ParserBuilder in regex_syntax::ast::parse - Rust (original) (raw)
Struct ParserBuilder
pub struct ParserBuilder { /* private fields */ }Expand description
A builder for a regular expression parser.
This builder permits modifying configuration options for the parser.
Create a new parser builder with a default configuration.
Build a parser from this configuration with the given pattern.
Set the nesting limit for this parser.
The nesting limit controls how deep the abstract syntax tree is allowed to be. If the AST exceeds the given limit (e.g., with too many nested groups), then an error is returned by the parser.
The purpose of this limit is to act as a heuristic to prevent stack overflow for consumers that do structural induction on an Ast using explicit recursion. While this crate never does this (instead using constant stack space and moving the call stack to the heap), other crates may.
This limit is not checked until the entire AST is parsed. Therefore, if callers want to put a limit on the amount of heap space used, then they should impose a limit on the length, in bytes, of the concrete pattern string. In particular, this is viable since this parser implementation will limit itself to heap space proportional to the length of the pattern string.
Note that a nest limit of 0 will return a nest limit error for most patterns but not all. For example, a nest limit of 0 permits a but not ab, since ab requires a concatenation, which results in a nest depth of 1. In general, a nest limit is not something that manifests in an obvious way in the concrete syntax, therefore, it should not be used in a granular way.
Whether to support octal syntax or not.
Octal syntax is a little-known way of uttering Unicode codepoints in a regular expression. For example, a, \x61, \u0061 and\141 are all equivalent regular expressions, where the last example shows octal syntax.
While supporting octal syntax isn’t in and of itself a problem, it does make good error messages harder. That is, in PCRE based regex engines, syntax like \0 invokes a backreference, which is explicitly unsupported in Rust’s regex engine. However, many users expect it to be supported. Therefore, when octal support is disabled, the error message will explicitly mention that backreferences aren’t supported.
Octal syntax is disabled by default.
Enable verbose mode in the regular expression.
When enabled, verbose mode permits insignificant whitespace in many places in the regular expression, as well as comments. Comments are started using # and continue until the end of the line.
By default, this is disabled. It may be selectively enabled in the regular expression by using the x flag regardless of this setting.
Allow using {,n} as an equivalent to {0,n}.
When enabled, the parser accepts {,n} as valid syntax for {0,n}. Most regular expression engines don’t support the {,n} syntax, but some others do it, namely Python’s re library.
This is disabled by default.