clap_complete_fig

Performance

• Improve build times by removing once_cell dependency

Features

• Stabilize Command::styles

compatibility

• update msrv to 1.70.0

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

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

• 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

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) 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)

Fixes

• Dependency upgrade

Features

• (help) Show PossibleValue::help in long help (--help) (gated behind unstable-v4) (#3312)

Fixes

• Don't panic when validating delimited defaults (#3514)

Fixes

• (derive) Allow other attribute with a subcommand that has subcommands

Documentation

• (examples) List example topics
• (derive) Clarify syntax and relation to builder API

Fixes

• Track caller for ArgMatches assertions so the user more easily sees where they need to fix the call

Compatibility

Changes in behavior of note that are not guaranteed to be compatible across releases:

• (help) help subcommand shows long help like --help, rather than short help (-h), deprecated clap::AppSettings::UseLongFormatForHelpSubcommand (#3440)
• (help) Pacman-style subcommands are now ordered the same as usage errors (#3470)
• (help) Pacman-style subcommands use standard alternate syntax in usage (#3470)

Deprecations

• clap::Command is now preferred over clap::App (#3089 in #3472)
  • clap::command! is now preferred over clap::app_from_crate (#3089 in #3474)
  • clap::CommandFactory::command is now preferred over clap::IntoApp::into_app (#3089 in #3473)
• (help) help subcommand shows long help like --help, rather than short help (-h), deprecated clap::AppSettings::UseLongFormatForHelpSubcommand (#3440)
• (error) Deprecate clap::AppSettings::WaitOnError, leaving it to the user to implement
• (validation) clap::Command::subcommand_required(true).arg_required_else_help(true) is now preferred over clap::AppSettings::SubcommandRequiredElseHelp (#3280)
• (builder) clap::AppSettings are nearly all deprecated and replaced with builder methods and getters (#2717)
• (builder) clap::ArgSettings is deprecated and replaced with builder methods and getters (#2717)
• (builder) clap::Arg::id and clap::ArgGroup::id are now preferred over clap::Arg::name and clap::ArgGroup::name (#3335)
• (help) clap::Command::next_help_heading is now preferred over clap::Command::help_heading (#1807, #1553)
• (error) clap::error::ErrorKind is now preferred over clap::ErrorKind (#3395)
• (error) clap::Error::kind() is now preferred over clap::Error::kind
• (error) clap::Error::context() is now preferred over clap::Error::info (#2628)

Note: All items deprecated in 3.0.0 are now hidden in the documentation. (#3458)

Features

• (matches) Add clap::ArgMatches::value_source to determine what insert the value (#1345)
• (help) Override derived display order with clap::Command::next_display_order (#1807)
• (error) Show possible values when an argument doesn't have a value (#3320)
• (error) New clap::Error::context API to open the door for fully-custom error messages (#2628)
  • (error) clap::error::ErrorKind now implements Display

Fixes

• (builder) Some functions were renamed for consistency and fixing spelling issues
• (builder) Allow clap::Command::color to override previous calls (#3449)
• (parse) Propagate globals with multiple subcommands (#3428)
• (validation) Give ArgRequiredElseHelp precedence over SubcommandRequired (#3456)
• (validation) Default values no longer count as "present" for conflicts, requires, clap::Command::arg_required_else_help, etc (#3076, #1264)
• (assert) Report invalid defaults (#3202)
• (help) Clarify how to handle -h conflicts (#3403)
• (help) Make it easier to debug the addition of help flags (#3425)
• (help) Pacman-style subcommands are now separated with spaces (#3470)
• (help) Pacman-style subcommands are now ordered the same as usage errors (#3470)
• (help) Pacman-style subcommands use standard alternate syntax in usage (#3470)
• (error) Be consistent in showing of required attributes between errors / usage (#3390)
• (error) Show user's order of possible values, like in --help (#1549)
• (error) Allow customizing error type in clap::error::Result (#3395)

Performance

• (error) Reduced stack size of clap::Error (#3395)

Documentation

• (builder) Correct data take accepted for clap::Arg::validator
• (derive) Clarify parse attribute
• (tutorial) Demonstrate custom parsing
• (example) Consistently list out required feature flags (#3448)

Fixes

• Ignore Last when checking hyphen values (see #3249 for details)
• Help catch bugs with #[must_use]

Fixes

• Don't panic when getting number of values (#3241)
• Don't warn when using default_value_t derive attribute with a Subcommand (#3245)

Documentation

• Added name attribute to ArgEnum variant derive reference

Note: clap v3 has been in development for several years and has changed hands multiple times. Unfortunately, our changelog might be incomplete, whether in changes or their motivation.

Highlights

A special thanks to the maintainers, contributors, beta users, and sponsors who have helped along this journey, especially kbknapp.

