Support os-specific $padding in config:install_tree

Providing only $padding or ${padding} results in an attempt to
substitute a padding of maximum system path length, while leaving
room for the parts of the install path spack generates.  Providing
$padding-<len> or ${padding-<len>} simply substitutes padding of
the specified length.

lib/spack/spack/test/config.py

@@ -23,7 +23,7 @@
 import spack.schema.mirrors
 import spack.schema.repos
 import spack.util.spack_yaml as syaml
-from spack.util.path import canonicalize_path
+import spack.util.path as spack_path
 
 
 # sample config data
@@ -272,31 +272,31 @@ def test_substitute_config_variables(mock_low_high_config):
 
     assert os.path.join(
         '/foo/bar/baz', prefix
-    ) == canonicalize_path('/foo/bar/baz/$spack')
+    ) == spack_path.canonicalize_path('/foo/bar/baz/$spack')
 
     assert os.path.join(
         spack.paths.prefix, 'foo/bar/baz'
-    ) == canonicalize_path('$spack/foo/bar/baz/')
+    ) == spack_path.canonicalize_path('$spack/foo/bar/baz/')
 
     assert os.path.join(
         '/foo/bar/baz', prefix, 'foo/bar/baz'
-    ) == canonicalize_path('/foo/bar/baz/$spack/foo/bar/baz/')
+    ) == spack_path.canonicalize_path('/foo/bar/baz/$spack/foo/bar/baz/')
 
     assert os.path.join(
         '/foo/bar/baz', prefix
-    ) == canonicalize_path('/foo/bar/baz/${spack}')
+    ) == spack_path.canonicalize_path('/foo/bar/baz/${spack}')
 
     assert os.path.join(
         spack.paths.prefix, 'foo/bar/baz'
-    ) == canonicalize_path('${spack}/foo/bar/baz/')
+    ) == spack_path.canonicalize_path('${spack}/foo/bar/baz/')
 
     assert os.path.join(
         '/foo/bar/baz', prefix, 'foo/bar/baz'
-    ) == canonicalize_path('/foo/bar/baz/${spack}/foo/bar/baz/')
+    ) == spack_path.canonicalize_path('/foo/bar/baz/${spack}/foo/bar/baz/')
 
     assert os.path.join(
         '/foo/bar/baz', prefix, 'foo/bar/baz'
-    ) != canonicalize_path('/foo/bar/baz/${spack/foo/bar/baz/')
+    ) != spack_path.canonicalize_path('/foo/bar/baz/${spack/foo/bar/baz/')
 
 
 packages_merge_low = {
@@ -345,19 +345,43 @@ def test_merge_with_defaults(mock_low_high_config, write_config_file):
 
 def test_substitute_user(mock_low_high_config):
     user = getpass.getuser()
-    assert '/foo/bar/' + user + '/baz' == canonicalize_path(
+    assert '/foo/bar/' + user + '/baz' == spack_path.canonicalize_path(
         '/foo/bar/$user/baz'
     )
 
 
 def test_substitute_tempdir(mock_low_high_config):
     tempdir = tempfile.gettempdir()
-    assert tempdir == canonicalize_path('$tempdir')
-    assert tempdir + '/foo/bar/baz' == canonicalize_path(
+    assert tempdir == spack_path.canonicalize_path('$tempdir')
+    assert tempdir + '/foo/bar/baz' == spack_path.canonicalize_path(
         '$tempdir/foo/bar/baz'
     )
 
 
+def test_substitute_padding(mock_low_high_config):
+    max_system_path = spack_path.get_system_path_max()
+    expected_length = (max_system_path -
+                       spack_path.SPACK_MAX_INSTALL_PATH_LENGTH)
+
+    install_path = spack_path.canonicalize_path('/foo/bar/${padding}/baz')
+
+    assert spack_path.SPACK_PATH_PADDING_CHARS in install_path
+    assert len(install_path) == expected_length
+
+    install_path = spack_path.canonicalize_path('/foo/bar/baz/gah/$padding')
+
+    assert spack_path.SPACK_PATH_PADDING_CHARS in install_path
+    assert len(install_path) == expected_length
+
+    i_path = spack_path.canonicalize_path('/foo/$padding:10')
+    i_expect = os.path.join('/foo', spack_path.SPACK_PATH_PADDING_CHARS[:10])
+    assert i_path == i_expect
+
+    i_path = spack_path.canonicalize_path('/foo/${padding:20}')
+    i_expect = os.path.join('/foo', spack_path.SPACK_PATH_PADDING_CHARS[:20])
+    assert i_path == i_expect
+
+
 def test_read_config(mock_low_high_config, write_config_file):
     write_config_file('config', config_low, 'low')
     assert spack.config.get('config') == config_low['config']

