1 files changed, 80 insertions, 0 deletions
diff --git a/ops/pipelines/depot.nix b/ops/pipelines/depot.nix
new file mode 100644
index 000000000000..878526e37484
--- /dev/null
+++ b/ops/pipelines/depot.nix
@@ -0,0 +1,80 @@
+# This file configures the primary build pipeline used for the
+# top-level list of depot targets.
+#
+# It outputs a "YAML" (actually JSON) file which is evaluated and
+# submitted to Buildkite at the start of each build. This means we can
+# dynamically configure the pipeline execution here.
+{ depot, lib, pkgs, ... }:
+
+let
+  inherit (builtins) concatStringsSep foldl' map toJSON;
+  inherit (pkgs) symlinkJoin writeText;
+
+  # Create an expression that builds the target at the specified
+  # location.
+  mkBuildExpr = target:
+    let
+      descend = expr: attr: "builtins.getAttr \"${attr}\" (${expr})";
+      targetExpr = foldl' descend "import ./. {}" target.__readTree;
+      subtargetExpr = descend targetExpr target.__subtarget;
+    in if target ? __subtarget then subtargetExpr else targetExpr;
+
+  # Create a pipeline label from the targets tree location.
+  mkLabel = target:
+    let label = concatStringsSep "/" target.__readTree;
+    in if target ? __subtarget
+      then "${label}:${target.__subtarget}"
+      else label;
+
+  # Create a pipeline step from a single target.
+  mkStep = target: {
+    command = let
+      drvPath = builtins.unsafeDiscardStringContext target.drvPath;
+    in lib.concatStringsSep " " [
+      # First try to realise the drvPath of the target so we don't evaluate twice.
+      # Nix has no concept of depending on a derivation file without depending on
+      # at least one of its `outPath`s, so we need to discard the string context
+      # if we don't want to build everything during pipeline construction.
+      "nix-store --realise '${drvPath}'"
+      # However, Nix doesn't track references of store paths to derivations, so
+      # there's no guarantee that the derivation file is not garbage collected.
+      # To handle this case we fall back to an ordinary build if the derivation
+      # file is missing.
+      "|| (test ! -f '${drvPath}' && nix-build -E '${mkBuildExpr target}' --show-trace)"
+    ];
+    label = ":nix: ${mkLabel target}";
+
+    # Skip build steps if their out path has already been built.
+    skip = let
+      shouldSkip = with builtins;
+        # Only skip in real Buildkite builds
+        (getEnv "BUILDKITE_BUILD_ID" != "") &&
+        # Always build everything for the canon branch.
+        (getEnv "BUILDKITE_BRANCH" != "refs/heads/canon") &&
+        # Discard string context to avoid realising the store path during
+        # pipeline construction.
+        (pathExists (unsafeDiscardStringContext target.outPath));
+      in if shouldSkip then "Target was already built." else false;
+  };
+
+  # Protobuf check step which validates that changes to .proto files
+  # between revisions don't cause backwards-incompatible or otherwise
+  # flawed changes.
+  protoCheck = {
+    command = "${depot.nix.bufCheck}/bin/ci-buf-check";
+    label = ":water_buffalo:";
+  };
+
+  # This defines the build pipeline, using the pipeline format
+  # documented on https://buildkite.com/docs/pipelines/defining-steps
+  #
+  # Pipeline steps need to stay in order.
+  pipeline.steps =
+    # Create build steps for each CI target
+    (map mkStep depot.ci.targets)
+
+    ++ [
+      # Simultaneously run protobuf checks
+      protoCheck
+    ];
+in (writeText "depot.yaml" (toJSON pipeline))