StructOpt Integration

StructOpt provides a serde-like declarative approach to defining your parser. The main benefits we've seen so far from integrating are:

• Tighter feedback between the design of clap and the derives
• More universal traits. Crates exist for common CLI patterns (example) and we've re-designed the StructOpt traits so crates built on clap3 can be reused not just with other derives but also people using the builder API. People can even hand implement these so people using the builder API won't have the pay the cost for derives.

Custom Help Headings

Previously, clap automatically grouped arguments in the help as either ARGS, FLAGS, OPTIONS, and SUBCOMMANDS.

You can now override the default group with Arg::help_heading and App::subcommand_help_heading. To apply a heading to a series of arguments, you can set App::help_heading.

Deprecations

While a lot of deprecations have been added to clean up the API (overloaded meaning of Arg::multiple) or make things more consistent, some particular highlights are:

• clap_app! has been deprecated in favor of the builder API with arg! (clap-rs/clap#2835)
• Arg::from_usage has been deprecated in favor of arg! (clap-rs/clap#3087)
  • Porting example
• The YAML API has been deprecated in favor the builder or derive APIs (clap-rs/clap#3087)

Migrating

From clap v2

1. Add CLI tests, -h and --help output at a minimum (recommendation: trycmd for snapshot testing)
2. Update your dependency
   1. If you use no-default-features: add the std feature
3. Resolve compiler errors
4. Resolve behavior changes
   1. Refactor your App creation to a function and add a test similar to the one below, resolving any of its assertions
   2. Look over the "subtle changes" under BREAKING CHANGES
   3. If using builder: test your application under various circumstances to see if ArgMatches asserts regarding AllowInvalidUtf8.
5. At your leisure: resolve deprecation notices

Example test:

fn app() -> clap::App<'static> {
    ...
}

#[test]
fn verify_app() {
    app().debug_assert();
}

From structopt 0.3.25 <a name="migrate-structopt"></a>

1. Add CLI tests, -h and --help output at a minimum (recommendation: trycmd for snapshot testing)
2. Replace your dependency from structopt = "..." to clap = { version = "3.0", features = ["derive"] }
   1. If you use no-default-features: add the std feature
3. Resolve compiler errors, including
   1. Update your use statements from structopt and structopt::clap to clap
4. Resolve behavior changes
   1. Add a test similar to the one below, resolving any of its assertions
   2. Look over the "subtle changes" under BREAKING CHANGES
5. At your leisure: resolve deprecation notices

Example test:

#[derive(clap::StructOpt)]
struct Args {
    ...
}

#[test]
fn verify_app() {
    use clap::IntoApp;
    Args::into_app().debug_assert()
}

From clap v3.0.0-beta.5

1. Add CLI tests, -h and --help output at a minimum (recommendation: trycmd for snapshot testing)
2. Update your dependency
   1. Add in derive, env, cargo, or unicode feature flags as needed
3. Resolve compiler errors
   1. If you use yaml, clap_app!, or usage parser: revert any changes you made for clap3
   2. Change Arg::about Arg::long_about back to help and long_help and change PossibleValue::about to help (clap-rs/clap#3075)
   3. Change AppSettings::HelpRequired to AppSettings::HelpExpected
   4. Change PossibleValue::hidden to PossibleValue::hide
   5. Change App::subcommand_placeholder to App::subcommand_value_name / App::subcommand_help_heading
4. Resolve behavior changes
   1. Add the above listed test appropriate for your application and resolve any problems it reports
   2. If using derive: see the structopt breaking changes section for Vec changes
   3. If using builder: test your application under various circumstances to see if ArgMatches asserts regarding AllowInvalidUtf8.
5. At your leisure: resolve deprecation notices

BREAKING CHANGES

From clap 2

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

• AppSettings::UnifiedHelpMessage is now default behaviour
  • {flags} and {unified} will assert if present in App::help_template
  • See clap-rs/clap#2807
• AppSettings::EnableColoredHelp is now the default behavior but can be opted-out with AppSettings::DisableColoredHelp (clap-rs/clap#2806)
• App::override_usage no longer implies a leading \t, allowing multi lined usages
• Arg::require_equals no longer implies ArgSettings::ForbidEmptyValues (#2233)
• Arg::require_delimiter no longer implies ArgSettings::TakesValue and ArgSettings::UseValueDelimiter (#2233)
• Arg::env, Arg::env_os, Arg::last, Arg::require_equals, Arg::allow_hyphen_values, Arg::hide_possible_values, Arg::hide_default_value, Arg::hide_env_values, Arg::case_insensitive and Arg::multiple_values no longer imply ArgSettings::TakesValue (#2233)
• ArgMatches::is_present no longer checks subcommand names
• Some env variable values are now considered false for flags, not just "not-present" (clap-rs/clap#2539)
• Changed ...s meaning in usage parser. Before, it always meant multiple which is still true for --option [val].... Now [name]... --option [val] results in ArgSettings::MultipleOccurrences.
• Usage exit code changed from 1 to 2 (clap-rs/clap#1327)
• Reject --foo=bar when takes_value(false) (clap-rs/clap#1543)
• No longer accept an arbitrary number of - for long arguments (-----long)

