I don't understand the Travis CI failure. It built successfully in two configurations, but a third ends up with an unexpected hash.

the first build only check for evaluation errors. The last two check builds on darwin and linux.

I get the same error as travis:

output path ‘/nix/store/5p4zqpdy61bh86l2hmjxsi07caj8zzbf-rtags’ has r:sha256 hash ‘1swcz4p5v6zqzqrxdbxbcvy009k509s4ni8qqg1wyp537qcibwdb’ when ‘0z32yncn3x1pm2l6r349kfwi6mi83vll820kka87agcla64pl1f2’ was expected  

I am also on Linux.

Thank you @Mic92! Can you think of a reason why the sha256 would be different between darwin and Linux? Doing a stdenv.isDarwin check on the hash of the source seems worrying, but I can do so if you think that's the way to go.

Maybe fetchgit (with submodules ?) is not so reproducible as it should be. It could be something fs related, which leads to a deviation in the checksum. However this is the first time I encounter that.

nix-prefetch-git is also consistent on my system:

nix-prefetch-git --fetch-submodules https://github.com/andersbakken/rtags.git refs/tags/v2.10
{                                 
  "url": "https://github.com/andersbakken/rtags.git",               
  "rev": "3b3ace901f53827daef81d4c13658ec4feb318b4",                
  "date": "2017-05-26T14:04:03-07:00",                              
  "sha256": "1swcz4p5v6zqzqrxdbxbcvy009k509s4ni8qqg1wyp537qcibwdb", 
  "fetchSubmodules": true         
}

I investigated a bit earlier today with some suggestions from IRC, and the most suspicious diff I could find between Linux and Darwin is a file with UTF8 characters in its name and contents. When I dumped file listings to a file on each system and opened in emacs, ediff highlighted that file name as a difference. Possibly a red herring, but it's all I came up with.

Probably HFS plus does unicode normalisation, which is not the case for other filesystems commonly found on Linux.

The quick fix would be to just have checksums per platform at the moment, if this is really the root cause.

Yep, it's the filesystem. I have a machine that doesn't use HFS+ for the store and I get the same hash as linux there.

With #26358 and this I get the same hash everywhere.

-    sha256 = "0z32yncn3x1pm2l6r349kfwi6mi83vll820kka87agcla64pl1f2";
+    sha256 = "0rv5hz4cfc1adpxvp4j4227nfc0p0yrjdc6l9i32jj11p69a5401";
+    postFetch = ''
+      rm $out/src/rct/tests/testfile_*.txt
+    '';

HFS+ will hopefully be deprecated soon.