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//- // Copyright 2017 Jason Lingle // // Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or // http://www.apache.org/licenses/LICENSE-2.0> or the MIT license // <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your // option. This file may not be copied, modified, or distributed // except according to those terms. //! Strategies for generating `char` values. //! //! Unlike most strategies in Proptest, character generation is by default //! biased to particular values known to be difficult to handle in various //! circumstances. //! //! The main things of interest are `any()` to generate truly arbitrary //! characters, and `range()` and `ranges()` to select characters from //! inclusive ranges. use crate::std_facade::Cow; use core::ops::RangeInclusive; use rand::Rng; use crate::num; use crate::strategy::*; use crate::test_runner::*; /// An inclusive char range from fst to snd. type CharRange = RangeInclusive<char>; /// A default set of characters to consider as "special" during character /// generation. /// /// Most of the characters here were chosen specifically because they are /// difficult to handle in particular contexts. pub const DEFAULT_SPECIAL_CHARS: &[char] = &[ // Things to give shell scripts and filesystem logic difficulties '/', '\\', '$', '.', '*', '{', '\'', '"', '`', ':', // Characters with special significance in URLs and elsewhere '?', '%', '=', '&', '<', // Interesting ASCII control characters // NUL, HT, CR, LF, VT ESC DEL '\x00', '\t', '\r', '\n', '\x0B', '\x1B', '\x7F', // ¥ both to test simple Unicode handling and because it has interesting // properties on MS Shift-JIS systems. '¥', // No non-Unicode encoding has both ¥ and Ѩ 'Ѩ', // In UTF-8, Ⱥ increases in length from 2 to 3 bytes when lowercased 'Ⱥ', // More Unicode edge-cases: BOM, replacement character, RTL override, and non-BMP '\u{FEFF}', '\u{FFFD}', '\u{202E}', '🕴', ]; /// A default sequence of ranges used preferentially when generating random /// characters. pub const DEFAULT_PREFERRED_RANGES: &[CharRange] = &[ // ASCII printable ' '..='~', ' '..='~', ' '..='~', ' '..='~', ' '..='~', // Latin-1 '\u{0040}'..='\u{00ff}', ]; /// Selects a random character the way `CharStrategy` does. /// /// If `special` is non-empty, there is a 50% chance that a character from this /// array is chosen randomly, and will be returned if that character falls /// within `ranges`. /// /// If `preferred` is non-empty, there is a 50% chance that any generation /// which gets past the `special` step picks a random element from this list, /// then a random character from within that range (both endpoints inclusive). /// That character will be returned if it falls within `ranges`. /// /// In all other cases, an element is picked randomly from `ranges` and a /// random character within the range (both endpoints inclusive) is chosen and /// returned. /// /// Notice that in all cases, `ranges` completely defines the set of characters /// that can possibly be defined. /// /// It is legal for ranges in all cases to contain non-characters. /// /// Both `preferred` and `ranges` bias selection towards characters in smaller /// ranges. This is deliberate. `preferred` is usually tuned to select /// particular characters anyway. `ranges` is usually derived from some /// external property, and the fact that a range is small often means it is /// more interesting. pub fn select_char( rnd: &mut impl Rng, special: &[char], preferred: &[CharRange], ranges: &[CharRange], ) -> char { let (base, offset) = select_range_index(rnd, special, preferred, ranges); ::core::char::from_u32(base + offset).expect("bad character selected") } fn select_range_index( rnd: &mut impl Rng, special: &[char], preferred: &[CharRange], ranges: &[CharRange], ) -> (u32, u32) { fn in_range(ranges: &[CharRange], ch: char) -> Option<(u32, u32)> { ranges .iter() .find(|r| ch >= *r.start() && ch <= *r.end()) .map(|r| (*r.start() as u32, ch as u32 - *r.start() as u32)) } if !special.is_empty() && rnd.gen() { let s = special[rnd.gen_range(0..special.len())]; if let Some(ret) = in_range(ranges, s) { return ret; } } if !preferred.is_empty() && rnd.gen() { let range = preferred[rnd.gen_range(0..preferred.len())].clone(); if let Some(ch) = ::core::char::from_u32( rnd.gen_range(*range.start() as u32..