Easier to catch changes:

• When using no-default-features, you now have to specify the std feature (reserved for future work)
• Gated env support behind env feature flag
  • Impacts Arg::env, Arg::env_os, Arg::hide_env_values, ArgSettings::HideEnvValues
  • See clap-rs/clap#2694
• Gated crate information behind cargo feature flag
  • Impacts crate_name!, crate_version!, crate_authors!, crate_description!, app_from_crate!
• AppSettings::StrictUtf8 is now default behaviour and asserts if AppSettings::AllowInvalidUtf8ForExternalSubcommands and ArgSettings::AllowInvalidUtf8 and ArgMatches::value_of_os aren't used together
  • AppSettings::AllowInvalidUtf8 has been removed
  • clap-rs/clap#751
• Arg::short and Arg::value_delimiter now take a char instead of a &str
• ArgMatches panics on unknown arguments
• Removed VersionlessSubcommands, making it the default (see clap-rs/clap#2812)
• Completion generation has been split out into clap_complete.
• Removed ArgSettings::EmptyValues in favor of ArgSettings::ForbidEmptyValues
• Validator signatures have been loosed:
  • Arg::validator now takes first argument as Fn(&str) -> Result<O, E: ToString> instead of Fn(String) -> Result<(), String>
  • Arg::validator_os now takes first argument as Fn(&OsStr) -> Result<O, OsString> instead of Fn(&OsStr) -> Result<(), OsString>
• Arg::value_name now sets, rather than appends (see clap-rs/clap#2634)
• Upgrade yaml-rust from 0.3 to 0.4
• Replaced ArgGroup::from(BTreeMap) to ArgGroup::from(yaml)
• Replaced ArgMatches::usage with App::generate_usage
• Replaced Arg::settings with Arg::setting(Setting1 | Setting2)
• App and Arg now need only one lifetime
• Removed deprecated App::with_defaults, replaced with app_from_crate
• Removed deprecated AppSettings::PropagateGlobalValuesDown (now the default)
• Some App functions, like App::write_help now take &mut self instead of &self
• Error::message is now private, use Error::to_string
• Arg::default_value_if, Arg::default_value_if_os, Arg::default_value_ifs, Arg::default_value_ifs_os now takes the default value parameter as an option (clap-rs/clap#1406)
• Changed App::print_help & App::print_long_help to now return std::io::Result
• Changed App::write_help & App::write_long_help to now return std::io::Result
• Changed Arg::index, Arg::number_of_values, Arg::min_values, Arg::max_values to taking usize instead of u64
• Changed Error::info to type Vec<String> instead of Option<Vec<String>>
• Changed ArgMatches::subcommand to now return Option<(&str, &ArgMatches)>
• Renamed ErrorKind::MissingArgumentOrSubcommand to ErrorKind::DisplayHelpOnMissingArgumentOrSubcommand
• Renamed ErrorKind::HelpDisplayed to ErrorKind::DisplayHelp
• Renamed ErrorKind::VersionDisplayed to ErrorKind::DisplayVersion
• Added #[non_exhaustive] to clap::{ValueHint, ErrorKind, AppSettings, ArgSettings} (clap-rs/clap#3167)

From structopt 0.3.25

• By default, the App isn't initialized with crate information anymore. Now opt-in via #[clap(author)], #[clap(about)], #[clap(version)] (clap-rs/clap#3034)
• #[clap(default_value)] is replaced with #[clap(default_value_t)] (clap-rs/clap#1694)
• Subcommands nested under subcommands now needs a #[clap(subcommand)] attribute (clap-rs/clap#2587)
• Vec<_> and Option<Vec<_>> have changed from multiple to multiple_occurrences

On top of the clap 2 changes

Performance

From clap 2

• Split out non-default unicode feature flag for faster builds and smaller binaries for ASCII-only CLIs.
• Split out non-default env feature flag for faster builds and smaller binaries.

