clap_complete

Fixes

• (help) Style required argument groups
• (derive) Improve error messages when unsupported fields are used

Fixes

• (derive) Improve error messages when derive feature is missing

Compatiblity

• (unstable-ext) Arg::remove changed return types

Fixes

• (unstable-ext) Make Arg::remove return the removed item

Features

• (unstable-ext) Added Arg::add for attaching arbitrary state, like completion hints, to Arg without Arg knowing about it

Fixes

• (derive) Improve error message when #[flatten]ing an optional #[group(skip)]
• (help) Properly wrap long subcommand descriptions in help

Features

• (dynamic) Support completing with num_args

Features

• (dynamic) Add support for -fbar and -f=bar completions

Fixes

• (error) When defining a custom help flag, be sure to suggest it like we do the built-in one

Fixes

• Reduce extra flushes

Fixes

• Clean up error message when too few arguments for num_args

Fixes

• Allow exclusive to override required_unless_present, required_unless_present_any, required_unless_present_all

Fixes

• (derive) Allow non-literal #[arg(id)] attributes again

Internal

• (derive) Update heck

Fixes

• (macros) Silence a warning

Fixes

• (error) Include suggestion to add -- even if there is a "did you mean" so long as last or trailing_var_arg is used

Compatibility

• Update MSRV to 1.74

Documentation

• Link out to changelog
• Cross link derive's attribute reference to derive tutorial

Fixes

• (help) Show correct Command::about under flattened headings
• (help) Respect hide when flattening subcommands

Features

• Add Command::flatten_help to allow git stash -h like help for subcommands

Performance

• Reduced code size

Internal

• Upgrade anstream

Fixes

• (parser) When inferring subcommand name or long_flag, allow ambiguous-looking matches that unambiguously map back to the same command
• (parser) When inferring subcommand long_flag, don't panic
• (assert) Clarify what action is causing a positional that doesn't set values which is especially useful for derive users

Internal

• Update terminal_size to 0.3

Documentation

• (derive) Clarify use of attributes within the tutorial
• Split sections in the builder and derive tutorials into separate modules

Performance

• Improve build times by removing once_cell dependency

Features

• Stabilize Command::styles

compatibility

• update msrv to 1.70.0

Fixes

• (derive) Don't produce unused_equalifications warnings when someone brings a clap type into scope

Performance

• (derive) Reduce the amount of generated code

Fixes

• (assert) Allow multiple, value-terminated, positional arguments
• (assert) Clear up language on last assertion
• (parser) Correctly assign values to arguments when using multiple, value-termianted, positional arguments
• (parser) Ensure value_terminator has higher precedence than allow_hyphen_values
• (help) Only use next-line-help on subcommand list when explicitly specified, not just with --help
• (help) Correctly align possible values list
• (help) Don't waste code, vertical space in moving possible value descriptions to next line

Features

• Command::styles for theming help/errors (behind unstable-styles)

Internal

• Update dependencies

Fixes

• Don't highlight uninteresting parts of the error message

Compatibility

• Removed the languishing unstable-replace feature (open to discussion at #2836)
• Removed the stablized unstable-grouped feature

Features

• Allow any StyledStr to accept text styled with ANSI escape codes
• Respect CLICOLOR, CLICOLOR_FORCE

Fixes

• Lighten the tone for "unexpected argument" errors (open to discussion at #4638)

Fixes

• (help) Don't show long help for --help just because hidden possible values include a description

Fixes

• (help) Don't show long help for --help just because a hidden arg has a possible value with a description

Fixes

• (help) Respect disable_colored_help when using arg_required_else_help

Performance

• Speed up compiling arg! macro

Fixes

• (error) Improve suggested flag/value/subcommand when two share a long preifx
• (error) When suggesting one of several subcommands, use the plural subcommands, rather than subcommand

Fixes

• In documentation, refer to get_flag, rather than get_one::<bool>

Fixes

• (error) Small softening attempt for "unexpected argument" error

Compatibility

MSRV changed to 1.64.0

For apps with custom --help and --version flags:

• Descriptions for --help and --version changed

When apps have errors imitating clap's error style:

