fix(handlers): Fix label position (#107)

Fixes #106

While fixing the bug I've also extended the handler to print not just
where label starts but also where label ends.

Also implements #97, but for narratabble handler only.

This adds dependency on `unicode-width`, but it was already in the
dependency chain (`textwidth` depends on it). Although, previously it
was only for `"fancy"` feature, now it always required since narratable
handler is supported without `"fancy"`.

Cargo.toml

@@ -15,6 +15,7 @@ exclude = ["images/", "tests/", "miette-derive/"]
 thiserror = "1.0.26"
 miette-derive = { path = "miette-derive", version = "=3.3.1-alpha.0"}
 once_cell = "1.8.0"
+unicode-width = "0.1.9"
 
 owo-colors = { version = "3.0.0", optional = true }
 atty = { version = "0.2.14", optional = true }
@@ -45,7 +46,7 @@ fancy = [
     "supports-hyperlinks",
     "supports-color",
     "supports-unicode",
-    "backtrace"
+    "backtrace",
 ]
 
 [workspace]

src/handlers/narratable.rs

@@ -1,5 +1,7 @@
 use std::fmt;
 
+use unicode_width::{UnicodeWidthChar, UnicodeWidthStr};
+
 use crate::chain::Chain;
 use crate::protocol::{Diagnostic, Severity};
 use crate::{LabeledSpan, MietteError, ReportHandler, SourceCode, SourceSpan, SpanContents};
@@ -208,23 +210,44 @@ impl NarratableReportHandler {
         writeln!(f)?;
         for line in &lines {
             writeln!(f, "snippet line {}: {}", line.line_number, line.text)?;
-            let relevant = labels.iter().filter(|l| line.span_starts(l.inner()));
-            for label in relevant {
-                let contents = source
-                    .read_span(label.inner(), self.context_lines, self.context_lines)
-                    .map_err(|_| fmt::Error)?;
-                if contents.line() + 1 == line.line_number {
-                    write!(
-                        f,
-                        "    label starting at line {}, column {}",
-                        contents.line() + 1,
-                        contents.column() + 1
-                    )?;
-                    if let Some(label) = label.label() {
-                        write!(f, ": {}", label)?;
+            let relevant = labels
+                .iter()
+                .filter_map(|l| line.span_attach(l.inner()).map(|a| (a, l)));
+            for (attach, label) in relevant {
+                match attach {
+                    SpanAttach::Contained { col_start, col_end } if col_start == col_end => {
+                        write!(
+                            f,
+                            "    label at line {}, column {}",
+                            line.line_number, col_start,
+                        )?;
+                    }
+                    SpanAttach::Contained { col_start, col_end } => {
+                        write!(
+                            f,
+                            "    label at line {}, columns {} to {}",
+                            line.line_number, col_start, col_end,
+                        )?;
+                    }
+                    SpanAttach::Starts { col_start } => {
+                        write!(
+                            f,
+                            "    label starting at line {}, column {}",
+                            line.line_number, col_start,
+                        )?;
                     }
-                    writeln!(f)?;
+                    SpanAttach::Ends { col_end } => {
+                        write!(
+                            f,
+                            "    label ending at line {}, column {}",
+                            line.line_number, col_end,
+                        )?;
+                    }
+                }
+                if let Some(label) = label.label() {
+                    write!(f, ": {}", label)?;
                 }
+                writeln!(f)?;
             }
         }
         Ok(())
@@ -281,6 +304,7 @@ impl NarratableReportHandler {
                     line_number: line,
                     offset: line_offset,
                     text: line_str.clone(),
+                    at_end_of_file,
                 });
                 line_str.clear();
                 line_offset = offset;
@@ -308,12 +332,62 @@ struct Line {
     line_number: usize,
     offset: usize,
     text: String,
+    at_end_of_file: bool,
+}
+
+enum SpanAttach {
+    Contained { col_start: usize, col_end: usize },
+    Starts { col_start: usize },
+    Ends { col_end: usize },
+}
+
+/// Returns column at offset, and nearest boundary if offset is in the middle of the character
+fn safe_get_column(text: &str, offset: usize, start: bool) -> usize {
+    let mut column = text.get(0..offset).map(|s| s.width()).unwrap_or_else(|| {
+        let mut column = 0;
+        for (idx, c) in text.char_indices() {
+            if offset <= idx {
+                break;
+            }
+            column += c.width().unwrap_or(0);
+        }
+        column
+    });
+    if start {
+        // Offset are zero-based, so plus one
+        column += 1;
+    } // On the other hand for end span, offset refers for the next column
+      // So we should do -1. column+1-1 == column
+    column
 }
 
