From 8e925b884ef3a5d19c8edff233614962db708c5c Mon Sep 17 00:00:00 2001
From: Lucien Cartier-Tilet <lucien@phundrak.com>
Date: Thu, 9 Feb 2023 11:59:39 +0100
Subject: [PATCH] perf(backend): Cache build of dependencies

When building the Docker image, first compile the project with a fake
main file, namely `dummy.rs`. Once dependencies are built, compile the
actual project by switching back to `src/main.rs`.

Signed-off-by: Lucien Cartier-Tilet <lucien@phundrak.com>
---
 Cargo.toml |  4 ++++
 Dockerfile | 14 +++++++++++---
 dummy.rs   |  1 +
 3 files changed, 16 insertions(+), 3 deletions(-)
 create mode 100644 dummy.rs

diff --git a/Cargo.toml b/Cargo.toml
index 54856fc..60e668f 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -15,3 +15,7 @@ serde = { version = "1.0", features = ["derive"] }
 dotenvy = "0.15"
 gql_client = "1.0.7"
 human-panic = "1.1.0"
+
+[[bin]]
+name = "phuncache"
+path = "src/main.rs"
diff --git a/Dockerfile b/Dockerfile
index 0f5472c..0d0e283 100644
--- a/Dockerfile
+++ b/Dockerfile
@@ -2,12 +2,20 @@ FROM rust:alpine
 
 WORKDIR /app
 
-COPY Cargo.toml /app/Cargo.toml
-COPY Cargo.lock  /app/Cargo.lock
-COPY src /app/src
 RUN apk update && apk add pkgconfig openssl-dev musl-dev
 
+COPY Cargo.toml .
+COPY dummy.rs .
+
+# Cache building
+RUN sed -i 's|src/main.rs|dummy.rs|' Cargo.toml
 RUN cargo build --release
+RUN cargo build
+RUN sed -i 's|dummy.rs|src/main.rs|' Cargo.toml
+
+# Building normally
+COPY src src
+RUN cargo build
 RUN cargo install --path .
 
 ENTRYPOINT [ "phuncache" ]
diff --git a/dummy.rs b/dummy.rs
new file mode 100644
index 0000000..f328e4d
--- /dev/null
+++ b/dummy.rs
@@ -0,0 +1 @@
+fn main() {}