• Error message style was changed, including
  • Moving away from "did you mean" to tips
  • Leading letter is lower case
  • "For more" added some punctuation

Features

• ArgMatches::get_occurrences support for argument values to be grouped by their occurrence

Fixes

• (derive) Allow upgrade_from when arguments / subcommands are explicitly marked as required
• (help) Try be more clearer and succinct with --help and --version (also helps with overflow)
• (error) Try to be more clearer and succinct with error messages
• (error) Officially adopt an error style guide

Features

• (derive) Populate implicit ArgGroup (#3165)

Fixes

• (derive) Support #[group(skip)] on Parser derive
• (derive) Tell users about implicit arg groups when running into group name conflicts
• (error) Don't report unrelated groups in conflict or requires errors

Features

• (derive) Support #[group(skip)] (#4279, #4301)

Features

• Added Shell::from_env

Fixes

• (error) Specialize the self-conflict error to look like clap v3

Fixes

• (error) Quote literals consistently
• (error) Stylize escape (--) suggestions
• (error) Format help flag as a literal

Fixes

• (parser) SetFalse should conflict with itself like SetTrue and Set
• (parser) Allow one-off overrides

Fixes

• (derive) Ensure #[clap(...)] attribute still works

Highlights

Arg::num_args(range)

Clap has had several ways for controlling how many values will be captured without always being clear on how they interacted, including

• Arg::multiple_values(true)
• Arg::number_of_values(4)
• Arg::min_values(2)
• Arg::max_values(20)
• Arg::takes_value(true)

These have now all been collapsed into Arg::num_args which accepts both single values and ranges of values. num_args controls how many raw arguments on the command line will be captured as values per occurrence and independent of value delimiters.

See Issue 2688 for more background.

Polishing Help

Clap strives to give a polished CLI experience out of the box with little ceremony. With some feedback that has accumulated over time, we took this release as an opportunity to re-evaluate our --help output to make sure it is meeting that goal.

In doing this evaluation, we wanted to keep in mind:

• Whether other CLIs had ideas that make sense to apply
• Providing an experience that fits within the rest of applications and works across all shells

Before:

git
A fictional versioning CLI

USAGE:
    git <SUBCOMMAND>

OPTIONS:
    -h, --help    Print help information

SUBCOMMANDS:
    add      adds things
    clone    Clones repos
    help     Print this message or the help of the given subcommand(s)
    push     pushes things
    stash

After:

A fictional versioning CLI

Usage: git <COMMAND>

Commands:
  clone  Clones repos
  push   pushes things
  add    adds things
  stash
  help   Print this message or the help of the given subcommand(s)

Options:
  -h, --help  Print help information

• name/version header was removed because we couldn't justify the space it occupied when
  • Usage already includes the name
  • --version is available for showing the same thing (if the program has a version set)
• Usage was dropped to one line to save space
• Focus is put on the subcommands
• Headings are now Title case
• The more general term "command" is used rather than being explicit about being "subcommands"
• The output is more dense with the expectation that it won't affect legibility but will allow more content
• We've moved to a more neutral palette for highlighting elements (not highlighted above)

In talking to users, we found some that liked clap's man-like experience. When deviating from this, we are making the assumption that those are more power users and that the majority of users wouldn't look as favorably on being consistent with man.

See Issue 4132 for more background.

More Dynamicism

Clap's API has focused on &str for performance but this can make dealing with owned data difficult, like #[arg(default_value_t)] generating a String from the default value.

Additionally, to avoid ArgMatches from borrowing (and for some features we decided to forgo), clap took the &str argument IDs and hashed them. This prevented us from providing a usable API for iterating over existing arguments.

Now clap has switched to a string newtype that gives us the flexibility to decide whether to use &'static str, Cow<'static, str> for fast dynamic behavior, or Box<str> for dynamic behavior with small binary size.

As an extension of that work, you can now call ArgMatches::ids to iterate over the arguments and groups that were found when parsing. The newtype Id was used to prevent some classes of bugs and to make it easier to understand when opaque Ids are used vs user-visible strings.

