Use Sass maps for global settings

- Default settings are contained within the `$_bourbon-defaults` map
- User settings to override defaults are placed within a `$bourbon` map

core/_bourbon.scss

@@ -3,10 +3,9 @@
 // Copyright 2011 thoughtbot, inc.
 // MIT License
 
-@import "bourbon/settings/asset-pipeline";
-@import "bourbon/settings/global-font-file-formats";
 @import "bourbon/settings/scales";
-@import "bourbon/settings/modular-scale";
+@import "bourbon/settings/settings";
+@import "bourbon/settings/bourbon-get-setting";
 
 @import "bourbon/functions/assign-inputs";
 @import "bourbon/functions/collapse-directionals";

core/bourbon/addons/_font-face.scss

@@ -14,7 +14,7 @@
 ///   use the Rails Asset Pipeline (place the fonts in `app/assets/fonts/').
 ///
 /// @argument {list} $file-formats [$global-font-file-formats]
-///   `$global-font-file-formats` is set to `ttf woff2 woff` by default. Pass a
+///   `$global-font-file-formats` is set to `("ttf", "woff2", "woff")` by default. Pass a
 ///   list of file formats to support. E.g. `eot woff2 woff ttf svg`.
 ///
 /// @example scss
@@ -31,14 +31,17 @@
 /// @require {function} font-url-prefixer
 ///
 /// @require {function} font-source-declaration
+///
+/// @require {function} _bourbon-get-setting
 
 @mixin font-face(
-  $font-family,
-  $file-path,
-  $weight: normal,
-  $style: normal,
-  $asset-pipeline: $asset-pipeline,
-  $file-formats: $global-font-file-formats) {
+    $font-family,
+    $file-path,
+    $weight: normal,
+    $style: normal,
+    $asset-pipeline: _bourbon-get-setting("rails-asset-pipeline"),
+    $file-formats: _bourbon-get-setting("global-font-file-formats")
+  ) {
 
   $font-url-prefix: font-url-prefixer($asset-pipeline);
 

core/bourbon/addons/_modular-scale.scss

@@ -51,11 +51,14 @@
 ///
 /// @return {number}
 ///
-/// @require {variable} $modular-scale-ratio
-///
-/// @require {variable} $modular-scale-base
+/// @require {function} _bourbon-get-setting
+
+@function modular-scale(
+    $increment,
+    $value: _bourbon-get-setting("modular-scale-base"),
+    $ratio: _bourbon-get-setting("modular-scale-ratio")
+  ) {
 
-@function modular-scale($increment, $value: $modular-scale-base, $ratio: $modular-scale-ratio) {
   $v1: nth($value, 1);
   $v2: nth($value, length($value));
   $value: $v1;

core/bourbon/settings/_bourbon-get-setting.scss

@@ -0,0 +1,12 @@
+/// Return a Bourbon setting.
+///
+/// @argument {string} $setting
+///
+/// @example scss
+///   _bourbon-get-setting(rails-asset-pipeline)
+///
+/// @access private
+
+@function _bourbon-get-setting($setting) {
+  @return map-get(map-merge($_bourbon-defaults, $bourbon), $setting);
+}

core/bourbon/settings/_settings.scss

@@ -0,0 +1,33 @@
+@charset "UTF-8";
+
+/// Default Bourbon configuration settings.
+///
+/// @type map
+///
+/// @property {list} global-font-file-formats [("ttf", "woff2", "woff")]
+///   Global font file formats for the `font-face` mixin.
+///
+/// @property {number (with unit)} modular-scale-base [1em]
+///   Global base value for the `modular-scale` function
+///
+/// @property {number (unitless)} modular-scale-ratio [$major-third (1.25)]
+///   Global base ratio for the `modular-scale` function
+///
+/// @property {bool} rails-asset-pipeline [false]
+///   Enable or disable the `$asset-pipeline` variable for all functions that
+///   accept it.
+///
+/// @access private
+
+$_bourbon-defaults: (
+  "global-font-file-formats": ("ttf", "woff2", "woff"),
+  "modular-scale-base": 1em,
+  "modular-scale-ratio": $major-third,
+  "rails-asset-pipeline": false,
+);
+
+/// User overrides of Bourbon configuration settings
+///
+/// @type map
+
+$bourbon: () !default;

spec/bourbon/settings/bourbon_get_setting_spec.rb

@@ -0,0 +1,33 @@
+require "spec_helper"
+
+describe "_bourbon-get-setting" do
+  before(:all) do
+    ParserSupport.parse_file("settings/bourbon-get-setting")
+  end
+
+  context "gets the modular-scale-base setting" do
+    it "and returns the default value" do
+      expect(".test-1").to have_rule("content: 1em")
+    end
+  end
+
+  context "gets the rails-asset-pipeline setting" do
+    it "and returns the user-overridden value" do
+      expect(".test-2").to have_rule("content: true")
+    end
+  end
+
+  context "called from the font-face mixin" do
+    it "outputs user-overridden font file formats" do
+      ruleset = 'font-family: "source-sans-pro"; ' +
+                "font-style: normal; " +
+                "font-weight: normal; " +
+                'src: font-url("source-sans-pro-regular.woff2") ' +
+                     'format("woff2"), ' +
+                     'font-url("source-sans-pro-regular.woff") ' +
+                     'format("woff");'
+
+      expect("@font-face").to have_ruleset(ruleset)
+    end
+  end
+end

spec/fixtures/settings/bourbon-get-setting.scss

@@ -0,0 +1,16 @@
+@import "setup";
+
+$bourbon: (
+  "global-font-file-formats": ("woff2", "woff"),
+  "rails-asset-pipeline": true,
+);
+
+.test-1 {
+  content: _bourbon-get-setting("modular-scale-base");
+}
+
+.test-2 {
+  content: _bourbon-get-setting("rails-asset-pipeline");
+}
+
+@include font-face("source-sans-pro", "source-sans-pro-regular");