Improve pretty-printing of braces.

Most notably, the `FIXME` for suboptimal printing of `use` groups in
`tests/ui/macros/stringify.rs` is fixed. And all other test output
changes result in pretty printed output being closer to the original
formatting in the source code.

compiler/rustc_ast_pretty/src/pprust/state.rs

@@ -634,6 +634,7 @@ pub trait PrintState<'a>: std::ops::Deref<Target = pp::Printer> + std::ops::Dere
                 false,
                 None,
                 *delim,
+                None,
                 tokens,
                 true,
                 span,
@@ -679,6 +680,7 @@ pub trait PrintState<'a>: std::ops::Deref<Target = pp::Printer> + std::ops::Dere
                     false,
                     None,
                     *delim,
+                    Some(spacing.open),
                     tts,
                     convert_dollar_crate,
                     dspan.entire(),
@@ -735,6 +737,7 @@ pub trait PrintState<'a>: std::ops::Deref<Target = pp::Printer> + std::ops::Dere
         has_bang: bool,
         ident: Option<Ident>,
         delim: Delimiter,
+        open_spacing: Option<Spacing>,
         tts: &TokenStream,
         convert_dollar_crate: bool,
         span: Span,
@@ -758,16 +761,26 @@ pub trait PrintState<'a>: std::ops::Deref<Target = pp::Printer> + std::ops::Dere
                     self.nbsp();
                 }
                 self.word("{");
-                if !tts.is_empty() {
+
+                // Respect `Alone`, if provided, and print a space. Unless the list is empty.
+                let open_space = (open_spacing == None || open_spacing == Some(Spacing::Alone))
+                    && !tts.is_empty();
+                if open_space {
                     self.space();
                 }
                 let ib = self.ibox(0);
                 self.print_tts(tts, convert_dollar_crate);
                 self.end(ib);
-                let empty = tts.is_empty();
-                self.bclose(span, empty, cb.unwrap());
+
+                // Use `open_space` for the spacing *before* the closing delim.
+                // Because spacing on delimiters is lost when going through
+                // proc macros, and otherwise we can end up with ugly cases
+                // like `{ x}`. Symmetry is better.
+                self.bclose(span, !open_space, cb.unwrap());
             }
             delim => {
+                // `open_spacing` is ignored. We never print spaces after
+                // non-brace opening delims or before non-brace closing delims.
                 let token_str = self.token_kind_to_string(&delim.as_open_token_kind());
                 self.word(token_str);
                 let ib = self.ibox(0);
@@ -797,6 +810,7 @@ pub trait PrintState<'a>: std::ops::Deref<Target = pp::Printer> + std::ops::Dere
             has_bang,
             Some(*ident),
             macro_def.body.delim,
+            None,
             &macro_def.body.tokens,
             true,
             sp,
@@ -844,9 +858,9 @@ pub trait PrintState<'a>: std::ops::Deref<Target = pp::Printer> + std::ops::Dere
         self.end(ib);
     }
 
-    fn bclose_maybe_open(&mut self, span: rustc_span::Span, empty: bool, cb: Option<BoxMarker>) {
+    fn bclose_maybe_open(&mut self, span: rustc_span::Span, no_space: bool, cb: Option<BoxMarker>) {
         let has_comment = self.maybe_print_comment(span.hi());
-        if !empty || has_comment {
+        if !no_space || has_comment {
             self.break_offset_if_not_bol(1, -INDENT_UNIT);
         }
         self.word("}");
@@ -855,9 +869,9 @@ pub trait PrintState<'a>: std::ops::Deref<Target = pp::Printer> + std::ops::Dere
         }
     }
 
-    fn bclose(&mut self, span: rustc_span::Span, empty: bool, cb: BoxMarker) {
+    fn bclose(&mut self, span: rustc_span::Span, no_space: bool, cb: BoxMarker) {
         let cb = Some(cb);
-        self.bclose_maybe_open(span, empty, cb)
+        self.bclose_maybe_open(span, no_space, cb)
     }
 
     fn break_offset_if_not_bol(&mut self, n: usize, off: isize) {
@@ -1423,8 +1437,8 @@ impl<'a> State<'a> {
             }
         }
 
-        let empty = !has_attrs && blk.stmts.is_empty();
-        self.bclose_maybe_open(blk.span, empty, cb);
+        let no_space = !has_attrs && blk.stmts.is_empty();
+        self.bclose_maybe_open(blk.span, no_space, cb);
         self.ann.post(self, AnnNode::Block(blk))
     }
 
