rustc_ast_pretty/pprust/state/
expr.rs

1use std::fmt::Write;
2
3use ast::{ForLoopKind, MatchKind};
4use itertools::{Itertools, Position};
5use rustc_ast::ptr::P;
6use rustc_ast::util::classify;
7use rustc_ast::util::literal::escape_byte_str_symbol;
8use rustc_ast::util::parser::{self, ExprPrecedence, Fixity};
9use rustc_ast::{
10    self as ast, BlockCheckMode, FormatAlignment, FormatArgPosition, FormatArgsPiece, FormatCount,
11    FormatDebugHex, FormatSign, FormatTrait, YieldKind, token,
12};
13
14use crate::pp::Breaks::Inconsistent;
15use crate::pprust::state::fixup::FixupContext;
16use crate::pprust::state::{AnnNode, INDENT_UNIT, PrintState, State};
17
18impl<'a> State<'a> {
19    fn print_else(&mut self, els: Option<&ast::Expr>) {
20        if let Some(_else) = els {
21            match &_else.kind {
22                // Another `else if` block.
23                ast::ExprKind::If(i, then, e) => {
24                    let cb = self.cbox(0);
25                    let ib = self.ibox(0);
26                    self.word(" else if ");
27                    self.print_expr_as_cond(i);
28                    self.space();
29                    self.print_block(then, cb, ib);
30                    self.print_else(e.as_deref())
31                }
32                // Final `else` block.
33                ast::ExprKind::Block(b, None) => {
34                    let cb = self.cbox(0);
35                    let ib = self.ibox(0);
36                    self.word(" else ");
37                    self.print_block(b, cb, ib)
38                }
39                // Constraints would be great here!
40                _ => {
41                    panic!("print_if saw if with weird alternative");
42                }
43            }
44        }
45    }
46
47    fn print_if(&mut self, test: &ast::Expr, blk: &ast::Block, elseopt: Option<&ast::Expr>) {
48        let cb = self.cbox(0);
49        let ib = self.ibox(0);
50        self.word_nbsp("if");
51        self.print_expr_as_cond(test);
52        self.space();
53        self.print_block(blk, cb, ib);
54        self.print_else(elseopt)
55    }
56
57    fn print_call_post(&mut self, args: &[P<ast::Expr>]) {
58        self.popen();
59        self.commasep_exprs(Inconsistent, args);
60        self.pclose()
61    }
62
63    /// Prints an expr using syntax that's acceptable in a condition position, such as the `cond` in
64    /// `if cond { ... }`.
65    fn print_expr_as_cond(&mut self, expr: &ast::Expr) {
66        self.print_expr_cond_paren(expr, Self::cond_needs_par(expr), FixupContext::new_cond())
67    }
68
69    /// Does `expr` need parentheses when printed in a condition position?
70    ///
71    /// These cases need parens due to the parse error observed in #26461: `if return {}`
72    /// parses as the erroneous construct `if (return {})`, not `if (return) {}`.
73    fn cond_needs_par(expr: &ast::Expr) -> bool {
74        match expr.kind {
75            ast::ExprKind::Break(..)
76            | ast::ExprKind::Closure(..)
77            | ast::ExprKind::Ret(..)
78            | ast::ExprKind::Yeet(..) => true,
79            _ => parser::contains_exterior_struct_lit(expr),
80        }
81    }
82
83    /// Prints `expr` or `(expr)` when `needs_par` holds.
84    pub(super) fn print_expr_cond_paren(
85        &mut self,
86        expr: &ast::Expr,
87        needs_par: bool,
88        mut fixup: FixupContext,
89    ) {
90        if needs_par {
91            self.popen();
92
93            // If we are surrounding the whole cond in parentheses, such as:
94            //
95            //     if (return Struct {}) {}
96            //
97            // then there is no need for parenthesizing the individual struct
98            // expressions within. On the other hand if the whole cond is not
99            // parenthesized, then print_expr must parenthesize exterior struct
100            // literals.
