Populate repo with initial version

README.md

@@ -1,2 +1,60 @@
 # direnv-cache
 
+## Setup
+
+direnv-cache consists of two components: the direnv-cache script and an
+extension to direnv's stdlib.
+
+To set up direnv-cache, make direnv read the provided direnvrc, eg. via
+
+    cp direnvrc ~/.config/direnv/direnvrc
+
+and install direnv-cache somewhere in your PATH.
+
+If you use home-manager, you can add the following to your configuration
+
+    ...
+    let
+        direnv-cache = pkgs.callPackage ./path/to/this/repo {};
+    in
+    ...
+
+    home.packages = [ ... direnv-cache ... ];
+    programs.direnv = {
+        enable = true;
+        enableBashIntegration = true;
+        stdlib = builtins.readFile direnv-cache.direnvrc;
+    };
+    ...
+
+## Usage
+
+The following assumes a working direnv setup.
+
+Use the cache function in your `.envrc` files, eg.
+
+    cache <<EOF
+      # everything in here will be cached
+      use nix -p hello
+    EOF
+
+    # you can also have stuff outside the cached region
+    export PATH=/some/other/path:$PATH
+
+If you now enter the directory, direnv will tell you that the environment
+is not yet cached. We can fix that by running `direnv-cache reload`. This
+will also tell direnv to reload. From now on, if you enter the directory,
+direnv will load the cached environment.
+
+Re-run `direnv-cache reload` whenever your `.envrc` or other dependencies change
+to update the cache.
+
+## How it works
+
+Everything piped into the `cache` function is stored in a recipe file in
+direnv-cache's cache directory when the `.envrc` is evaluated. Then, if the
+environment cache exists, it is sourced.
+
+When `direnv-cache reload` is called, it looks for a recipe file for the
+current directory, and runs it. A diff of the environments before and after the
+recipe is run is written to the directory-specific cache file.

default.nix

@@ -0,0 +1,3 @@
+{ pkgs ? import <nixpkgs> {} }:
+(pkgs.writers.writeBashBin "direnv-cache" ./direnv-cache).overrideAttrs
+  (o: { passthru = { direnvrc = ./direnvrc; }; })

direnv-cache

@@ -0,0 +1,106 @@
+#!/usr/bin/env bash
+
+set -eo pipefail
+
+# Dumps all environment variables sorted alphabetically.  Uses zero byte as a
+# delimiter since bash variables can not contain '\0'.
+dumpEnv() {
+    env -0 | sort -z
+}
+
+# Retrieves the value of variable name passed as $1 in dumped environment
+# passed as $2 (see dumpEnv)
+getByName() {
+    local name="$1"
+    local envFile="$2"
+    grep -z "^${name}=" $envFile | cut -z -f2- -d '=' | tr -d '\0'
+}
+
+# Produces a diff of two given environment dumps, suitable for consumption by
+# bash. Given environment dumps A and B (both generated by dumpEnv),
+#
+#     source A; source <(diffEnvs A B)
+#
+# shall be equivalent to
+#
+#     source B
+#
+diffEnvs() {
+    local name
+    local old="$1"
+    local new="$2"
+
+    while read -r -d '' line; do
+        name=$(tr -d '\0' <<<"$line" | head -n1 | cut -f1 -d'=')
+        if ! getByName "$name" "$new" >/dev/null; then
+            echo "export -n '${name}'"
+        fi
+    done <"$old"
+
+    while read -rd $'\0' line; do
+        name=$(tr -d '\0' <<<"$line" | head -n1 | cut -f1 -d'=')
+        if getByName "$name" "$old" >/dev/null; then
+            # found in old env, check if values match
+            if ! grep -z "^${line}\$" "$old" >/dev/null; then
+                # variable has changed
+                echo "export ${line@Q}"
+            fi
+        else
+            # variable is new
+            echo "export ${line@Q}"
+        fi
+    done <"$new"
+}
+
+usage() {
+    echo "${BASH_SOURCE[0]} COMMAND"
+    echo
+    echo "Commands:"
+    echo -e "\tstatus,s: Show cache status"
+    echo -e "\treload,r: Recreate cache from .envrc"
+    echo -e "\tclear,c: Remove cache file for current directory"
+}
+
+getCacheFilePath() {
+    local cacheDir="${XDG_CACHE_HOME:-$HOME/.cache}/direnv-cache"
+    echo "${cacheDir}/$(pwd | sha1sum | tr -d ' -')"
+}
+
+cmd="$1"
+
+if ! [[ -e .envrc ]]; then
+    echo "Error, no .envrc found in current directory"
+    exit 1
+fi
+
+cacheFile=$(getCacheFilePath)
+
+case $cmd in
+    reload|r)
+        echo "Re-creating cache"
+        mkdir -p "$(dirname ${cacheFile})"
+        dumpEnv > "${cacheFile}.pre"
+        source <(direnv stdlib)
+        if [[ .envrc -nt ${cacheFile}.recipe ]]; then
+            direnv exec . true > /dev/null
+        fi
+        source "${cacheFile}.recipe"
+        dumpEnv > "${cacheFile}.post"
+        diffEnvs "${cacheFile}.pre" "${cacheFile}.post" > "$cacheFile"
+        rm "${cacheFile}.pre" "${cacheFile}.post"
+        echo "Environment cached in $cacheFile, telling direnv to reload"
+        direnv reload
+        ;;
+    status|s)
+        shift
+        ls "$cacheFile" "$@"
+        ;;
+    clear|c)
+        if [[ -e "$cacheFile" ]]; then
+            rm "$cacheFile"
+        fi
+        ;;
+    *)
+        usage
+        exit 1
+esac

direnvrc

@@ -0,0 +1,17 @@
+# -*- mode: sh -*-
+
+cache() {
+
+    local cacheDir="${XDG_CACHE_HOME:-$HOME/.cache}/direnv-cache"
+    mkdir -p "$cacheDir"
+    local cacheFile
+    cacheFile="${cacheDir}/$(pwd | sha1sum | tr -d ' -')"
+    cat - > "${cacheFile}.recipe"
+    if [[ -e "$cacheFile" ]]; then
+        echo "Using cached environment from $cacheFile"
+        . $cacheFile
+    else
+        echo "Environment not cached"
+    fi
+}
+