3 files changed, 24 insertions, 2 deletions
diff --git a/lib/spack/docs/packaging_guide.rst b/lib/spack/docs/packaging_guide.rst
index c1077e4497..519c0da232 100644
--- a/lib/spack/docs/packaging_guide.rst
+++ b/lib/spack/docs/packaging_guide.rst
@@ -1844,6 +1844,20 @@ dedicated process.
 
 .. _prefix-objects:
 
+
+Failing the build
+----------------------
+
+Sometimes you don't want a package to successfully install unless some
+condition is true.  You can explicitly cause the build to fail from
+``install()`` by raising an ``InstallError``, for example:
+
+.. code-block:: python
+
+   if spec.architecture.startswith('darwin'):
+       raise InstallError('This package does not build on Mac OS X!')
+
+
 Prefix objects
 ----------------------
 
diff --git a/lib/spack/spack/__init__.py b/lib/spack/spack/__init__.py
index 0ba42bbbfc..aee11f061f 100644
--- a/lib/spack/spack/__init__.py
+++ b/lib/spack/spack/__init__.py
@@ -189,5 +189,9 @@ import spack.util.executable
 from spack.util.executable import *
 __all__ += spack.util.executable.__all__
 
-from spack.package import install_dependency_symlinks, flatten_dependencies, DependencyConflictError
-__all__ += ['install_dependency_symlinks', 'flatten_dependencies', 'DependencyConflictError']
+from spack.package import \
+    install_dependency_symlinks, flatten_dependencies, DependencyConflictError, \
+    InstallError, ExternalPackageError
+__all__ += [
+    'install_dependency_symlinks', 'flatten_dependencies', 'DependencyConflictError',
+    'InstallError', 'ExternalPackageError']
diff --git a/lib/spack/spack/package.py b/lib/spack/spack/package.py
index b488e4c49d..dafad0b184 100644
--- a/lib/spack/spack/package.py
+++ b/lib/spack/spack/package.py
@@ -1351,6 +1351,10 @@ class InstallError(spack.error.SpackError):
         super(InstallError, self).__init__(message, long_msg)
 
 
+class ExternalPackageError(InstallError):
+    """Raised by install() when a package is only for external use."""
+
+
 class PackageStillNeededError(InstallError):
     """Raised when package is still needed by another on uninstall."""
     def __init__(self, spec, dependents):