Don't escape unicode escape braces in print_literal

clippy_lints/src/write.rs

@@ -486,9 +486,9 @@ fn check_literal(cx: &LateContext<'_>, format_args: &FormatArgs, name: &str) {
             && let rustc_ast::ExprKind::Lit(lit) = &arg.expr.kind
             && !arg.expr.span.from_expansion()
             && let Some(value_string) = snippet_opt(cx, arg.expr.span)
-    {
+        {
             let (replacement, replace_raw) = match lit.kind {
-                LitKind::Str | LitKind::StrRaw(_)  => match extract_str_literal(&value_string) {
+                LitKind::Str | LitKind::StrRaw(_) => match extract_str_literal(&value_string) {
                     Some(extracted) => extracted,
                     None => return,
                 },
@@ -538,7 +538,7 @@ fn check_literal(cx: &LateContext<'_>, format_args: &FormatArgs, name: &str) {
                 // `format!("{}", "a")`, `format!("{named}", named = "b")
                 //              ~~~~~                      ~~~~~~~~~~~~~
                 && let Some(removal_span) = format_arg_removal_span(format_args, index) {
-                let replacement = replacement.replace('{', "{{").replace('}', "}}");
+                let replacement = escape_braces(&replacement, !format_string_is_raw && !replace_raw);
                 suggestion.push((*placeholder_span, replacement));
                 suggestion.push((removal_span, String::new()));
             }
@@ -631,3 +631,47 @@ fn conservative_unescape(literal: &str) -> Result<String, UnescapeErr> {
 
     if err { Err(UnescapeErr::Lint) } else { Ok(unescaped) }
 }
+
+/// Replaces `{` with `{{` and `}` with `}}`. If `preserve_unicode_escapes` is `true` the braces in
+/// `\u{xxxx}` are left unmodified
+#[expect(clippy::match_same_arms)]
+fn escape_braces(literal: &str, preserve_unicode_escapes: bool) -> String {
+    #[derive(Clone, Copy)]
+    enum State {
+        Normal,
+        Backslash,
+        UnicodeEscape,
+    }
+
+    let mut escaped = String::with_capacity(literal.len());
+    let mut state = State::Normal;
+
+    for ch in literal.chars() {
+        state = match (ch, state) {
+            // Escape braces outside of unicode escapes by doubling them up
+            ('{' | '}', State::Normal) => {
+                escaped.push(ch);
+                State::Normal
+            },
+            // If `preserve_unicode_escapes` isn't enabled stay in `State::Normal`, otherwise:
+            //
+            // \u{aaaa} \\ \x01
+            // ^        ^  ^
+            ('\\', State::Normal) if preserve_unicode_escapes => State::Backslash,
+            // \u{aaaa}
+            //  ^
+            ('u', State::Backslash) => State::UnicodeEscape,
+            // \xAA \\
+            //  ^    ^
+            (_, State::Backslash) => State::Normal,
+            // \u{aaaa}
+            //        ^
+            ('}', State::UnicodeEscape) => State::Normal,
+            _ => state,
+        };
+
+        escaped.push(ch);
+    }
+
+    escaped
+}

tests/ui/print_literal.fixed

@@ -51,4 +51,18 @@ fn main() {
     // The string literal from `file!()` has a callsite span that isn't marked as coming from an
     // expansion
     println!("file: {}", file!());
+
+    // Braces in unicode escapes should not be escaped
+    println!("{{}} \x00 \u{ab123} \\\u{ab123} {{:?}}");
+    println!("\\\u{1234}");
+    // This does not lint because it would have to suggest unescaping the character
+    println!(r"{}", "\u{ab123}");
+    // These are not unicode escapes
+    println!("\\u{{ab123}} \\u{{{{");
+    println!(r"\u{{ab123}} \u{{{{");
+    println!("\\{{ab123}} \\u{{{{");
+    println!("\\u{{ab123}}");
+    println!("\\\\u{{1234}}");
+
+    println!("mixed: {{hello}} {world}");
 }