101            //
102            //     if x == (Struct {}) {}
103            //
104            fixup = FixupContext::default();
105        }
106
107        self.print_expr(expr, fixup);
108
109        if needs_par {
110            self.pclose();
111        }
112    }
113
114    fn print_expr_vec(&mut self, exprs: &[P<ast::Expr>]) {
115        let ib = self.ibox(INDENT_UNIT);
116        self.word("[");
117        self.commasep_exprs(Inconsistent, exprs);
118        self.word("]");
119        self.end(ib);
120    }
121
122    pub(super) fn print_expr_anon_const(
123        &mut self,
124        expr: &ast::AnonConst,
125        attrs: &[ast::Attribute],
126    ) {
127        let ib = self.ibox(INDENT_UNIT);
128        self.word("const");
129        self.nbsp();
130        if let ast::ExprKind::Block(block, None) = &expr.value.kind {
131            let cb = self.cbox(0);
132            let ib = self.ibox(0);
133            self.print_block_with_attrs(block, attrs, cb, ib);
134        } else {
135            self.print_expr(&expr.value, FixupContext::default());
136        }
137        self.end(ib);
138    }
139
140    fn print_expr_repeat(&mut self, element: &ast::Expr, count: &ast::AnonConst) {
141        let ib = self.ibox(INDENT_UNIT);
142        self.word("[");
143        self.print_expr(element, FixupContext::default());
144        self.word_space(";");
145        self.print_expr(&count.value, FixupContext::default());
146        self.word("]");
147        self.end(ib);
148    }
149
150    fn print_expr_struct(
151        &mut self,
152        qself: &Option<P<ast::QSelf>>,
153        path: &ast::Path,
154        fields: &[ast::ExprField],
155        rest: &ast::StructRest,
156    ) {
157        if let Some(qself) = qself {
158            self.print_qpath(path, qself, true);
159        } else {
160            self.print_path(path, true, 0);
161        }
162        self.nbsp();
163        self.word("{");
164        let has_rest = match rest {
165            ast::StructRest::Base(_) | ast::StructRest::Rest(_) => true,
166            ast::StructRest::None => false,
167        };
168        if fields.is_empty() && !has_rest {
169            self.word("}");
170            return;
171        }
172        let cb = self.cbox(0);
173        for (pos, field) in fields.iter().with_position() {
174            let is_first = matches!(pos, Position::First | Position::Only);
175            let is_last = matches!(pos, Position::Last | Position::Only);
176            self.maybe_print_comment(field.span.hi());
177            self.print_outer_attributes(&field.attrs);
178            if is_first {
179                self.space_if_not_bol();
180            }
181            if !field.is_shorthand {
182                self.print_ident(field.ident);
183                self.word_nbsp(":");
184            }
185            self.print_expr(&field.expr, FixupContext::default());
186            if !is_last || has_rest {
187                self.word_space(",");
188            } else {
189                self.trailing_comma_or_space();
190            }
191        }
192        if has_rest {
193            if fields.is_empty() {
194                self.space();
195            }
196            self.word("..");
197            if let ast::StructRest::Base(expr) = rest {
198                self.print_expr(expr, FixupContext::default());
199            }
200            self.space();
201        }
202        self.offset(-INDENT_UNIT);
203        self.end(cb);
204        self.word("}");
205    }
206
207    fn print_expr_tup(&mut self, exprs: &[P<ast::Expr>]) {
208        self.popen();
209        self.commasep_exprs(Inconsistent, exprs);
210        if exprs.len() == 1 {
211            self.word(",");
212        }
213        self.pclose()
214    }
215
216    fn print_expr_call(&mut self, func: &ast::Expr, args: &[P<ast::Expr>], fixup: FixupContext) {
217        let needs_paren = match func.kind {
218            // In order to call a named field, needs parens: `(self.fun)()`
219            // But not for an unnamed field: `self.0()`
220            ast::ExprKind::Field(_, name) => !name.is_numeric(),
221            _ => func.precedence() < ExprPrecedence::Unambiguous,
222        };
223
224        // Independent of parenthesization related to precedence, we must
225        // parenthesize `func` if this is a statement context in which without
226        // parentheses, a statement boundary would occur inside `func` or
227        // immediately after `func`.
