Fix wrong indenting with hard tabs in binop pairs

src/pairs.rs

@@ -7,7 +7,8 @@ use crate::rewrite::{Rewrite, RewriteContext, RewriteErrorExt, RewriteResult};
 use crate::shape::Shape;
 use crate::spanned::Spanned;
 use crate::utils::{
-    first_line_width, is_single_line, last_line_width, trimmed_last_line_width, wrap_str,
+    first_line_width, is_single_line, last_line_width, last_line_width_cfg,
+    trimmed_last_line_width, wrap_str,
 };
 
 /// Sigils that decorate a binop pair.
@@ -132,7 +133,7 @@ fn rewrite_pairs_multiline<T: Rewrite>(
         } else {
             shape.used_width()
         };
-        if last_line_width(&result) + offset <= nested_shape.used_width() {
+        if last_line_width_cfg(context.config, &result) + offset <= nested_shape.used_width() {
             // We must snuggle the next line onto the previous line to avoid an orphan.
             if let Some(line_shape) =
                 shape.offset_left_opt(s.len() + 2 + trimmed_last_line_width(&result))

src/utils.rs

@@ -222,6 +222,14 @@ pub(crate) fn last_line_width(s: &str) -> usize {
     unicode_str_width(s.rsplitn(2, '\n').next().unwrap_or(""))
 }
 
+/// The width of the last line in s.
+#[inline]
+pub(crate) fn last_line_width_cfg(config: &Config, s: &str) -> usize {
+    let last_line = s.rsplitn(2, '\n').next().unwrap_or("");
+    let (prefix_width, prefix_end) = get_prefix_space_width2(&config, last_line);
+    prefix_width + unicode_str_width(&last_line[prefix_end..])
+}
+
 /// The total used width of the last line.
 #[inline]
 pub(crate) fn last_line_used_width(s: &str, offset: usize) -> usize {
@@ -697,6 +705,20 @@ fn get_prefix_space_width(config: &Config, s: &str) -> usize {
     width
 }
 
+fn get_prefix_space_width2(config: &Config, s: &str) -> (usize, usize) {
+    let mut width = 0;
+    let mut prefix_end = 0;
+    for c in s.chars() {
+        match c {
+            ' ' => width += 1,
+            '\t' => width += config.tab_spaces(),
+            _ => return (width, prefix_end),
+        }
+        prefix_end += 1;
+    }
+    (width, prefix_end)
+}
+
 pub(crate) trait NodeIdExt {
     fn root() -> Self;
 }

tests/target/issue_6859_hard_tab_breaks.rs

@@ -0,0 +1,11 @@
+// rustfmt-hard_tabs: true
+
+fn testing() {
+	let _ = some_long_name
+		| if some_other_long_name {
+			foo
+		}
+		| if some_other_name {
+			bar
+		};
+}