spack: no stacktrace if not in debug mode + fix emacs variant (#4098)

* spack: no stacktrace if not in debug mode + fix emacs variant

* emacs: removed dead code

1 files changed, 2 insertions, 2 deletions

diff --git a/lib/spack/spack/variant.py b/lib/spack/spack/variant.py
index 7102676b69..2d02ab1253 100644
--- a/lib/spack/spack/variant.py
+++ b/lib/spack/spack/variant.py
@@ -389,9 +389,9 @@ class BoolValuedVariant(SingleValuedVariant):
             self._original_value = value
             self._value = False
         else:
-            msg = 'cannot construct a BoolValuedVariant from '
+            msg = 'cannot construct a BoolValuedVariant for "{0}" from '
             msg += 'a value that does not represent a bool'
-            raise ValueError(msg)
+            raise ValueError(msg.format(self.name))
 
     def __contains__(self, item):
         return item is self.value