Extract build from force_release target to script

This moves the conditional build dependency installation logic and
build logic from the force_release Makefile target to a shell
script build-release.sh, which force_release calls. The code is
changed to clean it up, and also to account for differences between
how output is displayed and errors reported in Makefiles and shell
scripts. (As in check-version.sh, the .sh suffix does not signify
anything about how the script is to be used: like the other shell
scripts in the project, this should be executed, no sourced.)

Author: EliahKagan

.gitattributes

@@ -1,4 +1,5 @@
 test/fixtures/* eol=lf
 init-tests-after-clone.sh eol=lf
-check-version.sh eol=lf
 Makefile eol=lf
+check-version.sh eol=lf
+build-release.sh eol=lf

Makefile

@@ -11,17 +11,6 @@ release: clean
 	make force_release
 
 force_release: clean
-	# IF we're in a virtual environment, add build tools
-	test -z "$$VIRTUAL_ENV" || pip install -U build twine
-
-	# Build the sdist and wheel that will be uploaded to PyPI.
-	if test -n "$$VIRTUAL_ENV"; then \
-		python -m build --sdist --wheel; \
-	else \
-		python3 -m build --sdist --wheel || \
-		{ echo "Use a virtual-env with 'python -m venv env && source env/bin/activate' instead" && false; }; \
-	fi
-
-	# Upload to PyPI and push the tag.
+	./build-release.sh
 	twine upload dist/*
 	git push --tags origin main

build-release.sh

@@ -0,0 +1,22 @@
+#!/usr/bin/env bash
+#
+# This script builds a release. If run in a venv, it auto-installs its tools.
+# You may want to run "make release" instead of running this script directly.
+
+set -eEu
+
+if test -n "${VIRTUAL_ENV:-}"; then
+    deps=(build twine)  # Install twine along with build, as we need it later.
+    printf 'Virtual environment detected. Adding packages: %s\n' "${deps[*]}"
+    pip install -U "${deps[@]}"
+    printf 'Starting the build.\n'
+    python -m build --sdist --wheel
+else
+    suggest_venv() {
+        venv_cmd='python -m venv env && source env/bin/activate'
+        printf "Use a virtual-env with '%s' instead.\n" "$venv_cmd"
+    }
+    trap suggest_venv ERR  # This keeps the original exit (error) code.
+    printf 'Starting the build.\n'
+    python3 -m build --sdist --wheel  # Outside a venv, use python3.
+fi

check-version.sh

@@ -1,7 +1,8 @@
 #!/usr/bin/env bash
 #
-# This script checks if we appear ready to build and publish a new release.
+# This script checks if we are in a consistent state to build a new release.
 # See the release instructions in README.md for the steps to make this pass.
+# You may want to run "make release" instead of running this script directly.
 
 set -eEfuo pipefail
 trap 'printf "%s: Check failed. Stopping.\n" "$0" >&2' ERR