fix: treat ** adjacent to a literal as a single star (#99)

In the fast-path regex builder, `**.ext` patterns (e.g. `**.js`,
`**.thing.js`) were reduced to a bare `**` and expanded to a globstar,
so they incorrectly matched across path separators — `**.thing.js`
matched `somepath/test.thing.js`.

Per Bash semantics, `**` is only a globstar when it is the sole content
of a path segment; adjacent to other characters it behaves as a single
star. Bail out of the fast path for this shape and let the full parser
produce the correct single-star regex (as it already did for patterns
the fast path skipped, e.g. `**.dash-thing.js`).

Closes #99

Author: fdma

lib/parse.js

@@ -1408,6 +1408,11 @@ parse.fastpaths = (input, options) => {
         const match = /^(.*?)\.(\w+)$/.exec(str);
         if (!match) return;
 
+        // A bare `**` here is adjacent to a literal extension in the same path
+        // segment (e.g. `**.js`), so it must act as a single star rather than a
+        // globstar. Bail out of the fast path and let the full parser handle it.
+        if (match[1] === '**') return;
+
         const source = create(match[1]);
         if (!source) return;
 

test/issue-related.js

@@ -72,4 +72,16 @@ describe('issue-related tests', () => {
     assert(!isMatch('test/utils', 'test(/utils/**)', { strictSlashes: true }));
     assert(!isMatch('test/utils', 'test(/utils/**)/file'));
   });
+
+  it('should treat a leading `**` followed by a literal as a single star (picomatch/issues#99)', () => {
+    // `**` only acts as a globstar when it is the sole content of a path segment.
+    // When it is adjacent to other characters in the same segment (here `.thing.js`),
+    // it must behave like a single star and not match across path separators.
+    assert(!isMatch('somepath/test.thing.js', '**.thing.js'));
+    assert(!isMatch('a/b/c.js', '**.js'));
+    // these sibling cases already behaved correctly and must keep working
+    assert(!isMatch('somepath/test.dash-thing.js', '**.dash-thing.js'));
+    assert(isMatch('test.thing.js', '**.thing.js'));
+    assert(isMatch('somepath/test.thing.js', '**/*.thing.js'));
+  });
 });