refactor-top-level-with-away.sh

#!/usr/bin/env bash

set -e

NIX_ID_RE="[a-zA-Z_][0-9A-Za-z_'-]*"
LIB_RE="$(sed -z 's/\n/|/g; s/|$/)/; s/^/(/' /tmp/names/lib)"

doWork() {
    f=$1

    # Find the top-level `with` statements
    for top in $(rg '^(in )?with ' $f | sed 's/in with //; s/with //; s/;//;'); do

        # We ought to have previously found all the names exported from that attrset.
        names="/tmp/names/$top"
        if [ ! -e "$names" ]; then
            echo Cannot find $names
            exit 1
        fi

        # Have Nix parse the file (no comments) then search through the identifiers for the names
        # that were being accessed through the top-level `with`. The pipeline does this:
        #
        # 1. Remove comments by parsing the nix file
        # 2. Select out just the identifiers (plus keywords)
        # 3. Deduplicate them with `sort` and `uniq`
        # 4. Have `nixfmt` format the expression
        # 5. Replace the top-level `with` with `let ... inherit expr ... in`
        replace="$(nix-instantiate --parse $f | \
            rg -o "$NIX_ID_RE" | \
            rg -xf $names | \
            sort | \
            uniq | \
            perl -0777 -p -e "s/^/let inherit ($top) /; s/\$/; in EOF/" | \
            nixfmt | \
            sed 's/^EOF//')"
        perl -i -p -e "s/^with $top*;/$replace/g" $f

        # Since we replaced the uses at the top level, remove excess with.
        perl -i -p -e "s/with $top;\s*//g" $f
    done

    # Access names from `lib` in just one way.
    perl -0777 -i -p -e "s/lib\.${LIB_RE}/\$1/g" $f

    # Combine adjacent `in ... let` scopes.
    perl -0777 -i -p -e 's/in\s*let\s*/\n  /g' $f

    # Make sure that the file still parses.
    while ! nix-instantiate --parse $f > /dev/null; do
        read -p "Press <Return> to re-parse $f "
    done

    # Show the changes
    git diff $f
    echo "Look through $f above"

    # Commit it with a standard commit message.
    read -p "Press <Return> to commit it! "

    # Make sure that the file still parses.
    while ! nix-instantiate --parse $f > /dev/null; do
        read -p "Press <Return> to re-parse $f "
    done

    git commit -m "$(printf 'Avoid top-level `with ...;` in %s' $f)" $f
}

ROOT="."

# If called with an argument, it's a either a file or a directory
if [ "$#" -ne 0 ]; then
    if [ -f "$1" ]; then
        doWork "$1"
        exit 0
    elif [ -d "$1" ]; then
        ROOT="$1"
    else
        echo "$1 is neither file nor directory"
        exit 1
    fi
fi

# Loop through each file, working on it.
for f in $(rg '^(in )?with ' -l --sort=path -tnix "$ROOT"); do
    doWork $f
done