fix: prevent newlines around quotes in macro invocations

src/macros.rs

@@ -14,7 +14,7 @@ use std::collections::HashMap;
 use std::panic::{AssertUnwindSafe, catch_unwind};
 
 use rustc_ast::ast;
-use rustc_ast::token::{Delimiter, Token, TokenKind};
+use rustc_ast::token::{Delimiter, LitKind, Token, TokenKind};
 use rustc_ast::tokenstream::{TokenStream, TokenStreamIter, TokenTree};
 use rustc_ast_pretty::pprust;
 use rustc_span::{BytePos, DUMMY_SP, Ident, Pos, Span, Symbol};
@@ -299,6 +299,22 @@ fn rewrite_macro_inner(
 
     match style {
         Delimiter::Parenthesis => {
+            if context.config.style_edition() >= StyleEdition::Edition2027 {
+                // Handle special case where there is one argument,
+                // a string literal containing a newline.
+                if let [MacroArg::Expr(expr)] = arg_vec.as_slice() {
+                    if let ast::ExprKind::Lit(lit) = expr.kind {
+                        if lit.kind == LitKind::Str && lit.symbol.as_str().contains("\n") {
+                            let rw = format!("{}(\"{}\")", macro_name, lit.symbol);
+                            return match position {
+                                MacroPosition::Item => Ok(format!("{};", rw)),
+                                _ => Ok(rw),
+                            };
+                        }
+                    }
+                }
+            }
+
             // Handle special case: `vec!(expr; expr)`
             if vec_with_semi {
                 handle_vec_semi(context, shape, arg_vec, macro_name, style, mac.span())

tests/source/issue_5029.rs

@@ -0,0 +1,33 @@
+// rustfmt-style_edition: 2027
+
+pub const FOO: &str = foo!("
+    foo
+    bar
+");
+
+pub const BAR: &str = foo!(
+    "
+    foo
+    bar
+"
+);
+
+pub const BAZ: &str = foo!("
+    foo bar
+");
+
+fn main() {
+    foo!("
+        foo bar
+    ");
+
+    let bytes1 = hex!("
+        00010203 04050607
+        08090a0b 0c0d0e0f
+    ");
+
+    let bytes2 = hex!(
+        "00010203 04050607" // first half
+        "08090a0b 0c0d0e0f" // second half
+    );
+}

tests/target/issue_5029.rs

@@ -0,0 +1,31 @@
+// rustfmt-style_edition: 2027
+
+pub const FOO: &str = foo!("
+    foo
+    bar
+");
+
+pub const BAR: &str = foo!("
+    foo
+    bar
+");
+
+pub const BAZ: &str = foo!("
+    foo bar
+");
+
+fn main() {
+    foo!("
+        foo bar
+    ");
+
+    let bytes1 = hex!("
+        00010203 04050607
+        08090a0b 0c0d0e0f
+    ");
+
+    let bytes2 = hex!(
+        "00010203 04050607" // first half
+        "08090a0b 0c0d0e0f" // second half
+    );
+}