lib/spack/spack/util/path.py

@@ -10,8 +10,12 @@
 import os
 import re
 import getpass
+import subprocess
 import tempfile
 
+import llnl.util.tty as tty
+from llnl.util.lang import memoized
+
 import spack.paths
 
 
@@ -27,6 +31,38 @@
     'tempdir': tempfile.gettempdir(),
 }
 
+# This is intended to be longer than the part of the install path
+# spack generates from the root path we give it.  Included in the
+# estimate:
+#
+#   os-arch      ->   30
+#   compiler     ->   30
+#   package name ->   50   (longest is currently 47 characters)
+#   version      ->   20
+#   hash         ->   32
+#   buffer       ->  138
+#  ---------------------
+#   total        ->  300
+SPACK_MAX_INSTALL_PATH_LENGTH = 300
+SPACK_PATH_PADDING_CHARS = 'spack_path_placeholder'
+
+
+@memoized
+def get_system_path_max():
+    # Choose a conservative default
+    sys_max_path_length = 256
+    try:
+        path_max_proc  = subprocess.Popen(['getconf', 'PATH_MAX', '/'],
+                                          stdout=subprocess.PIPE,
+                                          stderr=subprocess.STDOUT)
+        proc_output = str(path_max_proc.communicate()[0].decode())
+        sys_max_path_length = int(proc_output)
+    except (ValueError, subprocess.CalledProcessError, OSError):
+        tty.msg('Unable to find system max path length, using: {0}'.format(
+            sys_max_path_length))
+
+    return sys_max_path_length
+
 
 def substitute_config_variables(path):
     """Substitute placeholders into paths.
@@ -58,8 +94,45 @@ def substitute_path_variables(path):
     return path
 
 
+def _get_padding_string(length):
+    spack_path_padding_size = len(SPACK_PATH_PADDING_CHARS)
+    num_reps = int(length / (spack_path_padding_size + 1))
+    extra_chars = length % (spack_path_padding_size + 1)
+    reps_list = [SPACK_PATH_PADDING_CHARS for i in range(num_reps)]
+    reps_list.append(SPACK_PATH_PADDING_CHARS[:extra_chars])
+    return os.path.sep.join(reps_list)
+
+
+def _add_computed_padding(path):
+    """Subtitute in padding of os-specific length.  The intent is to leave
+    SPACK_MAX_INSTALL_PATH_LENGTH characters available for parts of the
+    path generated by spack.  This is to allow for not-completely-known
+    lengths of things like os/arch, compiler, package name, hash length,
+    etc.
+    """
+    padding_regex = re.compile(r'(\$[\w\d\:]+\b|\$\{[\w\d\:]+\})')
+    m = padding_regex.search(path)
+    if m and m.group(0).strip('${}').startswith('padding'):
+        padding_part = m.group(0)
+        len_pad_part = len(m.group(0))
+        p_match = re.search(r'\:(\d+)', padding_part)
+        if p_match:
+            computed_padding = _get_padding_string(int(p_match.group(1)))
+        else:
+            # Take whatever has been computed/substituted so far and add some
+            # room
+            path_len = len(path) - len_pad_part + SPACK_MAX_INSTALL_PATH_LENGTH
+            system_max_path = get_system_path_max()
+            needed_pad_len = system_max_path - path_len
+            computed_padding = _get_padding_string(needed_pad_len)
+        return padding_regex.sub(computed_padding, path)
+    return path
+
+
 def canonicalize_path(path):
     """Same as substitute_path_variables, but also take absolute path."""
     path = substitute_path_variables(path)
     path = os.path.abspath(path)
+    path = _add_computed_padding(path)
+
     return path