Rollup merge of #94316 - nnethercote:improve-string-literal-unescaping, r=petrochenkov

Improve string literal unescaping

Some easy wins that affect a few popular crates.

r? ```@matklad```

2 files changed, 23 insertions, 17 deletions

diff --git a/compiler/rustc_ast/src/lib.rs b/compiler/rustc_ast/src/lib.rs
index 84fe9ad2672..21183121e15 100644
--- a/compiler/rustc_ast/src/lib.rs
+++ b/compiler/rustc_ast/src/lib.rs
@@ -16,6 +16,7 @@
 #![feature(min_specialization)]
 #![recursion_limit = "256"]
 #![feature(slice_internals)]
+#![feature(stmt_expr_attributes)]
 
 #[macro_use]
 extern crate rustc_macros;
diff --git a/compiler/rustc_ast/src/util/literal.rs b/compiler/rustc_ast/src/util/literal.rs
index 1cc5ddfd8ee..224afbd553f 100644
--- a/compiler/rustc_ast/src/util/literal.rs
+++ b/compiler/rustc_ast/src/util/literal.rs
@@ -56,25 +56,30 @@ impl LitKind {
                 // new symbol because the string in the LitKind is different to the
                 // string in the token.
                 let s = symbol.as_str();
-                let symbol =
-                    if s.contains(&['\\', '\r']) {
-                        let mut buf = String::with_capacity(s.len());
-                        let mut error = Ok(());
-                        unescape_literal(&s, Mode::Str, &mut |_, unescaped_char| {
-                            match unescaped_char {
-                                Ok(c) => buf.push(c),
-                                Err(err) => {
-                                    if err.is_fatal() {
-                                        error = Err(LitError::LexerError);
-                                    }
+                let symbol = if s.contains(&['\\', '\r']) {
+                    let mut buf = String::with_capacity(s.len());
+                    let mut error = Ok(());
+                    // Force-inlining here is aggressive but the closure is
+                    // called on every char in the string, so it can be
+                    // hot in programs with many long strings.
+                    unescape_literal(
+                        &s,
+                        Mode::Str,
+                        &mut #[inline(always)]
+                        |_, unescaped_char| match unescaped_char {
+                            Ok(c) => buf.push(c),
+                            Err(err) => {
+                                if err.is_fatal() {
+                                    error = Err(LitError::LexerError);
                                 }
                             }
-                        });
-                        error?;
-                        Symbol::intern(&buf)
-                    } else {
-                        symbol
-                    };
+                        },
+                    );
+                    error?;
+                    Symbol::intern(&buf)
+                } else {
+                    symbol
+                };
                 LitKind::Str(symbol, ast::StrStyle::Cooked)
             }
             token::StrRaw(n) => {