bug 1241272 - Allow error() in moz.build files to be treated as non-fatal. r=gps

Calling error() in moz.build files to indicate unsupported configurations is
useful, but readers using EmptyConfig will trigger them currently. This patch
allows a Config to have an `error_is_fatal` attribute, which will make
error emit a warning instead.

python/mozbuild/mozbuild/frontend/context.py

@@ -128,6 +128,11 @@ class Context(KeyedDefaultDict):
         if path not in self._all_paths:
             self._all_paths.insert(0, path)
 
+    @property
+    def error_is_fatal(self):
+        """Returns True if the error function should be fatal."""
+        return self.config and getattr(self.config, 'error_is_fatal', True)
+
     @property
     def all_paths(self):
         """Returns all paths ever added to the context."""

python/mozbuild/mozbuild/frontend/reader.py

@@ -134,6 +134,7 @@ class EmptyConfig(object):
         self.substs_unicode = self.PopulateOnGetDict(EmptyValue, udict)
         self.defines = self.substs
         self.external_source_dir = None
+        self.error_is_fatal = False
 
 
 def is_read_allowed(path, config):
@@ -325,7 +326,10 @@ class MozbuildSandbox(Sandbox):
         print('WARNING: %s' % message, file=sys.stderr)
 
     def _error(self, message):
-        raise SandboxCalledError(self._context.source_stack, message)
+        if self._context.error_is_fatal:
+            raise SandboxCalledError(self._context.source_stack, message)
+        else:
+            self._warning(message)
 
     def _template_decorator(self, func):
         """Registers a template function."""

python/mozbuild/mozbuild/test/common.py

@@ -18,7 +18,11 @@ log_manager.add_terminal_logging()
 # mozconfig is not a reusable type (it's actually a module) so, we
 # have to mock it.
 class MockConfig(object):
-    def __init__(self, topsrcdir='/path/to/topsrcdir', extra_substs={}):
+    def __init__(self,
+                 topsrcdir='/path/to/topsrcdir',
+                 extra_substs={},
+                 error_is_fatal=True,
+             ):
         self.topsrcdir = mozpath.abspath(topsrcdir)
         self.topobjdir = mozpath.abspath('/path/to/topobjdir')
 
@@ -41,3 +45,4 @@ class MockConfig(object):
         self.import_suffix = '.so'
         self.dll_prefix = 'lib'
         self.dll_suffix = '.so'
+        self.error_is_fatal = error_is_fatal

python/mozbuild/mozbuild/test/frontend/test_reader.py

@@ -42,11 +42,13 @@ class TestBuildReader(unittest.TestCase):
 
         return MockConfig(path, **kwargs)
 
-    def reader(self, name, enable_tests=False, **kwargs):
+    def reader(self, name, enable_tests=False, error_is_fatal=True, **kwargs):
         extra = {}
         if enable_tests:
             extra['ENABLE_TESTS'] = '1'
-        config = self.config(name, extra_substs=extra)
+        config = self.config(name,
+                             extra_substs=extra,
+                             error_is_fatal=error_is_fatal)
 
         return BuildReader(config, **kwargs)
 
@@ -239,6 +241,11 @@ class TestBuildReader(unittest.TestCase):
         self.assertIn('A moz.build file called the error() function.', str(e))
         self.assertIn('    Some error.', str(e))
 
+    def test_error_error_func_ok(self):
+        reader = self.reader('reader-error-error-func', error_is_fatal=False)
+
+        contexts = list(reader.read_topsrcdir())
+
     def test_inheriting_variables(self):
         reader = self.reader('inheriting-variables')