Provide support for '--ignore-pythranrc'

This should help reproducible builds.

Related to #2170

docs/CLI.rst

@@ -102,6 +102,7 @@ To know more options about Pythran, you can check::
                          compiler
     -U macro_definition  any macro undef relevant to the underlying C++ compiler
     --config config      config additional params
+    --ignore-pythranrc   ignore .pythranrc content
     -ftime-report        report time spent in each optimization/transformation
   
   It's a megablast!

docs/MANUAL.rst

@@ -559,7 +559,10 @@ For example::
 
 would specify that pythran-openblas is the blas library to use.
 
-Options specified using command-line arguments override the options found in the ``.pythranrc`` file
+Options specified using command-line arguments override the options found in the ``.pythranrc`` file.
+
+``--ignore-pythranrc`` can be passed down to ``pythran`` and ``pythran-config``
+to ignore this file, which helps for reproducible builds.
 
 
 ``[compiler]``

pythran/config.py

@@ -55,31 +55,55 @@ def get_paths_cfg(
         platform_config_path = os.path.join(sys_config_dir,
                                             "pythran-default.cfg")
 
-    user_config_path = os.environ.get('PYTHRANRC', None)
-    if not user_config_path:
-        user_config_dir = os.environ.get('XDG_CONFIG_HOME', None)
-        if not user_config_dir:
-            user_config_dir = os.environ.get('HOME', None)
-        if not user_config_dir:
-            user_config_dir = '~'
-        user_config_path = os.path.expanduser(
-            os.path.join(user_config_dir, user_file))
-    return {"sys": sys_config_path,
-            "platform": platform_config_path,
-            "user": user_config_path}
-
-
-def init_cfg(sys_file, platform_file, user_file, config_args=None):
+    paths = {"sys": sys_config_path,
+             "platform": platform_config_path}
+
+    if user_file:
+        user_config_path = os.environ.get('PYTHRANRC', None)
+        if not user_config_path:
+            user_config_dir = os.environ.get('XDG_CONFIG_HOME', None)
+            if not user_config_dir:
+                user_config_dir = os.environ.get('HOME', None)
+            if not user_config_dir:
+                user_config_dir = '~'
+            user_config_path = os.path.expanduser(
+                os.path.join(user_config_dir, user_file))
+        paths["user"] = user_config_path
+
+    return paths
+
+
+class UninitializedConfig:
+    pass
+
+
+cfg = UninitializedConfig
+
+
+def init_cfg(ignore_userfile=False):
+    global cfg
+    if cfg is not UninitializedConfig:
+        return cfg
+
+    # load platform specific configuration then user configuration
+    cfg = _init_cfg('pythran.cfg',
+                    'pythran-{}.cfg'.format(sys.platform),
+                    None if ignore_userfile else '.pythranrc')
+    return cfg
+
+def _init_cfg(sys_file, platform_file, user_file, config_args=None):
     paths = get_paths_cfg(sys_file, platform_file, user_file)
 
     sys_config_path = paths["sys"]
     platform_config_path = paths["platform"]
-    user_config_path = paths["user"]
+    user_config_path = paths.get("user")
 
     cfgp = ConfigParser()
     for required in (sys_config_path, platform_config_path):
         cfgp.read([required])
-    cfgp.read([user_config_path])
+
+    if user_config_path:
+        cfgp.read([user_config_path])
 
     if config_args is not None:
         update_cfg(cfgp, config_args)
@@ -111,6 +135,8 @@ def lint_cfg(cfgp, **paths):
 
     # Check if pythran configuration files exists
     for loc, path in paths.items():
+        if path is None:
+            continue
         exists = os.path.exists(path)
 
         msg = " ".join([
@@ -120,6 +146,10 @@ def lint_cfg(cfgp, **paths):
         ])
         logger.info(msg) if exists else logger.warning(msg)
 
+    user_config_path = paths.get("user")
+    if user_config_path:
+        cfgp_ref.read(user_config_path)
+
     for section in cfgp.sections():
         # Check if section in the current configuration exists in the
         # reference configuration
@@ -150,10 +180,10 @@ def lint_cfg(cfgp, **paths):
 
 def make_extension(python, **extra):
     # load platform specific configuration then user configuration
-    cfg = init_cfg('pythran.cfg',
-                   'pythran-{}.cfg'.format(sys.platform),
-                   '.pythranrc',
-                   extra.get('config', None))
+    cfg = _init_cfg('pythran.cfg',
+                    'pythran-{}.cfg'.format(sys.platform),
+                    None if extra.get('ignore_pythranrc') else '.pythranrc',
+                    extra.get('config', None))
 
     if 'config' in extra:
         extra.pop('config')
@@ -279,16 +309,13 @@ def compiler():
     Returns None if none is set or if it's set to the empty string
 
     """
+    init_cfg()
     cfg_cxx = str(cfg.get('compiler', 'CXX'))
     if not cfg_cxx:
         cfg_cxx = None
     return os.environ.get('CXX', cfg_cxx) or None
 
 
-# load platform specific configuration then user configuration
-cfg = init_cfg('pythran.cfg',
-               'pythran-{}.cfg'.format(sys.platform),
-               '.pythranrc')
 
 
 def run():
@@ -319,6 +346,10 @@ def run():
     parser.add_argument('--no-python', action='store_true',
                         help='do not include Python-related flags')
 
+    parser.add_argument('--ignore-pythranrc', dest='ignore_pythranrc',
+                        action='store_true',
+                        help='ignore .pythranrc content')
+
     parser.add_argument('--verbose', '-v', action='count', default=0,
                         help=(
                             'verbose mode: [-v] prints warnings if pythranrc '

pythran/run.py

@@ -123,6 +123,10 @@ def run():
                         help='config additional params',
                         default=list())
 
+    parser.add_argument('--ignore-pythranrc', dest='ignore_pythranrc',
+                        action='store_true',
+                        help='ignore .pythranrc content')
+
     parser.add_argument('-ftime-report', dest='report_times',
                         action='store_true',
                         help='report time spent in each optimization/transformation')
@@ -146,6 +150,9 @@ def run():
     if args.warn_off:
         logger.setLevel(logging.ERROR)
 
+
+    pythran.config.init_cfg(args.ignore_pythranrc)
+
     if args.config:
         pythran.config.update_cfg(pythran.config.cfg, args.config)