perf(parser): Take up less memory with ArgAction::Count

Someone should not reasonably expect a coun flag to go up to billions,
millions, or even thousands.  255 should be sufficient for anyone,
right?

The original type was selected to be consistent with
`ArgMatches::occurrences_of` but that is also used for tracking how
many values appear which can be large with `xargs`.

I'm still conflicted on what the "right type" is an wish we could
support any numeric type.  When I did a search on github though, every
case was for debug/quiet flags and only supported 2-3 occurrences,
making a `u8` overkill.

This came out of a discussion on clap-rs#3792

CHANGELOG.md

@@ -87,7 +87,7 @@ Replaced
 - `Arg::validator_regex` with users providing their own `builder::TypedValueParser` (#3756)
 - `Arg::forbid_empty_values` with `builder::NonEmptyStringValueParser` / `builder::PathBufValueParser` (#3753)
 - `Arg::possible_values` with `Arg::value_parser([...])`, `builder::PossibleValuesParser`, or `builder::EnumValueParser` (#3753)
-- `Arg::max_occurrences` with `arg.action(ArgAction::Count).value_parser(value_parser!(u64).range(..N))` for flags (#3797)
+- `Arg::max_occurrences` with `arg.action(ArgAction::Count).value_parser(value_parser!(u8).range(..N))` for flags (#3797)
 - `Arg::multiple_occurrences` with `ArgAction::Append` or `ArgAction::Count` though positionals will need `Arg::multiple_values` (#3772, #3797)
 - `Command::args_override_self` with `ArgAction::Set` (#2627, #3797)
 - `AppSettings::NoAutoVersion` with `ArgAction` or `Command::disable_version_flag` (#3800)
@@ -99,7 +99,7 @@ Replaced
 - `ArgAction::StoreValue` with `ArgAction::Set` or `ArgAction::Append` (#3797)
 - `ArgAction::IncOccurrences` with `ArgAction::SetTrue` or `ArgAction::Count` (#3797)
 - *(derive)* `#[clap(parse(from_flag))]` replaced with `#[clap(action = ArgAction::SetTrue)]` (#3794)
-- *(derive)* `#[clap(parse(from_occurrences))]` replaced with `#[clap(action = ArgAction::Count)]` though the field's type must be `u64` (#3794)
+- *(derive)* `#[clap(parse(from_occurrences))]` replaced with `#[clap(action = ArgAction::Count)]` though the field's type must be `u8` (#3794)
 - *(derive)* `#[clap(parse(...))]` replaced with `#[clap(value_parser)]`  (#3589, #3794)
 
 ## [3.1.18] - 2022-05-10

examples/tutorial_builder/01_quick.rs

@@ -40,7 +40,7 @@ fn main() {
     // You can see how many times a particular flag or argument occurred
     // Note, only flags can have multiple occurrences
     match matches
-        .get_one::<u64>("debug")
+        .get_one::<u8>("debug")
         .expect("Count's are defaulted")
     {
         0 => println!("Debug mode is off"),

examples/tutorial_builder/03_01_flag_count.rs

@@ -10,7 +10,7 @@ fn main() {
     println!(
         "verbose: {:?}",
         matches
-            .get_one::<u64>("verbose")
+            .get_one::<u8>("verbose")
             .expect("Count always defaulted")
     );
 }

examples/tutorial_derive/01_quick.rs

@@ -15,7 +15,7 @@ struct Cli {
 
     /// Turn debugging information on
     #[clap(short, long, action = clap::ArgAction::Count)]
-    debug: u64,
+    debug: u8,
 
     #[clap(subcommand)]
     command: Option<Commands>,

examples/tutorial_derive/03_01_flag_count.rs

@@ -4,7 +4,7 @@ use clap::Parser;
 #[clap(author, version, about, long_about = None)]
 struct Cli {
     #[clap(short, long, action = clap::ArgAction::Count)]
-    verbose: u64,
+    verbose: u8,
 }
 