@@ -1471,6 +1485,7 @@ impl<'a> State<'a> {
             true,
             None,
             m.args.delim,
+            None,
             &m.args.tokens,
             true,
             m.span(),

compiler/rustc_builtin_macros/src/autodiff.rs

@@ -323,9 +323,9 @@ mod llvm_enzyme {
             Spacing::Joint,
         )];
         let never_arg = ast::DelimArgs {
-            dspan: ast::tokenstream::DelimSpan::from_single(span),
+            dspan: DelimSpan::from_single(span),
             delim: ast::token::Delimiter::Parenthesis,
-            tokens: ast::tokenstream::TokenStream::from_iter(ts2),
+            tokens: TokenStream::from_iter(ts2),
         };
         let inline_item = ast::AttrItem {
             unsafety: ast::Safety::Default,

compiler/rustc_expand/src/build.rs

@@ -1,8 +1,10 @@
 use rustc_ast::ptr::P;
+use rustc_ast::token::Delimiter;
+use rustc_ast::tokenstream::TokenStream;
 use rustc_ast::util::literal;
 use rustc_ast::{
     self as ast, AnonConst, AttrVec, BlockCheckMode, Expr, LocalKind, MatchKind, PatKind, UnOp,
-    attr, token,
+    attr, token, tokenstream,
 };
 use rustc_span::source_map::Spanned;
 use rustc_span::{DUMMY_SP, Ident, Span, Symbol, kw, sym};
@@ -55,13 +57,13 @@ impl<'a> ExtCtxt<'a> {
         &self,
         span: Span,
         path: ast::Path,
-        delim: ast::token::Delimiter,
-        tokens: ast::tokenstream::TokenStream,
+        delim: Delimiter,
+        tokens: TokenStream,
     ) -> P<ast::MacCall> {
         P(ast::MacCall {
             path,
             args: P(ast::DelimArgs {
-                dspan: ast::tokenstream::DelimSpan { open: span, close: span },
+                dspan: tokenstream::DelimSpan { open: span, close: span },
                 delim,
                 tokens,
             }),
@@ -480,8 +482,8 @@ impl<'a> ExtCtxt<'a> {
                     span,
                     [sym::std, sym::unreachable].map(|s| Ident::new(s, span)).to_vec(),
                 ),
-                ast::token::Delimiter::Parenthesis,
-                ast::tokenstream::TokenStream::default(),
+                Delimiter::Parenthesis,
+                TokenStream::default(),
             ),
         )
     }

compiler/rustc_hir_pretty/src/lib.rs

@@ -146,6 +146,7 @@ impl<'a> State<'a> {
                     false,
                     None,
                     *delim,
+                    None,
                     &tokens,
                     true,
                     span,

tests/ui/macros/stringify.rs

@@ -356,7 +356,7 @@ fn test_item() {
     c1!(item, [ pub extern crate self as std; ], "pub extern crate self as std;");
 
     // ItemKind::Use
-    c1!(item, [ pub use crate::{a, b::c}; ], "pub use crate::{ a, b::c };"); // FIXME
+    c1!(item, [ pub use crate::{a, b::c}; ], "pub use crate::{a, b::c};");
     c1!(item, [ pub use crate::{ e, ff }; ], "pub use crate::{ e, ff };");
     c1!(item, [ pub use A::*; ], "pub use A::*;");
 
@@ -491,7 +491,7 @@ fn test_item() {
     c1!(item, [ mac! {} ], "mac! {}");
     c1!(item, [ mac!(...); ], "mac!(...);");
     c1!(item, [ mac![...]; ], "mac![...];");
-    c1!(item, [ mac! {...} ], "mac! { ... }");
+    c1!(item, [ mac! {...} ], "mac! {...}");
 
