demos: run scripts in a fixed environment and record with term-transcript

Currently, there is no way provided to merely run scripts in
a fixed environment (without recording).

Short-term TODOs (done in descendant commits):
  - Fix the terminal width
  - Document the script

demos/run_scripts.sh

@@ -0,0 +1,59 @@
+#!/bin/bash
+set -euo pipefail
+. "$(dirname "$0")"/setup_standard_config.sh
+
+# NOTE ON TOOLS: the only two nice tools I'm aware of that support our use-case
+# (non-animated svgs) are https://github.com/slowli/term-transcript and
+# https://github.com/FHPythonUtils/AnsiToImg. They have slightly different
+# limitations and advantages. If one of them stops being developed, we could
+# look at the other one.
+#
+# AnsiToImg can also generate PNGs, but that is currently harder to setup than
+# `convert`. `convert` supports different backends. I do not completely
+# understand them. On Debian, it did not work well without `sudo apt install
+# inkscape`. It's unclear to me whether `convert` used Inkscape or one of its
+# dependencies. Inkscape can be also used manually for SVG -> PNG conversion.
+which term-transcript > /dev/null \
+  || (echo '`term-transcipt` must be installed with e.g.'\
+           '`cargo binstall term-transcript-cli`.' \
+           'See also https://github.com/slowli/term-transcript' >&2;
+      false)
+which convert > /dev/null \
+  || echo '`convert` from ImageMagick needs to be installed to create pngs.' \
+          'Only svgs will be created.' >&2
+
+echo "jj --version: (set PATH to change)"
+jj --version
+
+run_script_through_term_transcript_and_pipe_result_to_stderr() {
+  script="$1"
+  script_base="${script%.sh}"
+  script_base="${script_base#demo_}"
+  outfile=$(mktemp --tmpdir "$script_base"-output-XXXX.ansi)
+  # We use `term-transcript capture` instead of `term-transcript exec` so that
+  # we can show the output of the script via `tee`.
+  (bash "$script" || (echo "SCRIPT FAILED WITH EXIT CODE $?"; false)) 2>&1 | \
+    tee "$outfile"
+  term-transcript capture \
+      --no-inputs --pure-svg --palette powershell \
+      --out "$script_base".svg "$script_base" \
+      < "$outfile"
+  rm "$outfile"
+}
+
+for script in "$@"; do
+  run_script_through_term_transcript_and_pipe_result_to_stderr "$script" 2>&1
+  # By default, 1 SVG unit becomes 1 pixel. The term-transcript output
+  # defaults to 720 SVG units width.
+  #
+  # `-background black` is important because the SVGs use transparency to make
+  # rounded corners, and the transparent portion becomes white by default.
+  # TODO(ilyagr): Figure out if `convert` can make PNGs have transparency.
+  #
+  # `-resize 100%` is a no-op. `-resize 700x10000`` would make the width 700 px
+  # and preserve aspect ratio.
+  which convert > /dev/null \
+    && convert  -colors 63 -background black -resize 100%  \
+            "$script_base".svg "$script_base".png \
+    || true
+done

demos/setup_standard_config.sh

@@ -0,0 +1,27 @@
+# This script is meant to be run with `source` from a fresh bash
+# shell. Thus no shebang.
+# shellcheck shell=bash
+set -euo pipefail
+
+JJ_CONFIG=$(mktemp --tmpdir jjconfig-XXXX.toml)
+export JJ_CONFIG
+cat <<'EOF' > "$JJ_CONFIG"
+[user]
+name = "JJ Fan"
+email = "jjfan@example.com"
+
+[operation]
+hostname = "jujube"
+username = "jjfan"
+
+[ui]
+color="always"
+paginate="never"
+EOF
+
+GIT_CONFIG_GLOBAL=$(mktemp --tmpdir gitconfig-XXXX)
+export GIT_CONFIG_GLOBAL
+cat <<'EOF' > "$GIT_CONFIG_GLOBAL"
+[color]
+ui=always
+EOF