 fn main() {

src/builder/action.rs

@@ -152,7 +152,7 @@ pub enum ArgAction {
     /// );
     /// ```
     SetFalse,
-    /// When encountered, increment a `u64` counter
+    /// When encountered, increment a `u8` counter
     ///
     /// If no [`default_value`][super::Arg::default_value] is set, it will be `0`.
     ///
@@ -174,15 +174,15 @@ pub enum ArgAction {
     /// assert!(matches.is_present("flag"));
     /// assert_eq!(matches.occurrences_of("flag"), 0);
     /// assert_eq!(
-    ///     matches.get_one::<u64>("flag").copied(),
+    ///     matches.get_one::<u8>("flag").copied(),
     ///     Some(2)
     /// );
     ///
     /// let matches = cmd.try_get_matches_from(["mycmd"]).unwrap();
     /// assert!(matches.is_present("flag"));
     /// assert_eq!(matches.occurrences_of("flag"), 0);
     /// assert_eq!(
-    ///     matches.get_one::<u64>("flag").copied(),
+    ///     matches.get_one::<u8>("flag").copied(),
     ///     Some(0)
     /// );
     /// ```
@@ -287,7 +287,7 @@ impl ArgAction {
             Self::IncOccurrence => None,
             Self::SetTrue => Some(super::ValueParser::bool()),
             Self::SetFalse => Some(super::ValueParser::bool()),
-            Self::Count => Some(crate::value_parser!(u64).into()),
+            Self::Count => Some(crate::value_parser!(u8).into()),
             Self::Help => None,
             Self::Version => None,
         }
@@ -313,4 +313,4 @@ impl ArgAction {
     }
 }
 
-pub(crate) type CountType = u64;
+pub(crate) type CountType = u8;

src/builder/arg.rs

@@ -788,12 +788,12 @@ impl<'help> Arg<'help> {
         }
     }
 
-    /// Deprecated, for flags this is replaced with `action(ArgAction::Count).value_parser(value_parser!(u64).range(..max))`
+    /// Deprecated, for flags this is replaced with `action(ArgAction::Count).value_parser(value_parser!(u8).range(..max))`
     #[inline]
     #[must_use]
     #[deprecated(
         since = "3.2.0",
-        note = "For flags, replaced with `action(ArgAction::Count).value_parser(value_parser!(u64).range(..max))`"
+        note = "For flags, replaced with `action(ArgAction::Count).value_parser(value_parser!(u8).range(..max))`"
     )]
     pub fn max_occurrences(mut self, qty: usize) -> Self {
         self.max_occurs = Some(qty);

tests/builder/action.rs

@@ -379,7 +379,7 @@ fn count() {
     let cmd = Command::new("test").arg(Arg::new("mammal").long("mammal").action(ArgAction::Count));
 
     let matches = cmd.clone().try_get_matches_from(["test"]).unwrap();
-    assert_eq!(*matches.get_one::<u64>("mammal").unwrap(), 0);
+    assert_eq!(*matches.get_one::<u8>("mammal").unwrap(), 0);
     assert_eq!(matches.is_present("mammal"), true);
     #[allow(deprecated)]
     {
@@ -391,7 +391,7 @@ fn count() {
         .clone()
         .try_get_matches_from(["test", "--mammal"])
         .unwrap();
-    assert_eq!(*matches.get_one::<u64>("mammal").unwrap(), 1);
+    assert_eq!(*matches.get_one::<u8>("mammal").unwrap(), 1);
     assert_eq!(matches.is_present("mammal"), true);
     #[allow(deprecated)]
     {
@@ -403,7 +403,7 @@ fn count() {
         .clone()
         .try_get_matches_from(["test", "--mammal", "--mammal"])
         .unwrap();
-    assert_eq!(*matches.get_one::<u64>("mammal").unwrap(), 2);
+    assert_eq!(*matches.get_one::<u8>("mammal").unwrap(), 2);
     assert_eq!(matches.is_present("mammal"), true);
     #[allow(deprecated)]
     {
@@ -425,7 +425,7 @@ fn count_with_explicit_default_value() {
         .clone()
         .try_get_matches_from(["test", "--mammal"])
         .unwrap();
-    assert_eq!(*matches.get_one::<u64>("mammal").unwrap(), 1);
+    assert_eq!(*matches.get_one::<u8>("mammal").unwrap(), 1);
     assert_eq!(matches.is_present("mammal"), true);
     #[allow(deprecated)]
     {
@@ -434,7 +434,7 @@ fn count_with_explicit_default_value() {
     assert_eq!(matches.index_of("mammal"), Some(1));
 
     let matches = cmd.clone().try_get_matches_from(["test"]).unwrap();
-    assert_eq!(*matches.get_one::<u64>("mammal").unwrap(), 10);
+    assert_eq!(*matches.get_one::<u8>("mammal").unwrap(), 10);
     assert_eq!(matches.is_present("mammal"), true);
     #[allow(deprecated)]
     {
@@ -455,19 +455,19 @@ fn count_with_default_value_if_present() {
         .arg(Arg::new("dog").long("dog").action(ArgAction::Count));
 
