Improve package manager bootstrap error messages

* Any errors are now indented using the same indent helper
  used for other buildpack subprocesses.
* Adds "temporary network issue" verbiage based on that now
  used for the Python runtime download step.

CHANGELOG.md

@@ -2,6 +2,7 @@
 
 ## [Unreleased]
 
+- Improved the error messages shown if installing pip/Poetry/Pipenv fails. ([#1764](https://github.com/heroku/heroku-buildpack-python/pull/1764))
 - Stopped installing pip into Poetry's virtual environment. ([#1761](https://github.com/heroku/heroku-buildpack-python/pull/1761))
 
 ## [v278] - 2025-02-24

lib/pip.sh

@@ -46,22 +46,26 @@ function pip::install_pip_setuptools_wheel() {
 	# app's requirements.txt in the last build). The install will be a no-op if the versions match.
 	output::step "Installing ${packages_display_text}"
 
+	# shellcheck disable=SC2310 # This function is invoked in an 'if' condition so set -e will be disabled.
 	if ! {
 		python "${bundled_pip_module_path}" \
 			install \
 			--disable-pip-version-check \
 			--no-cache-dir \
 			--no-input \
 			--quiet \
-			"${packages_to_install[@]}"
+			"${packages_to_install[@]}" \
+			|& output::indent
 	}; then
 		output::error <<-EOF
 			Error: Unable to install pip.
 
+			In some cases, this happens due to a temporary issue with
+			the network connection or Python Package Index (PyPI).
+
 			Try building again to see if the error resolves itself.
 
-			If that does not help, check the status of PyPI (the Python
-			package repository service), here:
+			If that does not help, check the status of PyPI here:
 			https://status.python.org
 		EOF
 		meta_set "failure_reason" "install-package-manager::pip"

lib/pipenv.sh

@@ -18,22 +18,27 @@ function pipenv::install_pipenv() {
 	# TODO: Install Pipenv into a venv so it isn't leaked into the app environment.
 	# TODO: Skip installing Pipenv if its version hasn't changed (once it's installed into a venv).
 	# TODO: Explore viability of making Pipenv only be available during the build, to reduce slug size.
+
+	# shellcheck disable=SC2310 # This function is invoked in an 'if' condition so set -e will be disabled.
 	if ! {
 		pip \
 			install \
 			--disable-pip-version-check \
 			--no-cache-dir \
 			--no-input \
 			--quiet \
-			"pipenv==${PIPENV_VERSION}"
+			"pipenv==${PIPENV_VERSION}" \
+			|& output::indent
 	}; then
 		output::error <<-EOF
 			Error: Unable to install Pipenv.
 
+			In some cases, this happens due to a temporary issue with
+			the network connection or Python Package Index (PyPI).
+
 			Try building again to see if the error resolves itself.
 
-			If that does not help, check the status of PyPI (the Python
-			package repository service), here:
+			If that does not help, check the status of PyPI here:
 			https://status.python.org
 		EOF
 		meta_set "failure_reason" "install-package-manager::pipenv"

lib/poetry.sh

@@ -46,7 +46,8 @@ function poetry::install_poetry() {
 		# it bundles its own copy for use as a fallback. As such we don't need to install pip
 		# into the Poetry venv (and in fact, Poetry wouldn't use this install anyway, since
 		# it only finds an external pip if it exists in the target venv).
-		if ! python -m venv --without-pip "${poetry_venv_dir}"; then
+		# shellcheck disable=SC2310 # This function is invoked in an 'if' condition so set -e will be disabled.
+		if ! python -m venv --without-pip "${poetry_venv_dir}" |& output::indent; then
 			output::error <<-EOF
 				Internal Error: Unable to create virtual environment for Poetry.
 
@@ -65,22 +66,26 @@ function poetry::install_poetry() {
 		# We must call the venv Python directly here, rather than relying on pip's `--python`
 		# option, since `--python` was only added in pip v22.3, so isn't supported by the older
 		# pip versions bundled with Python 3.9/3.10.
+		# shellcheck disable=SC2310 # This function is invoked in an 'if' condition so set -e will be disabled.
 		if ! {
 			"${poetry_venv_dir}/bin/python" "${bundled_pip_module_path}" \
 				install \
 				--disable-pip-version-check \
 				--no-cache-dir \
 				--no-input \
 				--quiet \
-				"poetry==${POETRY_VERSION}"
+				"poetry==${POETRY_VERSION}" \
+				|& output::indent
 		}; then
 			output::error <<-EOF
 				Error: Unable to install Poetry.
 
+				In some cases, this happens due to a temporary issue with
+				the network connection or Python Package Index (PyPI).
+
 				Try building again to see if the error resolves itself.
 
-				If that does not help, check the status of PyPI (the Python
-				package repository service), here:
+				If that does not help, check the status of PyPI here:
 				https://status.python.org
 			EOF
 			meta_set "failure_reason" "install-package-manager::poetry"