image(debian): move the shell history to a mountable directory

debian/Dockerfile

@@ -51,3 +51,6 @@ COPY --chown=${USERNAME}:${USERNAME} assets/.bashrc /home/${USERNAME}/.bashrc
 
 USER ${USERNAME}
 WORKDIR /workspaces
+
+ENV HISTFILE=/home/${USERNAME}/.local/state/bash/history
+RUN mkdir -p "${HISTFILE%/*}"

debian/README.md

@@ -55,6 +55,12 @@ The image runs as the non-root user `dev` (UID/GID 1000) and its working directo
 Container clients pick up the user without extra configuration. Every image built on this one
 inherits that label.
 
+`dev`'s login shell is bash, which appends each command to `$HISTFILE` as it is entered rather
+than at exit. `HISTFILE` is `/home/dev/.local/state/bash/history` rather than the default
+`~/.bash_history`, and that directory is created in the image, so mounting a volume on it keeps
+the shell history across container rebuilds, which is what the
+[Dev Container template](#dev-container-template) does.
+
 ## Not installed
 
 - **No development headers beyond libc.** `build-essential` covers the compiler, linker, and

debian/assets/.bashrc

@@ -9,6 +9,9 @@ HISTCONTROL=ignoreboth
 HISTSIZE=${HISTSIZE:-10000}
 HISTFILESIZE=${HISTFILESIZE:-20000}
 shopt -s histappend
+# Append each command to HISTFILE as it is entered. Waiting for the shell to exit
+# loses the session when the container is stopped before bash gets to write it.
+PROMPT_COMMAND=${PROMPT_COMMAND:+${PROMPT_COMMAND}$'\n'}'history -a'
 
 # Check terminal size after each command.
 shopt -s checkwinsize

debian/smoke-test.sh

@@ -7,6 +7,9 @@ git --version
 cc --version
 make --version
 
+echo "=== Verifying the shell history directory is writable ==="
+[ -w "${HISTFILE%/*}" ]
+
 echo "=== Verifying the C toolchain compiles and links ==="
 TMPDIR=$(mktemp -d)
 trap 'rm -rf "$TMPDIR"' EXIT