Save/restore target/ directory between builds

.buildkite/hooks/post-command

@@ -0,0 +1,14 @@
+#!/bin/bash -e
+
+[[ -n "$CARGO_TARGET_CACHE_NAME" ]] || exit 0
+
+#
+# Save target/ for the next CI build on this machine
+#
+(
+  d=$HOME/cargo-target-cache/"$CARGO_TARGET_CACHE_NAME"
+  mkdir -p $d
+  set -x
+  rsync -a --delete target $d
+  du -hs $d
+)

.buildkite/hooks/pre-command

@@ -0,0 +1,13 @@
+#!/bin/bash -e
+
+[[ -n "$CARGO_TARGET_CACHE_NAME" ]] || exit 0
+
+#
+# Restore target/ from the previous CI build on this machine
+#
+(
+  d=$HOME/cargo-target-cache/"$CARGO_TARGET_CACHE_NAME"
+  mkdir -p $d/target
+  set -x
+  rsync -a --delete $d/target .
+)

ci/buildkite.yml

@@ -1,15 +1,21 @@
 steps:
   - command: "ci/docker-run.sh rust ci/test-stable.sh"
     name: "stable [public]"
+    env:
+      CARGO_TARGET_CACHE_NAME: "stable"
     timeout_in_minutes: 20
   - command: "ci/shellcheck.sh"
     name: "shellcheck [public]"
     timeout_in_minutes: 20
   - command: "ci/docker-run.sh rustlang/rust:nightly ci/test-nightly.sh"
     name: "nightly [public]"
+    env:
+      CARGO_TARGET_CACHE_NAME: "nightly"
     timeout_in_minutes: 30
   - command: "ci/test-stable-perf.sh"
     name: "stable-perf [public]"
+    env:
+      CARGO_TARGET_CACHE_NAME: "stable-perf"
     timeout_in_minutes: 20
     retry:
       automatic: