Subject: bug#45828: guix build: error: got unexpected path `Backtrace:' from substituter

From: Leo Famulari <[email-masked]>
Date: Tue, 12 Jan 2021 17:09:08 -0500

Recently, many people on the #guix IRC channel reported frequent
non-deterministic failures of any operation involving substitution, like
this:

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$ ./pre-inst-env guix build --no-grafts poezio mpdris2 sonata beets-bandcamp beets
substitute: 
guix build: error: got unexpected path `Backtrace:' from substituter
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`guix describe` reports commit b4384e61165623b16b77b8cab16c81423c6853ed
for both my user's Guix and the guix-dameon.