From f231e78be5b8edaae62e93fb728fc2d6f505a2bd Mon Sep 17 00:00:00 2001
From: Yarchik <spoko.dev@gmail.com>
Date: Wed, 17 Jun 2026 15:31:25 +0100
Subject: [PATCH] fix: don't treat a non-prefix token before `|` as a namespace
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`namespace()` used the previous token's content as the namespace prefix
whenever a `|` was seen. For an empty namespace written as a bare `|`
(e.g. `|b`), the previous token is whatever precedes it — a comment,
comma, combinator or whitespace — and that was emitted as the prefix.
So `/* c */|b` round-tripped to `/* c */\/\*\ c\ \*\/|b`, `.a,|b` to
`.a,\,|b`, `.a > |b` to `.a >  |b`, and so on.

Only use the previous token as a prefix when it can be one: a type/word,
the universal `*`, or the nesting `&` (the tokens whose parsing hands off
to `namespace()`). Otherwise the namespace is empty.
---
 src/__tests__/namespaces.mjs | 15 +++++++++++++++
 src/parser.js                | 12 +++++++++++-
 2 files changed, 26 insertions(+), 1 deletion(-)

diff --git a/src/__tests__/namespaces.mjs b/src/__tests__/namespaces.mjs
index 46e66b6..50cdde1 100644
--- a/src/__tests__/namespaces.mjs
+++ b/src/__tests__/namespaces.mjs
@@ -77,6 +77,21 @@ test("ns alias for namespace", "f\\oo|h1.foo", (t, tree) => {
   t.deepEqual(tag.ns, "bar");
 });
 
+test("empty namespace after a comment is not a prefix", "/* c */|b", (t, tree) => {
+  t.deepEqual(tree.nodes[0].nodes[1].namespace, true);
+  t.deepEqual(tree.nodes[0].nodes[1].value, "b");
+});
+
+test("empty namespace after a comma is not a prefix", ".a,|b", (t, tree) => {
+  t.deepEqual(tree.nodes[1].nodes[0].namespace, true);
+  t.deepEqual(tree.nodes[1].nodes[0].value, "b");
+});
+
+test("empty namespace after a combinator is not a prefix", ".a > |b", (t, tree) => {
+  t.deepEqual(tree.nodes[0].nodes[2].namespace, true);
+  t.deepEqual(tree.nodes[0].nodes[2].value, "b");
+});
+
 throws("lone pipe symbol", "|");
 throws("lone pipe symbol with leading spaces", " |");
 throws("lone pipe symbol with trailing spaces", "| ");
diff --git a/src/parser.js b/src/parser.js
index 3b00836..efc1789 100644
--- a/src/parser.js
+++ b/src/parser.js
@@ -696,7 +696,17 @@ export default class Parser {
   }
 
   namespace() {
-    const before = (this.prevToken && this.content(this.prevToken)) || true;
+    const prev = this.prevToken;
+    // Only treat the previous token as a namespace prefix when it can actually
+    // be one (a type/word or the universal `*`). A comment, comma, combinator
+    // or whitespace before `|` means an empty namespace, not a prefix.
+    const before =
+      prev &&
+      (prev[TOKEN.TYPE] === tokens.word ||
+        prev[TOKEN.TYPE] === tokens.asterisk ||
+        prev[TOKEN.TYPE] === tokens.ampersand)
+        ? this.content(prev)
+        : true;
     if (this.nextToken[TOKEN.TYPE] === tokens.word) {
       this.position++;
       return this.word(before);