1 files changed, 151 insertions, 0 deletions
diff --git a/python/mozbuild/mozpack/errors.py b/python/mozbuild/mozpack/errors.py
new file mode 100644
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+++ b/python/mozbuild/mozpack/errors.py
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+# This Source Code Form is subject to the terms of the Mozilla Public
+# License, v. 2.0. If a copy of the MPL was not distributed with this
+# file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
+import sys
+from contextlib import contextmanager
+
+
+class ErrorMessage(Exception):
+    """Exception type raised from errors.error() and errors.fatal()"""
+
+
+class AccumulatedErrors(Exception):
+    """Exception type raised from errors.accumulate()"""
+
+
+class ErrorCollector(object):
+    """
+    Error handling/logging class. A global instance, errors, is provided for
+    convenience.
+
+    Warnings, errors and fatal errors may be logged by calls to the following
+    functions:
+      - errors.warn(message)
+      - errors.error(message)
+      - errors.fatal(message)
+
+    Warnings only send the message on the logging output, while errors and
+    fatal errors send the message and throw an ErrorMessage exception. The
+    exception, however, may be deferred. See further below.
+
+    Errors may be ignored by calling:
+      - errors.ignore_errors()
+
+    After calling that function, only fatal errors throw an exception.
+
+    The warnings, errors or fatal errors messages may be augmented with context
+    information when a context is provided. Context is defined by a pair
+    (filename, linenumber), and may be set with errors.context() used as a
+
+    context manager:
+
+    .. code-block:: python
+
+        with errors.context(filename, linenumber):
+            errors.warn(message)
+
+    Arbitrary nesting is supported, both for errors.context calls:
+
+    .. code-block:: python
+
+        with errors.context(filename1, linenumber1):
+            errors.warn(message)
+            with errors.context(filename2, linenumber2):
+                errors.warn(message)
+
+    as well as for function calls:
+
+    .. code-block:: python
+
+        def func():
+            errors.warn(message)
+            with errors.context(filename, linenumber):
+                func()
+
+    Errors and fatal errors can have their exception thrown at a later time,
+    allowing for several different errors to be reported at once before
+    throwing. This is achieved with errors.accumulate() as a context manager:
+
+    .. code-block:: python
+
+        with errors.accumulate():
+            if test1:
+                errors.error(message1)
+            if test2:
+                errors.error(message2)
+
+    In such cases, a single AccumulatedErrors exception is thrown, but doesn't
+    contain information about the exceptions. The logged messages do.
+    """
+
+    out = sys.stderr
+    WARN = 1
+    ERROR = 2
+    FATAL = 3
+    _level = ERROR
+    _context = []
+    _count = None
+
+    def ignore_errors(self, ignore=True):
+        if ignore:
+            self._level = self.FATAL
+        else:
+            self._level = self.ERROR
+
+    def _full_message(self, level, msg):
+        if level >= self._level:
+            level = "error"
+        else:
+            level = "warning"
+        if self._context:
+            file, line = self._context[-1]
+            return "%s: %s:%d: %s" % (level, file, line, msg)
+        return "%s: %s" % (level, msg)
+
+    def _handle(self, level, msg):
+        msg = self._full_message(level, msg)
+        if level >= self._level:
+            if self._count is None:
+                raise ErrorMessage(msg)
+            self._count += 1
+        print(msg, file=self.out)
+
+    def fatal(self, msg):
+        self._handle(self.FATAL, msg)
+
+    def error(self, msg):
+        self._handle(self.ERROR, msg)
+
+    def warn(self, msg):
+        self._handle(self.WARN, msg)
+
+    def get_context(self):
+        if self._context:
+            return self._context[-1]
+
+    @contextmanager
+    def context(self, file, line):
+        if file and line:
+            self._context.append((file, line))
+        yield
+        if file and line:
+            self._context.pop()
+
+    @contextmanager
+    def accumulate(self):
+        assert self._count is None
+        self._count = 0
+        yield
+        count = self._count
+        self._count = None
+        if count:
+            raise AccumulatedErrors()
+
+    @property
+    def count(self):
+        # _count can be None.
+        return self._count if self._count else 0
+
+
+errors = ErrorCollector()