Drop docker compose, use layer cache instead

This drops the bat-server setup with a docker-compose in favor of a not
so over-engineered dockerfile.

This leverages the docker layer cache on each image re-build, so there's
no need to run `bat cache --build` if the syntax didn't change.

The point of bat-server was being able to use it for both highlight_ and
theme_regression.sh. But we can do that with a plain old Docker image if
we overwrite the entrypoint (run_highlight_ vs run_theme_regression.sh).

This improves DX for two reasons:

1. no need to `docker compose down` at the end of a coding session. (I
always forget.)
2. doesn't `bat cache --build` when the syntax file didn't change, which
makes that case speedup 2-3x.

.dockerignore

@@ -0,0 +1,6 @@
+# only used for bat-test.dockerfile
+
+*
+!/syntaxes/
+!/tests/docker/*regression.sh
+!/tests/source

tests/docker/bat-test.dockerfile

@@ -0,0 +1,18 @@
+# usage: through highlight_regression.sh and theme_regression.sh
+
+FROM curlimages/curl:latest AS fetch-pkg
+LABEL keep=false
+ARG BAT_VERSION=0.21.0
+RUN curl -LJ \
+    https://github.com/sharkdp/bat/releases/download/v$BAT_VERSION/bat_${BAT_VERSION}_amd64.deb \
+    --output /tmp/bat.deb
+
+FROM debian:bullseye-slim
+COPY --from=fetch-pkg  /tmp/bat.deb  /tmp
+RUN dpkg --install /tmp/bat.deb
+ENV COLORTERM=truecolor
+COPY ./tests/docker/*regression.sh  /tests/
+COPY ./tests/source  /tests/source
+COPY ./syntaxes/cmd-help.sublime-syntax  /root/.config/bat/syntaxes/
+RUN bat cache --build > /dev/null
+ENTRYPOINT /tests/run_highlight_regression.sh

tests/docker/run_highlight_regression.sh

@@ -4,10 +4,8 @@ set -euo pipefail
 
 cd "$(dirname "${BASH_SOURCE[0]}")"
 
-bat cache --build > /dev/null
-
 for source_path in source/* ; do
-    # this dir is only for theme_regression.sh
+    # this dir is only for run_theme_regression.sh
     [ "$source_path" = source/theme ] && continue
 
     filename=$(basename "$source_path")

tests/docker/run_theme_regression.sh

@@ -4,8 +4,6 @@ set -euo pipefail
 
 cd "$(dirname "${BASH_SOURCE[0]}")"
 
-bat cache --build > /dev/null
-
 readarray -t themes <<< "$(bat --list-themes --color=never)"
 cmd_prefix="bat --no-config -fpl cmd-help source/theme/synthetic.txt"
 

tests/highlight_regression.sh

@@ -4,9 +4,10 @@ set -euo pipefail
 
 cd "$(dirname "${BASH_SOURCE[0]}")"
 
-docker compose -f docker/bat-server.compose.yaml up -d
+docker build --quiet -f docker/bat-test.dockerfile -t bat-test ..
 
-docker exec bat-server bash /tests/run_highlight_regression.sh
+volume="$PWD"/highlighted:/tests/highlighted
+docker run -v "$volume" bat-test
 
 # have git tell the effective difference between the version of the syntax
 # in staging/HEAD and the one in working dir, for all highlighted samples

tests/theme_regression.sh

@@ -4,9 +4,12 @@ set -euo pipefail
 
 cd "$(dirname "${BASH_SOURCE[0]}")"
 
-docker compose -f docker/bat-server.compose.yaml up -d
+docker build --quiet -f docker/bat-test.dockerfile -t bat-test ..
 
-docker exec bat-server bash /tests/run_theme_regression.sh
+volume="$PWD"/theme:/tests/theme
+docker run -v "$volume" \
+    --entrypoint /tests/run_theme_regression.sh \
+    bat-test
 
 # effective difference between HEAD/staging and working dir
 GIT_PAGER='LESS=R less' git diff -- theme/