228        //
229        // Suppose `func` represents `match () { _ => f }`. We must produce:
230        //
231        //     (match () { _ => f })();
232        //
233        // instead of:
234        //
235        //     match () { _ => f } ();
236        //
237        // because the latter is valid syntax but with the incorrect meaning.
238        // It's a match-expression followed by tuple-expression, not a function
239        // call.
240        self.print_expr_cond_paren(func, needs_paren, fixup.leftmost_subexpression());
241
242        self.print_call_post(args)
243    }
244
245    fn print_expr_method_call(
246        &mut self,
247        segment: &ast::PathSegment,
248        receiver: &ast::Expr,
249        base_args: &[P<ast::Expr>],
250        fixup: FixupContext,
251    ) {
252        // The fixup here is different than in `print_expr_call` because
253        // statement boundaries never occur in front of a `.` (or `?`) token.
254        //
255        // Needs parens:
256        //
257        //     (loop { break x; })();
258        //
259        // Does not need parens:
260        //
261        //     loop { break x; }.method();
262        //
263        self.print_expr_cond_paren(
264            receiver,
265            receiver.precedence() < ExprPrecedence::Unambiguous,
266            fixup.leftmost_subexpression_with_dot(),
267        );
268
269        self.word(".");
270        self.print_ident(segment.ident);
271        if let Some(args) = &segment.args {
272            self.print_generic_args(args, true);
273        }
274        self.print_call_post(base_args)
275    }
276
277    fn print_expr_binary(
278        &mut self,
279        op: ast::BinOpKind,
280        lhs: &ast::Expr,
281        rhs: &ast::Expr,
282        fixup: FixupContext,
283    ) {
284        let binop_prec = op.precedence();
285        let left_prec = lhs.precedence();
286        let right_prec = rhs.precedence();
287
288        let (mut left_needs_paren, right_needs_paren) = match op.fixity() {
289            Fixity::Left => (left_prec < binop_prec, right_prec <= binop_prec),
290            Fixity::Right => (left_prec <= binop_prec, right_prec < binop_prec),
291            Fixity::None => (left_prec <= binop_prec, right_prec <= binop_prec),
292        };
293
294        match (&lhs.kind, op) {
295            // These cases need parens: `x as i32 < y` has the parser thinking that `i32 < y` is
296            // the beginning of a path type. It starts trying to parse `x as (i32 < y ...` instead
297            // of `(x as i32) < ...`. We need to convince it _not_ to do that.
298            (&ast::ExprKind::Cast { .. }, ast::BinOpKind::Lt | ast::BinOpKind::Shl) => {
299                left_needs_paren = true;
300            }
301            // We are given `(let _ = a) OP b`.
302            //
303            // - When `OP <= LAnd` we should print `let _ = a OP b` to avoid redundant parens
304            //   as the parser will interpret this as `(let _ = a) OP b`.
305            //
306            // - Otherwise, e.g. when we have `(let a = b) < c` in AST,
307            //   parens are required since the parser would interpret `let a = b < c` as
308            //   `let a = (b < c)`. To achieve this, we force parens.
