Prototype out a help trait

argh/src/help.rs

@@ -0,0 +1,330 @@
+// Copyright (c) 2022 Google LLC All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+//! TODO
+
+use {
+    argh_shared::{write_description, CommandInfo, INDENT},
+    std::fmt,
+};
+
+const SECTION_SEPARATOR: &str = "\n\n";
+
+const HELP_FLAG: HelpFlagInfo = HelpFlagInfo {
+    short: None,
+    long: "--help",
+    description: "display usage information",
+    optionality: HelpOptionality::Optional,
+    kind: HelpFieldKind::Switch,
+};
+
+/// TODO
+pub trait Help {
+    /// TODO
+    const HELP_INFO: HelpInfo<'static>;
+}
+
+/// TODO
+pub trait HelpSubCommands {
+    /// TODO
+    const HELP_INFO: HelpSubCommandsInfo<'static>;
+}
+
+/// TODO
+pub trait HelpSubCommand {
+    /// TODO
+    const HELP_INFO: HelpSubCommandInfo<'static>;
+}
+
+impl<T: HelpSubCommand> HelpSubCommands for T {
+    /// TODO
+    const HELP_INFO: HelpSubCommandsInfo<'static> =
+        HelpSubCommandsInfo { optional: false, commands: &[<T as HelpSubCommand>::HELP_INFO] };
+}
+
+/// TODO
+pub struct HelpInfo<'a> {
+    /// TODO
+    pub description: &'a str,
+    /// TODO
+    pub examples: &'a [fn(&[&str]) -> String],
+    /// TODO
+    pub notes: &'a [fn(&[&str]) -> String],
+    /// TODO
+    pub flags: &'a [HelpFlagInfo<'a>],
+    /// TODO
+    pub positionals: &'a [HelpPositionalInfo<'a>],
+    /// TODO
+    pub subcommand: Option<HelpSubCommandsInfo<'a>>,
+    /// TODO
+    pub error_codes: &'a [(isize, &'a str)],
+}
+
+fn help_section(
+    out: &mut String,
+    command_name: &[&str],
+    heading: &str,
+    sections: &[fn(&[&str]) -> String],
+) {
+    if !sections.is_empty() {
+        out.push_str(SECTION_SEPARATOR);
+        for section_fn in sections {
+            let section = section_fn(command_name);
+
+            out.push_str(heading);
+            for line in section.split('\n') {
+                out.push('\n');
+                out.push_str(INDENT);
+                out.push_str(line);
+            }
+        }
+    }
+}
+
+impl<'a> HelpInfo<'a> {
+    /// TODO
+    pub fn help(&self, command_name: &[&str]) -> String {
+        let mut out = format!("Usage: {}", command_name.join(" "));
+
+        for positional in self.positionals {
+            out.push(' ');
+            positional.help_usage(&mut out);
+        }
+
+        for flag in self.flags {
+            out.push(' ');
+            flag.help_usage(&mut out);
+        }
+
+        if let Some(subcommand) = &self.subcommand {
+            out.push(' ');
+            if subcommand.optional {
+                out.push('[');
+            }
+            out.push_str("<command>");
+            if subcommand.optional {
+                out.push(']');
+            }
+            out.push_str(" [<args>]");
+        }
+
+        out.push_str(SECTION_SEPARATOR);
+
+        out.push_str(self.description);
+
+        if !self.positionals.is_empty() {
+            out.push_str(SECTION_SEPARATOR);
+            out.push_str("Positional Arguments:");
+            for positional in self.positionals {
+                positional.help_description(&mut out);
+            }
+        }
+
+        out.push_str(SECTION_SEPARATOR);
+        out.push_str("Options:");
+        for flag in self.flags {
+            flag.help_description(&mut out);
+        }
+
+        // Also include "help"
+        HELP_FLAG.help_description(&mut out);
+
+        if let Some(subcommand) = &self.subcommand {
+            out.push_str(SECTION_SEPARATOR);
+            out.push_str("Commands:");
+            for cmd in subcommand.commands {
+                let info = CommandInfo { name: cmd.name, description: cmd.info.description };
+                write_description(&mut out, &info);
+            }
+        }
+
+        help_section(&mut out, command_name, "Examples:", self.examples);
+
+        help_section(&mut out, command_name, "Notes:", self.notes);
+
+        if !self.error_codes.is_empty() {
+            out.push_str(SECTION_SEPARATOR);
+            out.push_str("Error codes:");
+            write_error_codes(&mut out, self.error_codes);
+        }
+
+        out.push('\n');
+
+        out
+    }
+}
+
+fn write_error_codes(out: &mut String, error_codes: &[(isize, &str)]) {
+    for (code, text) in error_codes {
+        out.push('\n');
+        out.push_str(INDENT);
+        out.push_str(&format!("{} {}", code, text));
+    }
+}
+
