Some error improvements (#659)

crates/nu-protocol/src/signature.rs

@@ -274,6 +274,33 @@ impl Signature {
         self
     }
 
+    pub fn call_signature(&self) -> String {
+        let mut one_liner = String::new();
+        one_liner.push_str(&self.name);
+        one_liner.push(' ');
+
+        for positional in &self.required_positional {
+            one_liner.push_str(&get_positional_short_name(positional, true));
+        }
+        for positional in &self.optional_positional {
+            one_liner.push_str(&get_positional_short_name(positional, false));
+        }
+
+        if self.rest_positional.is_some() {
+            one_liner.push_str("...args ");
+        }
+
+        // if !self.subcommands.is_empty() {
+        //     one_liner.push_str("<subcommand> ");
+        // }
+
+        if !self.named.is_empty() {
+            one_liner.push_str("{flags} ");
+        }
+
+        one_liner
+    }
+
     /// Get list of the short-hand flags
     pub fn get_shorts(&self) -> Vec<char> {
         self.named.iter().filter_map(|f| f.short).collect()
@@ -431,6 +458,25 @@ impl Command for Predeclaration {
     }
 }
 
+fn get_positional_short_name(arg: &PositionalArg, is_required: bool) -> String {
+    match &arg.shape {
+        SyntaxShape::Keyword(name, ..) => {
+            if is_required {
+                format!("{} <{}> ", String::from_utf8_lossy(name), arg.name)
+            } else {
+                format!("({} <{}>) ", String::from_utf8_lossy(name), arg.name)
+            }
+        }
+        _ => {
+            if is_required {
+                format!("<{}> ", arg.name)
+            } else {
+                format!("({}) ", arg.name)
+            }
+        }
+    }
+}
+
 #[derive(Clone)]
 struct BlockCommand {
     signature: Signature,

crates/nu-protocol/src/span.rs

@@ -46,6 +46,15 @@ impl Span {
     pub fn contains(&self, pos: usize) -> bool {
         pos >= self.start && pos < self.end
     }
+
+    /// Point to the space just past this span, useful for missing
+    /// values
+    pub fn past(&self) -> Span {
+        Span {
+            start: self.end,
+            end: self.end,
+        }
+    }
 }
 
 /// Used when you have a slice of spans of at least size 1