309            (&ast::ExprKind::Let { .. }, _) if !parser::needs_par_as_let_scrutinee(binop_prec) => {
310                left_needs_paren = true;
311            }
312            _ => {}
313        }
314
315        self.print_expr_cond_paren(lhs, left_needs_paren, fixup.leftmost_subexpression());
316        self.space();
317        self.word_space(op.as_str());
318        self.print_expr_cond_paren(rhs, right_needs_paren, fixup.subsequent_subexpression());
319    }
320
321    fn print_expr_unary(&mut self, op: ast::UnOp, expr: &ast::Expr, fixup: FixupContext) {
322        self.word(op.as_str());
323        self.print_expr_cond_paren(
324            expr,
325            expr.precedence() < ExprPrecedence::Prefix,
326            fixup.subsequent_subexpression(),
327        );
328    }
329
330    fn print_expr_addr_of(
331        &mut self,
332        kind: ast::BorrowKind,
333        mutability: ast::Mutability,
334        expr: &ast::Expr,
335        fixup: FixupContext,
336    ) {
337        self.word("&");
338        match kind {
339            ast::BorrowKind::Ref => self.print_mutability(mutability, false),
340            ast::BorrowKind::Raw => {
341                self.word_nbsp("raw");
342                self.print_mutability(mutability, true);
343            }
344        }
345        self.print_expr_cond_paren(
346            expr,
347            expr.precedence() < ExprPrecedence::Prefix,
348            fixup.subsequent_subexpression(),
349        );
350    }
351
352    pub(super) fn print_expr(&mut self, expr: &ast::Expr, fixup: FixupContext) {
353        self.print_expr_outer_attr_style(expr, true, fixup)
354    }
355
356    pub(super) fn print_expr_outer_attr_style(
357        &mut self,
358        expr: &ast::Expr,
359        is_inline: bool,
360        mut fixup: FixupContext,
361    ) {
362        self.maybe_print_comment(expr.span.lo());
363
364        let attrs = &expr.attrs;
365        if is_inline {
366            self.print_outer_attributes_inline(attrs);
367        } else {
368            self.print_outer_attributes(attrs);
369        }
370
371        let ib = self.ibox(INDENT_UNIT);
372
373        // The Match subexpression in `match x {} - 1` must be parenthesized if
374        // it is the leftmost subexpression in a statement:
375        //
376        //     (match x {}) - 1;
377        //
378        // But not otherwise:
379        //
380        //     let _ = match x {} - 1;
381        //
382        // Same applies to a small set of other expression kinds which eagerly
383        // terminate a statement which opens with them.
384        let needs_par = fixup.would_cause_statement_boundary(expr);
385        if needs_par {
386            self.popen();
387            fixup = FixupContext::default();
388        }
389
390        self.ann.pre(self, AnnNode::Expr(expr));
391
392        match &expr.kind {
393            ast::ExprKind::Array(exprs) => {
394                self.print_expr_vec(exprs);
395            }
396            ast::ExprKind::ConstBlock(anon_const) => {
397                self.print_expr_anon_const(anon_const, attrs);
398            }
399            ast::ExprKind::Repeat(element, count) => {
400                self.print_expr_repeat(element, count);
401            }
402            ast::ExprKind::Struct(se) => {
403                self.print_expr_struct(&se.qself, &se.path, &se.fields, &se.rest);
404            }
405            ast::ExprKind::Tup(exprs) => {
406                self.print_expr_tup(exprs);
407            }
408            ast::ExprKind::Call(func, args) => {
409                self.print_expr_call(func, args, fixup);
410            }
411            ast::ExprKind::MethodCall(box ast::MethodCall { seg, receiver, args, .. }) => {
412                self.print_expr_method_call(seg, receiver, args, fixup);
413            }
414            ast::ExprKind::Binary(op, lhs, rhs) => {
415                self.print_expr_binary(op.node, lhs, rhs, fixup);
416            }
417            ast::ExprKind::Unary(op, expr) => {
418                self.print_expr_unary(*op, expr, fixup);
419            }
420            ast::ExprKind::AddrOf(k, m, expr) => {
421                self.print_expr_addr_of(*k, *m, expr, fixup);
422            }
423            ast::ExprKind::Lit(token_lit) => {
424                self.print_token_literal(*token_lit, expr.span);
425            }
426            ast::ExprKind::IncludedBytes(bytes) => {
427                let lit = token::Lit::new(token::ByteStr, escape_byte_str_symbol(bytes), None);
428                self.print_token_literal(lit, expr.span)
429            }
430            ast::ExprKind::Cast(expr, ty) => {
431                self.print_expr_cond_paren(
432                    expr,
433                    expr.precedence() < ExprPrecedence::Cast,
434                    fixup.leftmost_subexpression(),
435                );
436                self.space();
437                self.word_space("as");
438                self.print_type(ty);
439            }
440            ast::ExprKind::Type(expr, ty) => {
441                self.word("builtin # type_ascribe");
442                self.popen();
443                let ib = self.ibox(0);
444                self.print_expr(expr, FixupContext::default());
445
446                self.word(",");
447                self.space_if_not_bol();
448                self.print_type(ty);
449
450                self.end(ib);
451                self.pclose();
452            }
453            ast::ExprKind::Let(pat, scrutinee, _, _) => {
454                self.print_let(pat, scrutinee, fixup);
455            }
456            ast::ExprKind::If(test, blk, elseopt) => self.print_if(test, blk, elseopt.as_deref()),
