Add 'spack blame' command: shows contributors to packages

`spack blame` prints out the contributors to a package.

By modification time:

```
$ spack blame --time llvm
LAST_COMMIT    LINES  %      AUTHOR               EMAIL
3 days ago     2      0.6    Andrey Prokopenko    <andrey.prok@gmail.com>
3 weeks ago    125    34.7   Massimiliano Culpo   <massimiliano.culpo@epfl.ch>
3 weeks ago    3      0.8    Peter Scheibel       <scheibel1@llnl.gov>
2 months ago   21     5.8    Adam J. Stewart      <ajstewart426@gmail.com>
2 months ago   1      0.3    Gregory Becker       <becker33@llnl.gov>
3 months ago   116    32.2   Todd Gamblin         <tgamblin@llnl.gov>
5 months ago   2      0.6    Jimmy Tang           <jcftang@gmail.com>
5 months ago   6      1.7    Jean-Paul Pelteret   <jppelteret@gmail.com>
7 months ago   65     18.1   Tom Scogland         <tscogland@llnl.gov>
11 months ago  13     3.6    Kelly (KT) Thompson  <kgt@lanl.gov>
a year ago     1      0.3    Scott Pakin          <pakin@lanl.gov>
a year ago     3      0.8    Erik Schnetter       <schnetter@gmail.com>
3 years ago    2      0.6    David Beckingsale    <davidbeckingsale@gmail.com>

3 days ago     360    100.0
```

Or by percent contribution:

```
$ spack blame --percent llvm
LAST_COMMIT    LINES  %      AUTHOR               EMAIL
3 weeks ago    125    34.7   Massimiliano Culpo   <massimiliano.culpo@epfl.ch>
3 months ago   116    32.2   Todd Gamblin         <tgamblin@llnl.gov>
7 months ago   65     18.1   Tom Scogland         <tscogland@llnl.gov>
2 months ago   21     5.8    Adam J. Stewart      <ajstewart426@gmail.com>
11 months ago  13     3.6    Kelly (KT) Thompson  <kgt@lanl.gov>
5 months ago   6      1.7    Jean-Paul Pelteret   <jppelteret@gmail.com>
3 weeks ago    3      0.8    Peter Scheibel       <scheibel1@llnl.gov>
a year ago     3      0.8    Erik Schnetter       <schnetter@gmail.com>
3 years ago    2      0.6    David Beckingsale    <davidbeckingsale@gmail.com>
3 days ago     2      0.6    Andrey Prokopenko    <andrey.prok@gmail.com>
5 months ago   2      0.6    Jimmy Tang           <jcftang@gmail.com>
2 months ago   1      0.3    Gregory Becker       <becker33@llnl.gov>
a year ago     1      0.3    Scott Pakin          <pakin@lanl.gov>

3 days ago     360    100.0
```

6 files changed, 280 insertions, 25 deletions

diff --git a/lib/spack/llnl/util/lang.py b/lib/spack/llnl/util/lang.py
index 667572dd8d..07338b21ef 100644
--- a/lib/spack/llnl/util/lang.py
+++ b/lib/spack/llnl/util/lang.py
@@ -27,6 +27,7 @@ import re
 import functools
 import collections
 import inspect
+from datetime import datetime
 from six import string_types
 