Clearing Out Deprecations

Instead of doing all development on clap 4.0.0, we implemented a lot of new features during clap 3's development, deprecating the old API while introducing the new API, including:

• Replacing the implicit behavior for args when parsing them with ArgAction
• Replacing various one-off forms of value validation with the ValueParser API
  • Allowing derives to automatically do the right thing for PathBuf (allowing invalid UTF-8)
• Replacing AppSettings and ArgSettings enums with getters/setters
• Clarifying terms and making them more consistent

Migrating

Steps:

1. Upgrade to v3 if you haven't already
2. Add CLI tests (including example below), -h and --help output at a minimum (recommendation: trycmd for snapshot testing)
3. If using Builder API: Explicitly set the arg.action(ArgAction::...) on each argument (StoreValue for options and IncOccurrences for flags)
4. Run cargo check --features clap/deprecated and resolve all deprecation warnings
5. Upgrade to v4
6. Update feature flags

• If default-features = false, run cargo add clap -F help,usage,error-context
• Run cargo add clap -F wrap_help unless you want to hard code line wraps

1. Resolve compiler errors
2. Resolve behavior changes (see "subtle changes" under BREAKING CHANGES)
3. At your leisure: resolve new deprecation notices

Example test (derive):

#[derive(clap::Parser)]
struct Cli {
    ...
}

#[test]
fn verify_cli() {
    use clap::CommandFactory;
    Cli::command().debug_assert()
}

Example test (builder):

fn cli() -> clap::Command {
    ...
}

#[test]
fn verify_cli() {
    cli().debug_assert();
}

Note: the idiomatic / recommended way of specifying different types of args in the Builder API has changed:

Before

.arg(Arg::new("flag").long("flag"))  # --flag
.arg(Arg::new("option").long("option").takes_value(true))  # --option <option>

After:

.arg(Arg::new("flag").long("flag").action(ArgAction::SetTrue))  # --flag
.arg(Arg::new("option").long("option"))  # --option <option>

In particular, num_args (the replacement for takes_value) will default appropriately from the ArgAction and generally only needs to be set explicitly for the other num_args use cases.

Breaking Changes

Subtle changes (i.e. compiler won't catch):

• arg! now sets one of (#3795):
  • ArgAction::SetTrue, requiring ArgMatches::get_flag instead of ArgMatches::is_present
  • ArgAction::Count, requiring ArgMatches::get_count instead of ArgMatches::occurrences_of
  • ArgAction::Set, requiring ArgMatches::get_one instead of ArgMatches::value_of
  • ArgAction::Append, requiring ArgMatches::get_many instead of ArgMatches::values_of
• ArgAction::Set, ArgAction::SetTrue, and Arg::Action::SetFalse now conflict by default to be like ArgAction::StoreValue and ArgAction::IncOccurrences, requiring cmd.args_override_self(true) to override instead (#4261)
• By default, an Args default action is ArgAction::Set, rather than ArgAction::IncOccurrence to reduce confusing magic through consistency (#2687, #4032, see also #3977)
• mut_arg can no longer be used to customize help and version arguments, instead disable them (Command::disable_help_flag, Command::disable_version_flag) and provide your own (#4056)
• Removed lifetimes from Command, Arg, ArgGroup, and PossibleValue, assuming 'static. string feature flag will enable support for Strings (#1041, #2150, #4223)
• arg!(--flag <value>) is now optional, instead of required. Add .required(true) at the end to restore the original behavior (#4206)
• Added default feature flags, help, usage and error-context, requiring adding them back in if default-features = false (#4236)
• (parser) Always fill in "" argument for external subcommands to make it easier to distinguish them from built-in commands (#3263)
• (parser) Short flags now have higher precedence than hyphen values with Arg::allow_hyphen_values, to be consistent with Command::allow_hyphen_values (#4187)
• (parser) Arg::value_terminator must be its own argument on the CLI rather than being in a delimited list (#4025)
• (help) Line wrapping of help is now behind the existing wrap_help feature flag, either enable it or hard code your wraps (#4258)
• (help) Make DeriveDisplayOrder the default and removed the setting. To sort help, set next_display_order(None) (#2808)
• (help) Subcommand display order respects Command::next_display_order instead of DeriveDisplayOrder and using its own initial display order value (#2808)
• (help) Subcommands are now listed before arguments. To get the old behavior, see Command::help_template (#4132)
• (help) Help headings are now title cased, making any user-provided help headings inconsistent. To get the old behavior, see Command::help_template, Arg::help_heading, and Command::subcommand_help_heading (#4132)
• (help) "Command" is used as the section heading for subcommands and COMMAND for the value name. To get the old behavior, see Command::subcommand_help_heading and Arg::subcommand_value_name (#4132, #4155)
• (help) Whitespace in help output is now trimmed to ensure consistency regardless of how well a template matches the users needs. (#4132, #4156)
• (help) name/version/author are removed by default from help output. To get the old behavior, see Command::help_template. (#4132, #4160)
• (help) Indentation for second-line usage changed. (#4132, #4188)
• (env) Parse --help and --version like any ArgAction::SetTrue flag (#3776)
• (derive) Leave Arg::id as verbatim casing, requiring updating of string references to other args like in conflicts_with or requires (#3282)
• (derive) Doc comments for ValueEnum variants will now show up in --help (#3312)
• (derive) When deriving Args, and ArgGroup is created using the type's name, reserving it for future use (#2621, #4209)
• (derive) next_help_heading can now leak out of a #[clap(flatten)], like all other command settings (#4222)

