg = 'import os\n'
-  cfg += "emsdk_path = os.path.dirname(os.getenv('EM_CONFIG')).replace('\\\\', '/')\n"
+  emroot = find_emscripten_root(active_tools)
+  version = None
+  if emroot and os.path.exists(os.path.join(emroot, 'emscripten-version.txt')):
+    version = parse_emscripten_version(emroot)
+
+  supports_cfgdir = version and version >= [6, 0, 4]
+
+  cfg = ''
+  if not supports_cfgdir:
+    cfg += 'import os\n'
+    cfg += "emsdk_path = os.path.dirname(os.getenv('EM_CONFIG')).replace('\\\\', '/')\n"
 
   # Different tools may provide the same activated configs; the latest to be
   # activated is the relevant one.
@@ -1806,9 +1815,7 @@
     else:
       cfg += f"{name} = '{value}'\n"
 
-  emroot = find_emscripten_root(active_tools)
-  if emroot:
-    version = parse_emscripten_version(emroot)
+  if version:
     # Older emscripten versions of emscripten depend on certain config
     # keys that are no longer used.
     # See https://github.com/emscripten-core/emscripten/pull/9469
@@ -1818,7 +1825,10 @@
     if version < [1, 38, 48]:
       cfg += 'JS_ENGINES = [NODE_JS]\n'
 
-  cfg = cfg.replace("'" + EMSDK_PATH, "emsdk_path + '")
+  if supports_cfgdir:
+    cfg = cfg.replace(EMSDK_PATH, '$CFGDIR')
+  else:
+    cfg = cfg.replace("'" + EMSDK_PATH, "emsdk_path + '")
 
   if os.path.exists(EM_CONFIG_PATH):
     backup_path = EM_CONFIG_PATH + ".old"
@@ -2087,7 +2097,7 @@
 
       # all paths are stored dynamically relative to the emsdk root, so
       # normalize those first.
-      config_value = EM_CONFIG_DICT[key].replace("emsdk_path + '", "'" + EMSDK_PATH)
+      config_value = EM_CONFIG_DICT[key].replace("emsdk_path + '", "'" + EMSDK_PATH).replace("$CFGDIR", EMSDK_PATH)
       config_value = config_value.strip("'")
       if config_value != value:
         debug_print(f'{self} is not active, because key="{key}" has value "{config_value}" but should have value "{value}"')
@@ -2356,8 +2366,16 @@
   version_file = os.path.join(emscripten_root, 'emscripten-version.txt')
   with open(version_file) as f:
     version = f.read().strip()
-    version = version.strip('"').split('-')[0].split('.')
-    return [int(v) for v in version]
+  version = version.strip('"')
+  suffix = None
+  if '-' in version:
+    version, suffix = version.split('-')
+  version = [int(v) for v in version.split('.')]
+  if suffix == 'git':
+    # Treat 1.2.3-git as 1.2.2 since it doesn't contain all the changes
+    # present in the final 1.2.3 release.
+    version[-1] -= 1
+  return version
 
 
 def get_emscripten_release_version(emscripten_releases_hash):

test/test.py

diff --git a/test/test.py b/test/test.py
index 3f22829..73a1365 100755
--- a/test/test.py
+++ b/test/test.py
@@ -223,9 +223,37 @@
 
   def test_config_contents(self):
     print('test .emscripten contents')
+    run_emsdk('install 6.0.3')
+    run_emsdk('activate 6.0.3')
     with open(emconfig) as f:
       config = f.read()
-    assert 'upstream' in config
+    self.assertIn('upstream', config)
+
+    # Older version of emscripten (prior to 6.0.3) don't support $CFGDIR
+    self.assertIn('import os', config)
+    self.assertIn('emsdk_path + ', config)
+    self.assertNotIn('$CFGDIR', config)
+
+    # For newer versions we use $CFGDIR
+    version_file = os.path.join('upstream', 'emscripten', 'emscripten-version.txt')
+    with open(version_file) as f:
+      old_ver = f.read()
+    try:
+      # Hack the version file to contain 6.0.4
+      with open(version_file, 'w') as f:
+        f.write('6.0.4\n')
+      # Re-activate 6.0.3 but with the hacked version file which makes it
+      # appear to contain 6.0.4.
+      run_emsdk('activate 6.0.3')
+      with open(emconfig) as f:
+        config = f.read()
+      self.assertNotIn('import os', config)
+      self.assertNotIn('emsdk_path', config)
+      self.assertIn('$CFGDIR', config)
+    finally:
+      with open(version_file, 'w') as f:
+        f.write(old_ver)
+      run_emsdk('activate 6.0.3')
 
   def test_lib_building(self):
     print('building proper system libraries')