From ef2726abac537f6711fc48826726fdfe157a7f6d Mon Sep 17 00:00:00 2001
From: Naseschwarz <naseschwarz@0x53a.de>
Date: Tue, 11 Mar 2025 17:46:45 +0100
Subject: [PATCH] Convert error line buffer to space indentation

The type of indentation is not important for error reporting. However,
keeping the indentation as tabs has two issues:

1. rustfmt keeps track of widths, not character offsets. For space
   indentation, these two are the same. For tab indentation, this leads
   to issues like [1].
2. annotate-snippet-rs always format leading tabs as four spaces. Thus,
   formatter error reporting is not faithful and ranges will not be
   marked correctly (or need another transformation).

Replacing tabs with spaces for error reporting as early as possible
solves these issues.

[1] https://github.com/rust-lang/rustfmt/issues/6442
---
 src/formatting.rs | 11 ++++++++++-
 1 file changed, 10 insertions(+), 1 deletion(-)

diff --git a/src/formatting.rs b/src/formatting.rs
index 1e1e329f624..374b56069e0 100644
--- a/src/formatting.rs
+++ b/src/formatting.rs
@@ -593,13 +593,22 @@ impl<'a> FormatLines<'a> {
         }
     }
 
+    fn line_buffer_with_leading_spaces(&self) -> String {
+        if self.config.hard_tabs() {
+            let leading_tabs = self.line_buffer.chars().take_while(|&c| c == '\t').count();
+            " ".repeat(self.config.tab_spaces() * leading_tabs) + &self.line_buffer[leading_tabs..]
+        } else {
+            self.line_buffer.clone()
+        }
+    }
+
     fn push_err(&mut self, kind: ErrorKind, is_comment: bool, is_string: bool) {
         self.errors.push(FormattingError {
             line: self.cur_line,
             kind,
             is_comment,
             is_string,
-            line_buffer: self.line_buffer.clone(),
+            line_buffer: self.line_buffer_with_leading_spaces(),
         });
     }