feat(promql): do not use regex for string labels (#7669)

In Prometheus, label values are treated as strings when used with the
`=` and `!=` operators, and as regular expressions when used with the
`=~` and `!~` operators.

Injecting and then highlighting all label values as regex leads to a
situation where entirely valid **string** label values containing regex
special characters are mistakenly parsed and highlighted as regex. This
results in syntax errors, causing labels to be highlighted incorrectly.

For example, in `foo{bar=~"[a-z]{1,3}"}`, `{` and `}` are regex special
characters, so regex highlighting is expected. However, in
`foo{path="/foo/{id}"}`, `{` and `}` are just part of the string and
have no special meaning, so the whole value should be highlighted as a
string.

1 files changed, 10 insertions, 0 deletions

diff --git a/tests/query/highlights/promql/regex.promql b/tests/query/highlights/promql/regex.promql
new file mode 100644
index 000000000..fa61094a3
--- /dev/null
+++ b/tests/query/highlights/promql/regex.promql
@@ -0,0 +1,10 @@
+foo{path=~"^foo$"}[5m] or
+#          ^ @string.regexp
+foo{path!~"[a-zA-Z0-9]{1,3}"}[5m] or
+#          ^ @string.regexp
+foo{path="/api/users/{userId}"}[5m] or
+#         ^ @string
+foo{path!="/api/users/{userId}"}[5m]
+#          ^ @string
+
+# vim: ft=promql