*range.end() as u32 + 1), ) { if let Some(ret) = in_range(ranges, ch) { return ret; } } } for _ in 0..65_536 { let range = ranges[rnd.gen_range(0..ranges.len())].clone(); if let Some(ch) = ::core::char::from_u32( rnd.gen_range(*range.start() as u32..*range.end() as u32 + 1), ) { return (*range.start() as u32, ch as u32 - *range.start() as u32); } } // Give up and return a character we at least know is valid. (*ranges[0].start() as u32, 0) } /// Strategy for generating `char`s. /// /// Character selection is more sophisticated than integer selection. Naïve /// selection (particularly in the larger context of generating strings) would /// result in starting inputs like `ꂡ螧轎ቶᢹ糦狥芹ᘆ㶏曊ᒀ踔虙ჲ` and "simplified" /// inputs consisting mostly of control characters. It also has difficulty /// locating edge cases, since the vast majority of code points (such as the /// enormous CJK regions) don't cause problems for anything with even basic /// Unicode support. /// /// Instead, character selection is always based on explicit ranges, and is /// designed to bias to specifically chosen characters and character ranges to /// produce inputs that are both more useful and easier for humans to /// understand. There are also hard-wired simplification targets based on ASCII /// instead of simply simplifying towards NUL to avoid problematic inputs being /// reduced to a bunch of NUL characters. /// /// Shrinking never crosses ranges. If you have a complex range like `[A-Za-z]` /// and the starting point `x` is chosen, it will not shrink to the first `A-Z` /// group, but rather simply to `a`. /// /// The usual way to get instances of this class is with the module-level `ANY` /// constant or `range` function. Directly constructing a `CharStrategy` is /// only necessary for complex ranges or to override the default biases. #[derive(Debug, Clone)] #[must_use = "strategies do nothing unless used"] pub struct CharStrategy<'a> { special: Cow<'a, [char]>, preferred: Cow<'a, [CharRange]>, ranges: Cow<'a, [CharRange]>, } impl<'a> CharStrategy<'a> { /// Construct a new `CharStrategy` with the parameters it will pass to the /// function underlying `select_char()`. /// /// All arguments as per `select_char()`. pub fn new( special: Cow<'a, [char]>, preferred: Cow<'a, [CharRange]>, ranges: Cow<'a, [CharRange]>, ) -> Self { CharStrategy { special, preferred, ranges, } } /// Same as `CharStrategy::new()` but using `Cow::Borrowed` for all parts. pub fn new_borrowed( special: &'a [char], preferred: &'a [CharRange], ranges: &'a [CharRange], ) -> Self { CharStrategy::new( Cow::Borrowed(special), Cow::Borrowed(preferred), Cow::Borrowed(ranges), ) } } const WHOLE_RANGE: &[CharRange] = &['\x00'..=::core::char::MAX]; /// Creates a `CharStrategy` which picks from literally any character, with the /// default biases. pub fn any() -> CharStrategy<'static> { CharStrategy { special: Cow::Borrowed(DEFAULT_SPECIAL_CHARS), preferred: Cow::Borrowed(DEFAULT_PREFERRED_RANGES), ranges: Cow::Borrowed(WHOLE_RANGE), } } /// Creates a `CharStrategy` which selects characters within the given /// endpoints, inclusive, using the default biases. pub fn range(start: char, end: char) -> CharStrategy<'static> { CharStrategy { special: Cow::Borrowed(DEFAULT_SPECIAL_CHARS), preferred: Cow::Borrowed(DEFAULT_PREFERRED_RANGES), ranges: Cow::Owned(vec![start..