Support \G in leading positive lookaround

README.md

@@ -578,7 +578,7 @@ Notice that nearly every feature below has at least subtle differences from Java
     <td align="middle">☑️</td>
     <td align="middle">☑️</td>
     <td>
-      ● Supported when used at start of pattern (if no top-level alternation) and when at start of all top-level alternatives<br>
+      ● Many common uses supported<br>
     </td>
   </tr>
   <tr valign="top">

spec/match-assertion.spec.js

@@ -91,6 +91,7 @@ describe('Assertion', () => {
       expect('a').toExactlyMatch(r`\A\Ga`);
       expect('a').toExactlyMatch(r`\b\Ga`);
       expect('a').toExactlyMatch(r`(?=a)\Ga`);
+      expect('a').toExactlyMatch(r`(?<=\A)\Ga`);
       expect('a').toExactlyMatch(r`(?<!a)\Ga`);
       expect('a').toExactlyMatch(r`(?<!a)(?=a)\Ga`);
     });
@@ -120,8 +121,23 @@ describe('Assertion', () => {
       expect(() => compile(r`(\Ga)+\G`)).toThrow();
     });
 
+    it('should allow if leading in a leading positive lookaround', () => {
+      expect('a').toExactlyMatch(r`(?=\G)a`);
+      expect('a').toExactlyMatch(r`(?<=\G)a`);
+      expect(() => compile(r`(?<=a\G)a`)).toThrow();
+      expect(() => compile(r`(?<=\G|)a`)).toThrow();
+      expect(() => compile(r`(?:(?<=\G))?a`)).toThrow();
+      expect('a').toExactlyMatch(r`(?=\G)a|\Gb`);
+      expect(() => compile(r`(?=\G)a|b`)).toThrow();
+    });
+
+    it('should throw if leading in a leading negative lookaround', () => {
+      expect(() => compile(r`(?!\G)a`)).toThrow();
+      expect(() => compile(r`(?<!\G)a`)).toThrow();
+    });
+
     // Documenting current behavior; supportable
-    it('should allow redundant assertions', () => {
+    it('should throw for redundant assertions', () => {
       expect(() => compile(r`\G\Ga`)).toThrow();
       expect(() => compile(r`\Ga|\G\Gb`)).toThrow();
     });

src/transform.js

@@ -1,5 +1,5 @@
 import emojiRegex from 'emoji-regex-xs';
-import {AstAssertionKinds, AstCharacterSetKinds, AstDirectiveKinds, AstTypes, AstVariableLengthCharacterSetKinds, createAlternative, createBackreference, createGroup, createLookaround, createUnicodeProperty, parse} from './parse.js';
+import {AstAssertionKinds, AstCharacterSetKinds, AstDirectiveKinds, AstTypes, AstVariableLengthCharacterSetKinds, createAlternative, createBackreference, createGroup, createLookaround, createUnicodeProperty, isLookaround, parse} from './parse.js';
 import {tokenize} from './tokenize.js';
 import {traverse} from './traverse.js';
 import {JsUnicodeProperties, PosixClassesMap} from './unicode.js';
@@ -645,6 +645,18 @@ function hasLeadingG(els, supportedGNodes) {
   if (!els.length) {
     return false;
   }
+  const first = els[0];
+  // Special case for leading positive lookaround with leading `\G`, else all leading assertions
+  // are ignored when looking for `\G`
+  if (
+    isLookaround(first) &&
+    !first.negate &&
+    first.alternatives.length === 1 &&
+    first.alternatives[0].elements[0]?.kind === AstAssertionKinds.search_start
+  ) {
+    supportedGNodes.add(first.alternatives[0].elements[0]);
+    return true;
+  }
   const firstToConsider = els.find(el => {
     return el.kind === AstAssertionKinds.search_start ?
       true :