Add rule-empty-line-before rule

lib/rules/rule-empty-line-before/README.md

@@ -110,7 +110,28 @@ b
 
 ## Optional secondary options
 
-### `except: ["after-single-line-comment", "inside-block-and-after-rule", "first-nested"]`
+### `except: ["after-rule", "after-single-line-comment", "inside-block-and-after-rule", "first-nested"]`
+
+#### `"after-rule"`
+
+Reverse the primary option if the rule comes after another rule.
+
+For example, with `"always"`:
+
+The following patterns are considered warnings:
+
+```css
+a {}
+
+b {}
+```
+
+The following patterns are *not* considered warnings:
+
+```css
+a {}
+b {}
+```
 
 #### `"after-single-line-comment"`
 

lib/rules/rule-empty-line-before/__tests__/index.js

@@ -96,6 +96,32 @@ testRule(rule, {
   }],
 })
 
+testRule(rule, {
+  ruleName,
+  config: [ "always", { except: ["after-rule"] } ],
+
+  accept: [ {
+    code: "a {} \n b {}",
+  }, {
+    code: "$var: pink;\n\nb {}",
+    description: "scss variable",
+  }, {
+    code: "@media {}\n\na{}",
+    description: "media rule",
+  } ],
+
+  reject: [ {
+    code: "a {}\n\nb {}",
+    message: messages.rejected,
+  }, {
+    code: "$var: pink;\nb {}",
+    message: messages.expected,
+  }, {
+    code: "@media {}\na{}",
+    message: messages.expected,
+  } ],
+})
+
 testRule(rule, {
   ruleName,
   config: [ "always", { except: ["after-single-line-comment"] } ],

lib/rules/rule-empty-line-before/index.js

@@ -33,6 +33,7 @@ const rule = function (expectation, options) {
           "inside-block",
         ],
         except: [
+          "after-rule",
           "after-single-line-comment",
           "first-nested",
           "inside-block-and-after-rule",
@@ -91,6 +92,15 @@ const rule = function (expectation, options) {
       }
 
       // Optionally reverse the expectation if a rule precedes this node
+      if (
+        optionsMatches(options, "except", "after-rule")
+        && rule.prev()
+        && rule.prev().type === "rule"
+      ) {
+        expectEmptyLineBefore = !expectEmptyLineBefore
+      }
+
+      // Optionally reverse the expectation if a rule precedes this node and is inside a block
       if (
         optionsMatches(options, "except", "inside-block-and-after-rule")
         && rule.prev()