Automate breakpoints

Breakpoints and container widths are now defined as maps.

scss/_forms.scss

@@ -541,14 +541,14 @@ input[type="checkbox"] {
   // Quick utility class for applying `.input-lg` and `.input-sm` styles to the
   // inputs and labels within a `.form-group`.
   .form-group-lg {
-    @media (min-width: $screen-sm-min) {
+    @include media-sm {
       .control-label {
         padding-top: $padding-lg-vertical;
       }
     }
   }
   .form-group-sm {
-    @media (min-width: $screen-sm-min) {
+    @include media-sm {
       .control-label {
         padding-top: ($padding-sm-vertical + .1);
       }

scss/_grid.scss

@@ -10,14 +10,11 @@
 .container {
   @include make-container();
 
-  @media (min-width: $screen-sm-min) {
-    max-width: $container-sm;
+  // For each breakpoint, define the maximum width of the container in a media query
+  @each $breakpoint, $container-max-width in $container-max-widths {
+    @include media-breakpoint-min($breakpoint) {
+      max-width: $container-max-width;
     }
-  @media (min-width: $screen-md-min) {
-    max-width: $container-md;
-  }
-  @media (min-width: $screen-lg-min) {
-    max-width: $container-lg;
   }
 }
 
@@ -47,47 +44,3 @@
 
 @include make-grid-columns();
 
-
-// Extra small grid
-//
-// Columns, offsets, pushes, and pulls for extra small devices like
-// smartphones.
-
-@include make-grid(xs);
-
-
-// Small grid
-//
-// Columns, offsets, pushes, and pulls for the small device range, from phones
-// to tablets.
-
-@include media-sm {
-  @include make-grid(sm);
-}
-
-
-// Medium grid
-//
-// Columns, offsets, pushes, and pulls for the desktop device range.
-
-@include media-md {
-  @include make-grid(md);
-}
-
-
-// Large grid
-//
-// Columns, offsets, pushes, and pulls for the large desktop device range.
-
-@include media-lg {
-  @include make-grid(lg);
-}
-
-
-// Large grid
-//
-// Columns, offsets, pushes, and pulls for the large desktop device range.
-
-@include media-lg {
-  @include make-grid(xl);
-}

scss/_mixins.scss

@@ -24,6 +24,7 @@
 }
 
 // Utilities
+@import "mixins/breakpoints";
 @import "mixins/media-queries";
 @import "mixins/hide-text";
 @import "mixins/image";

scss/_modal.scss

@@ -126,7 +126,7 @@
 }
 
 // Scale up the modal
-@media (min-width: $screen-sm-min) {
+@include media-sm {
   // Automatically set modal's width for larger viewports
   .modal-dialog {
     width: $modal-md;
@@ -140,6 +140,6 @@
   .modal-sm { width: $modal-sm; }
 }
 
-@media (min-width: $screen-md-min) {
+@include media-md {
   .modal-lg { width: $modal-lg; }
 }

scss/_variables.scss

@@ -272,29 +272,22 @@ $zindex-modal:             1040 !default;
 //
 //## Define the minimum and maximum dimensions at which your layout will change, adapting to different screen sizes.
 
-// Extra large screen / wide desktop
-$screen-xl-min:              75em !default;
-
-// Large screen / desktop
-$screen-lg-max:              ($screen-xl-min - .1) !default;
-$screen-lg-min:              62em !default;
-
-// Medium screen / tablet
-$screen-md-max:              ($screen-lg-min - .1) !default;
-$screen-md-min:              48em !default;
-
-// Small screen / phone
-$screen-sm-max:              ($screen-md-min - .1) !default;
-$screen-sm-min:              34em !default;
-
-// Extra small screen / phone
-$screen-xs-max:              ($screen-sm-min - .1) !default;
-
-
 //== Grid system
 //
 //## Define your custom responsive grid.
-$grid-breakpoints: (xs sm md lg xl);
+$grid-breakpoints: (
+  // Extra small screen / phone
+  xs: 0,
+  // Small screen / phone
+  sm: 34em,
+  // Medium screen / tablet
+  md: 48em,
+  // Large screen / desktop
+  lg: 62em,
+  // Extra large screen / wide desktop
+  xl: 75em
+) !default;
+
 //** Number of columns in the grid.
 $grid-columns:               12 !default;
 //** Padding between columns. Gets divided in half for the left and right.
@@ -305,17 +298,12 @@ $grid-gutter-width:          1.5rem !default;
 //
 //## Define the maximum width of `.container` for different screen sizes.
 