 # Ignore emacs backups when listing modules
@@ -385,6 +386,75 @@ def dedupe(sequence):
             seen.add(x)
 
 
+def pretty_date(time, now=None):
+    """Convert a datetime or timestamp to a pretty, relative date.
+
+    Args:
+        time (datetime or int): date to print prettily
+        now (datetime): dateimte for 'now', i.e. the date the pretty date
+            is relative to (default is datetime.now())
+
+    Returns:
+        (str): pretty string like 'an hour ago', 'Yesterday',
+            '3 months ago', 'just now', etc.
+
+    Adapted from https://stackoverflow.com/questions/1551382.
+
+    """
+    if now is None:
+        now = datetime.now()
+
+    if type(time) is int:
+        diff = now - datetime.fromtimestamp(time)
+    elif isinstance(time, datetime):
+        diff = now - time
+    else:
+        raise ValueError("pretty_date requires a timestamp or datetime")
+
+    second_diff = diff.seconds
+    day_diff = diff.days
+
+    if day_diff < 0:
+        return ''
+
+    if day_diff == 0:
+        if second_diff < 10:
+            return "just now"
+        if second_diff < 60:
+            return str(second_diff) + " seconds ago"
+        if second_diff < 120:
+            return "a minute ago"
+        if second_diff < 3600:
+            return str(second_diff / 60) + " minutes ago"
+        if second_diff < 7200:
+            return "an hour ago"
+        if second_diff < 86400:
+            return str(second_diff / 3600) + " hours ago"
+    if day_diff == 1:
+        return "yesterday"
+    if day_diff < 7:
+        return str(day_diff) + " days ago"
+    if day_diff < 28:
+        weeks = day_diff / 7
+        if weeks == 1:
+            return "a week ago"
+        else:
+            return str(day_diff / 7) + " weeks ago"
+    if day_diff < 365:
+        months = day_diff / 30
+        if months == 1:
+            return "a month ago"
+        elif months == 12:
+            months -= 1
+        return str(months) + " months ago"
+
+    diff = day_diff / 365
+    if diff == 1:
+        return "a year ago"
+    else:
+        return str(diff) + " years ago"
+
+
 class RequiredAttributeError(ValueError):
 
     def __init__(self, message):
diff --git a/lib/spack/spack/cmd/__init__.py b/lib/spack/spack/cmd/__init__.py
index 08dbf55dc2..f1e36c2377 100644
--- a/lib/spack/spack/cmd/__init__.py
+++ b/lib/spack/spack/cmd/__init__.py
@@ -32,6 +32,7 @@ import llnl.util.tty as tty
 from llnl.util.lang import *
 from llnl.util.tty.colify import *
 from llnl.util.tty.color import *
+from llnl.util.filesystem import working_dir
 
