test: add regression test for line overflow panic with hard_tabs (6442)

src/test/mod.rs

@@ -263,7 +263,11 @@ fn warning_tests() {
         config.set().error_on_unformatted(true);
 
         let snapshot_name = file.file_stem().unwrap().to_str().unwrap();
-        let (parsing_errors, _, report) = format_file(file, config.clone());
+        let mut config = config.clone();
+        for (key, val) in read_significant_comments(file) {
+            config.override_value(&key, &val);
+        }
+        let (parsing_errors, _, report) = format_file(file, config);
         assert!(!parsing_errors, "{} failed to parse", file.display());
         assert!(
             report.has_warnings(),

tests/warning/snapshots/issue_6442.snap

@@ -0,0 +1,12 @@
+---
+source: src/test/mod.rs
+---
+error[internal]: line formatted, but exceeded maximum width (maximum: 100 (see `max_width` option), found: 125)
+ --> tests/warning/source/issue_6442.rs:4:4:98
+  |
+4 |     // aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa
+  |                                                                                                     ^^^^^^^^^^^^^^^^^^^^^^^^^
+  |
+  = note: set `error_on_unformatted = false` to suppress the warning against comments or string literals
+
+warning: rustfmt has failed to format. See previous 1 errors.

tests/warning/source/issue_6442.rs

@@ -0,0 +1,5 @@
+// rustfmt-hard_tabs: true
+
+fn main() {
+	// aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa
+}