Refactoring: Move ElementError and SourceError to their respective classes, create SandboxError

These errors are a part of public facing API, and the exceptions
module contains a lot of internal details to be hidden from public API.

This move required creating SandboxError because sandbox related
code had previously been hijacking the ElementError and raising that.

6 files changed, 47 insertions, 40 deletions

diff --git a/buildstream/__init__.py b/buildstream/__init__.py
index f8a2db354..3d800610e 100644
--- a/buildstream/__init__.py
+++ b/buildstream/__init__.py
@@ -20,7 +20,7 @@
 
 # Exceptions and utilities first
 from .exceptions import PluginError, LoadError, LoadErrorReason, \
-    SourceError, ElementError, ImplError, ProgramNotFoundError, PlatformError
+    ImplError, ProgramNotFoundError, PlatformError, SandboxError
 
 # Core components
 from .context import Context
@@ -29,7 +29,7 @@ from .sandbox import Sandbox, SandboxFlags
 
 # Plugin auther facing APIs
 from .plugin import Plugin
-from .source import Source, Consistency
-from .element import Element, Scope
+from .source import Source, SourceError, Consistency
+from .element import Element, ElementError, Scope
 from .buildelement import BuildElement
 from .scriptelement import ScriptElement
diff --git a/buildstream/element.py b/buildstream/element.py
index 7c1da4b5f..0c121cd1c 100644
--- a/buildstream/element.py
+++ b/buildstream/element.py
@@ -38,7 +38,7 @@ import shutil
 from . import _yaml
 from ._variables import Variables
 from .exceptions import _BstError, _ArtifactError
-from . import LoadError, LoadErrorReason, ElementError, ImplError
+from . import LoadError, LoadErrorReason, ImplError
 from . import Plugin, Consistency
 from .project import BST_ARTIFACT_VERSION as BST_CORE_ARTIFACT_VERSION
 from . import SandboxFlags
@@ -48,6 +48,21 @@ from . import _site
 from ._platform import Platform
 
 
+# _KeyStrength():
+#
+# Strength of cache key
+#
+class _KeyStrength(Enum):
+
+    # Includes strong cache keys of all build dependencies and their
+    # runtime dependencies.
+    STRONG = 1
+
+    # Includes names of direct build dependencies but does not include
+    # cache keys of dependencies.
+    WEAK = 2
+
+
 class Scope(Enum):
     """Types of scope for a given element"""
 
@@ -67,18 +82,12 @@ class Scope(Enum):
     """
 
 
-class _KeyStrength(Enum):
-    """Strength of cache key"""
+class ElementError(_BstError):
+    """Raised by Element implementations.
 
-    STRONG = 1
-    """Includes strong cache keys of all build dependencies and their
-    runtime dependencies.
-    """
-
-    WEAK = 2
-    """Includes names of direct build dependencies but does not include
-    cache keys of dependencies.
+    This exception is raised when an :class:`.Element` encounters an error.
     """
+    pass
 
 
 class Element(Plugin):
diff --git a/buildstream/exceptions.py b/buildstream/exceptions.py
index 5a9cd455d..e896c0c20 100644
--- a/buildstream/exceptions.py
+++ b/buildstream/exceptions.py
@@ -125,22 +125,6 @@ class LoadError(_BstError):
         """
 
 
-class SourceError(_BstError):
-    """Raised by Source implementations.
-
-    This exception is raised when a :class:`.Source` encounters an error.
-    """
-    pass
-
-
-class ElementError(_BstError):
-    """Raised by Element implementations.
-
-    This exception is raised when an :class:`.Element` encounters an error.
-    """
-    pass
-
-
 class ImplError(_BstError):
     """Raised when a :class:`.Source` or :class:`.Element` plugin fails to
     implement a mandatory method"""
@@ -164,5 +148,10 @@ class PlatformError(_BstError):
     pass
 