457            ast::ExprKind::While(test, blk, opt_label) => {
458                if let Some(label) = opt_label {
459                    self.print_ident(label.ident);
460                    self.word_space(":");
461                }
462                let cb = self.cbox(0);
463                let ib = self.ibox(0);
464                self.word_nbsp("while");
465                self.print_expr_as_cond(test);
466                self.space();
467                self.print_block_with_attrs(blk, attrs, cb, ib);
468            }
469            ast::ExprKind::ForLoop { pat, iter, body, label, kind } => {
470                if let Some(label) = label {
471                    self.print_ident(label.ident);
472                    self.word_space(":");
473                }
474                let cb = self.cbox(0);
475                let ib = self.ibox(0);
476                self.word_nbsp("for");
477                if kind == &ForLoopKind::ForAwait {
478                    self.word_nbsp("await");
479                }
480                self.print_pat(pat);
481                self.space();
482                self.word_space("in");
483                self.print_expr_as_cond(iter);
484                self.space();
485                self.print_block_with_attrs(body, attrs, cb, ib);
486            }
487            ast::ExprKind::Loop(blk, opt_label, _) => {
488                let cb = self.cbox(0);
489                let ib = self.ibox(0);
490                if let Some(label) = opt_label {
491                    self.print_ident(label.ident);
492                    self.word_space(":");
493                }
494                self.word_nbsp("loop");
495                self.print_block_with_attrs(blk, attrs, cb, ib);
496            }
497            ast::ExprKind::Match(expr, arms, match_kind) => {
498                let cb = self.cbox(0);
499                let ib = self.ibox(0);
500
501                match match_kind {
502                    MatchKind::Prefix => {
503                        self.word_nbsp("match");
504                        self.print_expr_as_cond(expr);
505                        self.space();
506                    }
507                    MatchKind::Postfix => {
508                        self.print_expr_cond_paren(
509                            expr,
510                            expr.precedence() < ExprPrecedence::Unambiguous,
511                            fixup.leftmost_subexpression_with_dot(),
512                        );
513                        self.word_nbsp(".match");
514                    }
515                }
516
517                self.bopen(ib);
518                self.print_inner_attributes_no_trailing_hardbreak(attrs);
519                for arm in arms {
520                    self.print_arm(arm);
521                }
522                let empty = attrs.is_empty() && arms.is_empty();
523                self.bclose(expr.span, empty, cb);
524            }
525            ast::ExprKind::Closure(box ast::Closure {
526                binder,
527                capture_clause,
528                constness,
529                coroutine_kind,
530                movability,
531                fn_decl,
532                body,
533                fn_decl_span: _,
534                fn_arg_span: _,
535            }) => {
536                self.print_closure_binder(binder);
537                self.print_constness(*constness);
538                self.print_movability(*movability);
539                coroutine_kind.map(|coroutine_kind| self.print_coroutine_kind(coroutine_kind));
540                self.print_capture_clause(*capture_clause);
541
542                self.print_fn_params_and_ret(fn_decl, true);
543                self.space();
544                self.print_expr(body, FixupContext::default());
545            }
546            ast::ExprKind::Block(blk, opt_label) => {
547                if let Some(label) = opt_label {
548                    self.print_ident(label.ident);
549                    self.word_space(":");
550                }
551                // containing cbox, will be closed by print-block at }
552                let cb = self.cbox(0);
553                // head-box, will be closed by print-block after {
554                let ib = self.ibox(0);
555                self.print_block_with_attrs(blk, attrs, cb, ib);
556            }
557            ast::ExprKind::Gen(capture_clause, blk, kind, _decl_span) => {
558                self.word_nbsp(kind.modifier());
559                self.print_capture_clause(*capture_clause);
560                // cbox/ibox in analogy to the `ExprKind::Block` arm above
561                let cb = self.cbox(0);
562                let ib = self.ibox(0);
563                self.print_block_with_attrs(blk, attrs, cb, ib);
564            }
565            ast::ExprKind::Await(expr, _) => {
566                self.print_expr_cond_paren(
567                    expr,
568                    expr.precedence() < ExprPrecedence::Unambiguous,
569                    fixup.leftmost_subexpression_with_dot(),
570                );
571                self.word(".await");
572            }
573            ast::ExprKind::Use(expr, _) => {
574                self.print_expr_cond_paren(
575                    expr,
576                    expr.precedence() < ExprPrecedence::Unambiguous,
577                    fixup,
578                );
579                self.word(".use");
580            }
581            ast::ExprKind::Assign(lhs, rhs, _) => {
582                self.print_expr_cond_paren(
583                    lhs,
584                    // Ranges are allowed on the right-hand side of assignment,
585                    // but not the left. `(a..b) = c` needs parentheses.
