From 5d6ab9a76c75a5f260d92b592d55ed5a424e0d09 Mon Sep 17 00:00:00 2001
From: "Seth R. Johnson" <johnsonsr@ornl.gov>
Date: Wed, 10 Aug 2022 05:01:07 -0400
Subject: core: add a helpful long message for UnknownPackageError (#31996)

```
Error: Package 'armpl' not found.
```
is pretty useless after an upgrade unless you're a spack pro. I've
recently hit this on multiple machines. See
https://github.com/spack/spack/issues/31453 ,
https://github.com/spack/spack/issues/31489  .
---
 lib/spack/spack/repo.py | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/lib/spack/spack/repo.py b/lib/spack/spack/repo.py
index 11a4e14416..814f84049a 100644
--- a/lib/spack/spack/repo.py
+++ b/lib/spack/spack/repo.py
@@ -1478,6 +1478,8 @@ class UnknownPackageError(UnknownEntityError):
             if name.endswith(".yaml"):
                 long_msg = "Did you mean to specify a filename with './{0}'?"
                 long_msg = long_msg.format(name)
+            else:
+                long_msg = "You may need to run 'spack clean -m'."
         else:
             msg = "Attempting to retrieve anonymous package."
 
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