commands: add `spack pkg source` and `spack pkg hash`

To make it easier to see how package hashes change and how they are computed, add two
commands:

* `spack pkg source <spec>`: dumps source code for a package to the terminal

* `spack pkg source --canonical <spec>`: dumps canonicalized source code for a
   package to the terminal. It strips comments, directives, and known-unused
   multimethods from the package. It is used to generate package hashes.

* `spack pkg hash <spec>`: This gives the package hash for a particular spec.
  It is generated from the canonical source code for the spec.

- [x] `add spack pkg source` and `spack pkg hash`
- [x] add tests
- [x] fix bug in multimethod resolution with boolean `@when` values

Co-authored-by: Greg Becker <becker33@llnl.gov>

3 files changed, 128 insertions, 7 deletions

diff --git a/lib/spack/spack/cmd/pkg.py b/lib/spack/spack/cmd/pkg.py
index 8440cbd82c..eda32d98fc 100644
--- a/lib/spack/spack/cmd/pkg.py
+++ b/lib/spack/spack/cmd/pkg.py
@@ -7,6 +7,7 @@ from __future__ import print_function
 
 import os
 import re
+import sys
 
 import llnl.util.tty as tty
 from llnl.util.filesystem import working_dir
@@ -16,6 +17,7 @@ import spack.cmd
 import spack.cmd.common.arguments as arguments
 import spack.paths
 import spack.repo
+import spack.util.package_hash as ph
 from spack.util.executable import which
 
 description = "query packages associated with particular git revisions"
@@ -70,6 +72,15 @@ def setup_parser(subparser):
         'rev2', nargs='?', default='HEAD',
         help="revision to compare to rev1 (default is HEAD)")
 
+    source_parser = sp.add_parser('source', help=pkg_source.__doc__)
+    source_parser.add_argument(
+        '-c', '--canonical', action='store_true', default=False,
+        help="dump canonical source as used by package hash.")
+    arguments.add_common_arguments(source_parser, ['spec'])
+
+    hash_parser = sp.add_parser('hash', help=pkg_hash.__doc__)
+    arguments.add_common_arguments(hash_parser, ['spec'])
+
 
 def packages_path():
     """Get the test repo if it is active, otherwise the builtin repo."""
@@ -201,14 +212,49 @@ def pkg_changed(args):
         colify(sorted(packages))
 
 
+def pkg_source(args):
+    """dump source code for a package"""
+    specs = spack.cmd.parse_specs(args.spec, concretize=False)
+    if len(specs) != 1:
+        tty.die("spack pkg source requires exactly one spec")
+
+    spec = specs[0]
+    filename = spack.repo.path.filename_for_package_name(spec.name)
+
+    # regular source dump -- just get the package and print its contents
+    if args.canonical:
+        message = "Canonical source for %s:" % filename
+        content = ph.canonical_source(spec)
+    else:
+        message = "Source for %s:" % filename
+        with open(filename) as f:
+            content = f.read()
+
+    if sys.stdout.isatty():
+        tty.msg(message)
+    sys.stdout.write(content)
+
+
+def pkg_hash(args):
+    """dump canonical source code hash for a package spec"""
+    specs = spack.cmd.parse_specs(args.spec, concretize=False)
+
+    for spec in specs:
+        print(ph.package_hash(spec))
+
+
 def pkg(parser, args):
     if not spack.cmd.spack_is_git_repo():
         tty.die("This spack is not a git clone. Can't use 'spack pkg'")
 
