Overhaul CLI error handling to allow multiple levels of context

cli/src/error.rs

@@ -1,46 +1,82 @@
+use std::fmt::Write;
 use std::io;
 use tree_sitter_highlight::PropertySheetError;
 
 #[derive(Debug)]
-pub struct Error(pub String);
+pub struct Error(pub Vec<String>);
 
 pub type Result<T> = std::result::Result<T, Error>;
 
 impl Error {
     pub fn grammar(message: &str) -> Self {
-        Error(format!("Grammar error: {}", message))
+        Error(vec![format!("Grammar error: {}", message)])
     }
 
     pub fn regex(message: &str) -> Self {
-        Error(format!("Regex error: {}", message))
+        Error(vec![format!("Regex error: {}", message)])
     }
 
     pub fn undefined_symbol(name: &str) -> Self {
-        Error(format!("Undefined symbol `{}`", name))
+        Error(vec![format!("Undefined symbol `{}`", name)])
+    }
+
+    pub fn new(message: String) -> Self {
+        Error(vec![message])
+    }
+
+    pub fn err<T>(message: String) -> Result<T> {
+        Err(Error::new(message))
+    }
+
+    pub fn wrap<E: Into<Self>, M: ToString, F: FnOnce() -> M>(
+        message_fn: F,
+    ) -> impl FnOnce(E) -> Self {
+        |e| {
+            let mut result = e.into();
+            result.0.push(message_fn().to_string());
+            result
+        }
+    }
+
+    pub fn message(&self) -> String {
+        let mut result = self.0.last().unwrap().clone();
+        if self.0.len() > 1 {
+            result.push_str("\nDetails:\n");
+            for msg in self.0[0..self.0.len() - 1].iter().rev() {
+                writeln!(&mut result, "  {}", msg).unwrap();
+            }
+        }
+        result
     }
 }
 
 impl From<serde_json::Error> for Error {
     fn from(error: serde_json::Error) -> Self {
-        Error(error.to_string())
+        Error::new(error.to_string())
     }
 }
 
 impl From<io::Error> for Error {
     fn from(error: io::Error) -> Self {
-        Error(error.to_string())
+        Error::new(error.to_string())
     }
 }
 
 impl From<rsass::Error> for Error {
     fn from(error: rsass::Error) -> Self {
-        Error(error.to_string())
+        Error::new(error.to_string())
+    }
+}
+
+impl From<regex_syntax::ast::Error> for Error {
+    fn from(error: regex_syntax::ast::Error) -> Self {
+        Error::new(error.to_string())
     }
 }
 
 impl From<String> for Error {
     fn from(error: String) -> Self {
-        Error(error)
+        Error::new(error)
     }
 }