initial commit

source/recipes/build/flake/flake.nix

@@ -0,0 +1,46 @@
+{
+  inputs = {
+    nixpkgs.url = "github:NixOS/nixpkgs";
+    flake-utils.url = "github:numtide/flake-utils";
+    hello-flake.url = "git+https://codeberg.org/mhwombat/hello-flake";
+  };
+
+  outputs = { self, nixpkgs, flake-utils, hello-flake }:
+    flake-utils.lib.eachDefaultSystem (system:
+      let
+        pkgs = import nixpkgs { inherit system; };
+      in
+      {
+        packages = rec {
+          hello = pkgs.stdenv.mkDerivation rec {
+            name = "hello-again";
+
+            src = ./.;
+
+            unpackPhase = "true";
+
+            buildPhase = ":";
+
+            installPhase =
+              ''
+                mkdir -p $out/bin
+                cp $src/hello-again $out/bin
+                chmod +x $out/bin/hello-again
+
+                # modify the hello-again script so it can find hello-flake
+                HELLO=$(type -p hello-flake)
+                sed "s_hello-flake_"$HELLO"_" --in-place $out/bin/hello-again
+              '';
+
+            buildInputs = [ hello-flake.packages.${system}.hello ];
+          };
+          default = hello;
+        };
+
+        apps = rec {
+          hello = flake-utils.lib.mkApp { drv = self.packages.${system}.hello; };
+          default = hello;
+        };
+      }
+    );
+}

source/recipes/build/flake/hello-again

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+#!/usr/bin/env sh
+
+echo "I'm a flake, and I'm running a command defined in a another flake."
+hello-flake

source/recipes/build/flake/main.adoc0

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+= Access a flake
+
+////
+$ mkdir tempwork
+$ cd tempwork
+$ cp ../hello-again ../flake.nix .
+$ git add hello-again flake.nix
+$ nix build
+$ git add flake.lock
+$ git commit -a -m temp
+////
+
+In this example, we will use a flake defined in a remote git repo.
+However, you can use any of the flake reference styles defined in <<#flakeref>>.
+
+[source,bash,linenums]
+.hello-again
+....
+$# cat hello-again
+....
+
+[source,nix,linenums,highlight='5,8,30..32,35']
+.flake.nix
+....
+$# cat flake.nix
+....
+
+Line 5 adds `hello-flake` as an input to this flake,
+Line 8 allows the output function to reference `hello-flake`.
+As expected, we need to add `hello-flake` as a build input, which we do in line 35.
+Let's take a closer look at the `buildInputs` expression from line 35.
+
+....
+$# grep buildInputs flake.nix | sed 's/ //g; s/.*\[//; s/\].*//'
+....
+
+Why is the first part `hello-flake` and the last part `hello`?
+The first part refers to the name we assigned in the input section of our flake,
+and the last part is the name of the package or app we want.
+(See <<_flake_outputs>> for how to identify flake outputs.)
+
+Line 35 does make `hello-flake` available at build and runtime,
+but it doesn't put it on the path,
+so our `hello-again` script won't be able to find it.
+There are various ways to deal with this problem.
+In this case we simply edited the script (lines 30-32) as we install it,
+by specifying the full path to `hello-nix`.
+
+[NOTE]
+====
+When you're packaging a program written in a more powerful language such as
+Haskell, Python, Java, C, C#, or Rust,
+the language build system will usually do all that is required
+to make the dependencies visible to the program at runtime.
+In that case, adding the dependency to `buildInputs` is sufficient.
+====
+
+Here's a demonstration using the flake.
+
+....
+$ nix run
+....
+
+////
+Good adoc0 scripts clean up after themselves.
+$ cd .. ; rm -rf tempwork # clean up
+////