Easier to catch changes:

• Looking up a group in ArgMatches now returns the arg Ids, rather than the values to reduce overhead and offer more flexibility. (#4072)
• Changed Arg::number_of_values (average-across-occurrences) to Arg::num_args (per-occurrence) (raw CLI args, not parsed values) (#2688, #4023)
  • num_args(0) no longer implies takes_value(true).multiple_values(true) (#4023)
  • num_args(1) no longer implies multiple_values(true) (#4023)
  • Does not check default or env values, only what the user explicitly passes in (#4025)
  • No longer terminates on delimited values (#4025)
• Replace Arg::min_values (across all occurrences) with Arg::num_args(N..) (per occurrence) to reduce confusion over different value count APIs (#4023)
• Replace Arg::max_values (across all occurrences) with Arg::num_args(1..=M) (per occurrence) to reduce confusion over different value count APIs (#4023)
• Replace Arg::multiple_values(true) with Arg::num_args(1..) and Arg::multiple_values(false) with Arg::num_args(0) to reduce confusion over different value count APIs (#4023)
• Replace Arg::takes_value(true) with Arg::num_args(1) and Arg::takes_value(false) with Arg::num_args(0) to reduce confusion over different value count APIs
• Remove Arg::require_value_delimiter, either users could use Arg::value_delimiter or implement a custom parser with TypedValueParser as it was mostly to make multiple_values(true) act like multiple_values(false) and isn't needed anymore (#4026)
• Arg::new("help") and Arg::new("version") no longer implicitly disable the built-in flags and be copied to all subcommands, instead disable the built-in flags (Command::disable_help_flag, Command::disable_version_flag) and mark the custom flags as global(true). (#4056)
• Arg::short('h') no longer implicitly disables the short flag for help, instead disable the built-in flags (Command::disable_help_flag, Command::disable_version_flag) provide your own Arg::new("help").long("help").action(ArgAction::Help).global(true). (#4056)
• ArgAction::SetTrue and ArgAction::SetFalse now prioritize Arg::default_missing_value over their standard behavior (#4000)
• Changed Arg::requires_ifs and Arg::default_value*_ifs* to taking an ArgPredicate, removing ambiguity with None when accepting owned and borrowed types (#4084)
• Removed PartialEq and Eq from Command so we could change external subcommands to use a ValueParser (#3990)
• Various Arg, Command, and ArgGroup calls were switched from accepting &[] to [] via IntoIterator to be more flexible (#4072)
• Arg::short_aliases and other builder functions that took &[] need the & dropped (#4081)
• ErrorKind and Result moved into the error module
• ErrorKind::EmptyValue replaced with ErrorKind::InvalidValue to remove an unnecessary special case (#3676, #3968)
• ErrorKind::UnrecognizedSubcommand replaced with ErrorKind::InvalidSubcommand to remove an unnecessary special case (#3676)
• Changed the default type of allow_external_subcommands from String to OsString as that is less likely to cause bugs in user applications (#3990)
• (help) Command::render_usage now returns a StyledStr (#4248)
• (derive) Changed the default for arguments from parse to value_parser, removing parse support (#3827, #3981)
  • #[clap(value_parser)] and #[clap(action)] are now redundant
• (derive) subcommand_required(true).arg_required_else_help(true) is set instead of SubcommandRequiredElseHelp to give more meaningful errors when subcommands are missing and to reduce redundancy (#3280)
• (derive) Remove arg_enum attribute in favor of value_enum to match the new name (we didn't have support in v3 to mark it deprecated) (#4127)
• (parser) Assert when the CLI looksup an unknown args when external subcommand support is enabled to help catch bugs (#3703)
• (assert) Sometimes Arg::default_missing_value didn't require num_args(0..=N), now it does (#4023)
• (assert) Leading dashes in Arg::long are no longer allowed (#3691)
• (assert) Disallow more value_names than num_args (#2695)
• (assert) Always enforce that version is specified when the ArgAction::Version is used
• (assert) Add missing #[track_caller]s to make it easier to debug asserts
• (assert) Ensure overrides_with IDs are valid
• (assert) Ensure no self-overrides_with now that Actions replace it
• (assert) Ensure subcommand names are not duplicated
• (assert) Assert on mut_arg receiving an invalid arg ID or mut_subcommand receiving an invalid command name

