Tests: Add additional coverage of editable package installation

Previously the editable installation mode test only checked whether
the build completed successfully, not whether the installed editable
packages worked.

Now the packages are tested via their entrypoints in the following scenarios:
1. During the `bin/post_compile` hook
2. By a later buildpack in the build
3. At runtime

In particular, (2) catches the issue described in #1006 when setuptools is upgraded,
and (1) + (3) will be useful to verify the solution to #1006 hasn't broken the other cases.

GUS-W-10047026.

[skip-changelog]

spec/fixtures/requirements_editable/bin/compile

@@ -0,0 +1,10 @@
+#!/usr/bin/env bash
+
+# This file is run by the inline buildpack, and tests that editable reqirements are
+# usable by buildpacks that run after the Python buildpack during the build.
+
+set -euo pipefail
+
+BUILD_DIR="${1}"
+
+exec "${BUILD_DIR}/bin/test-entrypoints"

spec/fixtures/requirements_editable/bin/detect

@@ -0,0 +1,7 @@
+#!/usr/bin/env bash
+
+# This file is run by the inline buildpack.
+
+set -euo pipefail
+
+echo "Inline"

spec/fixtures/requirements_editable/bin/post_compile

@@ -0,0 +1,5 @@
+#!/usr/bin/env bash
+
+set -euo pipefail
+
+exec bin/test-entrypoints

spec/fixtures/requirements_editable/bin/test-entrypoints

@@ -0,0 +1,9 @@
+#!/usr/bin/env bash
+
+set -euo pipefail
+
+echo -n "Running entrypoint for the local package: "
+local_package
+
+echo -n "Running entrypoint for the VCS package: "
+gunicorn --version

spec/fixtures/requirements_editable/local_package/local_package/__init__.py

@@ -0,0 +1,2 @@
+def hello():
+    print("Hello!")

spec/fixtures/requirements_editable/local_package/setup.cfg

@@ -0,0 +1,10 @@
+[metadata]
+name = local_package
+version = 0.0.1
+
+[options]
+packages = local_package
+
+[options.entry_points]
+console_scripts =
+    local_package = local_package:hello

spec/fixtures/requirements_editable/setup.py → spec/fixtures/requirements_editable/local_package/setup.py

@@ -1,5 +1,3 @@
 from setuptools import setup
 
-setup(
-  name='test',
-)
+setup()

spec/fixtures/requirements_editable/requirements.txt

@@ -1,2 +1,2 @@
--e git+https://github.com/certifi/python-certifi#egg=certifi
--e .
+-e ./local_package
+-e git+https://github.com/benoitc/[email protected]#egg=gunicorn

spec/hatchet/pip_spec.rb

@@ -88,12 +88,63 @@
   end
 
   context 'when requirements.txt contains editable requirements' do
-    let(:app) { Hatchet::Runner.new('spec/fixtures/requirements_editable') }
+    let(:buildpacks) { [:default, 'heroku-community/inline'] }
+    let(:app) { Hatchet::Runner.new('spec/fixtures/requirements_editable', buildpacks: buildpacks) }
 
-    # TODO: Make this test the path rewriting, and --src directory handling,
-    # and that the packages work during all of hooks, later buildpacks, runtime,
-    # and on subsequent builds (where the paths have to be migrated back).
-    include_examples 'installs successfully using pip'
+    it 'rewrites .pth paths correctly for hooks, later buildpacks, runtime and cached builds' do
+      app.deploy do |app|
+        expect(clean_output(app.output)).to match(Regexp.new(<<~REGEX))
+          remote: -----> Installing requirements with pip
+          remote:        Obtaining file:///tmp/build_.*/local_package \\(from -r /tmp/build_.*/requirements.txt \\(line 1\\)\\)
+          remote:        Obtaining gunicorn from git\\+https://github.com/benoitc/[email protected]#egg=gunicorn \\(from -r /tmp/build_.*/requirements.txt \\(line 2\\)\\)
+          remote:          Cloning https://github.com/benoitc/gunicorn \\(to revision 20.1.0\\) to /app/.heroku/src/gunicorn
+          remote:        Installing collected packages: gunicorn, local-package
+          remote:          Running setup.py develop for gunicorn
+          remote:          Running setup.py develop for local-package
+          remote:        Successfully installed gunicorn local-package
+          remote: -----> Running post-compile hook
+          remote: Running entrypoint for the local package: Hello!
+          remote: Running entrypoint for the VCS package: gunicorn \\(version 20.1.0\\)
+          remote: -----> Inline app detected
+          remote: Running entrypoint for the local package: Hello!
+          remote: Running entrypoint for the VCS package: gunicorn \\(version 20.1.0\\)
+        REGEX
+
+        # Test rewritten paths work at runtime.
+        expect(app.run('bin/test-entrypoints')).to include(<<~OUTPUT)
+          Running entrypoint for the local package: Hello!
+          Running entrypoint for the VCS package: gunicorn (version 20.1.0)
+        OUTPUT
+
+        # Test restoring paths in the cached .pth files works correctly.
+        app.commit!
+        app.push!
+        expect(clean_output(app.output)).to match(Regexp.new(<<~REGEX))
+          remote: -----> No change in requirements detected, installing from cache
+          remote: -----> Using cached install of python-#{DEFAULT_PYTHON_VERSION}
+          remote: -----> Installing pip 20.2.4, setuptools 47.1.1 and wheel 0.36.2
+          remote: -----> Installing SQLite3
+          remote: -----> Installing requirements with pip
+          remote:        Obtaining file:///tmp/build_.*/local_package \\(from -r /tmp/build_.*/requirements.txt \\(line 1\\)\\)
+          remote:        Obtaining gunicorn from git\\+https://github.com/benoitc/[email protected]#egg=gunicorn \\(from -r /tmp/build_.*/requirements.txt \\(line 2\\)\\)
+          remote:          Cloning https://github.com/benoitc/gunicorn \\(to revision 20.1.0\\) to /app/.heroku/src/gunicorn
+          remote:        Installing collected packages: gunicorn, local-package
+          remote:          Attempting uninstall: gunicorn
+          remote:            Found existing installation: gunicorn 20.1.0
+          remote:            Uninstalling gunicorn-20.1.0:
+          remote:              Successfully uninstalled gunicorn-20.1.0
+          remote:          Running setup.py develop for gunicorn
+          remote:          Running setup.py develop for local-package
+          remote:        Successfully installed gunicorn local-package
+          remote: -----> Running post-compile hook
+          remote: Running entrypoint for the local package: Hello!
+          remote: Running entrypoint for the VCS package: gunicorn \\(version 20.1.0\\)
+          remote: -----> Inline app detected
+          remote: Running entrypoint for the local package: Hello!
+          remote: Running entrypoint for the VCS package: gunicorn \\(version 20.1.0\\)
+        REGEX
+      end
+    end
   end
 
   context 'when there is only a setup.py' do