=end]), } } /// Creates a `CharStrategy` which selects characters within the given ranges, /// all inclusive, using the default biases. pub fn ranges(ranges: Cow<[CharRange]>) -> CharStrategy { CharStrategy { special: Cow::Borrowed(DEFAULT_SPECIAL_CHARS), preferred: Cow::Borrowed(DEFAULT_PREFERRED_RANGES), ranges, } } /// The `ValueTree` corresponding to `CharStrategy`. #[derive(Debug, Clone, Copy)] pub struct CharValueTree { value: num::u32::BinarySearch, } impl<'a> Strategy for CharStrategy<'a> { type Tree = CharValueTree; type Value = char; fn new_tree(&self, runner: &mut TestRunner) -> NewTree<Self> { let (base, offset) = select_range_index( runner.rng(), &self.special, &self.preferred, &self.ranges, ); // Select a minimum point more convenient than 0 let start = base + offset; let bottom = if start >= '¡' as u32 && base < '¡' as u32 { '¡' as u32 } else if start >= 'a' as u32 && base < 'a' as u32 { 'a' as u32 } else if start >= 'A' as u32 && base < 'A' as u32 { 'A' as u32 } else if start >= '0' as u32 && base < '0' as u32 { '0' as u32 } else if start >= ' ' as u32 && base < ' ' as u32 { ' ' as u32 } else { base }; Ok(CharValueTree { value: num::u32::BinarySearch::new_above(bottom, start), }) } } impl CharValueTree { fn reposition(&mut self) { while ::core::char::from_u32(self.value.current()).is_none() { if !self.value.complicate() { panic!("Converged to non-char value"); } } } } impl ValueTree for CharValueTree { type Value = char; fn current(&self) -> char { ::core::char::from_u32(self.value.current()) .expect("Generated non-char value") } fn simplify(&mut self) -> bool { if self.value.simplify() { self.reposition(); true } else { false } } fn complicate(&mut self) -> bool { if self.value.complicate() { self.reposition(); true } else { false } } } #[cfg(test)] mod test { use std::cmp::{max, min}; use std::vec::Vec; use super::*; use crate::collection; proptest! { #[test] fn stays_in_range(input_ranges in collection::vec( (0..::std::char::MAX as u32, 0..::std::char::MAX as u32), 1..5)) { let input = ranges(Cow::Owned(input_ranges.iter().map( |&(lo, hi)| ::std::char::from_u32(lo).and_then( |lo| ::std::char::from_u32(hi).map( |hi| min(lo, hi) ..= max(lo, hi))) .ok_or_else(|| TestCaseError::reject("non-char"))) .collect::<Result<Vec<CharRange>,_>>()?)); let mut runner = TestRunner::default(); for _ in 0..256 { let mut value = input.new_tree(&mut runner).unwrap(); loop { let ch = value.current() as u32; assert!(input_ranges.iter().any( |&(lo, hi)| ch >= min(lo, hi) && ch <= max(lo, hi))); if !value.simplify() { break; } } } } } #[test] fn applies_desired_bias() { let mut men_in_business_suits_levitating = 0; let mut ascii_printable = 0; let mut runner = TestRunner::deterministic(); for _ in 0..1024 { let ch = any().new_tree(&mut runner).unwrap().current(); if '🕴' == ch { men_in_business_suits_levitating += 1; } else if ch >= ' ' && ch <= '~' { ascii_printable += 1; } } assert!(ascii_printable >= 256); assert!(men_in_business_suits_levitating >= 1); } #[test] fn doesnt_shrink_to_ascii_control() { let mut accepted = 0; let mut runner = TestRunner::deterministic(); for _ in 0..256 { let mut value = any().new_tree(&mut runner).unwrap(); if value.current() <= ' ' { continue; } while value.simplify() {} assert!(value.current() >= ' '); accepted += 1; } assert!(accepted >= 200); } #[test] fn test_sanity() { check_strategy_sanity( any(), Some(CheckStrategySanityOptions { // `simplify()` can itself `complicate()` back to the starting // position, so the overly strict complicate-after-simplify check // must be disabled. strict_complicate_after_simplify: false, ..CheckStrategySanityOptions::default() }), ); } }