Compatibility

MSRV is now 1.60.0

Deprecated

• Arg::use_value_delimiter in favor of Arg::value_delimiter to avoid having multiple ways of doing the same thing
• Arg::requires_all in favor of Arg::requires_ifs now that it takes an ArgPredicate to avoid having multiple ways of doing the same thing
• Arg::number_of_values in favor of Arg::num_args to clarify semantic differences
• default_value_os, default_values_os, default_value_if_os, and default_value_ifs_os as the non _os variants now accept either a str or an OsStr (#4141)
• Arg::env_os in favor of Arg::env
• Command::dont_collapse_args_in_usage is now the default (#4151)
• Command::trailing_var_arg in favor of Arg::trailing_var_arg to make it clearer which arg it is meant to apply to (#4187)
• Command::allow_hyphen_values in favor of Arg::allow_hyphen_values to make it clearer which arg it is meant to apply to (#4187)
• Command::allow_negative_numbers in favor of Arg::allow_negative_numbers to make it clearer which arg it is meant to apply to (#4187)
• (help) Deprecated Command::write_help and Command::write_long_help in favor of Command::render_help and Command::render_long_help (#4248)
• (derive) structopt and clap attributes in favor of the more specific command, arg, and value to open the door for more features and clarify relationship to the builder (#1807, #4180)
• (derive) #[clap(value_parser)] and #[clap(action)] defaulted attributes (its the default) (#3976)

Behavior Changes

• (help) With wrap_help feature, if the terminal size cannot be determined, LINES and COLUMNS variables are used (#4186)

Features

• Arg::num_args now accepts ranges, allowing setting both the minimum and maximum number of values per occurrence (#2688, #4023)
• Allow non-bool value_parsers for ArgAction::SetTrue / ArgAction::SetFalse (#4092)
• Add From<&OsStr>, From<OsString>, From<&str>, and From<String> to value_parser! (#4257)
• Allow resetting most builder methods
• Can now pass runtime generated data to Command, Arg, ArgGroup, PossibleValue, etc without managing lifetimes with the string feature flag (#2150, #4223)
• New default error-context, help and usage feature flags that can be turned off for smaller binaries (#4236)
• Added StyledStr::ansi() to Display with ANSI escape codes (#4248)
• (error) Error::apply for changing the formatter for dropping binary size (#4111)
• (error) Error::renderfor formatting the error into a StyledStr
• (help) Show PossibleValue::help in long help (--help) (#3312)
• (help) New {tab} variable for Command::help_template (#4161)
• (help) Command::render_help and Command::render_long_help for formatting the error into a StyledStr (#3873, #4248)
• (help) Command::render_usage now returns a StyledStr (#4248)

