proptest/char.rs
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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()
}),
);
}
}