-//** For `$screen-xs-min` and up.
-$container-sm:               34em !default; // 480
-
-//** For `$screen-sm-min` and up.
-$container-md:               45rem !default; // 720
-
-//** For `$screen-md-min` and up.
-$container-lg:               60rem !default; // 960
-
-//** For `$screen-lg-min` and up.
-$container-xl:               72.25rem !default; // 1140
+$container-max-widths: (
+  sm: 34rem,    // 480
+  md: 45rem,    // 720
+  lg: 60rem,    // 960
+  xl: 72.25rem  // 1140
+) !default;
 
 
 //== Navbar

scss/mixins/_breakpoints.scss

+// Breakpoint viewport sizes and media queries.
+//
+// Breakpoints are defined as a map of (name: minimum width), order from small to large:
+//
+//    (xs: 0, sm: 34rem, md: 45rem)
+//
+// The map defined in the `$grid-breakpoints` global variable is used as the `$breakpoints` argument by default.
+
+// Name of the next breakpoint, or null for the last breakpoint.
+//
+//    >> breakpoint-next(sm)
+//    md
+//    >> breakpoint-next(sm, $breakpoints: (xs: 0, sm: 34rem, md: 45rem))
+//    md
+//    >> breakpoint-next(sm, $breakpoint-names: (xs sm md))
+//    md
+@function breakpoint-next($name, $breakpoints: $grid-breakpoints, $breakpoint-names: map-keys($breakpoints)) {
+  $n: index($breakpoint-names, $name);
+  @return if($n < length($breakpoint-names), nth($breakpoint-names, $n + 1), null);
+}
+
+// Minimum breakpoint width. Null for the smallest (first) breakpoint.
+//
+//    >> breakpoint-min(sm, (xs: 0, sm: 34rem, md: 45rem))
+//    34rem
+@function breakpoint-min($name, $breakpoints: $grid-breakpoints) {
+  $min: map-get($breakpoints, $name);
+  @return if($min != 0, $min, null);
+}
+
+// Maximum breakpoint width. Null for the largest (last) breakpoint.
+// The maximum value is calculated as the minimum of the next one less 0.1.
+//
+//    >> breakpoint-max(sm, (xs: 0, sm: 34rem, md: 45rem))
+//    44.9rem
+@function breakpoint-max($name, $breakpoints: $grid-breakpoints) {
+  $next: breakpoint-next($name, $breakpoints);
+  @return if($next, breakpoint-min($next, $breakpoints) - 0.1, null);
+}
+
+// Media of at least the minimum breakpoint width. No query for the smallest breakpoint.
+@mixin media-breakpoint-min($name, $breakpoints: $grid-breakpoints) {
+  $min: breakpoint-min($name, $breakpoints);
+  @if $min {
+    @media (min-width: $min) {
+      @content;
+    }
+  } @else {
+    @content;
+  }
+}
+
+// Media of at most the maximum breakpoint width. No query for the largest breakpoint.
+@mixin media-breakpoint-max($name, $breakpoints: $grid-breakpoints) {
+  $max: breakpoint-max($name, $breakpoints);
+  @if $max {
+    @media (max-width: $max) {
+      @content;
+    }
+  } @else {
+    @content;
+  }
+}
+
+// Media between the breakpoint's minimum and maximum widths.
+// No minimum for the smallest breakpoint, and no maximum for the largest one.
+@mixin media-breakpoint-only($name, $breakpoints: $grid-breakpoints) {
+  // Nested media query combination does not work in libsass yet
+  // https://github.com/sass/libsass/issues/185
+  // Work around until the issue is resolved:
+  $min: breakpoint-min($name, $breakpoints);
+  $max: breakpoint-max($name, $breakpoints);
+  @if $min and $max {
+    @media (min-width: $min) and (max-width: $max) {
+      @content;
+    }
+  } @else {
+    // One of min or max is a no-op, so this branch is not affected by libsass#185
+    @include media-breakpoint-min($name, $breakpoints) {
+      @include media-breakpoint-max($name, $breakpoints) {
+        @content;
+      }
+    }
+  }
+}

scss/mixins/_grid-framework.scss

@@ -3,27 +3,23 @@
 // Used only by Bootstrap to generate the correct number of grid classes given
 // any value of `$grid-columns`.
 