     let matches = cmd.clone().try_get_matches_from(["test"]).unwrap();
-    assert_eq!(*matches.get_one::<u64>("dog").unwrap(), 0);
-    assert_eq!(*matches.get_one::<u64>("mammal").unwrap(), 0);
+    assert_eq!(*matches.get_one::<u8>("dog").unwrap(), 0);
+    assert_eq!(*matches.get_one::<u8>("mammal").unwrap(), 0);
 
     let matches = cmd.clone().try_get_matches_from(["test", "--dog"]).unwrap();
-    assert_eq!(*matches.get_one::<u64>("dog").unwrap(), 1);
-    assert_eq!(*matches.get_one::<u64>("mammal").unwrap(), 10);
+    assert_eq!(*matches.get_one::<u8>("dog").unwrap(), 1);
+    assert_eq!(*matches.get_one::<u8>("mammal").unwrap(), 10);
 
     let matches = cmd
         .clone()
         .try_get_matches_from(["test", "--mammal"])
         .unwrap();
-    assert_eq!(*matches.get_one::<u64>("dog").unwrap(), 0);
-    assert_eq!(*matches.get_one::<u64>("mammal").unwrap(), 1);
+    assert_eq!(*matches.get_one::<u8>("dog").unwrap(), 0);
+    assert_eq!(*matches.get_one::<u8>("mammal").unwrap(), 1);
 }
 
 #[test]
@@ -482,24 +482,24 @@ fn count_with_default_value_if_value() {
         .arg(Arg::new("dog").long("dog").action(ArgAction::Count));
 
     let matches = cmd.clone().try_get_matches_from(["test"]).unwrap();
-    assert_eq!(*matches.get_one::<u64>("dog").unwrap(), 0);
-    assert_eq!(*matches.get_one::<u64>("mammal").unwrap(), 0);
+    assert_eq!(*matches.get_one::<u8>("dog").unwrap(), 0);
+    assert_eq!(*matches.get_one::<u8>("mammal").unwrap(), 0);
 
     let matches = cmd.clone().try_get_matches_from(["test", "--dog"]).unwrap();
-    assert_eq!(*matches.get_one::<u64>("dog").unwrap(), 1);
-    assert_eq!(*matches.get_one::<u64>("mammal").unwrap(), 0);
+    assert_eq!(*matches.get_one::<u8>("dog").unwrap(), 1);
+    assert_eq!(*matches.get_one::<u8>("mammal").unwrap(), 0);
 
     let matches = cmd
         .clone()
         .try_get_matches_from(["test", "--dog", "--dog"])
         .unwrap();
-    assert_eq!(*matches.get_one::<u64>("dog").unwrap(), 2);
-    assert_eq!(*matches.get_one::<u64>("mammal").unwrap(), 10);
+    assert_eq!(*matches.get_one::<u8>("dog").unwrap(), 2);
+    assert_eq!(*matches.get_one::<u8>("mammal").unwrap(), 10);
 
     let matches = cmd
         .clone()
         .try_get_matches_from(["test", "--mammal"])
         .unwrap();
-    assert_eq!(*matches.get_one::<u64>("dog").unwrap(), 0);
-    assert_eq!(*matches.get_one::<u64>("mammal").unwrap(), 1);
+    assert_eq!(*matches.get_one::<u8>("dog").unwrap(), 0);
+    assert_eq!(*matches.get_one::<u8>("mammal").unwrap(), 1);
 }

tests/builder/legacy/action.rs

@@ -379,7 +379,7 @@ fn count() {
     let cmd = Command::new("test").arg(Arg::new("mammal").long("mammal").action(ArgAction::Count));
 
     let matches = cmd.clone().try_get_matches_from(["test"]).unwrap();
-    assert_eq!(*matches.get_one::<u64>("mammal").unwrap(), 0);
+    assert_eq!(*matches.get_one::<u8>("mammal").unwrap(), 0);
     assert_eq!(matches.is_present("mammal"), true);
     #[allow(deprecated)]
     {
@@ -391,7 +391,7 @@ fn count() {
         .clone()
         .try_get_matches_from(["test", "--mammal"])
         .unwrap();
-    assert_eq!(*matches.get_one::<u64>("mammal").unwrap(), 1);
+    assert_eq!(*matches.get_one::<u8>("mammal").unwrap(), 1);
     assert_eq!(matches.is_present("mammal"), true);
     #[allow(deprecated)]
     {
@@ -403,7 +403,7 @@ fn count() {
         .clone()
         .try_get_matches_from(["test", "--mammal", "--mammal"])
         .unwrap();
-    assert_eq!(*matches.get_one::<u64>("mammal").unwrap(), 2);
+    assert_eq!(*matches.get_one::<u8>("mammal").unwrap(), 2);
     assert_eq!(matches.is_present("mammal"), true);
     #[allow(deprecated)]
     {
@@ -425,7 +425,7 @@ fn count_with_explicit_default_value() {
         .clone()
         .try_get_matches_from(["test", "--mammal"])
         .unwrap();
-    assert_eq!(*matches.get_one::<u64>("mammal").unwrap(), 1);
+    assert_eq!(*matches.get_one::<u8>("mammal").unwrap(), 1);
     assert_eq!(matches.is_present("mammal"), true);
     #[allow(deprecated)]
     {
@@ -434,7 +434,7 @@ fn count_with_explicit_default_value() {
     assert_eq!(matches.index_of("mammal"), Some(1));
 