Fixes

• Verify required is not used with conditional required settings (#3660)
• Replaced cmd.allow_invalid_for_utf8_external_subcommands with cmd.external_subcommand_value_parser (#3733)
• Arg::default_missing_value now applies per occurrence rather than if a value is missing across all occurrences (#3998)
• arg!(--long [value]) to accept 0..=1 per occurrence rather than across all occurrences, making it safe to use with ArgAction::Append (#4001)
• Allow OsStrs for Arg::{required_if_eq,required_if_eq_any,required_if_eq_all} (#4084)
• (help) With wrap_help feature, if the terminal size cannot be determined, LINES and COLUMNS variables are used (#4186)
• (help) Use Command::display_name in the help title rather than Command::bin_name
• (help) Show when a flag is ArgAction::Count by adding an ... (#4003)
• (help) Use a more neutral palette for coloring (#4132, #4117)
• (help) Don't rely on ALL CAPS for help headers (#4132, #4123)
• (help) List subcommands first, focusing the emphasis on them (#4132, #4125)
• (help) Do not include global args in cmd help help (#4131)
• (help) Use [positional] in list when relevant (#4144)
• (help) Show all [positional] in usage (#4151)
• (help) Polish up subcommands by referring to them as commands (#4132, #4155)
• (help) Trim extra whitespace to avoid artifacts from different uses of templates (#4132, #4156)
• (help) Hint to the user the difference between -h / --help when applicable (#4132, #4159)
• (help) Shorten help by eliding name/version/author (#4132, #4160)
• (help) When short help is long enough to activate next_line_help, don't add blank lines (#4132, #4190)
• (help) Make help output more dense (reducing horizontal whitespace) (#4132, #4192)
• (help) Separate subcommand flags with "," like option flags (#4232, #4235)
• (help) Quote the suggested help flag (#4220)
• (version) Use Command::display_name rather than Command::bin_name (#3966)
• (parser) Always fill in "" argument for external subcommands (#3263)
• (parser) Short flags now have higher precedence than hyphen values with Arg::allow_hyphen_values, like Command::allow_hyphen_values (#4187)
• (parser) Prefer InvalidSubcommand over UnknownArgument in more cases (#4219)
• (derive) Detect escaped external subcommands that look like built-in subcommands (#3703)
• (derive) Leave Arg::id as verbatim casing (#3282)
• (derive) Default to #[clap(value_parser, action)] instead of #[clap(parse)] (#3827)

Fixes

• (derive) Fix regression with #[clap(default_value_os_t ...)] introduced in v3.2.3

Fixes

• (derive) Provide more clearer deprecation messages for #[clap(parse)] attribute (#3832)

Fixes

• Moved deprecations to be behind the deprecated Cargo.toml feature (#3830)
  • For now, it is disabled by default though we are considering enabling it by default as we release the next major version to help draw attention to the deprecation migration path

Fixes

• (derive) Improve the highlighted code for deprecation warnings

gated behind unstable-v4

• (derive) Default to #[clap(value_parser, action)] instead of #[clap(parse)] (#3827)

Compatibility

MSRV is now 1.56.0 (#3732)

Behavior

• Defaults no longer satisfy required and its variants (#3793)
• When misusing ArgMatches::value_of and friends, debug asserts were turned into panics

Moving (old location deprecated)

• clap::{PossibleValue, ValueHint} to clap::builder::{PossibleValue, ValueHint}
• clap::{Indices, OsValues, ValueSource, Values} to clap::parser::{Indices, OsValues, ValueSource, Values}
• clap::ArgEnum to clap::ValueEnum (#3799)