 impl Line {
-    // Does this line contain the *beginning* of this multiline span?
-    // This assumes self.span_applies() is true already.
-    fn span_starts(&self, span: &SourceSpan) -> bool {
-        span.offset() >= self.offset
+    fn span_attach(&self, span: &SourceSpan) -> Option<SpanAttach> {
+        let span_end = span.offset() + span.len();
+        let line_end = self.offset + self.text.len();
+
+        let start_after = span.offset() >= self.offset;
+        let end_before = self.at_end_of_file || span_end <= line_end;
+
+        if start_after && end_before {
+            let col_start = safe_get_column(&self.text, span.offset() - self.offset, true);
+            let col_end = if span.is_empty() {
+                col_start
+            } else {
+                // span_end refers to the next character after token
+                // while col_end refers to the exact character, so -1
+                safe_get_column(&self.text, span_end - self.offset, false)
+            };
+            return Some(SpanAttach::Contained { col_start, col_end });
+        }
+        if start_after && span.offset() <= line_end {
+            let col_start = safe_get_column(&self.text, span.offset() - self.offset, true);
+            return Some(SpanAttach::Starts { col_start });
+        }
+        if end_before && span_end >= self.offset {
+            let col_end = safe_get_column(&self.text, span_end - self.offset, false);
+            return Some(SpanAttach::Ends { col_end });
+        }
+        None
     }
 }

tests/narrated.rs

@@ -46,8 +46,8 @@ fn single_line_with_wide_char() -> Result<(), MietteError> {
 Begin snippet for bad_file.rs starting at line 1, column 1
 
 snippet line 1: source
-    label starting at line 1, column 1: this bit here
 snippet line 2:   👼🏼text
+    label at line 2, columns 3 to 6: this bit here
 snippet line 3:     here
 diagnostic help: try doing it better next time?
 diagnostic code: oops::my::bad
@@ -82,8 +82,8 @@ fn single_line_highlight() -> Result<(), MietteError> {
 Begin snippet for bad_file.rs starting at line 1, column 1
 
 snippet line 1: source
-    label starting at line 1, column 1: this bit here
 snippet line 2:   text
+    label at line 2, columns 3 to 6: this bit here
 snippet line 3:     here
 diagnostic help: try doing it better next time?
 diagnostic code: oops::my::bad
@@ -118,7 +118,7 @@ fn single_line_highlight_offset_zero() -> Result<(), MietteError> {
 Begin snippet for bad_file.rs starting at line 1, column 1
 
 snippet line 1: source
-    label starting at line 1, column 1: this bit here
+    label at line 1, column 1: this bit here
 snippet line 2:   text
 diagnostic help: try doing it better next time?
 diagnostic code: oops::my::bad
@@ -153,8 +153,8 @@ fn single_line_highlight_with_empty_span() -> Result<(), MietteError> {
 Begin snippet for bad_file.rs starting at line 1, column 1
 
 snippet line 1: source
-    label starting at line 1, column 1: this bit here
 snippet line 2:   text
+    label at line 2, column 3: this bit here
 snippet line 3:     here
 diagnostic help: try doing it better next time?
 diagnostic code: oops::my::bad
@@ -189,8 +189,8 @@ fn single_line_highlight_no_label() -> Result<(), MietteError> {
 Begin snippet for bad_file.rs starting at line 1, column 1
 