     let matches = cmd.clone().try_get_matches_from(["test"]).unwrap();
-    assert_eq!(*matches.get_one::<u64>("mammal").unwrap(), 10);
+    assert_eq!(*matches.get_one::<u8>("mammal").unwrap(), 10);
     assert_eq!(matches.is_present("mammal"), true);
     #[allow(deprecated)]
     {
@@ -455,19 +455,19 @@ fn count_with_default_value_if_present() {
         .arg(Arg::new("dog").long("dog").action(ArgAction::Count));
 
     let matches = cmd.clone().try_get_matches_from(["test"]).unwrap();
-    assert_eq!(*matches.get_one::<u64>("dog").unwrap(), 0);
-    assert_eq!(*matches.get_one::<u64>("mammal").unwrap(), 0);
+    assert_eq!(*matches.get_one::<u8>("dog").unwrap(), 0);
+    assert_eq!(*matches.get_one::<u8>("mammal").unwrap(), 0);
 
     let matches = cmd.clone().try_get_matches_from(["test", "--dog"]).unwrap();
-    assert_eq!(*matches.get_one::<u64>("dog").unwrap(), 1);
-    assert_eq!(*matches.get_one::<u64>("mammal").unwrap(), 10);
+    assert_eq!(*matches.get_one::<u8>("dog").unwrap(), 1);
+    assert_eq!(*matches.get_one::<u8>("mammal").unwrap(), 10);
 
     let matches = cmd
         .clone()
         .try_get_matches_from(["test", "--mammal"])
         .unwrap();
-    assert_eq!(*matches.get_one::<u64>("dog").unwrap(), 0);
-    assert_eq!(*matches.get_one::<u64>("mammal").unwrap(), 1);
+    assert_eq!(*matches.get_one::<u8>("dog").unwrap(), 0);
+    assert_eq!(*matches.get_one::<u8>("mammal").unwrap(), 1);
 }
 
 #[test]
@@ -482,24 +482,24 @@ fn count_with_default_value_if_value() {
         .arg(Arg::new("dog").long("dog").action(ArgAction::Count));
 
     let matches = cmd.clone().try_get_matches_from(["test"]).unwrap();
-    assert_eq!(*matches.get_one::<u64>("dog").unwrap(), 0);
-    assert_eq!(*matches.get_one::<u64>("mammal").unwrap(), 0);
+    assert_eq!(*matches.get_one::<u8>("dog").unwrap(), 0);
+    assert_eq!(*matches.get_one::<u8>("mammal").unwrap(), 0);
 
     let matches = cmd.clone().try_get_matches_from(["test", "--dog"]).unwrap();
-    assert_eq!(*matches.get_one::<u64>("dog").unwrap(), 1);
-    assert_eq!(*matches.get_one::<u64>("mammal").unwrap(), 0);
+    assert_eq!(*matches.get_one::<u8>("dog").unwrap(), 1);
+    assert_eq!(*matches.get_one::<u8>("mammal").unwrap(), 0);
 
     let matches = cmd
         .clone()
         .try_get_matches_from(["test", "--dog", "--dog"])
         .unwrap();
-    assert_eq!(*matches.get_one::<u64>("dog").unwrap(), 2);
-    assert_eq!(*matches.get_one::<u64>("mammal").unwrap(), 10);
+    assert_eq!(*matches.get_one::<u8>("dog").unwrap(), 2);
+    assert_eq!(*matches.get_one::<u8>("mammal").unwrap(), 10);
 
     let matches = cmd
         .clone()
         .try_get_matches_from(["test", "--mammal"])
         .unwrap();
-    assert_eq!(*matches.get_one::<u64>("dog").unwrap(), 0);
-    assert_eq!(*matches.get_one::<u64>("mammal").unwrap(), 1);
+    assert_eq!(*matches.get_one::<u8>("dog").unwrap(), 0);
+    assert_eq!(*matches.get_one::<u8>("mammal").unwrap(), 1);
 }