nice errors

src/errors.rs

@@ -0,0 +1,78 @@
+use std::fmt::Debug;
+
+#[derive(Debug, Copy, Clone, PartialOrd, PartialEq, Ord, Eq, Hash)]
+pub struct Span {
+    start: usize,
+    len: usize,
+}
+
+impl Span {
+    pub fn new(start: usize, len: usize) -> Self {
+        Self { start, len }
+    }
+
+    pub fn start_end(start: usize, end: usize) -> Self {
+        Self::new(start, end - start)
+    }
+
+    pub fn single(start: usize) -> Self {
+        Self { start, len: 1 }
+    }
+}
+
+pub trait CompilerError {
+    fn span(&self) -> Span;
+    fn message(&self) -> String;
+    fn note(&self) -> Option<String>;
+}
+
+pub fn display_error<E>(source: &str, error: E)
+where
+    E: CompilerError + Debug,
+{
+    let mut chars = 0;
+    let mut lines = source.split_inclusive('\n').enumerate();
+    while let Some((idx, line)) = lines.next() {
+        if chars + line.len() + 1 > error.span().start {
+            let offset_on_line = error.span().start - chars;
+
+            println!("{}error: {}{}", RED, error.message(), RESET);
+            println!("      {}|{}", CYAN, RESET);
+            println!(
+                "{}{:>5} |{} {}",
+                CYAN,
+                idx + 1,
+                RESET,
+                &line[..line.len() - 1]
+            );
+            print!("      {}|{} ", CYAN, RESET);
+            println!(
+                "{}{}{}{}",
+                " ".repeat(offset_on_line),
+                RED,
+                "^".repeat(error.span().len),
+                RESET,
+            );
+            if let Some(note) = error.note() {
+                println!("      {}|{}", CYAN, RESET);
+                println!(
+                    "      {}|{}   {}note: {}{}",
+                    CYAN, RESET, GREEN, note, RESET
+                );
+            }
+            break;
+        }
+        chars += line.len();
+    }
+}
+
+macro_rules! color {
+    ($name:ident: $value:literal) => {
+        const $name: &str = concat!("\x1B[", $value);
+    };
+}
+
+color!(RED: "0;31m");
+color!(RESET: "0m");
+color!(CYAN: "0;36m");
+color!(GREEN: "0;32m");