Do not write requirements.txt for pyproject.toml-based projects

Install pyproject.toml-based projects using `pip install .`. Do not use a
requirements.txt for this. The requirements.txt file is needed to handle pinned
versions extracted from the poetry.lock file.

Note that we cannot simply append `.` to the exported requirements.txt file.
Currently pip requires that either all requirements have a hash or none.
Including `.` would thus force us to omit hashes for all requirements.

Author: cjolowicz

bin/compile

@@ -265,14 +265,8 @@ mtime "pip.uninstall.time" "${start}"
 # If no requirements.txt file given, assume `setup.py develop` is intended.
 # This allows for people to ship a setup.py application to Heroku
 # (which is rare, but I vouch that it should work!)
-
-if [ ! -f requirements.txt ] && [ ! -f Pipfile ] ; then
-    if [ -f pyproject.toml ] ; then
-        # Editable installs are not supported for pyproject.toml-style projects.
-        echo "." > requirements.txt
-    else
-        echo "-e ." > requirements.txt
-    fi
+if [ ! -f requirements.txt ] && [ ! -f Pipfile ] && [ ! -f pyproject.toml ]; then
+    echo "-e ." > requirements.txt
 fi
 
 # Fix egg-links.

bin/steps/pip-install

@@ -34,15 +34,26 @@ if [ ! "$SKIP_PIP_INSTALL" ]; then
     mcount "tool.pip"
 
     # Count expected build failures.
-    if grep -q '==0.0.0' requirements.txt; then
+    if [ -f requirements.txt ] && grep -q '==0.0.0' requirements.txt; then
         mcount "failure.none-version"
     fi
 
     if [ ! -f "$BUILD_DIR/.heroku/python/bin/pip" ]; then
         exit 1
     fi
-    /app/.heroku/python/bin/pip install -r "$BUILD_DIR/requirements.txt" --exists-action=w --src=/app/.heroku/src --disable-pip-version-check --no-cache-dir 2>&1 | tee "$WARNINGS_LOG" | cleanup | indent
-    PIP_STATUS="${PIPESTATUS[0]}"
+
+    if [ -f requirements.txt ]; then
+        /app/.heroku/python/bin/pip install -r "$BUILD_DIR/requirements.txt" --exists-action=w --src=/app/.heroku/src --disable-pip-version-check --no-cache-dir 2>&1 | tee "$WARNINGS_LOG" | cleanup | indent
+        PIP_STATUS="${PIPESTATUS[0]}"
+    else
+        PIP_STATUS=0
+    fi
+
+    if [ "$PIP_STATUS" -eq 0 ] && [ -f pyproject.toml ]; then
+        /app/.heroku/python/bin/pip install . --exists-action=w --disable-pip-version-check --no-cache-dir 2>&1 | tee -a "$WARNINGS_LOG" | cleanup | indent
+        PIP_STATUS="${PIPESTATUS[0]}"
+    fi
+
     set -e
 
     show-warnings
@@ -53,8 +64,10 @@ if [ ! "$SKIP_PIP_INSTALL" ]; then
     fi
 
     # Smart Requirements handling
-    cp requirements.txt .heroku/python/requirements-declared.txt
-    /app/.heroku/python/bin/pip freeze --disable-pip-version-check > .heroku/python/requirements-installed.txt
+    if [ -f requirements.txt ]; then
+        cp requirements.txt .heroku/python/requirements-declared.txt
+        /app/.heroku/python/bin/pip freeze --disable-pip-version-check > .heroku/python/requirements-installed.txt
+    fi
 
     echo
 

bin/steps/pip-uninstall

@@ -5,7 +5,7 @@ set +e
 # shellcheck source=bin/utils
 source "$BIN_DIR/utils"
 
-if [ ! "$SKIP_PIP_INSTALL" ]; then
+if [ ! "$SKIP_PIP_INSTALL" ] && [ -f requirements.txt ]; then
 
   if [[ -f .heroku/python/requirements-declared.txt ]]; then