Handle installation when not running from a full git checkout

[newhouseb]

I'm working on setting up a Nix shell environment, which builds nmigen from a checkout that does not contain a full .git directory. In the this scenario, setuptools_scm is installed correctly, but parse/parse_git returns None because there's no active git checkout.

As a fix, I check to see if git is falsey and, if so, return a blank version string.

I've verified that this installs properly from nix via fetchFromGithub

[codecov]

Codecov Report

Merging #516 into master will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master     #516   +/-   ##
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  Coverage   81.37%   81.37%           
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  Files          49       49           
  Lines        6410     6410           
  Branches     1280     1280           
=======================================
  Hits         5216     5216           
  Misses       1005     1005           
  Partials      189      189           

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[whitequark]

Is this for Nixpkgs?

[newhouseb]

I might build up to submitting to Nixpkgs, but am just setting up a shell for the moment (I'm a nix noob).

For future travelers, here's an example package definition (note this is against my fork, rather than the merged diff, but should work if you swap out the owner, rev and sha256 with the appropriate bits):

    nmigen = python38.pkgs.buildPythonPackage rec {
      pname = "nmigen";
      version = "0.2";

      src = pkgs.fetchFromGitHub {
        name = "nmigen";
        owner = "newhouseb";
        repo = "nmigen";
        rev = "6e585a6ad850cbc02ab730acbb01f17f08eb7152";
        sha256 = "121fa20cd5q9ijbihpcj04j2pil78h2i1gdciq2ysj2vjkg46zk8";
        fetchSubmodules = true;
      };

      doCheck = false;

      propagatedBuildInputs = [ python38.pkgs.numpy python38.pkgs.jinja2 python38.pkgs.pyvcd python38.pkgs.importlib-resources ];
      nativeBuildInputs = [ python38.pkgs.setuptools_scm ];
      preBuild = ''
           export SETUPTOOLS_SCM_PRETEND_VERSION="0.2"
           '';

      meta = {
        homepage = "https://github.com/nmigen/nmigen";
        description = "A refreshed Python toolbox for building complex digital hardware";
      };
    };

[whitequark]

I might build up to submitting to Nixpkgs, but am just setting up a shell for the moment (I'm a nix noob).

Nixpkgs should already have an nMigen package.

[whitequark]

export SETUPTOOLS_SCM_PRETEND_VERSION="0.2"

Ah I wasn't aware of that. It would have been nicer to return that instead of "" in your patch, though it's not especially important either way (it only really matters for PyPI I think).

[newhouseb]

Ah, I missed that Nixpkgs already has a package, looking now it's basically what I posted, but better (although pinned to a version from April, before the offending code was landed).

My macro use-case is pinning a deterministic set of of newish {lambdasoc, nmigensoc, nmigen, minerva, etc} with my code, since the aforementioned packages are all (understandably) moving targets.