home-environment: allow adding to $PATH

[afontaine]

Description

Sometimes I'll have some things installed to my dot files that provide
a collection of executables (doom-emacs, org-capture), or need a
$HOME/bin or similar to keep a handful of quick scripts and wanted to
be able to do it decrlaratively.

Checklist

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[afontaine]

Hmm looks like the build failed because fetching etex failed, which is very unrelated. Can we try restarting the build to see if the etex servers are awake?

[turion]

Does that work for you locally?

I tried home.sessionVariables.PATH = "$PATH:/foo/bar";, which should have given me an equivalent result (and it does produce the same .nix-profile/etc/profile.d/hm-session-vars.sh as yours), but PATH is not modified by that.

[turion]

Hmm looks like the build failed because fetching etex failed, which is very unrelated. Can we try restarting the build to see if the etex servers are awake?

Either @rycee can restart the build on Travis or you can make some change and force-push, that might trigger the build as well.

[turion]

I tried home.sessionVariables.PATH = "$PATH:/foo/bar";, which should have given me an equivalent result (and it does produce the same .nix-profile/etc/profile.d/hm-session-vars.sh as yours), but PATH is not modified by that.

Hmm, I think I'm wrong and that does indeed work. I just needed to restart my system.

[teto]

For reference, Nixos has the weird limited option:

environment.homeBinInPath
     Include ~/bin/ in $PATH.

what if you want to prepend to PATH instead ? can't you just modify home.sessionVariables instead ? I don't believe we need a specific option for that.

[turion]

@teto

what if you want to prepend to PATH instead ?

Does that have a different effect:

can't you just modify home.sessionVariables instead ? I don't believe we need a specific option for that.

See my previous comment: #1292 (comment) It doesn't work straightforwardly.

[teto]

Hmm, I think I'm wrong and that does indeed work. I just needed to restart my system.

Seems like it worked ?! this behaves no differently: if you change sessions variables, you have to relog, otherwise, you could change it into your shell variables.

[turion]

Hmm, I think I'm wrong and that does indeed work. I just needed to restart my system.

Seems like it worked ?!

You're right, I forgot!

[afontaine]

@turion sorry for letting this stall for so long, but I've updated the documentation a bit more and fixed the default example.

As for why this and not just home.sessionVariables.PATH, this approach allows users to break declarations apart and use them across files/modules/etc if you aren't about having one long file for home-manager.

I have ~/.config/emacs/bin in my path for Doom Emacs (as it is not yet very nix-able), and .git/safe/../../bin, primarily for working with non-nix'd projects. These belong in the emacs set-up file I have and the git setup file, respectively.

The prepend/append issue is interesting, but I'm not sure what the best approach is to this beyond complicating this even further with something like {path = "some/path"; prepend = true;}

[turion]

I think this is a good option to add.

@rycee probably your input is needed here :)

[teto]

one can already adjust the PATH via export PATH=/my/bin:${PATH} so this looks overengineered ?

[afontaine]

one can already adjust the PATH via export PATH=/my/bin:${PATH} so this looks overengineered ?

@teto How? Where? Through sessionVariables? in myShell.initExtra?

If in either of those options, how do we append to it across multiple nix files? do I need to keep track of all the path adjustments I want to make and keep them in one location? That feels strange.

Admittedly, it does feel slightly overkill, but at the same time, the current solutions feel... lacking. I'm not really sure what the best solution is though.

[turion]

I don't think this is overkill or overengineered. It abstracts adding directories to the PATH from the actual mechanism. It's good that one can configure the PATH variable without having to read the home-manager source code in order to understand where and when and how hm-session-vars.sh is called. And it probably does no harm because it has a unit test.

[rycee]

Perhaps it would suffice to fix the type of sessionVariables to be a attrsOf instead of attrs with a list value being concatenated by :? Something like

diff --git a/modules/home-environment.nix b/modules/home-environment.nix
index 209df4ff..7691e6a1 100644
--- a/modules/home-environment.nix
+++ b/modules/home-environment.nix
@@ -228,7 +228,11 @@ in
 
     home.sessionVariables = mkOption {
       default = {};
-      type = types.attrs;
+      type = with types;
+        let
+          primitive = either bool (either int str);
+          var = either primitive (listOf str);
+        in attrsOf var;
       example = { EDITOR = "emacs"; GS_OPTIONS = "-sPAPERSIZE=a4"; };
       description = ''
         Environment variables to always set at login.
diff --git a/modules/lib/shell.nix b/modules/lib/shell.nix
index 5e5743f5..7b57596d 100644
--- a/modules/lib/shell.nix
+++ b/modules/lib/shell.nix
@@ -2,7 +2,10 @@
 
 rec {
   # Produces a Bourne shell like variable export statement.
-  export = n: v: ''export ${n}="${toString v}"'';
+  export = let
+    toShell = v:
+      if lib.isList v then lib.concatStringsSep ":" v else toString v;
+  in n: v: ''export ${n}="${toShell v}"'';
 
   # Given an attribute set containing shell variable names and their
   # assignment, this function produces a string containing an export

Then the configuration

home.sessionVariables = lib.mkMerge [
  (lib.mkAfter {
    PATH = ["$PATH"];
  })
  {
    PATH = ["$HOME/path1"];
  }
  {
    PATH = ["$HOME/path2"];
  }
];

would place

export PATH="$HOME/path1:$HOME/path2:$PATH"

in hm-session-vars.sh.

It wouldn't correctly handle an empty PATH variable, though.

[berbiche]

@rycee Quick question: why would you use either when listOf is available? Are the documentation/error strings clearer?

[rycee]

@berbiche I assume you mean types.oneOf. It's mainly out of habit. Probably better to use oneOf since it is a more stylish and the generated code should be identical to using either explicitly.

[afontaine]

Perhaps it would suffice to fix the type of sessionVariables to be a
attrsOf instead of attrs with a list value being concatenated by :?

This was my initial thought as well, @rycee, but I am relatively new to writing nix so
I'm not too familiar with how to go about it. I initially just started by trying
to edit toShell to work with lists as well.

It wouldn't correctly handle an empty PATH variable, though.

This was my big blocker though. PATH is such a frustratingly special case, and
I couldn't find an elegant way to inject a :$PATH into the variable building
logic, so it felt easier to split it out into a separate option. It is also
required here unfortunately 😞

[turion]

Perhaps it would suffice to fix the type of sessionVariables to be a attrsOf instead of attrs with a list value being concatenated by :?

But there are lots of session variables that aren't paths.

[afontaine]

@rycee is there anything I can change here to move this along, aside from merge conflicts?

[rycee]

I made some minor changes and merged to master. Thanks for the contribution!

[afontaine]

awesome, thanks @rycee