 import spack
 import spack.config
@@ -287,3 +288,9 @@ def display_specs(specs, args=None, **kwargs):
             raise ValueError(
                 "Invalid mode for display_specs: %s. Must be one of (paths,"
                 "deps, short)." % mode)
+
+
+def spack_is_git_repo():
+    """Ensure that this instance of Spack is a git clone."""
+    with working_dir(spack.prefix):
+        return os.path.isdir('.git')
diff --git a/lib/spack/spack/cmd/blame.py b/lib/spack/spack/cmd/blame.py
new file mode 100644
index 0000000000..3bf5e37abb
--- /dev/null
+++ b/lib/spack/spack/cmd/blame.py
@@ -0,0 +1,122 @@
+##############################################################################
+# Copyright (c) 2013-2017, Lawrence Livermore National Security, LLC.
+# Produced at the Lawrence Livermore National Laboratory.
+#
+# This file is part of Spack.
+# Created by Todd Gamblin, tgamblin@llnl.gov, All rights reserved.
+# LLNL-CODE-647188
+#
+# For details, see https://github.com/llnl/spack
+# Please also see the NOTICE and LICENSE files for our notice and the LGPL.
+#
+# This program is free software; you can redistribute it and/or modify
+# it under the terms of the GNU Lesser General Public License (as
+# published by the Free Software Foundation) version 2.1, February 1999.
+#
+# This program is distributed in the hope that it will be useful, but
+# WITHOUT ANY WARRANTY; without even the IMPLIED WARRANTY OF
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the terms and
+# conditions of the GNU Lesser General Public License for more details.
+#
+# You should have received a copy of the GNU Lesser General Public
+# License along with this program; if not, write to the Free Software
+# Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
+##############################################################################
+import re
+
+import llnl.util.tty as tty
+from llnl.util.lang import pretty_date
+from llnl.util.filesystem import working_dir
+from llnl.util.tty.colify import colify_table
+
+import spack
+from spack.util.executable import which
+from spack.cmd import spack_is_git_repo
+
+
+description = "show contributors to packages"
+section = "developer"
+level = "long"
+
+
+def setup_parser(subparser):
+    view_group = subparser.add_mutually_exclusive_group()
+    view_group.add_argument(
+        '-t', '--time', dest='view', action='store_const', const='time',
+        default='time', help='sort by last modification date (default)')
+    view_group.add_argument(
+        '-p', '--percent', dest='view', action='store_const', const='percent',
+        help='sort by percent of code')
+    view_group.add_argument(
+        '-g', '--git', dest='view', action='store_const', const='git',
+        help='show git blame output instead of summary')
+
+    subparser.add_argument(
+        'package_name', help='name of package to show contributions for')
+
+
+def blame(parser, args):
+    # make sure this is a git repo
+    if not spack_is_git_repo():
+        tty.die("This spack is not a git clone. Can't use 'spack pkg'")
+    git = which('git', required=True)
+
+    # Get package and package file name
+    pkg = spack.repo.get(args.package_name)
+    package_py = pkg.module.__file__.rstrip('c')  # .pyc -> .py
+
+    # get git blame for the package
+    with working_dir(spack.prefix):
+        if args.view == 'git':
+            git('blame', package_py)
+            return
+        else:
+            output = git('blame', '--line-porcelain', package_py, output=str)
+            lines = output.split('\n')
+
+    # Histogram authors
+    counts = {}
+    emails = {}
+    last_mod = {}
+    total_lines = 0
+    for line in lines:
+        match = re.match(r'^author (.*)', line)
+        if match:
+            author = match.group(1)
+
+        match = re.match(r'^author-mail (.*)', line)
+        if match:
+            email = match.group(1)
+
+        match = re.match(r'^author-time (.*)', line)
+        if match:
+            mod = int(match.group(1))
+            last_mod[author] = max(last_mod.setdefault(author, 0), mod)
+
+        # ignore comments
+        if re.match(r'^\t[^#]', line):
+            counts[author] = counts.setdefault(author, 0) + 1
+            emails.setdefault(author, email)
+            total_lines += 1
+
+    if args.view == 'time':
+        rows = sorted(
+            counts.items(), key=lambda t: last_mod[t[0]], reverse=True)
+    else:  # args.view == 'percent'
+        rows = sorted(counts.items(), key=lambda t: t[1], reverse=True)
+
+    # Print a nice table with authors and emails
+    table = [['LAST_COMMIT', 'LINES', '%', 'AUTHOR', 'EMAIL']]
+    for author, nlines in rows:
+        table += [[
+            pretty_date(last_mod[author]),
+            nlines,
+            round(nlines / float(total_lines) * 100, 1),
+            author,
+            emails[author]]]
+
+    table += [[''] * 5]
+    table += [[pretty_date(max(last_mod.values())), total_lines, '100.0'] +
+              [''] * 3]
+
+    colify_table(table)
diff --git a/lib/spack/spack/cmd/pkg.py b/lib/spack/spack/cmd/pkg.py
index 7673955db5..8cd6534724 100644
--- a/lib/spack/spack/cmd/pkg.py
+++ b/lib/spack/spack/cmd/pkg.py
@@ -29,9 +29,11 @@ import os
 import argparse
 import llnl.util.tty as tty
 from llnl.util.tty.colify import colify
+from llnl.util.filesystem import working_dir
 
 import spack
 from spack.util.executable import *
+from spack.cmd import spack_is_git_repo
 
 description = "query packages associated with particular git revisions"
 section = "developer"
@@ -75,26 +77,14 @@ def setup_parser(subparser):
         help="revision to compare to rev1 (default is HEAD)")
 
 
-def get_git(fatal=True):
-    # cd to spack prefix to do git operations
-    os.chdir(spack.prefix)
-
-    # If this is a non-git version of spack, give up.
-    if not os.path.isdir('.git'):
-        if fatal:
-            tty.die("No git repo in %s. Can't use 'spack pkg'" % spack.prefix)
-        else:
-            return None
-
-    return which("git", required=True)
-
-
 def list_packages(rev):
-    git = get_git()
     pkgpath = os.path.join(spack.packages_path, 'packages')
     relpath = pkgpath[len(spack.prefix + os.path.sep):] + os.path.sep
-    output = git('ls-tree', '--full-tree', '--name-only', rev, relpath,
-                 output=str)
+
+    git = which('git', required=True)
+    with working_dir(spack.prefix):
+        output = git('ls-tree', '--full-tree', '--name-only', rev, relpath,
+                     output=str)
     return sorted(line[len(relpath):] for line in output.split('\n') if line)
 
