flake: Add nix flake

.envrc

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+use flake

.gitignore

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+.direnv

flake.lock

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+{
+  "nodes": {
+    "devshell": {
+      "inputs": {
+        "flake-utils": "flake-utils",
+        "nixpkgs": "nixpkgs"
+      },
+      "locked": {
+        "lastModified": 1658746384,
+        "narHash": "sha256-CCJcoMOcXyZFrV1ag4XMTpAPjLWb4Anbv+ktXFI1ry0=",
+        "owner": "numtide",
+        "repo": "devshell",
+        "rev": "0ffc7937bb5e8141af03d462b468bd071eb18e1b",
+        "type": "github"
+      },
+      "original": {
+        "owner": "numtide",
+        "repo": "devshell",
+        "type": "github"
+      }
+    },
+    "flake-utils": {
+      "locked": {
+        "lastModified": 1642700792,
+        "narHash": "sha256-XqHrk7hFb+zBvRg6Ghl+AZDq03ov6OshJLiSWOoX5es=",
+        "owner": "numtide",
+        "repo": "flake-utils",
+        "rev": "846b2ae0fc4cc943637d3d1def4454213e203cba",
+        "type": "github"
+      },
+      "original": {
+        "owner": "numtide",
+        "repo": "flake-utils",
+        "type": "github"
+      }
+    },
+    "nixpkgs": {
+      "locked": {
+        "lastModified": 1643381941,
+        "narHash": "sha256-pHTwvnN4tTsEKkWlXQ8JMY423epos8wUOhthpwJjtpc=",
+        "owner": "NixOS",
+        "repo": "nixpkgs",
+        "rev": "5efc8ca954272c4376ac929f4c5ffefcc20551d5",
+        "type": "github"
+      },
+      "original": {
+        "owner": "NixOS",
+        "ref": "nixpkgs-unstable",
+        "repo": "nixpkgs",
+        "type": "github"
+      }
+    },
+    "nixpkgs_2": {
+      "locked": {
+        "lastModified": 1659494082,
+        "narHash": "sha256-XRwMisQY/BcvDMDRVkd4n3/CT89HOtlPgWIQUNPvWSc=",
+        "owner": "NixOS",
+        "repo": "nixpkgs",
+        "rev": "8c7576622aeb4707351a17e83429667f42e7d910",
+        "type": "github"
+      },
+      "original": {
+        "id": "nixpkgs",
+        "type": "indirect"
+      }
+    },
+    "root": {
+      "inputs": {
+        "devshell": "devshell",
+        "nixpkgs": "nixpkgs_2",
+        "utils": "utils"
+      }
+    },
+    "utils": {
+      "locked": {
+        "lastModified": 1656928814,
+        "narHash": "sha256-RIFfgBuKz6Hp89yRr7+NR5tzIAbn52h8vT6vXkYjZoM=",
+        "owner": "numtide",
+        "repo": "flake-utils",
+        "rev": "7e2a3b3dfd9af950a856d66b0a7d01e3c18aa249",
+        "type": "github"
+      },
+      "original": {
+        "owner": "numtide",
+        "repo": "flake-utils",
+        "type": "github"
+      }
+    }
+  },
+  "root": "root",
+  "version": 7
+}

flake.nix

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+{
+  description = "Twitter follower counts in Prometheus.";
+
+  inputs.utils.url = "github:numtide/flake-utils";
+  inputs.devshell = {
+    url = "github:numtide/devshell";
+    inputs.utils.follows = "utils";
+  };
+
+  outputs = {
+    self,
+    nixpkgs,
+    utils,
+    devshell,
+  }:
+    utils.lib.eachDefaultSystem (system: let
+      pkgs = import nixpkgs {
+        inherit system;
+        overlays = [devshell.overlay];
+      };
+    in rec {
+      packages.default = pkgs.buildGoModule {
+        name = "twitter-prometheus";
+        src = self;
+        vendorSha256 = "PNOP2y6MYKYyD8QcvulenSj/iUb8/otoByfmtSBNc8E=";
+
+        # Inject the git version if you want
+        #ldflags = ''
+        #  -X main.version=${if self ? rev then self.rev else "dirty"}
+        #'';
+      };
+
+      apps.default = utils.lib.mkApp {drv = packages.default;};
+
+      devShells.default =
+        pkgs.devshell.mkShell {packages = with pkgs; [go gopls];};
+      formatter = pkgs.alejandra;
+    });
+}