tests/ui/print_literal.rs

@@ -51,4 +51,18 @@ fn main() {
     // The string literal from `file!()` has a callsite span that isn't marked as coming from an
     // expansion
     println!("file: {}", file!());
+
+    // Braces in unicode escapes should not be escaped
+    println!("{}", "{} \x00 \u{ab123} \\\u{ab123} {:?}");
+    println!("{}", "\\\u{1234}");
+    // This does not lint because it would have to suggest unescaping the character
+    println!(r"{}", "\u{ab123}");
+    // These are not unicode escapes
+    println!("{}", r"\u{ab123} \u{{");
+    println!(r"{}", r"\u{ab123} \u{{");
+    println!("{}", r"\{ab123} \u{{");
+    println!("{}", "\\u{ab123}");
+    println!("{}", "\\\\u{1234}");
+
+    println!("mixed: {} {world}", "{hello}");
 }

tests/ui/print_literal.stderr

@@ -96,5 +96,101 @@ LL -     println!("{bar} {foo}", foo = "hello", bar = "world");
 LL +     println!("world hello");
    |
 
-error: aborting due to 8 previous errors
+error: literal with an empty format string
+  --> $DIR/print_literal.rs:56:20
+   |
+LL |     println!("{}", "{} \x00 \u{ab123} \\\u{ab123} {:?}");
+   |                    ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+   |
+help: try
+   |
+LL -     println!("{}", "{} \x00 \u{ab123} \\\u{ab123} {:?}");
+LL +     println!("{{}} \x00 \u{ab123} \\\u{ab123} {{:?}}");
+   |
+
+error: literal with an empty format string
+  --> $DIR/print_literal.rs:57:20
+   |
+LL |     println!("{}", "\\\u{1234}");
+   |                    ^^^^^^^^^^^^
+   |
+help: try
+   |
+LL -     println!("{}", "\\\u{1234}");
+LL +     println!("\\\u{1234}");
+   |
+
+error: literal with an empty format string
+  --> $DIR/print_literal.rs:61:20
+   |
+LL |     println!("{}", r"\u{ab123} \u{{");
+   |                    ^^^^^^^^^^^^^^^^^
+   |
+help: try
+   |
+LL -     println!("{}", r"\u{ab123} \u{{");
+LL +     println!("\\u{{ab123}} \\u{{{{");
+   |
+
+error: literal with an empty format string
+  --> $DIR/print_literal.rs:62:21
+   |
+LL |     println!(r"{}", r"\u{ab123} \u{{");
+   |                     ^^^^^^^^^^^^^^^^^
+   |
+help: try
+   |
+LL -     println!(r"{}", r"\u{ab123} \u{{");
+LL +     println!(r"\u{{ab123}} \u{{{{");
+   |
+
+error: literal with an empty format string
+  --> $DIR/print_literal.rs:63:20
+   |
+LL |     println!("{}", r"\{ab123} \u{{");
+   |                    ^^^^^^^^^^^^^^^^
+   |
+help: try
+   |
+LL -     println!("{}", r"\{ab123} \u{{");
+LL +     println!("\\{{ab123}} \\u{{{{");
+   |
+
+error: literal with an empty format string
+  --> $DIR/print_literal.rs:64:20
+   |
+LL |     println!("{}", "\\u{ab123}");
+   |                    ^^^^^^^^^^^^
+   |
+help: try
+   |
+LL -     println!("{}", "\\u{ab123}");
+LL +     println!("\\u{{ab123}}");
+   |
+
+error: literal with an empty format string
+  --> $DIR/print_literal.rs:65:20
+   |
+LL |     println!("{}", "\\\\u{1234}");
+   |                    ^^^^^^^^^^^^^
+   |
+help: try
+   |
+LL -     println!("{}", "\\\\u{1234}");
+LL +     println!("\\\\u{{1234}}");
+   |
+
+error: literal with an empty format string
+  --> $DIR/print_literal.rs:67:35
+   |
+LL |     println!("mixed: {} {world}", "{hello}");
+   |                                   ^^^^^^^^^
+   |
+help: try
+   |
+LL -     println!("mixed: {} {world}", "{hello}");
+LL +     println!("mixed: {{hello}} {world}");
+   |
+
+error: aborting due to 16 previous errors