+impl<'a> fmt::Debug for HelpInfo<'a> {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        let examples = self.examples.iter().map(|f| f(&["{command_name}"])).collect::<Vec<_>>();
+        let notes = self.notes.iter().map(|f| f(&["{command_name}"])).collect::<Vec<_>>();
+        f.debug_struct("HelpInfo")
+            .field("description", &self.description)
+            .field("examples", &examples)
+            .field("notes", &notes)
+            .field("flags", &self.flags)
+            .field("positionals", &self.positionals)
+            .field("subcommand", &self.subcommand)
+            .field("error_codes", &self.error_codes)
+            .finish()
+    }
+}
+
+/// TODO
+#[derive(Debug)]
+pub struct HelpSubCommandsInfo<'a> {
+    /// TODO
+    pub optional: bool,
+    /// TODO
+    pub commands: &'a [HelpSubCommandInfo<'a>],
+}
+
+/// TODO
+#[derive(Debug)]
+pub struct HelpSubCommandInfo<'a> {
+    /// TODO
+    pub name: &'a str,
+    /// TODO
+    pub info: HelpInfo<'a>,
+}
+
+/// TODO
+#[derive(Copy, Clone, Debug, PartialEq, Eq)]
+pub enum HelpOptionality {
+    /// TODO
+    None,
+    /// TODO
+    Optional,
+    /// TODO
+    Repeating,
+}
+
+impl HelpOptionality {
+    /// TODO
+    fn is_required(&self) -> bool {
+        matches!(self, HelpOptionality::None)
+    }
+}
+
+/// TODO
+#[derive(Debug)]
+pub struct HelpPositionalInfo<'a> {
+    /// TODO
+    pub name: &'a str,
+    /// TODO
+    pub description: &'a str,
+    /// TODO
+    pub optionality: HelpOptionality,
+}
+
+impl<'a> HelpPositionalInfo<'a> {
+    /// TODO
+    pub fn help_usage(&self, out: &mut String) {
+        if !self.optionality.is_required() {
+            out.push('[');
+        }
+
+        out.push('<');
+        out.push_str(self.name);
+
+        if self.optionality == HelpOptionality::Repeating {
+            out.push_str("...");
+        }
+
+        out.push('>');
+
+        if !self.optionality.is_required() {
+            out.push(']');
+        }
+    }
+
+    /// TODO
+    pub fn help_description(&self, out: &mut String) {
+        let info = CommandInfo { name: self.name, description: self.description };
+        write_description(out, &info);
+    }
+}
+
+/// TODO
+#[derive(Debug)]
+pub struct HelpFlagInfo<'a> {
+    /// TODO
+    pub short: Option<char>,
+    /// TODO
+    pub long: &'a str,
+    /// TODO
+    pub description: &'a str,
+    /// TODO
+    pub optionality: HelpOptionality,
+    /// TODO
+    pub kind: HelpFieldKind<'a>,
+}
+
+/// TODO
+#[derive(Debug)]
+pub enum HelpFieldKind<'a> {
+    /// TODO
+    Switch,
+    /// TODO
+    Option {
+        /// TODO
+        arg_name: &'a str,
+    },
+}
+
+impl<'a> HelpFlagInfo<'a> {
+    /// TODO
+    pub fn help_usage(&self, out: &mut String) {
+        if !self.optionality.is_required() {
+            out.push('[');
+        }
+
+        if let Some(short) = self.short {
+            out.push('-');
+            out.push(short);
+        } else {
+            out.push_str(self.long);
+        }
+
+        match self.kind {
+            HelpFieldKind::Switch => {}
+            HelpFieldKind::Option { arg_name } => {
+                out.push_str(" <");
+                out.push_str(arg_name);
+
+                if self.optionality == HelpOptionality::Repeating {
+                    out.push_str("...");
+                }
+
+                out.push('>');
+            }
+        }
+
+        if !self.optionality.is_required() {
+            out.push(']');
+        }
+    }
+
+    /// TODO
+    pub fn help_description(&self, out: &mut String) {
+        let mut name = String::new();
+        if let Some(short) = self.short {
+            name.push('-');
+            name.push(short);
+            name.push_str(", ");
+        }
+        name.push_str(self.long);
+
+        let info = CommandInfo { name: &name, description: self.description };
+        write_description(out, &info);
+    }
+}

argh/src/lib.rs

@@ -171,7 +171,15 @@
 
 use std::str::FromStr;
 
-pub use argh_derive::FromArgs;
+mod help;
+
+pub use {
+    crate::help::{
+        Help, HelpFieldKind, HelpFlagInfo, HelpInfo, HelpOptionality, HelpPositionalInfo,
+        HelpSubCommand, HelpSubCommandInfo, HelpSubCommands, HelpSubCommandsInfo,
+    },
+    argh_derive::FromArgs,
+};
 
 /// Information about a particular command used for output.
 pub type CommandInfo = argh_shared::CommandInfo<'static>;