Struct regex_syntax::ParserBuilder

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pub struct ParserBuilder { /* private fields */ }

Expand description

A builder for a regular expression parser.

This builder permits modifying configuration options for the parser.

This type combines the builder options for both the AST ParserBuilder and the HIR TranslatorBuilder.

Implementations§

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impl ParserBuilder

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pub fn new() -> ParserBuilder

Create a new parser builder with a default configuration.

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pub fn build(&self) -> Parser

Build a parser from this configuration with the given pattern.

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pub fn nest_limit(&mut self, limit: u32) -> &mut ParserBuilder

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.

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pub fn octal(&mut self, yes: bool) -> &mut ParserBuilder

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.

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pub fn allow_invalid_utf8(&mut self, yes: bool) -> &mut ParserBuilder

When enabled, the parser will permit the construction of a regular expression that may match invalid UTF-8.

When disabled (the default), the parser is guaranteed to produce an expression that will only ever match valid UTF-8 (otherwise, the parser will return an error).

Perhaps surprisingly, when invalid UTF-8 isn’t allowed, a negated ASCII word boundary (uttered as (?-u:\B) in the concrete syntax) will cause the parser to return an error. Namely, a negated ASCII word boundary can result in matching positions that aren’t valid UTF-8 boundaries.

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pub fn ignore_whitespace(&mut self, yes: bool) -> &mut ParserBuilder

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.

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pub fn case_insensitive(&mut self, yes: bool) -> &mut ParserBuilder

Enable or disable the case insensitive flag by default.

By default this is disabled. It may alternatively be selectively enabled in the regular expression itself via the i flag.

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pub fn multi_line(&mut self, yes: bool) -> &mut ParserBuilder

Enable or disable the multi-line matching flag by default.

By default this is disabled. It may alternatively be selectively enabled in the regular expression itself via the m flag.

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pub fn dot_matches_new_line(&mut self, yes: bool) -> &mut ParserBuilder

Enable or disable the “dot matches any character” flag by default.

By default this is disabled. It may alternatively be selectively enabled in the regular expression itself via the s flag.

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pub fn swap_greed(&mut self, yes: bool) -> &mut ParserBuilder

Enable or disable the “swap greed” flag by default.

By default this is disabled. It may alternatively be selectively enabled in the regular expression itself via the U flag.

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pub fn unicode(&mut self, yes: bool) -> &mut ParserBuilder

Enable or disable the Unicode flag (u) by default.

By default this is enabled. It may alternatively be selectively disabled in the regular expression itself via the u flag.

Note that unless allow_invalid_utf8 is enabled (it’s disabled by default), a regular expression will fail to parse if Unicode mode is disabled and a sub-expression could possibly match invalid UTF-8.