Replaced

• Arg::allow_invalid_utf8 with Arg::value_parser(value_parser!(PathBuf)) (#3753)
• Arg::validator / Arg::validator_os with Arg::value_parser (#3753)
• 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!(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)
• AppSettings::NoHelpVersion with ArgAction or Command::disable_help_flag / Command::disable_help_subcommand (#3800)
• ArgMatches::{value_of, value_of_os, value_of_os_lossy, value_of_t} with ArgMatches::{get_one,remove_one} (#3753)
• ArgMatches::{values_of, values_of_os, values_of_os_lossy, values_of_t} with ArgMatches::{get_many,remove_many} (#3753)
• ArgMatches::is_valid_arg with ArgMatches::{try_get_one,try_get_many} (#3753)
• ArgMatches::occurrences_of with ArgMatches::value_source or ArgAction::Count (#3797)
• ArgMatches::is_present with ArgMatches::contains_id or ArgAction::SetTrue (#3797)
• ArgAction::StoreValue with ArgAction::Set or ArgAction::Append (#3797)
• ArgAction::IncOccurrences with ArgAction::SetTrue or ArgAction::Count (#3797)
• (derive) #[clap(parse(...))] replaced with: (#3589, #3794)
  • For default parsers (no parse attribute), deprecation warnings can be silenced by opting into the new behavior by adding either #[clap(action)] or #[clap(value_parser)] (ie requesting the default behavior for these attributes). Alternatively, the unstable-v4 feature changes the default away from parse to action/value_parser.
  • For #[clap(parse(from_flag))] replaced with #[clap(action = ArgAction::SetTrue)] (#3794)
  • For #[clap(parse(from_occurrences))] replaced with #[clap(action = ArgAction::Count)] though the field's type must be u8 (#3794)
  • For #[clap(parse(from_os_str)] for PathBuf, replace it with #[clap(value_parser)] (as mentioned earlier this will call value_parser!(PathBuf) which will auto-select the right ValueParser automatically).
  • For #[clap(parse(try_from_str = ...)], replace it with #[clap(value_parser = ...)]
  • For most other cases, a type implementing TypedValueParser will be needed and specify it with #[clap(value_parser = ...)]

Features

• Parsed, typed arguments via Arg::value_parser / ArgMatches::{get_one,get_many} (#2683, #3732)
  • Several built-in TypedValueParsers available with an API open for expansion
  • value_parser!(T) macro for selecting a parser for a given type (#3732) and open to expansion via the ValueParserFactory trait (#3755)
  • [&str] is implicitly a value parser for possible values
  • All ArgMatches getters do not assume required arguments (#2505)
  • Add ArgMatches::remove_* variants to transfer ownership
  • Add ArgMatches::try_* variants to avoid panics for developer errors (#3621)
  • Add a get_raw to access the underlying OsStrs
  • PathBuf value parsers imply ValueHint::AnyPath for completions (#3732)
• Explicit control over parsing via Arg::action (#3774)
  • ArgAction::StoreValue: existing takes_value(true) behavior
  • ArgAction::IncOccurrences: existing takes_value(false) behavior
  • ArgAction::Help: existing --help behavior
  • ArgAction::Version: existing --version behavior
  • ArgAction::Set: Overwrite existing values (like Arg::multiple_occurrences mixed with Command::args_override_self) (#3777)
  • ArgAction::Append: like Arg::multiple_occurrences (#3777)
  • ArgAction::SetTrue: Treat --flag as --flag=true (#3775)
    • Implies Arg::default_value("false") (#3786)
    • Parses Arg::env via Arg::value_parser
  • ArgAction::SetFalse: Treat --flag as --flag=false (#3775)
    • Implies Arg::default_value("true") (#3786)
    • Parses Arg::env via Arg::value_parser
  • ArgAction::Count: Treat --flag --flag --flag as --flag=1 --flag=2 --flag=3 (#3775)
    • Implies Arg::default_value("0") (#3786)
    • Parses Arg::env via Arg::value_parser
• (derive) Opt-in to new Arg::value_parser / Arg::action with either #[clap(value_parser)] (#3589, #3742) / #[clap(action)] attributes (#3794)
  • Default ValueParser is determined by value_parser! (#3199, #3496)
  • Default ArgAction is determine by a hard-coded lookup on the type (#3794)
• Command::multicall is now stable for busybox-like programs and REPLs (#2861, #3684)
• ArgMatches::{try_,}contains_id for checking if there are values for an argument that mirrors the new get_{one,many} API

Fixes

• Don't correct argument id in default_value_ifs_os(#3815)

parser

• Set ArgMatches::value_source and ArgMatches::occurrences_of for external subcommands (#3732)
• Use value delimiter for Arg::default_missing_values (#3761, #3765)
• SplitArg::default_value / Arg::env on value delimiters independent of whether -- was used (#3765)
• Allow applying defaults to flags (#3294, 3775)
• Defaults no longer satisfy required and its variants (#3793)