-// Common properties for all breakpoints
-@mixin make-grid-columns($columns: $grid-columns, $breakpoints: $grid-breakpoints) {
+@mixin make-grid-columns($columns: $grid-columns, $gutter: $grid-gutter-width, $breakpoints: $grid-breakpoints) {
+  // Common properties for all breakpoints
   %grid-column {
     position: relative;
     // Prevent columns from collapsing when empty
     min-height: 1px;
     // Inner gutter via padding
-    padding-left: ($grid-gutter-width / 2);
-    padding-right: ($grid-gutter-width / 2);
+    padding-left: ($gutter / 2);
+    padding-right: ($gutter / 2);
   }
+  @each $breakpoint in map-keys($breakpoints) {
     @for $i from 1 through $columns {
-    @each $breakpoint in $breakpoints {
       .col-#{$breakpoint}-#{$i} {
         @extend %grid-column;
       }
     }
-  }
-}
-
-// Breakpoint-specific properties
-@mixin make-grid($breakpoint, $columns: $grid-columns) {
+    @include media-breakpoint-min($breakpoint) {
       // Work around cross-media @extend (https://github.com/sass/sass/issues/1050)
       %grid-column-float-#{$breakpoint} {
         float: left;
@@ -31,41 +27,16 @@
       @for $i from 1 through $columns {
         .col-#{$breakpoint}-#{$i} {
           @extend %grid-column-float-#{$breakpoint};
-      @include grid-column-width($i, $columns);
+          @include make-col-span($i, $columns);
         }
       }
       @each $modifier in (pull, push, offset) {
         @for $i from 0 through $columns {
           .col-#{$breakpoint}-#{$modifier}-#{$i} {
-        @include grid-column-modifier($modifier, $i, $columns)
+            @include make-col-modifier($modifier, $i, $columns)
+          }
         }
       }
     }
-}
-
-@mixin grid-column-width($index, $columns) {
-  width: percentage($index / $columns);
-}
-
-@mixin grid-column-push($index, $columns) {
-  left: if($index > 0, percentage($index / $columns), auto);
-}
-
-@mixin grid-column-pull($index, $columns) {
-  right: if($index > 0, percentage($index / $columns), auto);
-}
-
-@mixin grid-column-offset($index, $columns) {
-  margin-left: percentage($index / $columns);
-}
-
-// Work around the lack of dynamic mixin @include support (https://github.com/sass/sass/issues/626)
-@mixin grid-column-modifier($type, $index, $columns) {
-  @if $type == push {
-    @include grid-column-push($index, $columns);
-  } @else if $type == pull {
-    @include grid-column-pull($index, $columns);
-  } @else if $type == offset {
-    @include grid-column-offset($index, $columns);
   }
 }

scss/mixins/_grid.scss

@@ -24,18 +24,29 @@
   padding-right: ($gutter / 2);
 }
 
-@mixin make-col-span($columns) {
-  width: percentage(($columns / $grid-columns));
+@mixin make-col-span($size, $columns: $grid-columns) {
+  width: percentage($size / $columns);
 }
 
-@mixin make-col-offset($columns) {
-  margin-left: percentage(($columns / $grid-columns));
+@mixin make-col-offset($size, $columns: $grid-columns) {
+  margin-left: percentage($size / $columns);
 }
 
-@mixin make-col-push($columns) {
-  left: percentage(($columns / $grid-columns));
+@mixin make-col-push($size, $columns: $grid-columns) {
+  left: if($size > 0, percentage($size / $columns), auto);
 }
 
-@mixin make-col-pull($columns) {
-  right: percentage(($columns / $grid-columns));
+@mixin make-col-pull($size, $columns: $grid-columns) {
+  right: if($size > 0, percentage($size / $columns), auto);
+}
+
+@mixin make-col-modifier($type, $size, $columns) {
+  // Work around the lack of dynamic mixin @include support (https://github.com/sass/sass/issues/626)
+  @if $type == push {
+    @include make-col-push($size, $columns);
+  } @else if $type == pull {
+    @include make-col-pull($size, $columns);
+  } @else if $type == offset {
+    @include make-col-offset($size, $columns);
+  }
 }

scss/mixins/_media-queries.scss

-// Media query mixins
+// Media query mixins for default breakpoints
 
 @mixin media-xs() {
-  @media (max-width: $screen-xs-max) { @content }
+  @include media-breakpoint-max(xs) { @content }
 }
 
 @mixin media-sm() {
-  @media (min-width: $screen-sm-min) { @content }
+  @include media-breakpoint-min(sm) { @content }
 }
 
 @mixin media-sm-max() {
-  @media (min-width: $screen-sm-min) and (max-width: $screen-sm-max) { @content }
+  @include media-breakpoint-only(sm) { @content }
 }
 
 @mixin media-md() {
-  @media (min-width: $screen-md-min) { @content }
+  @include media-breakpoint-min(md) { @content }
 }
 
 @mixin media-md-max() {
-  @media (min-width: $screen-md-min) and (max-width: $screen-md-max) { @content }
+  @include media-breakpoint-only(md) { @content }
 }
 
 @mixin media-lg() {
-  @media (min-width: $screen-lg-min) { @content }
+  @include media-breakpoint-min(lg) { @content }
 }