chore: refactor Dockerfile

Dockerfile

@@ -1,27 +1,30 @@
 # syntax=docker/dockerfile:1
 FROM dlang2/dmd-ubuntu
 
-WORKDIR /app
-COPY . .
-RUN --mount=type=cache,target=/root/.dub dub build
-RUN ln -s /app/myrc /usr/local/bin/myrc
+COPY . /app
+RUN --mount=type=cache,target=/root/.dub <<BUILD
+cd /app
+dub build
+ln -s /app/myrc /usr/local/bin/myrc
+BUILD
 
 ARG example_dir_1=/home/dlang/dotfiles/example1
 ARG example_dir_2=/home/dlang/dotfiles/example2
+COPY test $example_dir_1
+RUN <<EOF
+mkdir -p $example_dir_2
+echo "echo wrong location 1" > $example_dir_2/wrong_location1
+EOF
 
 USER dlang
-
-WORKDIR $example_dir_1
-COPY test .
-
-WORKDIR $example_dir_2
-RUN echo "echo wrong location 1" > wrong_location1
-
 WORKDIR /home/dlang
-RUN ln -s $example_dir_1/zshrc ~/.zshrc
-RUN ln -s ./dotfiles/example1/ls_colors ~/.ls_colors
-RUN ln -s $example_dir_2/wrong_location1 ~/.zshenv
 
-WORKDIR $example_dir_1
+RUN <<LN
+set -e
+ln -s $example_dir_1/zshrc ~/.zshrc
+ln -s ./dotfiles/example1/ls_colors ~/.ls_colors
+ln -s $example_dir_2/wrong_location1 ~/.zshenv
+LN
 
+WORKDIR $example_dir_1
 CMD mkdir ~/.zsh && myrc && myrc install && myrc && ls -la ~