586                    lhs.precedence() <= ExprPrecedence::Range,
587                    fixup.leftmost_subexpression(),
588                );
589                self.space();
590                self.word_space("=");
591                self.print_expr_cond_paren(
592                    rhs,
593                    rhs.precedence() < ExprPrecedence::Assign,
594                    fixup.subsequent_subexpression(),
595                );
596            }
597            ast::ExprKind::AssignOp(op, lhs, rhs) => {
598                self.print_expr_cond_paren(
599                    lhs,
600                    lhs.precedence() <= ExprPrecedence::Range,
601                    fixup.leftmost_subexpression(),
602                );
603                self.space();
604                self.word_space(op.node.as_str());
605                self.print_expr_cond_paren(
606                    rhs,
607                    rhs.precedence() < ExprPrecedence::Assign,
608                    fixup.subsequent_subexpression(),
609                );
610            }
611            ast::ExprKind::Field(expr, ident) => {
612                self.print_expr_cond_paren(
613                    expr,
614                    expr.precedence() < ExprPrecedence::Unambiguous,
615                    fixup.leftmost_subexpression_with_dot(),
616                );
617                self.word(".");
618                self.print_ident(*ident);
619            }
620            ast::ExprKind::Index(expr, index, _) => {
621                self.print_expr_cond_paren(
622                    expr,
623                    expr.precedence() < ExprPrecedence::Unambiguous,
624                    fixup.leftmost_subexpression(),
625                );
626                self.word("[");
627                self.print_expr(index, FixupContext::default());
628                self.word("]");
629            }
630            ast::ExprKind::Range(start, end, limits) => {
631                // Special case for `Range`. `AssocOp` claims that `Range` has higher precedence
632                // than `Assign`, but `x .. x = x` gives a parse error instead of `x .. (x = x)`.
633                // Here we use a fake precedence value so that any child with lower precedence than
634                // a "normal" binop gets parenthesized. (`LOr` is the lowest-precedence binop.)
