Make side effect import sorting deterministic

This fixes the test failures on Node.js 10 and 8.

README.md

@@ -364,8 +364,8 @@ The inner arrays are joined with one newline; the outer arrays are joined with
 two (creating a blank line).
 
 Every group is sorted internally as mentioned in [Sort order]. Side effect
-imports are sorted too – but will keep their internal order. It’s recommended to
-keep side effect imports in their own group.
+imports are always placed first in the group and keep their internal order. It’s
+recommended to keep side effect imports in their own group.
 
 These are the default groups:
 

examples/groups.custom.js

@@ -11,7 +11,7 @@ import {CATEGORIES} from "../"
 import {truncate, removeWhitespace} from "../../utils";
 import cssGlobals from "../../css/globals"
 import styles from "./styles.scss";
-import circleSyles from "./circle.scss";
+import circleStyles from "./circle.scss";
 import "./global.scss"
 import {name} from "@company/config"
 import Button from "@ui/Button";

src/sort.js

@@ -777,7 +777,12 @@ function sortImportItems(items) {
     // If both items are side effect imports, keep their original order.
     itemA.isSideEffectImport && itemB.isSideEffectImport
       ? 0
-      : // First compare the `from` part.
+      : // If one of the items is a side effect import, move it first.
+      itemA.isSideEffectImport
+      ? -1
+      : itemB.isSideEffectImport
+      ? 1
+      : // Compare the `from` part.
         compare(itemA.source.source, itemB.source.source) ||
         // The `.source` has been slightly tweaked. To stay fully deterministic,
         // also sort on the original value.

test/__snapshots__/examples.test.js.snap

@@ -94,9 +94,9 @@ import tomorrow from "./time/tomorrow"
 import {providers} from "./providers"
 import {PRODUCT_NAMES} from "."
 
-import circleSyles from "./circle.scss";
 import "./global.scss"
 import "../../alert.css"
+import circleStyles from "./circle.scss";
 import styles from "./styles.scss";
 
 `;

test/sort.test.js

@@ -75,6 +75,15 @@ function getLoc(depth = 1) {
   return match != null ? match[0] : "?";
 }
 
+function ifSupported(regexString, fallbackRegexString) {
+  try {
+    RegExp(regexString, "u");
+    return regexString;
+  } catch (_error) {
+    return fallbackRegexString;
+  }
+}
+
 const baseTests = expect => ({
   valid: [
     // Simple cases.
@@ -1433,8 +1442,9 @@ const baseTests = expect => ({
     },
 
     // `groups` – `u` flag.
+    // Node.js 8 supports `u` but not `\p{L}`.
     {
-      options: [{ groups: [["^\\p{L}"], ["^\\."]] }],
+      options: [{ groups: [[ifSupported("^\\p{L}", "^[^.]")], ["^\\."]] }],
       code: input`
           |import b from '.';
           |import a from 'ä';
@@ -1533,11 +1543,11 @@ const baseTests = expect => ({
       `,
       output: actual => {
         expect(actual).toMatchInlineSnapshot(`
-          |import x from './x';
-          |import b from 'b';
           |import 'c';
           |import 'a';
           |import '.';
+          |import x from './x';
+          |import b from 'b';
           |import d from 'd';
         `);
       },