Features

From clap 2

• Integration of structopt::StructOpt via clap::Parser (requires derive feature flag)

• Custom help headings

  • App::help_heading (apply to all future args)
  • Arg::help_heading (apply to current arg)
  • App::subcommand_help_heading along with App::subcommand_value_name (apply to subcommands)
  • See clap-rs/clap#805
  • AppSettings::UnifiedHelpMessage is now default behaviour (clap-rs/clap#2807)

• Deriving of ArgEnum for generating Arg::possible_values (requires derive feature flag)

• Disable built-in help/version behavior with AppSettings::NoAutoHelp and AppSettings::NoAutoVersion

• Change an existing arg with new builder method mut_arg (particularly helpful for --help and --version)

• Provide extra context in long help messages (--help) with before_long_help and after_long_help (clap-rs/clap#1903)

• Detect missing help descriptions via debug asserts by enabling AppSettings::HelpExpected

• Aliases for short flags (clap-rs/clap#1896)

• Validate UTF-8 values, rather than panicing during ArgMatches::value_of thanks to AppSettings::AllowInvalidUtf8ForExternalSubcommands and ArgSettings::AllowInvalidUtf8

  • Debug builds will assert when the ArgMatches calls do not match the UTF-8 setting.
  • See clap-rs/clap#751

• clap::PossibleValue to allow

  • Hiding (clap-rs/clap#2756)
  • Completion help for possible values for args (clap-rs/clap#2731)

• Allow arguments to conflict with all others via Arg::exclusive (clap-rs/clap#1583)

• Validate arguments with a regex (required regex feature flag)

  • See clap-rs/clap

• Arg::default_missing_value for cases like --color[=<WHEN>] (clap-rs/clap#1587)

• clap::App::color / clap::ColorChoice to specify color setting for the app

• Custom error reporting with App::error

• App::debug_assert test helper

• Replace Arg::multiple(bool) with Arg::multiple_values / Arg::multiple_occurrences

  • Positionals can be either

• Added support for flag subcommands like pacman (clap-rs/clap#1361)

• Partial parsing via AppSettings::IgnoreErrors (clap-rs/clap#1880)

• Enable cmd help to print long help (--help instead of -h) with AppSettings::UseLongFormatForHelpSubcommand (clap-rs/clap#2435)

• Allow long arg abbreviations like we do with subcommands via AppSettings::InferLongArgs (clap-rs/clap#2435)

• Detect subcommands among positional arguments with AppSettings::SubcommandPrecedenceOverArg

• Give completion scripts hints with Arg::value_hint (clap-rs/clap#1793)

• Allow unsetting defaults with

• Arg::default_value_if, Arg::default_value_if_os, Arg::default_value_ifs, Arg::default_value_ifs_os (clap-rs/clap#1406)

• Interpret some env variable values as false for flags, in addition to "not-present" (clap-rs/clap#2539)

  • n, no, f, false, off, 0

• Added arg! macro for creating an Arg from a compile-time usage parser

• (Experimental) Busybox-like multi-call support

  • See AppSettings::Multicall behind unstable-multicall feature flag
  • See clap-rs/clap#1120

• (Experimental) Alias an argument to anything group of arguments

  • See App::replace behind unstable-replace feature flag
  • See clap-rs#1603

• (Experimental) Grouping of multiple values within multiple occurrences

  • See ArgMatches::grouped_values_of behind unstable-grouped feature flag
  • See clap-rs/clap#1026

From structopt 0.3.25

• Allow defaulting with native types via new default_value_t [= <expr>] attribute (clap-rs/clap#1694)
• New update API
• New arg_enum attribute for integrating with ArgEnum trait

On top of the clap 2 changes

Fixes

From clap 2

• Correctly handle colored output on Windows
• Only generate version flags when App::version, App::long_version are set (see clap-rs/clap#2812)
• General completion script improvements
• Limited default help text wrapping to 100 when wrap_help feature is not enabled
• Be more specific than Arg::multiple with Arg::multiple_values and Arg::multiple_occurrences
• app_from_crate! defaults to separating multiple authors with ", "
• Ensure all examples work
• IgnoreCase is now unicode aware (requires unicode feature flag)
• Always respect ColorChoice::Never, even if that means we skip colors in some cases
• ArgMatches panics on unknown arguments
• Gracefully handle empty authors field in Cargo.toml with app_from_crate
• Do not show --help in cmd help with DisableHelpFlag (clap-rs/clap#3169)
• Do not show --help in cmd help help that doesn't work (clap-rs/clap#3169)

From structopt 0.3.25

• Support SubcommandsNegateReqs by allowing required Option<_>s (clap-rs/clap#2255)
• Infer AllowInvalidUtf8 based on parser (clap-rs/clap#751)
• Gracefully handle empty authors field in Cargo.toml
• Don't panic with default_value_os but treat it like default_value (clap-rs/clap#3031)
• When using flatten and subcommand, ensure our doc comment always overrides the nested container's doc comment, whether it has only about or about and long_about (clap-rs/clap#3175)

On top of the clap 2 changes

Minimum Required Rust

• As of this release, clap requires rustc 1.54.0 or greater.