Extract checks from release target to script

This extracts the check logic from the release target in Makefile
to a new script, check-version.sh. The code is also modified,
mainly to account for different ways output is displayed and errors
are reported and treated in a Makefile versus a standalone shell
script. (The .sh suffix is for consistency with the naming of
init-tests-after-clone.sh and is *not* intended to suggest sourcing
the script; this script should be executed, not sourced.)

.gitattributes

@@ -1,3 +1,4 @@
 test/fixtures/* eol=lf
 init-tests-after-clone.sh eol=lf
+check-version.sh eol=lf
 Makefile eol=lf

Makefile

@@ -7,31 +7,7 @@ clean:
 	rm -rf build/ dist/ .eggs/ .tox/
 
 release: clean
-	# Check that VERSION and changes.rst exist and have no uncommitted changes
-	test -f VERSION
-	test -f doc/source/changes.rst
-	git status -s VERSION doc/source/changes.rst
-	@test -z "$$(git status -s VERSION doc/source/changes.rst)"
-
-	# Check that ALL changes are commited (can comment out if absolutely necessary)
-	git status -s
-	@test -z "$$(git status -s)"
-
-	# Check that latest tag matches version and is the current head we're releasing
-	@version_file="$$(cat VERSION)" && \
-	changes_file="$$(awk '/^[0-9]/ {print $$0; exit}' doc/source/changes.rst)" && \
-	config_opts="$$(printf ' -c versionsort.suffix=-%s' alpha beta pre rc RC)" && \
-	latest_tag=$$(git $$config_opts tag -l '[0-9]*' --sort=-v:refname | head -n1) && \
-	head_sha=$$(git rev-parse HEAD) latest_tag_sha=$$(git rev-parse "$$latest_tag") && \
-	printf '%-14s = %s\n' 'VERSION file'   "$$version_file" \
-	                      'changes.rst'    "$$changes_file" \
-	                      'Latest tag'     "$$latest_tag" \
-	                      'HEAD SHA'       "$$head_sha" \
-	                      'Latest tag SHA' "$$latest_tag_sha" && \
-	test "$$version_file" = "$$changes_file" && \
-	test "$$latest_tag" = "$$version_file" && \
-	test "$$head_sha" = "$$latest_tag_sha"
-
+	./check-version.sh
 	make force_release
 
 force_release: clean

check-version.sh

@@ -0,0 +1,46 @@
+#!/usr/bin/env bash
+#
+# This script checks if we appear ready to build and publish a new release.
+# See the release instructions in README.md for the steps to make this pass.
+
+set -eEfuo pipefail
+trap 'printf "%s: Check failed. Stopping.\n" "$0" >&2' ERR
+
+readonly version_path='VERSION'
+readonly changes_path='doc/source/changes.rst'
+
+printf 'Checking current directory.\n'
+test "$(cd -- "$(dirname -- "$0")" && pwd)" = "$(pwd)"  # Ugly, but portable.
+
+printf 'Checking that %s and %s exist and have no committed changes.\n' \
+    "$version_path" "$changes_path"
+test -f "$version_path"
+test -f "$changes_path"
+git status -s -- "$version_path" "$changes_path"
+test -z "$(git status -s -- "$version_path" "$changes_path")"
+
+# This section can be commented out, if absolutely necessary.
+printf 'Checking that ALL changes are committed.\n'
+git status -s
+test -z "$(git status -s)"
+
+printf 'Gathering current version, latest tag, and current HEAD commit info.\n'
+version_version="$(cat "$version_path")"
+changes_version="$(awk '/^[0-9]/ {print $0; exit}' "$changes_path")"
+config_opts="$(printf ' -c versionsort.suffix=-%s' alpha beta pre rc RC)"
+latest_tag="$(git $config_opts tag -l '[0-9]*' --sort=-v:refname | head -n1)"
+head_sha="$(git rev-parse HEAD)"
+latest_tag_sha="$(git rev-parse "$latest_tag")"
+
+# Display a table of all the current version, tag, and HEAD commit information.
+printf '%-14s = %s\n' 'VERSION file'   "$version_version" \
+                      'changes.rst'    "$changes_version" \
+                      'Latest tag'     "$latest_tag" \
+                      'HEAD SHA'       "$head_sha" \
+                      'Latest tag SHA' "$latest_tag_sha"
+
+# Check that latest tag matches version and is the current HEAD we're releasing
+test "$version_version" = "$changes_version"
+test "$latest_tag" = "$version_version"
+test "$head_sha" = "$latest_tag_sha"
+printf 'OK, everything looks good.\n'