Support non-ASCII Unicode in grammar rule names#2196
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The grammar currently supports only ASCII rule names. We want to support non-ASCII Unicode symbols such as `⊥` (bottom) since we plan to add that rule. In this commit, we add `is_name_start` and `is_name_continue` predicates that centralize the decision of what can appear in a rule name. `is_name_start` accepts alphabetic characters, underscores, and non-ASCII characters; `is_name_continue` accepts alphanumeric characters, underscores, and non-ASCII characters. We use `is_name_start` in the `parse_expr1` condition that routes to `parse_nonterminal`. The previous condition (`is_alphanumeric`) was slightly misaligned with what `parse_name` actually accepts -- it included digits (which `parse_name` rejects) and excluded underscores (which `parse_name` accepts). Using `is_name_start` makes the dispatch condition match `parse_name` exactly. The `NAMES_RE` regex in `mdbook-spec` encodes the same name-matching logic as a regex pattern, so let's add a comment tying it to the predicates.
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The grammar currently supports only ASCII rule names. We want to support non-ASCII Unicode symbols such as
⊥(bottom) since we plan to add that rule.In this commit, we add
is_name_startandis_name_continuepredicates that centralize the decision of what can appear in a rule name.is_name_startaccepts alphabetic characters, underscores, and non-ASCII characters;is_name_continueaccepts alphanumeric characters, underscores, and non-ASCII characters.We use
is_name_startin theparse_expr1condition that routes toparse_nonterminal. The previous condition (is_alphanumeric) was slightly misaligned with whatparse_nameactually accepts -- it included digits (whichparse_namerejects) and excluded underscores (whichparse_nameaccepts). Usingis_name_startmakes the dispatch condition matchparse_nameexactly.The
NAMES_REregex inmdbook-specencodes the same name-matching logic as a regex pattern, so let's add a comment tying it to the predicates.cc @ehuss