guix: Add source-able bash prelude and utils

Author: dongcarl

Diff for: contrib/guix/libexec/prelude.bash

@@ -0,0 +1,60 @@
+#!/usr/bin/env bash
+export LC_ALL=C
+set -e -o pipefail
+
+# shellcheck source=../../shell/realpath.bash
+source contrib/shell/realpath.bash
+
+# shellcheck source=../../shell/git-utils.bash
+source contrib/shell/git-utils.bash
+
+################
+# Required non-builtin commands should be invokable
+################
+
+check_tools() {
+    for cmd in "$@"; do
+        if ! command -v "$cmd" > /dev/null 2>&1; then
+            echo "ERR: This script requires that '$cmd' is installed and available in your \$PATH"
+            exit 1
+        fi
+    done
+}
+
+check_tools cat env readlink dirname basename git
+
+################
+# We should be at the top directory of the repository
+################
+
+same_dir() {
+    local resolved1 resolved2
+    resolved1="$(bash_realpath "${1}")"
+    resolved2="$(bash_realpath "${2}")"
+    [ "$resolved1" = "$resolved2" ]
+}
+
+if ! same_dir "${PWD}" "$(git_root)"; then
+cat << EOF
+ERR: This script must be invoked from the top level of the git repository
+
+Hint: This may look something like:
+    env FOO=BAR ./contrib/guix/guix-<blah>
+
+EOF
+exit 1
+fi
+
+################
+# Set common variables
+################
+
+VERSION="${VERSION:-$(git_head_version)}"
+DISTNAME="${DISTNAME:-bitcoin-${VERSION}}"
+
+version_base_prefix="${PWD}/guix-build-"
+VERSION_BASE="${version_base_prefix}${VERSION}"  # TOP
+
+DISTSRC_BASE="${DISTSRC_BASE:-${VERSION_BASE}}"
+
+OUTDIR_BASE="${OUTDIR_BASE:-${VERSION_BASE}/output}"

Diff for: contrib/shell/git-utils.bash

@@ -0,0 +1,14 @@
+#!/usr/bin/env bash
+
+git_root() {
+    git rev-parse --show-toplevel 2> /dev/null
+}
+
+git_head_version() {
+    local recent_tag
+    if recent_tag="$(git describe --exact-match HEAD 2> /dev/null)"; then
+        echo "${recent_tag#v}"
+    else
+        git rev-parse --short=12 HEAD
+    fi
+}

Diff for: contrib/shell/realpath.bash

@@ -0,0 +1,71 @@
+#!/usr/bin/env bash
+
+# Based on realpath.sh written by Michael Kropat
+# Found at: https://github.com/mkropat/sh-realpath/blob/65512368b8155b176b67122aa395ac580d9acc5b/realpath.sh
+
+bash_realpath() {
+    canonicalize_path "$(resolve_symlinks "$1")"
+}
+
+resolve_symlinks() {
+    _resolve_symlinks "$1"
+}
+
+_resolve_symlinks() {
+    _assert_no_path_cycles "$@" || return
+
+    local dir_context path
+    if path=$(readlink -- "$1"); then
+        dir_context=$(dirname -- "$1")
+        _resolve_symlinks "$(_prepend_dir_context_if_necessary "$dir_context" "$path")" "$@"
+    else
+        printf '%s\n' "$1"
+    fi
+}
+
+_prepend_dir_context_if_necessary() {
+    if [ "$1" = . ]; then
+        printf '%s\n' "$2"
+    else
+        _prepend_path_if_relative "$1" "$2"
+    fi
+}
+
+_prepend_path_if_relative() {
+    case "$2" in
+        /* ) printf '%s\n' "$2" ;;
+         * ) printf '%s\n' "$1/$2" ;;
+    esac
+}
+
+_assert_no_path_cycles() {
+    local target path
+
+    target=$1
+    shift
+
+    for path in "$@"; do
+        if [ "$path" = "$target" ]; then
+            return 1
+        fi
+    done
+}
+
+canonicalize_path() {
+    if [ -d "$1" ]; then
+        _canonicalize_dir_path "$1"
+    else
+        _canonicalize_file_path "$1"
+    fi
+}
+
+_canonicalize_dir_path() {
+    (cd "$1" 2>/dev/null && pwd -P)
+}
+
+_canonicalize_file_path() {
+    local dir file
+    dir=$(dirname -- "$1")
+    file=$(basename -- "$1")
+    (cd "$dir" 2>/dev/null && printf '%s/%s\n' "$(pwd -P)" "$file")
+}