refactor: Reduce code size of testing tokens if they're a number

This commit is a tiny win in compiled code size of a final binary
including `clap` which shaves off 19k of compiled code locally.
Previously tokens were checked if they were a number by using
`.parse::<f64>().is_ok()`, but parsing floats is relatively heavyweight
in terms of code size. This replaces the check with a more naive "does
this string have lots of ascii digits" check where the compiled size of
this check should be much smaller.

clap_builder/src/parser/parser.rs

@@ -643,7 +643,7 @@ impl<'cmd> Parser<'cmd> {
 
         if self.cmd[current_positional.get_id()].is_allow_hyphen_values_set()
             || (self.cmd[current_positional.get_id()].is_allow_negative_numbers_set()
-                && next.is_number())
+                && next.is_negative_number())
         {
             // If allow hyphen, this isn't a new arg.
             debug!("Parser::is_new_arg: Allow hyphen");
@@ -841,7 +841,7 @@ impl<'cmd> Parser<'cmd> {
 
         #[allow(clippy::blocks_in_if_conditions)]
         if matches!(parse_state, ParseState::Opt(opt) | ParseState::Pos(opt)
-                if self.cmd[opt].is_allow_hyphen_values_set() || (self.cmd[opt].is_allow_negative_numbers_set() && short_arg.is_number()))
+                if self.cmd[opt].is_allow_hyphen_values_set() || (self.cmd[opt].is_allow_negative_numbers_set() && short_arg.is_negative_number()))
         {
             debug!("Parser::parse_short_args: prior arg accepts hyphenated values",);
             return Ok(ParseResult::MaybeHyphenValue);
@@ -851,7 +851,7 @@ impl<'cmd> Parser<'cmd> {
             .get(&pos_counter)
             .map(|arg| arg.is_allow_negative_numbers_set())
             .unwrap_or_default()
-            && short_arg.is_number()
+            && short_arg.is_negative_number()
         {
             debug!("Parser::parse_short_arg: negative number");
             return Ok(ParseResult::MaybeHyphenValue);

clap_lex/src/lib.rs

@@ -300,10 +300,14 @@ impl<'s> ParsedArg<'s> {
         self.inner == "--"
     }
 
-    /// Does the argument look like a number
-    pub fn is_number(&self) -> bool {
+    /// Does the argument look like a negative number?
+    ///
+    /// This won't parse the number in full but attempts to see if this looks
+    /// like something along the lines of `-3`, `-0.3`, or `-33.03`
+    pub fn is_negative_number(&self) -> bool {
         self.to_value()
-            .map(|s| s.parse::<f64>().is_ok())
+            .ok()
+            .and_then(|s| Some(is_number(s.strip_prefix('-')?)))
             .unwrap_or_default()
     }
 
@@ -408,8 +412,8 @@ impl<'s> ShortFlags<'s> {
     /// Does the short flag look like a number
     ///
     /// Ideally call this before doing any iterator
-    pub fn is_number(&self) -> bool {
-        self.invalid_suffix.is_none() && self.utf8_prefix.as_str().parse::<f64>().is_ok()
+    pub fn is_negative_number(&self) -> bool {
+        self.invalid_suffix.is_none() && is_number(self.utf8_prefix.as_str())
     }
 
     /// Advance the iterator, returning the next short flag on success
@@ -466,3 +470,35 @@ fn split_nonutf8_once(b: &OsStr) -> (&str, Option<&OsStr>) {
         }
     }
 }
+
+fn is_number(arg: &str) -> bool {
+    // Return true if this looks like an integer or a float where it's all
+    // digits plus an optional single dot after some digits.
+    //
+    // For floats allow forms such as `1.`, `1.2`, `1.2e10`, etc.
+    let mut seen_dot = false;
+    let mut position_of_e = None;
+    for (i, c) in arg.as_bytes().iter().enumerate() {
+        match c {
+            // Digits are always valid
+            b'0'..=b'9' => {}
+
+            // Allow a `.`, but only one, only if it comes before an
+            // optional exponent, and only if it's not the first character.
+            b'.' if !seen_dot && position_of_e.is_none() && i > 0 => seen_dot = true,
+
+            // Allow an exponent `e` but only at most one after the first
+            // character.
+            b'e' if position_of_e.is_none() && i > 0 => position_of_e = Some(i),
+
+            _ => return false,
+        }
+    }
+
+    // Disallow `-1e` which isn't a valid float since it doesn't actually have
+    // an exponent.
+    match position_of_e {
+        Some(i) => i != arg.len() - 1,
+        None => true,
+    }
+}

