Add a jobset for doing SDK releases (#164)

ci/release.nix is called by the sdk-release jobset on hydra. It calls
release-jobset.nix which returns the dfx-release and
install-sh-release derivations but only when the git revision has been
tagged with a release tag (v0.1.2). In that case the version in those
derivations is set to the version in the tag ensuring that they get
rebuild.

ci/release.nix

@@ -0,0 +1,5 @@
+{ supportedSystems ? [ "x86_64-linux" "x86_64-darwin" ]
+, scrubJobs ? true
+, src ? null
+}:
+(import ../nix {}).ci ../release-jobset.nix { inherit supportedSystems scrubJobs src; }

jobset.nix

@@ -2,6 +2,7 @@
 , crossSystem ? null
 , config ? {}
 , overlays ? []
+, src ? null
 }: {
   inherit (import ./nix { inherit system crossSystem config overlays; }) dfinity-sdk;
 }

nix/default.nix

@@ -4,6 +4,7 @@
 , crossSystem ? null
 , config ? {}
 , overlays ? []
+, releaseVersion ? "latest"
 }:
 let
   # The `common` repo provides code (mostly Nix) that is used in the
@@ -20,9 +21,9 @@ let
     else builtins.fetchGit {
       name = "common-sources";
       url = "ssh://[email protected]/dfinity-lab/common";
-      rev = "d5af3fda55af07de25f06fc46a2bf5f83424f02b";
+      rev = "bbf39c31e08b4ab7db82f799a3e3c693a0fdced6";
     };
 in import commonSrc {
   inherit system crossSystem config;
-  overlays = import ./overlays ++ overlays;
+  overlays = import ./overlays ++ [ (_self: _super: { inherit releaseVersion; }) ] ++ overlays;
  }

nix/overlays/dfinity-sdk.nix

@@ -29,19 +29,15 @@ in {
         public-folder = super.callPackage ../public.nix {};
     };
 
-    dfx-release = mkRelease "dfx"
-      # This is not the tagged version, but something afterwards
-      "latest" # once INF-495 is in, we will use: packages.rust-workspace.version
-      packages.rust-workspace-standalone
-      "dfx";
+    dfx-release = mkRelease "dfx" self.releaseVersion packages.rust-workspace-standalone "dfx";
 
     # The following prepares a manifest for copying install.sh
     # The release part also checks if the install.sh script is well formatted and has no shellcheck issues.
     # We ignore 'local' warning by shellcheck, because any existing sh implementation supports it.
     # TODO: streamline mkRelease and this
     install-sh-release =
       let
-        version = "latest";
+        version = self.releaseVersion;
         shfmtOpts = "-p -i 4 -ci -bn -s";
         shellcheckOpts = "-s sh -S warning";
         # We want to include the last revision of the install script into

release-jobset.nix

@@ -0,0 +1,41 @@
+{ system ? builtins.currentSystem
+, crossSystem ? null
+, config ? {}
+, overlays ? []
+
+# Hydra will pass an argument to this jobset expression for every
+# input of the jobset. In our case we only have a single `src` input
+# representing the git checkout of the SDK repo:
+#
+#   https://hydra.dfinity.systems/jobset/dfinity-ci-build/sdk#tabs-configuration
+#
+# This `src` argument contains information about the input for example:
+#
+#   { outPath = builtins.storePath /nix/store/ma2dfyfyxdi6idbza6dyp34zhxh12nmm-source;
+#     inputType = "git";
+#     uri = "[email protected]:dfinity-lab/sdk.git";
+#     rev = "8882d8c97decbb3c33923ca9e8ab785621a61207";
+#     revCount = 2514;
+#     gitTag = "8882d8c9"; # This defaults to the rev when there's no git tag.
+#     shortRev = "8882d8c9";
+#   }
+#
+# See: https://github.com/NixOS/hydra/blob/037f6488f633dbf15ca2d93a0c117f6738c707fe/src/lib/Hydra/Plugin/GitInput.pm#L241:L248
+#
+# We're  primarily interested in the `src.gitTag` since that should trigger a release.
+, src ? null
+}:
+let
+  # doRelease is true when the git tag is of the right release format like `0.1.2`.
+  doRelease = src != null && versionMatches != null;
+
+  # versionMatch is `null` if `src.gitTag` is not of the right format like "1.23.456"
+  # and it's a list of matches like [ "1.23.456" ] when it is.
+  versionMatches = builtins.match "([0-9]+\.[0-9]+\.[0-9]+)" src.gitTag;
+  releaseVersion = if versionMatches == null then "latest" else builtins.head versionMatches;
+
+  pkgs = import ./nix { inherit system config overlays releaseVersion; };
+
+in pkgs.lib.optionalAttrs doRelease {
+  inherit (pkgs.dfinity-sdk) dfx-release install-sh-release;
+}