feat(printer): use uparrow for empty highlights and fix 0-offset display bug

src/handlers/graphical.rs

@@ -401,7 +401,9 @@ impl GraphicalReportHandler {
                         "{:width$}{}{}{}",
                         "",
                         chars.underline.to_string().repeat(num_left),
-                        if hl.label().is_some() {
+                        if hl.len() == 0 {
+                            chars.uarrow
+                        } else if hl.label().is_some() {
                             chars.underbar
                         } else {
                             chars.underline
@@ -427,7 +429,7 @@ impl GraphicalReportHandler {
                 let num_right = local_offset + hl_len - vbar_offset - 1;
                 let lines = format!(
                     "{:width$}{}{} {}",
-                    " ",
+                    "",
                     chars.lbot,
                     chars.hbar.to_string().repeat(num_right + 1),
                     label,

tests/printer.rs

@@ -65,6 +65,48 @@ fn single_line_highlight() -> Result<(), MietteError> {
     Ok(())
 }
 
+#[test]
+fn single_line_highlight_offset_zero() -> Result<(), MietteError> {
+    #[derive(Debug, Diagnostic, Error)]
+    #[error("oops!")]
+    #[diagnostic(code(oops::my::bad), help("try doing it better next time?"))]
+    struct MyBad {
+        src: NamedSource,
+        #[snippet(src, message("This is the part that broke"))]
+        ctx: SourceSpan,
+        #[highlight(ctx, label = "this bit here")]
+        highlight: SourceSpan,
+    }
+
+    let src = "source\n  text\n    here".to_string();
+    let len = src.len();
+    let err = MyBad {
+        src: NamedSource::new("bad_file.rs", src),
+        ctx: (0, len).into(),
+        highlight: (0, 0).into(),
+    };
+    let out = fmt_report(err.into());
+    println!("{}", out);
+    let expected = r#"
+────[oops::my::bad]────────────────────
+
+    × oops!
+
+   ╭───[bad_file.rs:1:1] This is the part that broke:
+ 1 │ source
+   · ▲
+   · ╰─ this bit here
+ 2 │   text
+ 3 │     here
+
+    ‽ try doing it better next time?
+"#
+    .trim_start()
+    .to_string();
+    assert_eq!(expected, out);
+    Ok(())
+}
+
 #[test]
 fn single_line_highlight_with_empty_span() -> Result<(), MietteError> {
     #[derive(Debug, Diagnostic, Error)]
@@ -95,7 +137,7 @@ fn single_line_highlight_with_empty_span() -> Result<(), MietteError> {
    ╭───[bad_file.rs:1:1] This is the part that broke:
  1 │ source
  2 │   text
-   ·   ┬
+   ·   ▲
    ·   ╰─ this bit here
  3 │     here