try to write the parameter on a new line in case the attribute/parameter together are over max_width

src/formatting/comment.rs

@@ -12,7 +12,8 @@ use crate::formatting::{
     string::{rewrite_string, StringFormat},
     utils::{
         count_newlines, first_line_width, format_code_block, last_line_width, tab_to_spaces,
-        trim_end_unless_two_whitespaces, trim_left_preserve_layout, unicode_str_width,
+        trim_end_unless_two_whitespaces, trim_left_preserve_layout, trimmed_last_line_width,
+        unicode_str_width,
     },
 };
 
@@ -177,11 +178,12 @@ pub(crate) fn combine_strs_with_missing_comments(
         String::with_capacity(prev_str.len() + next_str.len() + shape.indent.width() + 128);
     result.push_str(prev_str);
     let mut allow_one_line = !prev_str.contains('\n') && !next_str.contains('\n');
-    let first_sep = if prev_str.is_empty() || next_str.is_empty() {
-        ""
-    } else {
-        " "
-    };
+    let first_sep =
+        if prev_str.is_empty() || next_str.is_empty() || trimmed_last_line_width(prev_str) == 0 {
+            ""
+        } else {
+            " "
+        };
     let mut one_line_width =
         last_line_width(prev_str) + first_line_width(next_str) + first_sep.len();
 

src/formatting/items.rs

@@ -2085,12 +2085,13 @@ impl Rewrite for ast::Param {
                 has_multiple_attr_lines,
             )
         } else if is_named_param(self) {
+            let param_name = &self
+                .pat
+                .rewrite(context, Shape::legacy(shape.width, shape.indent))?;
             let mut result = combine_strs_with_missing_comments(
                 context,
                 &param_attrs_result,
-                &self
-                    .pat
-                    .rewrite(context, Shape::legacy(shape.width, shape.indent))?,
+                param_name,
                 span,
                 shape,
                 !has_multiple_attr_lines,
@@ -2104,10 +2105,30 @@ impl Rewrite for ast::Param {
                 result.push_str(&after_comment);
                 let overhead = last_line_width(&result);
                 let max_width = shape.width.checked_sub(overhead)?;
-                let ty_str = self
+                if let Some(ty_str) = self
                     .ty
-                    .rewrite(context, Shape::legacy(max_width, shape.indent))?;
-                result.push_str(&ty_str);
+                    .rewrite(context, Shape::legacy(max_width, shape.indent))
+                {
+                    result.push_str(&ty_str);
+                } else {
+                    result = combine_strs_with_missing_comments(
+                        context,
+                        &(param_attrs_result + &shape.to_string_with_newline(context.config)),
+                        param_name,
+                        span,
+                        shape,
+                        !has_multiple_attr_lines,
+                    )?;
+                    result.push_str(&before_comment);
+                    result.push_str(colon_spaces(context.config));
+                    result.push_str(&after_comment);
+                    let overhead = last_line_width(&result);
+                    let max_width = shape.width.checked_sub(overhead)?;
+                    let ty_str = self
+                        .ty
+                        .rewrite(context, Shape::legacy(max_width, shape.indent))?;
+                    result.push_str(&ty_str);
+                }
             }
 
             Some(result)

tests/target/issue_4032.rs

@@ -1,9 +1,11 @@
 fn a1(
-    #[aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa] a: u8,
+    #[aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa]
+    a: u8,
 ) {
 }
 fn b1(
-    #[aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa] bb: u8,
+    #[aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa]
+    bb: u8,
 ) {
 }
 fn a2(