 
@@ -105,8 +95,9 @@ def pkg_add(args):
             tty.die("No such package: %s.  Path does not exist:" %
                     pkg_name, filename)
 
-        git = get_git()
-        git('-C', spack.packages_path, 'add', filename)
+        git = which('git', required=True)
+        with working_dir(spack.prefix):
+            git('-C', spack.packages_path, 'add', filename)
 
 
 def pkg_list(args):
@@ -150,6 +141,9 @@ def pkg_added(args):
 
 
 def pkg(parser, args):
+    if not 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,
diff --git a/lib/spack/spack/hooks/case_consistency.py b/lib/spack/spack/hooks/case_consistency.py
index 48f9606444..b76408e66e 100644
--- a/lib/spack/spack/hooks/case_consistency.py
+++ b/lib/spack/spack/hooks/case_consistency.py
@@ -31,7 +31,7 @@ import platform
 from llnl.util.filesystem import *
 
 import spack
-from spack.cmd.pkg import get_git
+from spack.cmd import spack_is_git_repo
 from spack.util.executable import *
 
 
@@ -64,12 +64,15 @@ def git_case_consistency_check(path):
     TODO: lowercase for a long while.
 
     """
-    with working_dir(path):
-        # Don't bother fixing case if Spack isn't in a git repository
-        git = get_git(fatal=False)
-        if git is None:
-            return
+    # Don't bother fixing case if Spack isn't in a git repository
+    if not spack_is_git_repo():
+        return
 
+    git = which('git', required=False)
+    if not git:
+        return
+
+    with working_dir(path):
         try:
             git_filenames = git('ls-tree', '--name-only', 'HEAD', output=str)
             git_filenames = set(re.split(r'\s+', git_filenames.strip()))
diff --git a/lib/spack/spack/test/cmd/blame.py b/lib/spack/spack/test/cmd/blame.py
new file mode 100644
index 0000000000..0031052b24
--- /dev/null
+++ b/lib/spack/spack/test/cmd/blame.py
@@ -0,0 +1,59 @@
+##############################################################################
+# Copyright (c) 2013-2017, Lawrence Livermore National Security, LLC.
+# Produced at the Lawrence Livermore National Laboratory.
+#
+# This file is part of Spack.
+# Created by Todd Gamblin, tgamblin@llnl.gov, All rights reserved.
+# LLNL-CODE-647188
+#
+# For details, see https://github.com/llnl/spack
+# Please also see the NOTICE and LICENSE files for our notice and the LGPL.
+#
+# This program is free software; you can redistribute it and/or modify
+# it under the terms of the GNU Lesser General Public License (as
+# published by the Free Software Foundation) version 2.1, February 1999.
+#
+# This program is distributed in the hope that it will be useful, but
+# WITHOUT ANY WARRANTY; without even the IMPLIED WARRANTY OF
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the terms and
+# conditions of the GNU Lesser General Public License for more details.
+#
+# You should have received a copy of the GNU Lesser General Public
+# License along with this program; if not, write to the Free Software
+# Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
+##############################################################################
+import pytest
+
+import spack.cmd
+from spack.main import SpackCommand
+from spack.util.executable import which
+
+pytestmark = pytest.mark.skipif(
+    not which('git') or not spack.cmd.spack_is_git_repo(),
+    reason="needs git")
+
+blame = SpackCommand('blame')
+
+
+def test_blame_by_modtime(builtin_mock):
+    """Sanity check the blame command to make sure it works."""
+    out = blame('--time', 'mpich')
+    assert 'LAST_COMMIT' in out
+    assert 'AUTHOR' in out
+    assert 'EMAIL' in out
+
+
+def test_blame_by_percent(builtin_mock):
+    """Sanity check the blame command to make sure it works."""
+    out = blame('--percent', 'mpich')
+    assert 'LAST_COMMIT' in out
+    assert 'AUTHOR' in out
+    assert 'EMAIL' in out
+
+
+def test_blame_by_git(builtin_mock, capfd):
+    """Sanity check the blame command to make sure it works."""
+    with capfd.disabled():
+        out = blame('--git', 'mpich')
+    assert 'Mpich' in out
+    assert 'mock_packages' in out