From fb507675b1563b0eedacf99b349565bddf2cb8d3 Mon Sep 17 00:00:00 2001
From: Raekye <Raekye@users.noreply.github.com>
Date: Wed, 7 Dec 2022 00:42:17 -0500
Subject: [PATCH 1/2] Fix panic in annotated_snippet dependency
 (rust-lang#4968).

* This change is based on the code review by camsteffen on PR
  rust-lang#5039 by karyon: have rustfmt internally replace tabs with
  the corresponding number of spaces, so that columns/indices in the
  buffer passed to annotated_snippet are counted unambiguously.
---
 src/formatting.rs | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/src/formatting.rs b/src/formatting.rs
index 1e1e329f624..047351aa084 100644
--- a/src/formatting.rs
+++ b/src/formatting.rs
@@ -582,12 +582,14 @@ impl<'a> FormatLines<'a> {
     fn char(&mut self, c: char, kind: FullCodeCharKind) {
         self.newline_count = 0;
         self.line_len += if c == '\t' {
+            self.line_buffer
+                .push_str(&" ".repeat(self.config.tab_spaces()));
             self.config.tab_spaces()
         } else {
-            1
+            self.line_buffer.push(c);
+            c.len_utf8()
         };
         self.last_was_space = c.is_whitespace();
-        self.line_buffer.push(c);
         if kind.is_string() {
             self.current_line_contains_string_literal = true;
         }

From 5e8ce93f9c579a87271a3b39b6c77e1758621101 Mon Sep 17 00:00:00 2001
From: Raekye <Raekye@users.noreply.github.com>
Date: Sat, 30 Dec 2023 18:46:33 -0500
Subject: [PATCH 2/2] Test case that can validate fix for rust-lang#4968.

* With hard_tabs, rustfmt preserves tabs and counts them as multiple
  characters/columns (based on configuration).
* The annotated_snippet dependency, used to display errors, always
  counts tabs as 1 character.
* If rustfmt tries to report an error on a line containing tabs,
  the indices are mismatched.
* annotated_snippet will display the wrong range of the source code
  slice; in the extreme case, it can panic with out-of-bounds access.
* The test case added in this commit is expected to currently fail,
  since this commit doesn't include the fix.
---
 src/test/parser.rs         | 19 +++++++++++++++++++
 tests/parser/issue_4968.rs | 12 ++++++++++++
 2 files changed, 31 insertions(+)
 create mode 100644 tests/parser/issue_4968.rs

diff --git a/src/test/parser.rs b/src/test/parser.rs
index d951c8469e6..3e8d3a73295 100644
--- a/src/test/parser.rs
+++ b/src/test/parser.rs
@@ -3,6 +3,7 @@ use std::path::PathBuf;
 
 use super::read_config;
 
+use crate::FormatReportFormatterBuilder;
 use crate::modules::{ModuleResolutionError, ModuleResolutionErrorKind};
 use crate::{ErrorKind, Input, Session};
 
@@ -69,3 +70,21 @@ fn crate_parsing_stashed_diag2() {
     let filename = "tests/parser/stashed-diag2.rs";
     assert_parser_error(filename);
 }
+
+#[test]
+fn indexing_mismatch_with_annotated_snippet() {
+    // See also https://github.com/rust-lang/rustfmt/issues/4968
+    let filename = "tests/parser/issue_4968.rs";
+    let file = PathBuf::from(filename);
+    let config = read_config(&file);
+    let mut session = Session::<io::Stdout>::new(config, None);
+    let report = session.format(Input::File(filename.into())).unwrap();
+    let report = FormatReportFormatterBuilder::new(&report).build();
+    {
+        // Panic can only be triggered if we actually try to write the report
+        // and call into the annotated_snippet dependency.
+        use std::io::Write;
+
+        write!(&mut Vec::new(), "{report}").unwrap();
+    }
+}
diff --git a/tests/parser/issue_4968.rs b/tests/parser/issue_4968.rs
new file mode 100644
index 00000000000..eb0c65756ef
--- /dev/null
+++ b/tests/parser/issue_4968.rs
@@ -0,0 +1,12 @@
+// rustfmt-hard_tabs: true
+// rustfmt-max_width: 40
+// rustfmt-error_on_unformatted: true
+// rustfmt-error_on_line_overflow: true
+
+fn foo(x: u32) {
+	if x > 10 {
+		if x > 20 {
+			println!("0123456789abcdefghijklmnopqrstuvwxyz");
+		}
+	}
+}