Rollup merge of #101308 - nerdypepper:feature/is-ascii-octdigit, r=joshtriplett

introduce `{char, u8}::is_ascii_octdigit`

This feature adds two new APIs: `char::is_ascii_octdigit` and `u8::is_ascii_octdigit`, under the feature gate `is_ascii_octdigit`. These methods are shorthands for `char::is_digit(self, 8)` and `u8::is_digit(self, 8)`:

```rust
// core::char

impl char {
    pub fn is_ascii_octdigit(self) -> bool;
}

// core::num

impl u8 {
    pub fn is_ascii_octdigit(self) -> bool;
}
```

---

Couple of things I need help understanding:

- `const`ness: have I used the right attribute in this case?
- is there a way to run the tests for `core::char` alone, instead of `./x.py test library/core`?

library/core/src/char/methods.rs

@@ -1444,6 +1444,38 @@ impl char {
         matches!(*self, '0'..='9')
     }
 
+    /// Checks if the value is an ASCII octal digit:
+    /// U+0030 '0' ..= U+0037 '7'.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// #![feature(is_ascii_octdigit)]
+    ///
+    /// let uppercase_a = 'A';
+    /// let a = 'a';
+    /// let zero = '0';
+    /// let seven = '7';
+    /// let nine = '9';
+    /// let percent = '%';
+    /// let lf = '\n';
+    ///
+    /// assert!(!uppercase_a.is_ascii_octdigit());
+    /// assert!(!a.is_ascii_octdigit());
+    /// assert!(zero.is_ascii_octdigit());
+    /// assert!(seven.is_ascii_octdigit());
+    /// assert!(!nine.is_ascii_octdigit());
+    /// assert!(!percent.is_ascii_octdigit());
+    /// assert!(!lf.is_ascii_octdigit());
+    /// ```
+    #[must_use]
+    #[unstable(feature = "is_ascii_octdigit", issue = "101288")]
+    #[rustc_const_unstable(feature = "is_ascii_octdigit", issue = "101288")]
+    #[inline]
+    pub const fn is_ascii_octdigit(&self) -> bool {
+        matches!(*self, '0'..='7')
+    }
+
     /// Checks if the value is an ASCII hexadecimal digit:
     ///
     /// - U+0030 '0' ..= U+0039 '9', or

library/core/src/lib.rs

@@ -164,6 +164,7 @@
 #![feature(const_slice_index)]
 #![feature(const_is_char_boundary)]
 #![feature(const_cstr_methods)]
+#![feature(is_ascii_octdigit)]
 //
 // Language features:
 #![feature(abi_unadjusted)]

library/core/src/num/mod.rs

@@ -622,6 +622,38 @@ impl u8 {
         matches!(*self, b'0'..=b'9')
     }
 
+    /// Checks if the value is an ASCII octal digit:
+    /// U+0030 '0' ..= U+0037 '7'.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// #![feature(is_ascii_octdigit)]
+    ///
+    /// let uppercase_a = b'A';
+    /// let a = b'a';
+    /// let zero = b'0';
+    /// let seven = b'7';
+    /// let nine = b'9';
+    /// let percent = b'%';
+    /// let lf = b'\n';
+    ///
+    /// assert!(!uppercase_a.is_ascii_octdigit());
+    /// assert!(!a.is_ascii_octdigit());
+    /// assert!(zero.is_ascii_octdigit());
+    /// assert!(seven.is_ascii_octdigit());
+    /// assert!(!nine.is_ascii_octdigit());
+    /// assert!(!percent.is_ascii_octdigit());
+    /// assert!(!lf.is_ascii_octdigit());
+    /// ```
+    #[must_use]
+    #[unstable(feature = "is_ascii_octdigit", issue = "101288")]
+    #[rustc_const_unstable(feature = "is_ascii_octdigit", issue = "101288")]
+    #[inline]
+    pub const fn is_ascii_octdigit(&self) -> bool {
+        matches!(*self, b'0'..=b'7')
+    }
+
     /// Checks if the value is an ASCII hexadecimal digit:
     ///
     /// - U+0030 '0' ..= U+0039 '9', or

library/core/tests/ascii.rs

@@ -251,6 +251,23 @@ fn test_is_ascii_digit() {
     );
 }
 
+#[test]
+fn test_is_ascii_octdigit() {
+    assert_all!(is_ascii_octdigit, "", "01234567");
+    assert_none!(
+        is_ascii_octdigit,
+        "abcdefghijklmnopqrstuvwxyz",
+        "ABCDEFGHIJKLMNOQPRSTUVWXYZ",
+        "!\"#$%&'()*+,-./:;<=>?@[\\]^_`{|}~",
+        " \t\n\x0c\r",
+        "\x00\x01\x02\x03\x04\x05\x06\x07",
+        "\x08\x09\x0a\x0b\x0c\x0d\x0e\x0f",
+        "\x10\x11\x12\x13\x14\x15\x16\x17",
+        "\x18\x19\x1a\x1b\x1c\x1d\x1e\x1f",
+        "\x7f",
+    );
+}
+
 #[test]
 fn test_is_ascii_hexdigit() {
     assert_all!(is_ascii_hexdigit, "", "0123456789", "abcdefABCDEF",);
@@ -454,6 +471,7 @@ fn ascii_ctype_const() {
         is_ascii_lowercase    => [true,  false, false, false, false];
         is_ascii_alphanumeric => [true,  true,  true,  false, false];
         is_ascii_digit        => [false, false, true,  false, false];
+        is_ascii_octdigit     => [false, false, false, false, false];
         is_ascii_hexdigit     => [true,  true,  true,  false, false];
         is_ascii_punctuation  => [false, false, false, true,  false];
         is_ascii_graphic      => [true,  true,  true,  true,  false];

library/core/tests/lib.rs

@@ -100,6 +100,7 @@
 #![feature(slice_flatten)]
 #![feature(provide_any)]
 #![feature(utf8_chunks)]
+#![feature(is_ascii_octdigit)]
 #![deny(unsafe_op_in_unsafe_fn)]
 
 extern crate test;