     // ItemKind::MacroDef
     c1!(item,

tests/ui/macros/trace_faulty_macros.stderr

@@ -87,9 +87,9 @@ LL |     let a = pat_macro!();
    |             ^^^^^^^^^^^^
    |
    = note: expanding `pat_macro! {  }`
-   = note: to `pat_macro! (A { a : a, b : 0, c : _, .. });`
-   = note: expanding `pat_macro! { A { a : a, b : 0, c : _, .. } }`
-   = note: to `A { a : a, b : 0, c : _, .. }`
+   = note: to `pat_macro! (A {a : a, b : 0, c : _, ..});`
+   = note: expanding `pat_macro! { A {a : a, b : 0, c : _, ..} }`
+   = note: to `A {a : a, b : 0, c : _, ..}`
 
 note: trace_macro
   --> $DIR/trace_faulty_macros.rs:53:5

tests/ui/proc-macro/attr-complex-fn.stdout

@@ -77,7 +77,7 @@ PRINT-ATTR INPUT (DEBUG): TokenStream [
         span: $DIR/attr-complex-fn.rs:19:42: 19:44 (#0),
     },
 ]
-PRINT-ATTR INPUT (DISPLAY): impl<T> MyTrait<T> for MyStruct<{ true }> { #![rustc_dummy] }
+PRINT-ATTR INPUT (DISPLAY): impl<T> MyTrait<T> for MyStruct<{true}> { #![rustc_dummy] }
 PRINT-ATTR RE-COLLECTED (DISPLAY): impl < T > MyTrait < T > for MyStruct < { true } > { #![rustc_dummy] }
 PRINT-ATTR DEEP-RE-COLLECTED (DISPLAY): impl < T > MyTrait < T > for MyStruct < { true } > { #! [rustc_dummy] }
 PRINT-ATTR INPUT (DEBUG): TokenStream [

tests/ui/proc-macro/weird-braces.stdout

@@ -5,7 +5,7 @@ PRINT-ATTR_ARGS INPUT (DEBUG): TokenStream [
         span: $DIR/weird-braces.rs:16:25: 16:36 (#0),
     },
 ]
-PRINT-ATTR INPUT (DISPLAY): #[print_target_and_args(second_outer)] impl Bar<{ 1 > 0 }> for Foo<{ true }>
+PRINT-ATTR INPUT (DISPLAY): #[print_target_and_args(second_outer)] impl Bar<{1 > 0}> for Foo<{true}>
 {
     #![print_target_and_args(first_inner)]
     #![print_target_and_args(second_inner)]
@@ -191,7 +191,7 @@ PRINT-ATTR_ARGS INPUT (DEBUG): TokenStream [
         span: $DIR/weird-braces.rs:17:25: 17:37 (#0),
     },
 ]
-PRINT-ATTR INPUT (DISPLAY): impl Bar<{ 1 > 0 }> for Foo<{ true }>
+PRINT-ATTR INPUT (DISPLAY): impl Bar<{1 > 0}> for Foo<{true}>
 {
     #![print_target_and_args(first_inner)]
     #![print_target_and_args(second_inner)]
@@ -350,8 +350,7 @@ PRINT-ATTR_ARGS INPUT (DEBUG): TokenStream [
         span: $DIR/weird-braces.rs:19:30: 19:41 (#0),
     },
 ]
-PRINT-ATTR INPUT (DISPLAY): impl Bar<{ 1 > 0 }> for Foo<{ true }>
-{ #![print_target_and_args(second_inner)] }
+PRINT-ATTR INPUT (DISPLAY): impl Bar<{1 > 0}> for Foo<{true}> { #![print_target_and_args(second_inner)] }
 PRINT-ATTR RE-COLLECTED (DISPLAY): impl Bar < { 1 > 0 } > for Foo < { true } >
 { #![print_target_and_args(second_inner)] }
 PRINT-ATTR DEEP-RE-COLLECTED (DISPLAY): impl Bar < { 1 > 0 } > for Foo < { true } >
@@ -470,7 +469,7 @@ PRINT-ATTR_ARGS INPUT (DEBUG): TokenStream [
         span: $DIR/weird-braces.rs:20:30: 20:42 (#0),
     },
 ]
-PRINT-ATTR INPUT (DISPLAY): impl Bar<{ 1 > 0 }> for Foo<{ true }> {}
+PRINT-ATTR INPUT (DISPLAY): impl Bar<{1 > 0}> for Foo<{true}> {}
 PRINT-ATTR RE-COLLECTED (DISPLAY): impl Bar < { 1 > 0 } > for Foo < { true } > {}
 PRINT-ATTR INPUT (DEBUG): TokenStream [
     Ident {

tests/ui/unpretty/expanded-exhaustive.stdout

@@ -505,7 +505,7 @@ mod items {
     mod item_mac_call { }
     /// ItemKind::MacroDef
     mod item_macro_def {
-        macro_rules! mac { () => { ... }; }
+        macro_rules! mac { () => {...}; }
         pub macro stringify { () => {} }
     }
     /// ItemKind::Delegation