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perf: Avoid retrieving possible_values unless used
In some sophisticated situations, these may be expensive to calculate. One example might be a '--branch' option accepting any single Git branch that exists on the remote -- in such a case, the remote would need to be queried for all possible_values. The cost is ultimately unavoidable at runtime since this validation has to happen eventually, but there's no need to pay it when generating help text if `is_hide_possible_values_set`. To keep '-h' fast, avoid collecting `possible_values` during '-h' unless we're actually going to use the values in display. This optimization is repeated for the manpage renderer. This is trivially based on the short-circuiting logic at [1], which at least supports the idea that actually consuming the iterator is not generally-guaranteed behavior when `hide_possible_values` is set. [1]: clap_builder/src/builder/command.rs:long_help_exists_
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,140 @@ | ||
| #![cfg(feature = "string")] | ||
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| use std::sync::{Arc, Mutex}; | ||
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| use clap::{Arg, Command}; | ||
| use clap_builder::builder::{PossibleValue, PossibleValuesParser, TypedValueParser}; | ||
|
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| #[cfg(feature = "error-context")] | ||
| use super::utils; | ||
|
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| #[derive(Clone)] | ||
| struct ExpensiveValues { | ||
| iterated: Arc<Mutex<bool>>, | ||
| } | ||
|
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| impl ExpensiveValues { | ||
| pub fn new() -> Self { | ||
| ExpensiveValues { | ||
| iterated: Arc::new(Mutex::new(false)), | ||
| } | ||
| } | ||
| } | ||
|
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| impl IntoIterator for ExpensiveValues { | ||
| type Item = String; | ||
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| type IntoIter = ExpensiveValuesIntoIterator; | ||
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| fn into_iter(self) -> Self::IntoIter { | ||
| ExpensiveValuesIntoIterator { me: self, index: 0 } | ||
| } | ||
| } | ||
|
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| struct ExpensiveValuesIntoIterator { | ||
| me: ExpensiveValues, | ||
| index: usize, | ||
| } | ||
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| impl Iterator for ExpensiveValuesIntoIterator { | ||
| type Item = String; | ||
| fn next(&mut self) -> Option<String> { | ||
| let mut guard = self | ||
| .me | ||
| .iterated | ||
| .lock() | ||
| .expect("not working across multiple threads"); | ||
|
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| *guard = true; | ||
| self.index += 1; | ||
|
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| if self.index < 3 { | ||
| Some(format!("expensive-value-{}", self.index)) | ||
| } else { | ||
| None | ||
| } | ||
| } | ||
| } | ||
|
|
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| impl TypedValueParser for ExpensiveValues { | ||
| type Value = String; | ||
|
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| fn parse_ref( | ||
| &self, | ||
| _cmd: &clap_builder::Command, | ||
| _arg: Option<&clap_builder::Arg>, | ||
| _value: &std::ffi::OsStr, | ||
| ) -> Result<Self::Value, clap_builder::Error> { | ||
| todo!() | ||
| } | ||
|
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| fn possible_values(&self) -> Option<Box<dyn Iterator<Item = PossibleValue> + '_>> { | ||
| Some(Box::new(self.clone().into_iter().map(PossibleValue::from))) | ||
| } | ||
| } | ||
|
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||
| #[test] | ||
| fn no_iterate_when_hidden() { | ||
| static PV_EXPECTED: &str = "\ | ||
| Usage: clap-test [some-cheap-option] [some-expensive-option] | ||
| Arguments: | ||
| [some-cheap-option] cheap [possible values: some, cheap, values] | ||
| [some-expensive-option] expensive | ||
| Options: | ||
| -h, --help Print help | ||
| "; | ||
| let expensive = ExpensiveValues::new(); | ||
| utils::assert_output( | ||
| Command::new("test") | ||
| .arg( | ||
| Arg::new("some-cheap-option") | ||
| .help("cheap") | ||
| .value_parser(PossibleValuesParser::new(["some", "cheap", "values"])), | ||
| ) | ||
| .arg( | ||
| Arg::new("some-expensive-option") | ||
| .help("expensive") | ||
| .hide_possible_values(true) | ||
| .value_parser(expensive.clone()), | ||
| ), | ||
| "clap-test -h", | ||
| PV_EXPECTED, | ||
| false, | ||
| ); | ||
| assert_eq!(*expensive.iterated.lock().unwrap(), false); | ||
| } | ||
|
|
||
| #[test] | ||
| fn iterate_when_displayed() { | ||
| static PV_EXPECTED: &str = "\ | ||
| Usage: clap-test [some-cheap-option] [some-expensive-option] | ||
| Arguments: | ||
| [some-cheap-option] cheap [possible values: some, cheap, values] | ||
| [some-expensive-option] expensive [possible values: expensive-value-1, expensive-value-2] | ||
| Options: | ||
| -h, --help Print help | ||
| "; | ||
| let expensive = ExpensiveValues::new(); | ||
| utils::assert_output( | ||
| Command::new("test") | ||
| .arg( | ||
| Arg::new("some-cheap-option") | ||
| .help("cheap") | ||
| .value_parser(PossibleValuesParser::new(["some", "cheap", "values"])), | ||
| ) | ||
| .arg( | ||
| Arg::new("some-expensive-option") | ||
| .help("expensive") | ||
| .hide_possible_values(false) | ||
| .value_parser(expensive.clone()), | ||
| ), | ||
| "clap-test -h", | ||
| PV_EXPECTED, | ||
| false, | ||
| ); | ||
| assert_eq!(*expensive.iterated.lock().unwrap(), true); | ||
| } |