feat(help): Expose clap's indentation to help_template

This will make it easier for help templates to be consistent with clap

CHANGELOG.md

@@ -74,6 +74,7 @@ Deprecated
 - Added `TypedValueParser::map` to make it easier to reuse existing value parsers
 - *(error)* `Error::apply` for changing the formatter for dropping binary size
 - *(help)* Show `PossibleValue::help` in long help (`--help`) (#3312)
+- *(help)* New `{tab}` variable for `Command::help_template`
 
 ### Fixes
 

src/builder/command.rs

@@ -1706,6 +1706,7 @@ impl Command {
     ///   * `{options}`             - Help for options.
     ///   * `{positionals}`         - Help for positional arguments.
     ///   * `{subcommands}`         - Help for subcommands.
+    ///   * `{tag}`                 - Standard tab sized used within clap
     ///   * `{after-help}`          - Help from [`Command::after_help`] or [`Command::after_long_help`].
     ///   * `{before-help}`         - Help from [`Command::before_help`] or [`Command::before_long_help`].
     ///

src/output/help.rs

@@ -31,15 +31,17 @@ pub(crate) struct Help<'cmd, 'writer> {
 // Public Functions
 impl<'cmd, 'writer> Help<'cmd, 'writer> {
     const DEFAULT_TEMPLATE: &'static str = "\
-        {before-help}{about-with-newline}\n\
+{before-help}{about-with-newline}
-        {usage-heading}\n    {usage}\n\
+{usage-heading}
-        \n\
+{tab}{usage}
-        {all-args}{after-help}\
+
+{all-args}{after-help}\
     ";
 
     const DEFAULT_NO_ARGS_TEMPLATE: &'static str = "\
-        {before-help}{about-with-newline}\n\
+{before-help}{about-with-newline}
-        {usage-heading}\n    {usage}{after-help}\
+{usage-heading}
+{tab}{usage}{after-help}\
     ";
 
     /// Create a new `Help` instance.
@@ -186,6 +188,9 @@ impl<'cmd, 'writer> Help<'cmd, 'writer> {
                     "subcommands" => {
                         self.write_subcommands(self.cmd);
                     }
+                    "tab" => {
+                        self.none(TAB);
+                    }
                     "after-help" => {
                         self.write_after_help();
                     }

tests/builder/utils.rs

@@ -9,7 +9,7 @@ pub const FULL_TEMPLATE: &str = "\
 {before-help}{name} {version}
 {author-with-newline}{about-with-newline}
 {usage-heading}
-    {usage}
+{tab}{usage}
 
 {all-args}{after-help}";
 

tests/derive/utils.rs

@@ -11,7 +11,7 @@ pub const FULL_TEMPLATE: &str = "\
 {before-help}{name} {version}
 {author-with-newline}{about-with-newline}
 {usage-heading}
-    {usage}
+{tab}{usage}
 
 {all-args}{after-help}";