Support descriptions for enum values in config.

The enum property may now specify options as a list of {value:,
description:} objects.

spec/config-spec.coffee

@@ -1572,6 +1572,14 @@ describe "Config", ->
                 items:
                   type: 'string'
                   enum: ['one', 'two', 'three']
+              str_options:
+                type: 'string'
+                default: 'one'
+                enum: [
+                  value: 'one', description: 'One'
+                  'two',
+                  value: 'three', description: 'Three'
+                ]
 
           atom.config.setSchema('foo.bar', schema)
 
@@ -1595,3 +1603,13 @@ describe "Config", ->
 
           expect(atom.config.set('foo.bar.arr', ['two', 'three'])).toBe true
           expect(atom.config.get('foo.bar.arr')).toEqual ['two', 'three']
+
+        it 'will honor the enum when specified as an array', ->
+          expect(atom.config.set('foo.bar.str_options', 'one')).toBe true
+          expect(atom.config.get('foo.bar.str_options')).toEqual 'one'
+
+          expect(atom.config.set('foo.bar.str_options', 'two')).toBe true
+          expect(atom.config.get('foo.bar.str_options')).toEqual 'two'
+
+          expect(atom.config.set('foo.bar.str_options', 'One')).toBe false
+          expect(atom.config.get('foo.bar.str_options')).toEqual 'two'

src/config.coffee

@@ -235,9 +235,13 @@ ScopeDescriptor = require './scope-descriptor'
 #
 # #### enum
 #
-# All types support an `enum` key. The enum key lets you specify all values
-# that the config setting can possibly be. `enum` _must_ be an array of values
-# of your specified type. Schema:
+# All types support an `enum` key, which lets you specify all the values the
+# setting can take. `enum` may be an array of allowed values (of the specified
+# type), or an array of objects with `value` and `description` properties, where
+# the `value` is an allowed value, and the `description` is a descriptive string
+# used in the settings view.
+#
+# In this example, the setting must be one of the 4 integers:
 #
 # ```coffee
 # config:
@@ -247,6 +251,20 @@ ScopeDescriptor = require './scope-descriptor'
 #     enum: [2, 4, 6, 8]
 # ```
 #
+# In this example, the setting must be either 'foo' or 'bar', which are
+# presented using the provided descriptions in the settings pane:
+#
+# ```coffee
+# config:
+#   someSetting:
+#     type: 'string'
+#     default: 'foo'
+#     enum: [
+#       {value: 'foo', description: 'Foo mode. You want this.'}
+#       {value: 'bar', description: 'Bar mode. Nobody wants that!'}
+#     ]
+# ```
+#
 # Usage:
 #
 # ```coffee
@@ -1132,6 +1150,11 @@ Config.addSchemaEnforcers
 
     validateEnum: (keyPath, value, schema) ->
       possibleValues = schema.enum
+
+      if Array.isArray(possibleValues)
+        possibleValues = possibleValues.map (value) ->
+          if value.hasOwnProperty('value') then value.value else value
+
       return value unless possibleValues? and Array.isArray(possibleValues) and possibleValues.length
 
       for possibleValue in possibleValues