635                let fake_prec = ExprPrecedence::LOr;
636                if let Some(e) = start {
637                    self.print_expr_cond_paren(
638                        e,
639                        e.precedence() < fake_prec,
640                        fixup.leftmost_subexpression(),
641                    );
642                }
643                match limits {
644                    ast::RangeLimits::HalfOpen => self.word(".."),
645                    ast::RangeLimits::Closed => self.word("..="),
646                }
647                if let Some(e) = end {
648                    self.print_expr_cond_paren(
649                        e,
650                        e.precedence() < fake_prec,
651                        fixup.subsequent_subexpression(),
652                    );
653                }
654            }
655            ast::ExprKind::Underscore => self.word("_"),
656            ast::ExprKind::Path(None, path) => self.print_path(path, true, 0),
657            ast::ExprKind::Path(Some(qself), path) => self.print_qpath(path, qself, true),
658            ast::ExprKind::Break(opt_label, opt_expr) => {
659                self.word("break");
660                if let Some(label) = opt_label {
661                    self.space();
662                    self.print_ident(label.ident);
663                }
664                if let Some(expr) = opt_expr {
665                    self.space();
666                    self.print_expr_cond_paren(
667                        expr,
668                        // Parenthesize if required by precedence, or in the
669                        // case of `break 'inner: loop { break 'inner 1 } + 1`
670                        expr.precedence() < ExprPrecedence::Jump
671                            || (opt_label.is_none() && classify::leading_labeled_expr(expr)),
672                        fixup.subsequent_subexpression(),
673                    );
674                }
675            }
676            ast::ExprKind::Continue(opt_label) => {
677                self.word("continue");
678                if let Some(label) = opt_label {
679                    self.space();
680                    self.print_ident(label.ident);
681                }
682            }
683            ast::ExprKind::Ret(result) => {
684                self.word("return");
685                if let Some(expr) = result {
686                    self.word(" ");
687                    self.print_expr_cond_paren(
688                        expr,
689                        expr.precedence() < ExprPrecedence::Jump,
690                        fixup.subsequent_subexpression(),
691                    );
692                }
693            }
694            ast::ExprKind::Yeet(result) => {
695                self.word("do");
696                self.word(" ");
697                self.word("yeet");
698                if let Some(expr) = result {
699                    self.word(" ");
700                    self.print_expr_cond_paren(
701                        expr,
702                        expr.precedence() < ExprPrecedence::Jump,
703                        fixup.subsequent_subexpression(),
704                    );
705                }
706            }
707            ast::ExprKind::Become(result) => {
708                self.word("become");
709                self.word(" ");
710                self.print_expr_cond_paren(
711                    result,
712                    result.precedence() < ExprPrecedence::Jump,
713                    fixup.subsequent_subexpression(),
714                );
715            }
716            ast::ExprKind::InlineAsm(a) => {
717                // FIXME: Print `builtin # asm` once macro `asm` uses `builtin_syntax`.
718                self.word("asm!");
719                self.print_inline_asm(a);
720            }
721            ast::ExprKind::FormatArgs(fmt) => {
722                // FIXME: Print `builtin # format_args` once macro `format_args` uses `builtin_syntax`.
723                self.word("format_args!");
724                self.popen();
725                let ib = self.ibox(0);
726                self.word(reconstruct_format_args_template_string(&fmt.template));
727                for arg in fmt.arguments.all_args() {
728                    self.word_space(",");
729                    self.print_expr(&arg.expr, FixupContext::default());
730                }
731                self.end(ib);
732                self.pclose();
733            }
734            ast::ExprKind::OffsetOf(container, fields) => {
735                self.word("builtin # offset_of");
736                self.popen();
737                let ib = self.ibox(0);
738                self.print_type(container);
739                self.word(",");
740                self.space();
741
742                if let Some((&first, rest)) = fields.split_first() {
743                    self.print_ident(first);
744
745                    for &field in rest {
746                        self.word(".");
747                        self.print_ident(field);
748                    }
749                }
750                self.end(ib);
751                self.pclose();
752            }
753            ast::ExprKind::MacCall(m) => self.print_mac(m),
754            ast::ExprKind::Paren(e) => {
755                self.popen();
756                self.print_expr(e, FixupContext::default());
757                self.pclose();
758            }
759            ast::ExprKind::Yield(YieldKind::Prefix(e)) => {
760                self.word("yield");
761
762                if let Some(expr) = e {
763                    self.space();
764                    self.print_expr_cond_paren(
765                        expr,
766                        expr.precedence() < ExprPrecedence::Jump,
767                        fixup.subsequent_subexpression(),
768                    );
769                }
770            }
771            ast::ExprKind::Yield(YieldKind::Postfix(e)) => {
772                self.print_expr_cond_paren(
773                    e,
774                    e.precedence() < ExprPrecedence::Unambiguous,
775                    fixup.leftmost_subexpression_with_dot(),
776                );
777                self.word(".yield");
778            }
779            ast::ExprKind::Try(e) => {
780                self.print_expr_cond_paren(
781                    e,
782                    e.precedence() < ExprPrecedence::Unambiguous,
783                    fixup.leftmost_subexpression_with_dot(),
784                );
785                self.word("?")
