ci: trying to fix nix-channel by removing unstable channel

NIX_PATH used to be enough to select the channel to use, but as Travis
add the nixpkgs-unstable channel we can get unexpected results when
nix decides to push a new unstable version out there in the public.

diff --git a/.travis.yml b/.travis.yml
index 7ce4540ee5c587a504d15499c6adb702ad6baf1e..4a7aa46b2134d55f8070b2110022c0402dce2d59 100644 (file)
--- a/.travis.yml
+++ b/.travis.yml
@@ -3,7 +3,12 @@ sudo: false
 language: nix
 nix: 2.3.4
 env:
-  - NIX_PATH=nixpkgs=channel:nixos-20.03
+  - CUSTOM_NIX_PATH=nixpkgs=channel:nixos-20.03
+
+# Travis nix integration will install nix AFTER the environment variables are set
+# and the nix installer will overide NIX_PATH variable thus we need to re-export it
+before_install:
+  - export NIX_PATH="$CUSTOM_NIX_PATH"
 
 install:
   - nix-env -i -f ./default.nix