 snippet line 1: source
-    label starting at line 1, column 1
 snippet line 2:   text
+    label at line 2, columns 3 to 6
 snippet line 3:     here
 diagnostic help: try doing it better next time?
 diagnostic code: oops::my::bad
@@ -225,8 +225,8 @@ fn single_line_highlight_at_line_start() -> Result<(), MietteError> {
 Begin snippet for bad_file.rs starting at line 1, column 1
 
 snippet line 1: source
-    label starting at line 1, column 1: this bit here
 snippet line 2: text
+    label at line 2, columns 1 to 4: this bit here
 snippet line 3:   here
 diagnostic help: try doing it better next time?
 diagnostic code: oops::my::bad
@@ -267,10 +267,10 @@ fn multiple_same_line_highlights() -> Result<(), MietteError> {
 Begin snippet for bad_file.rs starting at line 1, column 1
 
 snippet line 1: source
-    label starting at line 1, column 1: x
-    label starting at line 1, column 1: y
-    label starting at line 1, column 1: z
 snippet line 2:   text text text text text
+    label at line 2, columns 3 to 6: x
+    label at line 2, columns 8 to 11: y
+    label at line 2, columns 18 to 21: z
 snippet line 3:     here
 diagnostic help: try doing it better next time?
 diagnostic code: oops::my::bad
@@ -305,9 +305,10 @@ fn multiline_highlight_adjacent() -> Result<(), MietteError> {
 Begin snippet for bad_file.rs starting at line 1, column 1
 
 snippet line 1: source
-    label starting at line 1, column 1: these two lines
 snippet line 2:   text
+    label starting at line 2, column 3: these two lines
 snippet line 3:     here
+    label ending at line 3, column 6: these two lines
 diagnostic help: try doing it better next time?
 diagnostic code: oops::my::bad
 "#
@@ -352,11 +353,13 @@ Begin snippet for bad_file.rs starting at line 1, column 1
 
 snippet line 1: line1
     label starting at line 1, column 1: block 1
-    label starting at line 1, column 1: block 2
 snippet line 2: line2
+    label starting at line 2, column 5: block 2
 snippet line 3: line3
 snippet line 4: line4
+    label ending at line 4, column 1: block 2
 snippet line 5: line5
+    label ending at line 5, column 5: block 1
 diagnostic help: try doing it better next time?
 diagnostic code: oops::my::bad
 "#
@@ -418,11 +421,13 @@ Begin snippet for bad_file.rs starting at line 1, column 1
 
 snippet line 1: line1
     label starting at line 1, column 1: block 1
-    label starting at line 1, column 1
 snippet line 2: line2
+    label starting at line 2, column 5
 snippet line 3: line3
 snippet line 4: line4
+    label ending at line 4, column 1
 snippet line 5: line5
+    label ending at line 5, column 5: block 1
 diagnostic help: try doing it better next time?
 diagnostic code: oops::my::bad
 "
@@ -461,9 +466,11 @@ Begin snippet for bad_file.rs starting at line 1, column 1
 snippet line 1: source
     label starting at line 1, column 1: this bit here
 snippet line 2:   text
-    label starting at line 2, column 1: also this bit
+    label ending at line 2, column 3: this bit here
 snippet line 3:     here
+    label starting at line 3, column 7: also this bit
 snippet line 4: more here
+    label ending at line 4, column 3: also this bit
 diagnostic help: try doing it better next time?
 diagnostic code: oops::my::bad
 "
@@ -575,8 +582,8 @@ fn related() -> Result<(), MietteError> {
 Begin snippet for bad_file.rs starting at line 1, column 1
 
 snippet line 1: source
-    label starting at line 1, column 1: this bit here
 snippet line 2:   text
+    label at line 2, columns 3 to 6: this bit here
 snippet line 3:     here
 diagnostic help: try doing it better next time?
 diagnostic code: oops::my::bad
@@ -587,7 +594,7 @@ Error: oops!
 Begin snippet for bad_file.rs starting at line 1, column 1
 
 snippet line 1: source
-    label starting at line 1, column 1: this bit here
+    label at line 1, columns 1 to 6: this bit here
 snippet line 2:   text
 diagnostic help: try doing it better next time?
 diagnostic code: oops::my::bad