SV variants are evaluated correctly in "when=" (#4118)

* SV variants are evaluated correctly in `when=` statements fixes #4113

The problem here was tricky:
```python
spec.satisfies(other)
```
changes already the MV variants in others into SV variants (where
necessary) if spec is concrete. If it is not concrete it does
nothing because we may be acting at a pure syntactical level.

When evaluating a `when=` keyword spec is for sure not concrete
as it is in the middle of the concretization process. In this case we
have to trigger manually the substitution in other to not end up
comparing a MV variant "foo=bar" to a SV variant "foo=bar" and having
False in return. Which is wrong.

* sv variants: improved error message for typos in "when=" statements

1 files changed, 2 insertions, 0 deletions

diff --git a/var/spack/repos/builtin.mock/packages/a/package.py b/var/spack/repos/builtin.mock/packages/a/package.py
index b697f4d2a9..e39ad13bd1 100644
--- a/var/spack/repos/builtin.mock/packages/a/package.py
+++ b/var/spack/repos/builtin.mock/packages/a/package.py
@@ -49,6 +49,8 @@ class A(AutotoolsPackage):
         multi=False
     )
 
+    depends_on('b', when='foobar=bar')
+
     def with_or_without_fee(self, activated):
         if not activated:
             return '--no-fee'