From 87cdfa2c255e86b9f89790349f2d8479c0eb86b8 Mon Sep 17 00:00:00 2001
From: Tamara Dahlgren <dahlgren1@llnl.gov>
Date: Tue, 17 Sep 2019 19:27:33 -0700
Subject: Add support for nested "overrides" scopes.

---
 lib/spack/spack/config.py      | 26 +++++++++++++++++++++--
 lib/spack/spack/test/config.py | 48 ++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 72 insertions(+), 2 deletions(-)

diff --git a/lib/spack/spack/config.py b/lib/spack/spack/config.py
index c73b5047f5..4a684986eb 100644
--- a/lib/spack/spack/config.py
+++ b/lib/spack/spack/config.py
@@ -32,6 +32,7 @@ schemas are in submodules of :py:mod:`spack.schema`.
 
 import copy
 import os
+import re
 import sys
 import multiprocessing
 from contextlib import contextmanager
@@ -354,6 +355,15 @@ class Configuration(object):
         """Non-internal scope with highest precedence."""
         return next(reversed(self.file_scopes), None)
 
+    def matching_scopes(self, reg_expr):
+        """
+        List of all scopes whose names match the provided regular expression.
+
+        For example, matching_scopes(r'^command') will return all scopes
+        whose names begin with `command`.
+        """
+        return [s for s in self.scopes.values() if re.search(reg_expr, s.name)]
+
     def _validate_scope(self, scope):
         """Ensure that scope is valid in this configuration.
 
@@ -539,13 +549,25 @@ def override(path_or_scope, value=None):
     an internal config scope for it and push/pop that scope.
 
     """
+    base_name = 'overrides-'
     if isinstance(path_or_scope, ConfigScope):
         overrides = path_or_scope
         config.push_scope(path_or_scope)
     else:
-        overrides = InternalConfigScope('overrides')
+        # Ensure the new override gets a unique scope name
+        current_overrides = [s.name for s in
+                             config.matching_scopes(r'^{0}'.format(base_name))]
+        num_overrides = len(current_overrides)
+        while True:
+            scope_name = '{0}{1}'.format(base_name, num_overrides)
+            if scope_name in current_overrides:
+                num_overrides += 1
+            else:
+                break
+
+        overrides = InternalConfigScope(scope_name)
         config.push_scope(overrides)
-        config.set(path_or_scope, value, scope='overrides')
+        config.set(path_or_scope, value, scope=scope_name)
 
     yield config
 
diff --git a/lib/spack/spack/test/config.py b/lib/spack/spack/test/config.py
index 163fc392d3..99e1d7499c 100644
--- a/lib/spack/spack/test/config.py
+++ b/lib/spack/spack/test/config.py
@@ -627,6 +627,54 @@ config:
     spack.config._add_command_line_scopes(mutable_config, [str(tmpdir)])
 
 
+@pytest.mark.nomockstage
+def test_nested_override():
+    """Ensure proper scope naming of nested overrides."""
+    # WARNING: Base name must match that used in `config.py`s `override()`.
+    base_name = 'overrides-'
+
+    def _check_scopes(num_expected, debug_values):
+        scope_names = [s.name for s in spack.config.config.scopes.values()]
+
+        for i in range(num_expected):
+            name = '{0}{1}'.format(base_name, i)
+            assert name in scope_names
+
+            data = spack.config.config.get_config('config', name)
+            assert data['debug'] == debug_values[i]
+
+    # Check results from single and nested override
+    with spack.config.override('config:debug', True):
+        with spack.config.override('config:debug', False):
+            _check_scopes(2, [True, False])
+
+        _check_scopes(1, [True])
+
+
+@pytest.mark.nomockstage
+def test_alternate_override(monkeypatch):
+    """Ensure proper scope naming of override when conflict present."""
+    # WARNING: Base name must match that used in `config.py`s `override()`.
+    base_name = 'overrides-'
+
+    def _matching_scopes(regexpr):
+        return [spack.config.InternalConfigScope('{0}1'.format(base_name))]
+
+    # Check that the alternate naming works
+    monkeypatch.setattr(spack.config.config, 'matching_scopes',
+                        _matching_scopes)
+
+    with spack.config.override('config:debug', False):
+        name = '{0}2'.format(base_name)
+
+        scope_names = [s.name for s in spack.config.config.scopes.values() if
+                       s.name.startswith(base_name)]
+        assert name in scope_names
+
+        data = spack.config.config.get_config('config', name)
+        assert data['debug'] is False
+
+
 def test_immutable_scope(tmpdir):
     config_yaml = str(tmpdir.join('config.yaml'))
     with open(config_yaml, 'w') as f:
-- 
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