Partially use standard formatter alignment for aligning option help text

jaarg/src/help.rs

@@ -74,17 +74,16 @@ impl<ID> core::fmt::Display for StandardFullHelpWriter<'_, ID> {
       writeln!(f, "{description}")?;
     }
 
-    fn calculate_left_pad<ID: 'static>(option: &Opt<ID>) -> usize {
+	  // Determine the alignment width from the longest option parameter
+    fn calculate_option_line_length<ID: 'static>(option: &Opt<ID>) -> usize {
       (match option.names {
         OptIdentifier::Single(name) => name.chars().count(),
         OptIdentifier::Multi(names) => (names.len() - 1) * 3 + names.iter()
           .fold(0, |accum, name| accum + name.chars().count()),
       }) + option.value_name.map_or(0, |v| v.len() + 3)
     }
-
+    let align_width = 3 + self.0.options.iter()
-	  // Determine the alignment width from the longest option parameter
+      .map(|o| calculate_option_line_length(o)).max().unwrap_or(0);
-    let align_width = 2 + self.0.options.iter()
-      .map(|o| calculate_left_pad(o)).max().unwrap_or(0);
 
     // Write positional argument descriptions
     let mut first = true;
@@ -97,15 +96,64 @@ impl<ID> core::fmt::Display for StandardFullHelpWriter<'_, ID> {
         first = false;
       }
 
-      // Write positional argument line
+      // Write positional argument line (name + optional aligned help text)
-      write!(f, "  {name}", name = option.first_name())?;
+      let name = option.first_name();
+      write!(f, "  {name}")?;
       if let Some(help_text) = option.help_string {
         write!(f, " {:.<width$} {help_text}", "",
-          width = align_width - calculate_left_pad(option))?;
+          width = align_width - name.chars().count() - 1)?;
       }
       writeln!(f)?;
     }
 
+    /// Formatter for option usage lines.
+    struct OptionUsageLine<'a, ID>(&'a Opt<ID>);
+    impl<ID> core::fmt::Display for OptionUsageLine<'_, ID> {
+      fn fmt(&self, f: &mut core::fmt::Formatter<'_>) -> core::fmt::Result {
+        use core::fmt::Write;
+        let mut length = 0;
+
+        // Write option flag name(s)
+        match self.0.names {
+          OptIdentifier::Single(name) => {
+            write!(f, "{name}")?;
+            length = name.chars().count();
+          }
+          OptIdentifier::Multi(names) => {
+            for (i, name) in names.iter().enumerate() {
+              if i == 0 {
+                write!(f, "{name}")?;
+                length += name.chars().count();
+              } else {
+                write!(f, " | {name}")?;
+                length += 3 + name.chars().count();
+              }
+            }
+          }
+        }
+
+        // Write value argument for value options parameters
+        if let Some(value_name) = self.0.value_name {
+          write!(f, " <{value_name}>")?;
+          length += 2 + value_name.chars().count() + 1;
+        }
+
+        // Write padding if requested
+        match (f.align(), f.width().unwrap_or(0).checked_sub(length)) {
+          (Some(core::fmt::Alignment::Left), Some(width)) if width > 0 => {
+            let fill = f.fill();
+            // First padding char is *always* a space
+            f.write_char(' ')?;
+            for _ in 1..width {
+              f.write_char(fill)?;
+            }
+            Ok(())
+          }
+          _ => Ok(()),
+        }
+      }
+    }
+
     // Write option parameter argument descriptions
     first = true;
     for option in self.0.options.iter()
@@ -117,25 +165,12 @@ impl<ID> core::fmt::Display for StandardFullHelpWriter<'_, ID> {
         first = false;
       }
 
-      // Write option flag name(s)
+      // Write line for option, with aligned help text if needed
-      match option.names {
+      let line = OptionUsageLine(&option);
-        OptIdentifier::Single(name) => {
-          write!(f, "  {name}")?;
-        }
-        OptIdentifier::Multi(names) => for (i, name) in names.iter().enumerate() {
-          write!(f, "{prefix}{name}", prefix = if i == 0 { "  " } else { " | " })?;
-        }
-      }
-
-      // Write value argument for value options parameters
-      if let Some(value_name) = option.value_name {
-        write!(f, " <{value_name}>")?;
-      }
-
-      // Write padding and help text
       if let Some(help_text) = option.help_string {
-        write!(f, " {:.<width$} {help_text}", "",
+        write!(f, "  {line:.<align_width$} {help_text}")?;
-          width = align_width - calculate_left_pad(option))?;
+      } else {
+        write!(f, "  {line}")?;
       }
       writeln!(f)?;
     }

jaarg/src/option.rs

@@ -132,6 +132,7 @@ impl<ID> Opt<ID> {
   }
 }
 
+#[allow(dead_code)]
 impl<ID: 'static> Opt<ID> {
   /// Get the first name of the option.
   pub const fn first_name(&self) -> &str {