Rollup merge of #95343 - dtolnay:literals, r=petrochenkov

Reduce unnecessary escaping in proc_macro::Literal::character/string

I noticed that https://doc.rust-lang.org/proc_macro/struct.Literal.html#method.character is producing unreadable literals that make macro-expanded code unnecessarily hard to read. Since the proc macro server was using `escape_unicode()`, every char is escaped using `\u{…}` regardless of whether there is any need to do so. For example `Literal::character('=')` would previously produce `'\u{3d}'` which unnecessarily obscures the meaning when reading the macro-expanded code.

I've changed Literal::string also in this PR because `str`'s `Debug` impl is also smarter than just calling `escape_debug` on every char. For example `Literal::string("ferris's")` would previously produce `"ferris\'s"` but will now produce `"ferris's"`.

compiler/rustc_expand/src/proc_macro_server.rs

@@ -658,16 +658,16 @@ fn f64(&mut self, n: &str) -> Self::Literal {
         self.lit(token::Float, Symbol::intern(n), Some(sym::f64))
     }
     fn string(&mut self, string: &str) -> Self::Literal {
-        let mut escaped = String::new();
-        for ch in string.chars() {
-            escaped.extend(ch.escape_debug());
-        }
-        self.lit(token::Str, Symbol::intern(&escaped), None)
+        let quoted = format!("{:?}", string);
+        assert!(quoted.starts_with('"') && quoted.ends_with('"'));
+        let symbol = &quoted[1..quoted.len() - 1];
+        self.lit(token::Str, Symbol::intern(symbol), None)
     }
     fn character(&mut self, ch: char) -> Self::Literal {
-        let mut escaped = String::new();
-        escaped.extend(ch.escape_unicode());
-        self.lit(token::Char, Symbol::intern(&escaped), None)
+        let quoted = format!("{:?}", ch);
+        assert!(quoted.starts_with('\'') && quoted.ends_with('\''));
+        let symbol = &quoted[1..quoted.len() - 1];
+        self.lit(token::Char, Symbol::intern(symbol), None)
     }
     fn byte_string(&mut self, bytes: &[u8]) -> Self::Literal {
         let string = bytes

src/test/ui/proc-macro/auxiliary/api/parse.rs

@@ -18,6 +18,17 @@ fn test_display_literal() {
         Literal::f64_unsuffixed(1e100).to_string(),
         "10000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000.0",
     );
+
+    assert_eq!(
+        Literal::string("a \t ❤ ' \" \u{1}").to_string(),
+        "\"a \\t ❤ ' \\\" \\u{1}\"",
+    );
+    assert_eq!(Literal::character('a').to_string(), "'a'");
+    assert_eq!(Literal::character('\t').to_string(), "'\\t'");
+    assert_eq!(Literal::character('❤').to_string(), "'❤'");
+    assert_eq!(Literal::character('\'').to_string(), "'\\''");
+    assert_eq!(Literal::character('"').to_string(), "'\"'");
+    assert_eq!(Literal::character('\u{1}').to_string(), "'\\u{1}'");
 }
 
 fn test_parse_literal() {

src/test/ui/proc-macro/quote-debug.stdout

@@ -22,7 +22,7 @@ fn main() {
                                     crate::Span::recover_proc_macro_span(0)))),
                         crate::TokenStream::from(crate::TokenTree::Ident(crate::Ident::new("hello",
                                     crate::Span::recover_proc_macro_span(1)))),
-                        crate::TokenStream::from(crate::TokenTree::Punct(crate::Punct::new('\u{3d}',
+                        crate::TokenStream::from(crate::TokenTree::Punct(crate::Punct::new('=',
                                     crate::Spacing::Alone))),
                         crate::TokenStream::from(crate::TokenTree::Literal({
                                     let mut iter =
@@ -35,7 +35,7 @@ fn main() {
                                            ::core::panicking::panic("internal error: entered unreachable code")
                                        }
                                 })),
-                        crate::TokenStream::from(crate::TokenTree::Punct(crate::Punct::new('\u{3b}',
+                        crate::TokenStream::from(crate::TokenTree::Punct(crate::Punct::new(';',
                                     crate::Spacing::Alone)))].iter().cloned().collect::<crate::TokenStream>()
 }
 const _: () =