Add no-empty-first-line rule

docs/user-guide/example-config.md

@@ -107,6 +107,7 @@ You might want to learn a little about [how rules are named and how they work to
     "no-duplicate-at-import-rules": true,
     "no-duplicate-selectors": true,
     "no-empty-source": true,
+    "no-empty-first-line": true,
     "no-eol-whitespace": true,
     "no-extra-semicolons": true,
     "no-invalid-double-slash-comments": true,

docs/user-guide/rules.md

@@ -355,3 +355,4 @@ Here are all the rules within stylelint, grouped first [by category](../../VISIO
 -   [`max-line-length`](../../lib/rules/max-line-length/README.md): Limit the length of a line.
 -   [`no-eol-whitespace`](../../lib/rules/no-eol-whitespace/README.md): Disallow end-of-line whitespace (Autofixable).
 -   [`no-missing-end-of-source-newline`](../../lib/rules/no-missing-end-of-source-newline/README.md): Disallow missing end-of-source newlines (Autofixable).
+-   [`no-empty-first-line`](../../lib/rules/no-empty-first-line/README.md): Disallow empty first lines. (Autofixable).

lib/rules/index.js

@@ -100,6 +100,7 @@ module.exports = [
   "no-duplicate-at-import-rules",
   "no-duplicate-selectors",
   "no-empty-source",
+  "no-empty-first-line",
   "no-eol-whitespace",
   "no-extra-semicolons",
   "no-invalid-double-slash-comments",

lib/rules/no-empty-first-line/README.md

@@ -0,0 +1,31 @@
+# no-empty-first-line
+
+Disallow empty first lines.
+
+```css
+    \n
+    /** ↑
+     * This newline */
+    a { color: pink; }
+```
+
+This rule ignores empty sources. Use the [`no-empty-source`](../no-empty-source/README.md) rule to disallow these.
+
+The `--fix` option on the [command line](../../../docs/user-guide/cli.md#autofixing-errors) can automatically fix all of the problems reported by this rule.
+
+## Options
+
+### `true`
+
+The following patterns are considered violations:
+
+```css
+\n
+a { color: pink; }
+```
+
+The following patterns are *not* considered violations:
+
+```css
+a { color: pink; }
+```

lib/rules/no-empty-first-line/__tests__/index.js

@@ -0,0 +1,96 @@
+"use strict";
+
+const rule = require("..");
+const { messages, ruleName } = rule;
+
+testRule(rule, {
+  ruleName,
+  config: [true],
+  skipBasicChecks: true,
+  fix: true,
+
+  accept: [
+    {
+      code: ""
+    },
+    {
+      code: "  "
+    },
+    {
+      code: "\n"
+    },
+    {
+      code: "\n\n"
+    },
+    {
+      code: ".class {}"
+    },
+    {
+      code: "\t.class {}   "
+    },
+    {
+      code: "   .class {}   "
+    },
+    {
+      code: "/* comment */"
+    }
+  ],
+  reject: [
+    {
+      code: "\n.class {} \n",
+      fixed: ".class {} \n",
+      description: "empty first line",
+      message: messages.rejected,
+      line: 1,
+      column: 1
+    },
+    {
+      code: "\r\n.class {}",
+      fixed: ".class {}",
+      description: "empty first line",
+      message: messages.rejected,
+      line: 1,
+      column: 1
+    },
+    {
+      code: "\n/*some comment*/\n",
+      fixed: "/*some comment*/\n",
+      description: "empty first line with comment",
+      message: messages.rejected,
+      line: 1,
+      column: 1
+    },
+    {
+      code: "\n/*some comment*/.class {}\na {}\n",
+      fixed: "/*some comment*/.class {}\na {}\n",
+      description: "empty first line with comment and css content",
+      message: messages.rejected,
+      line: 1,
+      column: 1
+    },
+    {
+      code: "\r\n\r\n\r\n\r\n.class {}",
+      fixed: ".class {}",
+      description: "multiple empty first lines",
+      message: messages.rejected,
+      line: 1,
+      column: 1
+    },
+    {
+      code: " \r\n\r\n\r\n\r\n.class {}",
+      fixed: ".class {}",
+      description: "multiple empty first lines with initial whitespace",
+      message: messages.rejected,
+      line: 1,
+      column: 1
+    },
+    {
+      code: "               \n.class {}",
+      fixed: ".class {}",
+      description: "empty first line with multiple initial whitespaces",
+      message: messages.rejected,
+      line: 1,
+      column: 1
+    }
+  ]
+});

lib/rules/no-empty-first-line/index.js

@@ -0,0 +1,51 @@
+"use strict";
+
+const eachRoot = require("../../utils/eachRoot");
+const report = require("../../utils/report");
+const ruleMessages = require("../../utils/ruleMessages");
+const validateOptions = require("../../utils/validateOptions");
+
+const ruleName = "no-empty-first-line";
+
+const messages = ruleMessages(ruleName, {
+  rejected: "Unexpected empty line"
+});
+
+const rule = function(actual, _, context) {
+  return (root, result) => {
+    const validOptions = validateOptions(result, ruleName, { actual });
+    if (!validOptions) {
+      return;
+    }
+
+    eachRoot(root, function(root) {
+      if (root.source.inline || root.source.lang === "object-literal") {
+        return;
+      }
+      const rootString = root.source.input.css;
+      if (rootString.trim() === "") {
+        return;
+      }
+
+      const noEmptyFirstLineTest = RegExp(/^(\s*\r?\n)+/g);
+
+      if (noEmptyFirstLineTest.test(rootString)) {
+        if (context.fix) {
+          root.nodes[0].raws.before = "";
+          return;
+        }
+
+        report({
+          message: messages.rejected,
+          node: root,
+          result,
+          ruleName
+        });
+      }
+    });
+  };
+};
+
+rule.ruleName = ruleName;
+rule.messages = messages;
+module.exports = rule;