Slightly more correctly formatting multiline attributes

src/attr.rs

@@ -16,6 +16,7 @@ use crate::shape::Shape;
 use crate::source_map::SpanUtils;
 use crate::types::{rewrite_path, PathContext};
 use crate::utils::{count_newlines, mk_sp};
+use std::ops::Add;
 
 mod doc_comment;
 
@@ -317,6 +318,7 @@ impl Rewrite for ast::MetaItem {
 impl Rewrite for ast::Attribute {
     fn rewrite(&self, context: &RewriteContext<'_>, shape: Shape) -> Option<String> {
         let snippet = context.snippet(self.span);
+        dbg!(snippet);
         if self.is_doc_comment() {
             rewrite_doc_comment(snippet, shape.comment(context.config), context.config)
         } else {
@@ -358,7 +360,29 @@ impl Rewrite for ast::Attribute {
                         .map_or_else(|| snippet.to_owned(), |rw| format!("{}[{}]", prefix, rw)),
                 )
             } else {
-                Some(snippet.to_owned())
+                let count = count_newlines(snippet);
+                if count > 0 {
+                    let mut lines = snippet.lines();
+                    let mut res = String::new();
+                    let first: &str = lines.next().unwrap();
+                    //first string without indent
+                    res.push_str(first);
+                    res.push('\n');
+                    let indent_last = shape.indent.to_string(context.config);
+                    let indent_middle = shape.indent.add(4).to_string(context.config);
+                    for _ in 1..count {
+                        let next = lines.next().unwrap().trim();
+                        res.push_str(&indent_middle);
+                        res.push_str(next);
+                        res.push('\n');
+                    }
+                    let last = lines.next().unwrap().trim();
+                    res.push_str(&indent_last);
+                    res.push_str(last);
+                    Some(res)
+                } else {
+                    Some(snippet.to_owned())
+                }
             }
         }
     }

tests/source/issue-5974/test.rs

@@ -0,0 +1,8 @@
+macro_rules! repro {
+() => {
+        #[doc = concat!("let var = ",
+        "false;")]
+        fn f() {}
+};
+}
+

tests/target/issue-5974/test.rs

@@ -0,0 +1,7 @@
+macro_rules! repro {
+    () => {
+        #[doc = concat!("let var = ",
+        "false;")]
+        fn f() {}
+    };
+}