clap_lex/tests/parsed.rs

@@ -120,12 +120,14 @@ fn to_short() {
 
 #[test]
 fn is_negative_number() {
-    let raw = clap_lex::RawArgs::new(["bin", "-10.0"]);
-    let mut cursor = raw.cursor();
-    assert_eq!(raw.next_os(&mut cursor), Some(std::ffi::OsStr::new("bin")));
-    let next = raw.next(&mut cursor).unwrap();
+    for number in ["-10.0", "-1", "-100", "-3.5", "-1e10", "-1.3e10"] {
+        let raw = clap_lex::RawArgs::new(["bin", number]);
+        let mut cursor = raw.cursor();
+        assert_eq!(raw.next_os(&mut cursor), Some(std::ffi::OsStr::new("bin")));
+        let next = raw.next(&mut cursor).unwrap();
 
-    assert!(next.is_number());
+        assert!(next.is_negative_number());
+    }
 }
 
 #[test]
@@ -135,17 +137,22 @@ fn is_positive_number() {
     assert_eq!(raw.next_os(&mut cursor), Some(std::ffi::OsStr::new("bin")));
     let next = raw.next(&mut cursor).unwrap();
 
-    assert!(next.is_number());
+    assert!(!next.is_negative_number());
 }
 
 #[test]
 fn is_not_number() {
-    let raw = clap_lex::RawArgs::new(["bin", "--10.0"]);
-    let mut cursor = raw.cursor();
-    assert_eq!(raw.next_os(&mut cursor), Some(std::ffi::OsStr::new("bin")));
-    let next = raw.next(&mut cursor).unwrap();
-
-    assert!(!next.is_number());
+    for number in ["--10.0", "-..", "-2..", "-e", "-1e", "-1e10.2", "-.2"] {
+        let raw = clap_lex::RawArgs::new(["bin", number]);
+        let mut cursor = raw.cursor();
+        assert_eq!(raw.next_os(&mut cursor), Some(std::ffi::OsStr::new("bin")));
+        let next = raw.next(&mut cursor).unwrap();
+
+        assert!(
+            !next.is_negative_number(),
+            "`{number}` is mistakenly classified as a number"
+        );
+    }
 }
 
 #[test]

clap_lex/tests/shorts.rs

@@ -151,23 +151,23 @@ fn is_exhausted_empty() {
 }
 
 #[test]
-fn is_number() {
+fn is_negative_number() {
     let raw = clap_lex::RawArgs::new(["bin", "-1.0"]);
     let mut cursor = raw.cursor();
     assert_eq!(raw.next_os(&mut cursor), Some(std::ffi::OsStr::new("bin")));
     let next = raw.next(&mut cursor).unwrap();
     let shorts = next.to_short().unwrap();
 
-    assert!(shorts.is_number());
+    assert!(shorts.is_negative_number());
 }
 
 #[test]
-fn is_not_number() {
+fn is_not_negaitve_number() {
     let raw = clap_lex::RawArgs::new(["bin", "-hello"]);
     let mut cursor = raw.cursor();
     assert_eq!(raw.next_os(&mut cursor), Some(std::ffi::OsStr::new("bin")));
     let next = raw.next(&mut cursor).unwrap();
     let shorts = next.to_short().unwrap();
 
-    assert!(!shorts.is_number());
+    assert!(!shorts.is_negative_number());
 }