implement new argument parser with --help support

src/main.rs

@@ -2,6 +2,8 @@
 #![feature(uefi_std)]
 
 use crate::context::{RootContext, SproutContext};
+use crate::options::SproutOptions;
+use crate::options::parser::OptionsRepresentable;
 use crate::phases::phase;
 use anyhow::{Context, Result};
 use log::info;
@@ -51,7 +53,7 @@ fn main() -> Result<()> {
     setup::init()?;
 
     // Parse the options to the sprout executable.
-    let options = options::parser::parse().context("unable to parse options")?;
+    let options = SproutOptions::parse().context("unable to parse options")?;
 
     // Load the configuration of sprout.
     // At this point, the configuration has been validated and the specified

src/options.rs

@@ -1,3 +1,7 @@
+use crate::options::parser::{OptionDescription, OptionForm, OptionsRepresentable};
+use anyhow::{Context, Result, bail};
+use std::collections::BTreeMap;
+
 /// The Sprout options parser.
 pub mod parser;
 
@@ -22,3 +26,59 @@ impl Default for SproutOptions {
         }
     }
 }
+
+/// The options parser mechanism for Sprout.
+impl OptionsRepresentable for SproutOptions {
+    /// Produce the [SproutOptions] structure.
+    type Output = Self;
+
+    /// All the Sprout options that are defined.
+    fn options() -> &'static [(&'static str, OptionDescription<'static>)] {
+        &[
+            (
+                "config",
+                OptionDescription {
+                    description: "Path to Sprout configuration file",
+                    form: OptionForm::Value,
+                },
+            ),
+            (
+                "boot",
+                OptionDescription {
+                    description: "Entry to boot, bypassing the menu",
+                    form: OptionForm::Value,
+                },
+            ),
+            (
+                "help",
+                OptionDescription {
+                    description: "Display Sprout Help",
+                    form: OptionForm::Help,
+                },
+            ),
+        ]
+    }
+
+    /// Produces [SproutOptions] from the parsed raw `options` map.
+    fn produce(options: BTreeMap<String, Option<String>>) -> Result<Self> {
+        // Use the default value of sprout options and have the raw options be parsed into it.
+        let mut result = Self::default();
+
+        for (key, value) in options {
+            match key.as_str() {
+                "config" => {
+                    // The configuration file to load.
+                    result.config = value.context("--config option requires a value")?;
+                }
+
+                "boot" => {
+                    // The entry to boot.
+                    result.boot = Some(value.context("--boot option requires a value")?);
+                }
+
+                _ => bail!("unknown option: --{key}"),
+            }
+        }
+        Ok(result)
+    }
+}

src/options/parser.rs

@@ -1,11 +1,49 @@
-use crate::options::SproutOptions;
 use anyhow::{Context, Result, bail};
 use std::collections::BTreeMap;
 
+/// The type of option. This disambiguates different behavior
+/// of how options are handled.
+#[derive(Debug, Clone, Ord, PartialOrd, Eq, PartialEq)]
+pub enum OptionForm {
+    /// A flag, like --verbose.
+    Flag,
+    /// A value, in the form --abc 123 or --abc=123.
+    Value,
+    /// Help flag, like --help.
+    Help,
+}
+
+/// The description of an option, used in the options parser
+/// to make decisions about how to progress.
+#[derive(Debug, Clone)]
+pub struct OptionDescription<'a> {
+    /// The description of the option.
+    pub description: &'a str,
+    /// The type of option to parse as.
+    pub form: OptionForm,
+}
+
+/// Represents a type that can be parsed from command line arguments.
+/// This is a super minimal options parser mechanism just for Sprout.
+pub trait OptionsRepresentable {
+    /// The output type that parsing will produce.
+    type Output;
+
+    /// The configured options for this type. This should describe all the options
+    /// that are valid to produce the type. The left hand side is the name of the option,
+    /// and the right hand side is the description.
+    fn options() -> &'static [(&'static str, OptionDescription<'static>)];
+
+    /// Produces the type by taking the `options` and processing it into the output.
+    fn produce(options: BTreeMap<String, Option<String>>) -> Result<Self::Output>;
+
     /// For minimalism, we don't want a full argument parser. Instead, we use
     /// a simple --xyz = xyz: None and --abc 123 = abc: Some("123") format.
     /// We also support --abc=123 = abc: Some("123") format.
     fn parse_raw() -> Result<BTreeMap<String, Option<String>>> {
+        // Access the configured options for this type.
+        let configured: BTreeMap<_, _> = BTreeMap::from_iter(Self::options().to_vec());
+
         // Collect all the arguments to Sprout.
         // Skip the first argument which is the path to our executable.
         let args = std::env::args().skip(1).collect::<Vec<_>>();
@@ -45,7 +83,18 @@ fn parse_raw() -> Result<BTreeMap<String, Option<String>>> {
                 value = Some(part_value);
             }
 
-        if value.is_none() {
+            // Error on empty option names.
+            if option.is_empty() {
+                bail!("invalid empty option");
+            }
+
+            // Find the description of the configured option, if any.
+            let Some(description) = configured.get(option.as_str()) else {
+                bail!("invalid option: --{option}");
+            };
+
+            // Check if the option requires a value and error if none was provided.
+            if description.form == OptionForm::Value && value.is_none() {
                 // Check for the next value.
                 let maybe_next = iterator.peek();
 
@@ -60,9 +109,29 @@ fn parse_raw() -> Result<BTreeMap<String, Option<String>>> {
                 };
             }
 
-        // Error on empty option names.
+            // If the option form does not support a value and there is a value, error.
-        if option.is_empty() {
+            if description.form != OptionForm::Value && value.is_some() {
-            bail!("invalid empty option: {option}");
+                bail!("option --{} does not take a value", option);
+            }
+
+            // Handle the --help flag case.
+            if description.form == OptionForm::Help {
+                // Generic configured options output.
+                println!("Configured Options:");
+                for (name, description) in &configured {
+                    println!(
+                        "  --{}{}: {}",
+                        name,
+                        if description.form == OptionForm::Value {
+                            " <value>"
+                        } else {
+                            ""
+                        },
+                        description.description
+                    );
+                }
+                // Exit because the help has been displayed.
+                std::process::exit(1);
             }
 
             // Insert the option and the value into the map.
@@ -71,26 +140,11 @@ fn parse_raw() -> Result<BTreeMap<String, Option<String>>> {
         Ok(options)
     }
 
-/// Parse the arguments to Sprout as a [SproutOptions] structure.
+    /// Parses the program arguments as a [Self::Output], calling [Self::parse_raw] and [Self::produce].
-pub fn parse() -> anyhow::Result<SproutOptions> {
+    fn parse() -> Result<Self::Output> {
-    // Use the default value of sprout options and have the raw options be parsed into it.
+        // Parse the program arguments into a raw map.
-    let mut result = SproutOptions::default();
+        let options = Self::parse_raw().context("unable to parse options")?;
-    let options = parse_raw().context("unable to parse options")?;
+        // Produce the options from the map.
-
+        Self::produce(options)
-    for (key, value) in options {
-        match key.as_str() {
-            "config" => {
-                // The configuration file to load.
-                result.config = value.context("--config option requires a value")?;
-            }
-
-            "boot" => {
-                // The entry to boot.
-                result.boot = Some(value.context("--boot option requires a value")?);
-            }
-
-            _ => bail!("unknown option: --{key}"),
     }
 }
-    Ok(result)
-}