From f91216dd3ce5f842c1c441d0bae5a852e689bccf Mon Sep 17 00:00:00 2001
From: Jonas Zohren <git-pbkyr@jzohren.de>
Date: Tue, 14 Dec 2021 11:16:02 +0100
Subject: [PATCH] CI: Optionally use sccache for compilation

This moves compiler caching for incremental builds away from GitLab
caching the whole target/ folder to caching each code unit in S3.
This aleviates the need to zip and unzip and just caches on the fly.

This feature is optional and gated behind the SCCACHE_BIN_URL env
---
 .gitlab-ci.yml | 21 ++++++++++++---------
 1 file changed, 12 insertions(+), 9 deletions(-)

diff --git a/.gitlab-ci.yml b/.gitlab-ci.yml
index a8d43842..664b5ea3 100644
--- a/.gitlab-ci.yml
+++ b/.gitlab-ci.yml
@@ -26,16 +26,19 @@ variables:
   cache:
     paths:
       - cargohome
-      - target/
-    key: "build_cache--$TARGET--$CI_COMMIT_BRANCH--release"
+    key: "build_cache--$TARGET--$CI_COMMIT_BRANCH"
   variables:
     CARGO_PROFILE_RELEASE_LTO: "true"
     CARGO_PROFILE_RELEASE_CODEGEN_UNITS: "1"
+    CARGO_INCREMENTAL: "false" # https://matklad.github.io/2021/09/04/fast-rust-builds.html#ci-workflow
+    CARGO_HOME: $CI_PROJECT_DIR/cargohome
   before_script:
     - 'echo "Building for target $TARGET"'
-    - 'mkdir -p cargohome && CARGOHOME="cargohome"'
+    - "mkdir -p $CARGO_HOME"
     - "rustc --version && cargo --version && rustup show" # Print version info for debugging
     - "rustup target add $TARGET"
+    # If provided, bring in caching through sccache, which uses an external S3 endpoint to store compilation results:
+    - if [ -n "${SCCACHE_BIN_URL}" ]; then curl $SCCACHE_BIN_URL --output /sccache && chmod +x /sccache && export RUSTC_WRAPPER=/sccache; fi
   script:
     - time cargo build --target $TARGET --release
     - 'cp "target/$TARGET/release/conduit" "conduit-$TARGET"'
@@ -216,20 +219,20 @@ test:cargo:
   image: "rust:latest"
   tags: ["docker"]
   variables:
-    CARGO_HOME: "cargohome"
+    CARGO_HOME: "$CI_PROJECT_DIR/cargohome"
+    CARGO_INCREMENTAL: "false" # https://matklad.github.io/2021/09/04/fast-rust-builds.html#ci-workflow
   cache:
     paths:
-      - target
       - cargohome
-    key: test_cache
+    key: "test_cache--$CI_COMMIT_BRANCH"
   interruptible: true
   before_script:
-    - mkdir -p $CARGO_HOME && echo "using $CARGO_HOME to cache cargo deps"
+    - mkdir -p $CARGO_HOME
     - apt-get update -yqq
     - apt-get install -yqq --no-install-recommends build-essential libssl-dev pkg-config wget
     - rustup component add clippy rustfmt
-    - wget "https://faulty-storage.de/gitlab-report"
-    - chmod +x ./gitlab-report
+    # If provided, bring in caching through sccache, which uses an external S3 endpoint to store compilation results:
+    - if [ -n "${SCCACHE_BIN_URL}" ]; then curl $SCCACHE_BIN_URL --output /sccache && chmod +x /sccache && export RUSTC_WRAPPER=/sccache; fi
   script:
     - rustc --version && cargo --version # Print version info for debugging
     - cargo fmt --all -- --check