better error outputs

1 files changed, 42 insertions, 3 deletions

diff --git a/src/main.rs b/src/main.rs
index 8edd75a..2e0c82f 100644
--- a/src/main.rs
+++ b/src/main.rs
@@ -1,12 +1,14 @@
 #![feature(trait_alias)]
 use std::collections::HashMap;
+use std::fmt;
 use std::fs::File;
 use std::io::{BufReader, Read, Seek};
 use std::path::PathBuf;
 use std::str::FromStr;
 
-use anyhow::Result;
+use anyhow::{anyhow, Error, Result};
 use chrono::{NaiveDateTime, Weekday};
+use colored::Colorize;
 use log::debug;
 use num_traits::cast::FromPrimitive;
 use structopt::StructOpt;
@@ -157,10 +159,38 @@ impl<R: Read + Seek> ZipWrapper<R> {
     }
 }
 
+#[derive(Clone, Debug)]
+struct InputError {
+    line: String,
+    location: usize,
+    msg: String,
+}
+
+impl fmt::Display for InputError {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        let prefix = "Input:";
+        writeln!(f, "{} {}", prefix.yellow(), self.line)?;
+        let prefix_len = prefix.len() + self.location;
+        writeln!(f, "{}{}", " ".repeat(prefix_len), " ^-".red())?;
+        write!(f, "{}: {}", "Error".red(), self.msg)?;
+        Ok(())
+    }
+}
+
+impl std::error::Error for InputError {}
+
 fn main() {
     let result = run();
     if let Err(err) = result {
-        eprintln!("Error: {}", err);
+        display_error(&err);
+    }
+}
+
+fn display_error(err: &Error) {
+    if let Some(err) = err.downcast_ref::<InputError>() {
+        eprintln!("{}", err);
+    } else {
+        eprintln!("{}: {}", "Error".red(), err);
     }
 }
 
@@ -207,7 +237,16 @@ fn build_filter(opt: &Opt) -> Result<Box<dyn LogFilter>> {
     // We're fine with the small memory leak, as we're only dealing with a small string in a
     // short-lived program.
     let expr_string = Box::leak(Box::new(opt.expression.join(" ")));
-    Ok(fexpr::parse_logfilter(expr_string)?)
+    if expr_string.trim().is_empty() {
+        return Err(anyhow!("Expected a filter to be given"));
+    }
+    Ok(
+        fexpr::parse_logfilter(expr_string).map_err(|error| InputError {
+            line: expr_string.to_string(),
+            location: fexpr::location(&error),
+            msg: error.to_string(),
+        })?,
+    )
 }
 
 /// Run the grep search with the given options.