 
+class SandboxError(_BstError):
+    """Raised when errors are encountered by the sandbox implementation"""
+    pass
+
+
 class _ArtifactError(_BstError):
     pass
diff --git a/buildstream/sandbox/_mount.py b/buildstream/sandbox/_mount.py
index 9b2c4cc1d..472534c9e 100644
--- a/buildstream/sandbox/_mount.py
+++ b/buildstream/sandbox/_mount.py
@@ -1,7 +1,7 @@
 import sys
 from contextlib import contextmanager
 
-from .. import ElementError
+from .. import SandboxError
 from .. import utils, _signals
 
 
@@ -32,7 +32,7 @@ class Mount(object):
         )
 
         if status != 0:
-            raise ElementError('`{}` failed with exit code {}'
+            raise SandboxError('`{}` failed with exit code {}'
                                .format(' '.join(argv), status))
 
         return dest
@@ -49,7 +49,7 @@ class Mount(object):
         )
 
         if status != 0:
-            raise ElementError('`{}` failed with exit code {}'
+            raise SandboxError('`{}` failed with exit code {}'
                                .format(' '.join(cmd), status))
 
     # mount()
diff --git a/buildstream/sandbox/_sandboxchroot.py b/buildstream/sandbox/_sandboxchroot.py
index de3220c22..b1c5997fa 100644
--- a/buildstream/sandbox/_sandboxchroot.py
+++ b/buildstream/sandbox/_sandboxchroot.py
@@ -27,7 +27,7 @@ import signal
 import subprocess
 from contextlib import contextmanager, ExitStack
 
-from .. import ElementError
+from .. import SandboxError
 from .. import utils
 from .. import _signals
 from ._mount import Mount
@@ -184,11 +184,11 @@ class SandboxChroot(Sandbox):
             # 'Exception occurred in preexec_fn', turn these into
             # a more readable message.
             if '{}'.format(e) == 'Exception occurred in preexec_fn.':
-                raise ElementError('Could not chroot into {} or chdir into {}. '
+                raise SandboxError('Could not chroot into {} or chdir into {}. '
                                    'Ensure you are root and that the relevant directory exists.'
                                    .format(rootfs, cwd)) from e
             else:
-                raise ElementError('Could not run command {}: {}'.format(command, e)) from e
+                raise SandboxError('Could not run command {}: {}'.format(command, e)) from e
 
         return code
 
@@ -219,7 +219,7 @@ class SandboxChroot(Sandbox):
                     devices.append(self.mknod(device, location))
                 except OSError as err:
                     if err.errno == 1:
-                        raise ElementError("Permission denied while creating device node: {}.".format(err) +
+                        raise SandboxError("Permission denied while creating device node: {}.".format(err) +
                                            "BuildStream reqiures root permissions for these setttings.")
                     else:
                         raise
@@ -307,10 +307,10 @@ class SandboxChroot(Sandbox):
             os.mknod(target, mode=stat.S_IFCHR | dev.st_mode, device=target_dev)
 
         except PermissionError as e:
-            raise ElementError('Could not create device {}, ensure that you have root permissions: {}')
+            raise SandboxError('Could not create device {}, ensure that you have root permissions: {}')
 
         except OSError as e:
-            raise ElementError('Could not create device {}: {}'
+            raise SandboxError('Could not create device {}: {}'
                                .format(target, e)) from e
 
         return target
diff --git a/buildstream/source.py b/buildstream/source.py
index 83386f45f..bab759989 100644
--- a/buildstream/source.py
+++ b/buildstream/source.py
@@ -28,7 +28,8 @@ import shutil
 from contextlib import contextmanager
 
 from . import _yaml, _signals, utils
-from . import ImplError, LoadError, LoadErrorReason, SourceError
+from .exceptions import _BstError
+from . import ImplError, LoadError, LoadErrorReason
 from . import Plugin
 
 
@@ -55,6 +56,14 @@ class Consistency():
     """
 
 
+class SourceError(_BstError):
+    """Raised by Source implementations.
+
+    This exception is raised when a :class:`.Source` encounters an error.
+    """
+    pass
+
+
 class Source(Plugin):
     """Source()