Allow more Docker build caching

.travis.yml

@@ -15,28 +15,27 @@ before_install:
 
 script:
   - mkdir deploy
-  # Windows .exe
-  - docker pull koalaman/winghc
-  - docker run --user="$UID" --rm -v "$PWD:/appdata" koalaman/winghc cuib
-  - for tag in $TAGS; do cp "dist/build/ShellCheck/shellcheck.exe" "deploy/shellcheck-$tag.exe"; done
-  - rm -rf dist || true
-  # Linux static executable
-  - docker pull koalaman/scbuilder
-  - docker run --user="$UID" --rm -v "$PWD:/mnt" koalaman/scbuilder
-  - for tag in $TAGS; do cp "shellcheck" "deploy/shellcheck-$tag.linux"; done
-  - ./shellcheck --version
-  - rm -rf dist || true
   # Linux Docker image
   - name="$DOCKER_BASE"
   - DOCKER_BUILDS="$DOCKER_BUILDS $name"
   - docker build -t "$name:current" .
   - docker run "$name:current" --version
+  # Copy static executable from docker image
+  - id=$(docker create "$name:current")
+  - docker cp "$id:/bin/shellcheck" "shellcheck"
+  - docker rm "$id"
+  - for tag in $TAGS; do cp "shellcheck" "deploy/shellcheck-$tag.linux"; done
   # Linux Alpine based Docker image
   - name="$DOCKER_BASE-alpine"
   - DOCKER_BUILDS="$DOCKER_BUILDS $name"
-  - sed -e 's/^FROM .*/FROM alpine:latest/' -e '/WORKDIR/d' -e '/ENTRYPOINT/d' Dockerfile > Dockerfile.alpine
+  - sed -e '/DELETE-MARKER/,$d' Dockerfile > Dockerfile.alpine
   - docker build -f Dockerfile.alpine -t "$name:current" .
   - docker run "$name:current" sh -c 'shellcheck --version'
+  # Windows .exe
+  - docker pull koalaman/winghc
+  - docker run --user="$UID" --rm -v "$PWD:/appdata" koalaman/winghc cuib
+  - for tag in $TAGS; do cp "dist/build/ShellCheck/shellcheck.exe" "deploy/shellcheck-$tag.exe"; done
+  - rm -rf dist || true
   # Misc packaging
   - ./.prepare_deploy
 

Dockerfile

@@ -1,23 +1,34 @@
-FROM ubuntu:16.04 AS build
-
-# Install GHC and cabal
+# Build-only image
+FROM ubuntu:17.10 AS build
 USER root
 WORKDIR /opt/shellCheck
 
-COPY . .
+# Install OS deps
+RUN apt-get update && apt-get install -y ghc cabal-install
 
-RUN apt-get update && apt-get install -y \
-  ghc \
-  cabal-install
-RUN cabal update && \
-  cabal install --dependencies-only
+# Install Haskell deps
+# (This is a separate copy/run so that source changes don't require rebuilding)
+COPY ShellCheck.cabal ./
+RUN cabal update && cabal install --dependencies-only
+
+# Copy source and build it
+COPY LICENSE Setup.hs shellcheck.hs ./
+COPY src src
 RUN cabal build Paths_ShellCheck && \
-  ghc -optl-static -optl-pthread -idist/build/autogen --make shellcheck && \
+  ghc -optl-static -optl-pthread -isrc -idist/build/autogen --make shellcheck && \
   strip --strip-all shellcheck
 
 RUN mkdir -p /out/bin && \
   cp shellcheck  /out/bin/
 
+# Resulting Alpine image
+FROM alpine:latest
+LABEL maintainer="Vidar Holen <vidar@vidarholen.net>"
+COPY --from=build /out /
+
+# DELETE-MARKER (Remove everything below to keep the alpine image)
+
+# Resulting ShellCheck image
 FROM scratch
 LABEL maintainer="Vidar Holen <vidar@vidarholen.net>"
 WORKDIR /