improve build speed

Dockerfile

@@ -1,7 +1,10 @@
 # syntax=docker/dockerfile:1
 
-FROM golang:1.21-alpine AS BUILD
-ARG Release=dev
+FROM golang:1.22-alpine AS BUILD
+
+ENV CGO_ENABLED 0
+ENV GOPATH /go
+ENV GOCACHE /go-build
 
 RUN apk add build-base alpine-sdk
 
@@ -10,19 +13,17 @@ WORKDIR /app
 # RUN apk update && apk add --no-cache musl-dev gcc build-base
 
 # pre-copy/cache go.mod for pre-downloading dependencies and only redownloading them in subsequent builds if they change
-COPY go.* ./
-RUN go mod download && go mod verify
-
-# don't look for dynamic libraries (like c libraries) since we're building a static binary
-ENV CGO_ENABLED false
+COPY go.mod go.sum ./
+RUN --mount=type=cache,target=/go/pkg/mod/cache \
+    go mod download && go mod verify
 
-# fix for sqlite3 not building on alpine
-# https://github.com/mattn/go-sqlite3/issues/1164#issuecomment-1635253695
-ENV CGO_CFLAGS "-D_LARGEFILE64_SOURCE"
+# copy the rest of the files
+COPY . .
 
-COPY . ./
-# based on https://www.cloudbees.com/blog/building-minimal-docker-containers-for-go-applications
-RUN go build -a -installsuffix cgo -v -o /app/bot .
+# build the binary
+RUN --mount=type=cache,target=/go/pkg/mod/cache \
+    --mount=type=cache,target=/go-build \
+    go build -a -installsuffix cgo -v -o /app/bot cmd/bot/entry.go
 
 FROM alpine as deployment