Some refactorings to the ISLE parser (#5693)

* Use is_ascii_digit and is_ascii_hexdigit in the ISLE lexer

* Use range pattern in ISLE lexer

* Use a couple of shorthands in the ISLE parser

* Use parse_ident instead of symbol + str_to_ident

* Introduce token eating api

This is a non-fatal version of the take api

* Rename take to expect and add expect_ prefixes to several methods

* Review comments

Author: bjorn3

cranelift/isle/isle/src/lexer.rs

@@ -232,7 +232,7 @@ impl<'a> Lexer<'a> {
                 debug_assert!(!s.is_empty());
                 Ok(Some((start_pos, Token::Symbol(s.to_string()))))
             }
-            c if (c >= b'0' && c <= b'9') || c == b'-' => {
+            c @ (b'0'..=b'9' | b'-') => {
                 let start_pos = self.pos();
                 let neg = if c == b'-' {
                     self.advance_pos();
@@ -258,16 +258,8 @@ impl<'a> Lexer<'a> {
                 // string-to-integer conversion.
                 let mut s = vec![];
                 while self.pos.offset < self.buf.len()
-                    && ((radix == 10
-                        && self.buf[self.pos.offset] >= b'0'
-                        && self.buf[self.pos.offset] <= b'9')
-                        || (radix == 16
-                            && ((self.buf[self.pos.offset] >= b'0'
-                                && self.buf[self.pos.offset] <= b'9')
-                                || (self.buf[self.pos.offset] >= b'a'
-                                    && self.buf[self.pos.offset] <= b'f')
-                                || (self.buf[self.pos.offset] >= b'A'
-                                    && self.buf[self.pos.offset] <= b'F')))
+                    && ((radix == 10 && self.buf[self.pos.offset].is_ascii_digit())
+                        || (radix == 16 && self.buf[self.pos.offset].is_ascii_hexdigit())
                         || self.buf[self.pos.offset] == b'_')
                 {
                     if self.buf[self.pos.offset] != b'_' {