[yuefdev]

PostgreSQL dollar-quote tags may start with an underscore and contain digits after the first character. The interpolator currently accepts only letters, so SELECT $tag_1$literal $2$tag_1$, $1 tries to bind the literal $2 and fails with a missing-argument error.

Recognise those tag characters while keeping a leading digit out of the tag. Tests preserve placeholders inside the literal and still bind the following $1; five tag cases fail before the fix. Empty and letter-only tags, Unicode letters and a digit-leading non-tag are also covered.

go test ./... -count=1, go vet ./... and formatting checks for the changed files pass. The tag rules are described in PostgreSQL's lexical syntax documentation.

[coveralls]

coverage: 96.183% (+0.01%) from 96.17% — yuefdev:fix/postgres-dollar-quote-tags into huandu:master

[huandu]

Requesting changes for one parser regression introduced by this change. The tag grammar itself is correct, and the reported cases now match PostgreSQL. However, the scanner still treats $ as a quote opener without checking the preceding token, which now also affects _-leading tags. There are two smaller cleanup suggestions as well. Details inline.