-    action = {'add': pkg_add,
-              'diff': pkg_diff,
-              'list': pkg_list,
-              'removed': pkg_removed,
-              'added': pkg_added,
-              'changed': pkg_changed}
+    action = {
+        'add': pkg_add,
+        'diff': pkg_diff,
+        'list': pkg_list,
+        'removed': pkg_removed,
+        'added': pkg_added,
+        'changed': pkg_changed,
+        'source': pkg_source,
+        'hash': pkg_hash,
+    }
     action[args.pkg_command](args)
diff --git a/lib/spack/spack/test/cmd/pkg.py b/lib/spack/spack/test/cmd/pkg.py
index 4036a33f95..54a6821677 100644
--- a/lib/spack/spack/test/cmd/pkg.py
+++ b/lib/spack/spack/test/cmd/pkg.py
@@ -236,3 +236,63 @@ def test_pkg_fails_when_not_git_repo(monkeypatch):
     monkeypatch.setattr(spack.cmd, 'spack_is_git_repo', lambda: False)
     with pytest.raises(spack.main.SpackCommandError):
         pkg('added')
+
+
+def test_pkg_source_requires_one_arg(mock_packages):
+    with pytest.raises(spack.main.SpackCommandError):
+        pkg("source", "a", "b")
+
+    with pytest.raises(spack.main.SpackCommandError):
+        pkg("source", "--canonical", "a", "b")
+
+
+def test_pkg_source(mock_packages):
+    fake_source = pkg("source", "fake")
+
+    fake_file = spack.repo.path.filename_for_package_name("fake")
+    with open(fake_file) as f:
+        contents = f.read()
+        assert fake_source == contents
+
+
+def test_pkg_canonical_source(mock_packages):
+    source = pkg("source", "multimethod")
+    assert "@when('@2.0')" in source
+    assert "Check that multimethods work with boolean values" in source
+
+    canonical_1 = pkg("source", "--canonical", "multimethod@1.0")
+    assert "@when" not in canonical_1
+    assert "should_not_be_reached by diamond inheritance test" not in canonical_1
+    assert "return 'base@1.0'" in canonical_1
+    assert "return 'base@2.0'" not in canonical_1
+    assert "return 'first_parent'" not in canonical_1
+    assert "'should_not_be_reached by diamond inheritance test'" not in canonical_1
+
+    canonical_2 = pkg("source", "--canonical", "multimethod@2.0")
+    assert "@when" not in canonical_2
+    assert "return 'base@1.0'" not in canonical_2
+    assert "return 'base@2.0'" in canonical_2
+    assert "return 'first_parent'" in canonical_2
+    assert "'should_not_be_reached by diamond inheritance test'" not in canonical_2
+
+    canonical_3 = pkg("source", "--canonical", "multimethod@3.0")
+    assert "@when" not in canonical_3
+    assert "return 'base@1.0'" not in canonical_3
+    assert "return 'base@2.0'" not in canonical_3
+    assert "return 'first_parent'" not in canonical_3
+    assert "'should_not_be_reached by diamond inheritance test'" not in canonical_3
+
+    canonical_4 = pkg("source", "--canonical", "multimethod@4.0")
+    assert "@when" not in canonical_4
+    assert "return 'base@1.0'" not in canonical_4
+    assert "return 'base@2.0'" not in canonical_4
+    assert "return 'first_parent'" not in canonical_4
+    assert "'should_not_be_reached by diamond inheritance test'" in canonical_4
+
+
+def test_pkg_hash(mock_packages):
+    output = pkg("hash", "a", "b").strip().split()
+    assert len(output) == 2 and all(len(elt) == 32 for elt in output)
+
+    output = pkg("hash", "multimethod").strip().split()
+    assert len(output) == 1 and all(len(elt) == 32 for elt in output)
diff --git a/lib/spack/spack/util/package_hash.py b/lib/spack/spack/util/package_hash.py
index 877dd7e458..d2b9055579 100644
--- a/lib/spack/spack/util/package_hash.py
+++ b/lib/spack/spack/util/package_hash.py
@@ -96,7 +96,22 @@ class TagMultiMethods(ast.NodeVisitor):
                 try:
                     # evaluate spec condition for any when's
                     cond = dec.args[0].s
-                    conditions.append(self.spec.satisfies(cond, strict=True))
+
+                    # Boolean literals come through like this
+                    if isinstance(cond, bool):
+                        conditions.append(cond)
+                        continue
+
+                    # otherwise try to make a spec
+                    try:
+                        cond_spec = spack.spec.Spec(cond)
+                    except Exception:
+                        # Spec parsing failed -- we don't know what this is.
+                        conditions.append(None)
+                    else:
+                        # Check statically whether spec satisfies the condition
+                        conditions.append(self.spec.satisfies(cond_spec, strict=True))
+
                 except AttributeError:
                     # In this case the condition for the 'when' decorator is
                     # not a string literal (for example it may be a Python