bugfix: config edit should work with a malformed spack.yaml

If you don't format `spack.yaml` correctly, `spack config edit` still fails and
you have to edit your `spack.yaml` manually.

- [x] Add some code to `_main()` to defer `ConfigFormatError` when loading the
  environment, until we know what command is being run.

- [x] Make `spack config edit` use `SPACK_ENV` instead of the config scope
  object to find `spack.yaml`, so it can work even if the environment is bad.

Co-authored-by: scheibelp <scheibel1@llnl.gov>

share/spack/qa/run-unit-tests

@@ -49,6 +49,8 @@ fi
 
 $coverage_run $(which spack) unit-test -x --verbose
 
+bash "$QA_DIR/test-env-cfg.sh"
+
 # Delete the symlink going from ./lib/spack/docs/_spack_root back to
 # the initial directory, since it causes ELOOP errors with codecov/actions@2
 if [[ "$COVERAGE" == "true" ]]; then

share/spack/qa/test-env-cfg.sh

@@ -0,0 +1,73 @@
+#!/bin/bash
+#
+# Copyright 2013-2021 Lawrence Livermore National Security, LLC and other
+# Spack Project Developers. See the top-level COPYRIGHT file for details.
+#
+# SPDX-License-Identifier: (Apache-2.0 OR MIT)
+
+#
+# This script ensures that Spack can help users edit an environment's
+# manifest file even when it has invalid configuration.
+#
+
+export QA_DIR=$(dirname "$0")
+export SHARE_DIR=$(cd "$QA_DIR/.." && pwd)
+
+# Include convenience functions
+. "$QA_DIR/test-framework.sh"
+. "$QA_DIR/setup.sh"
+
+# Source setup-env.sh before tests
+. "$SHARE_DIR/setup-env.sh"
+
+env_cfg=""
+
+function cleanup {
+  # Regardless of whether the test fails or succeeds, we can't remove the
+  # environment without restoring spack.yaml to match the schema
+  if [ ! -z "env_cfg" ]; then
+    echo "\
+spack:
+  specs: []
+  view: False
+" > "$env_cfg"
+  fi
+
+  spack env deactivate
+  spack env rm -y broken-cfg-env
+}
+
+trap cleanup EXIT
+
+spack env create broken-cfg-env
+echo "Activating test environment"
+spack env activate broken-cfg-env
+env_cfg=`spack config --scope=env:broken-cfg-env edit --print-file`
+# Save this, so we can make sure it is reported correctly when the environment
+# contains broken configuration
+orig_manifest_path="$env_cfg"
+
+echo "Environment config file: $env_cfg"
+# Make sure we got a manifest file path
+contains "spack.yaml" echo "$env_cfg"
+
+# Create an invalid packages.yaml configuration for the environment
+echo "\
+spack:
+  specs: []
+  view: False
+  packages:
+    what:
+" > "$env_cfg"
+
+echo "Try 'spack config edit' with broken environment"
+manifest_path=`spack config edit --print-file`
+# Re-run command for coverage purposes
+$coverage_run $(which spack) config edit --print-file
+
+if [ $orig_manifest_path = $manifest_path ]; then
+  pass
+else
+  fail
+fi
+