786            }
787            ast::ExprKind::TryBlock(blk) => {
788                let cb = self.cbox(0);
789                let ib = self.ibox(0);
790                self.word_nbsp("try");
791                self.print_block_with_attrs(blk, attrs, cb, ib)
792            }
793            ast::ExprKind::UnsafeBinderCast(kind, expr, ty) => {
794                self.word("builtin # ");
795                match kind {
796                    ast::UnsafeBinderCastKind::Wrap => self.word("wrap_binder"),
797                    ast::UnsafeBinderCastKind::Unwrap => self.word("unwrap_binder"),
798                }
799                self.popen();
800                let ib = self.ibox(0);
801                self.print_expr(expr, FixupContext::default());
802
803                if let Some(ty) = ty {
804                    self.word(",");
805                    self.space();
806                    self.print_type(ty);
807                }
808
809                self.end(ib);
810                self.pclose();
811            }
812            ast::ExprKind::Err(_) => {
813                self.popen();
814                self.word("/*ERROR*/");
815                self.pclose()
816            }
817            ast::ExprKind::Dummy => {
818                self.popen();
819                self.word("/*DUMMY*/");
820                self.pclose();
821            }
822        }
823
824        self.ann.post(self, AnnNode::Expr(expr));
825
826        if needs_par {
827            self.pclose();
828        }
829
830        self.end(ib);
831    }
832
833    fn print_arm(&mut self, arm: &ast::Arm) {
834        // Note, I have no idea why this check is necessary, but here it is.
835        if arm.attrs.is_empty() {
836            self.space();
837        }
838        let cb = self.cbox(INDENT_UNIT);
839        let ib = self.ibox(0);
840        self.maybe_print_comment(arm.pat.span.lo());
841        self.print_outer_attributes(&arm.attrs);
842        self.print_pat(&arm.pat);
843        self.space();
844        if let Some(e) = &arm.guard {
845            self.word_space("if");
846            self.print_expr(e, FixupContext::default());
847            self.space();
848        }
849
850        if let Some(body) = &arm.body {
851            self.word_space("=>");
852
853            match &body.kind {
854                ast::ExprKind::Block(blk, opt_label) => {
855                    if let Some(label) = opt_label {
856                        self.print_ident(label.ident);
857                        self.word_space(":");
858                    }
859
860                    self.print_block_unclosed_indent(blk, ib);
861
862                    // If it is a user-provided unsafe block, print a comma after it.
863                    if let BlockCheckMode::Unsafe(ast::UserProvided) = blk.rules {
864                        self.word(",");
865                    }
866                }
867                _ => {
868                    self.end(ib);
869                    self.print_expr(body, FixupContext::new_match_arm());
870                    self.word(",");
871                }
872            }
873        } else {
874            self.end(ib);
875            self.word(",");
876        }
877        self.end(cb);
878    }
879
880    fn print_closure_binder(&mut self, binder: &ast::ClosureBinder) {
881        match binder {
882            ast::ClosureBinder::NotPresent => {}
883            ast::ClosureBinder::For { generic_params, .. } => {
884                self.print_formal_generic_params(generic_params)
885            }
886        }
887    }
888
889    fn print_movability(&mut self, movability: ast::Movability) {
890        match movability {
891            ast::Movability::Static => self.word_space("static"),
892            ast::Movability::Movable => {}
893        }
894    }
895
896    fn print_capture_clause(&mut self, capture_clause: ast::CaptureBy) {
897        match capture_clause {
898            ast::CaptureBy::Value { .. } => self.word_space("move"),
899            ast::CaptureBy::Use { .. } => self.word_space("use"),
900            ast::CaptureBy::Ref => {}
901        }
902    }
903}
904
905fn reconstruct_format_args_template_string(pieces: &[FormatArgsPiece]) -> String {
906    let mut template = "\"".to_string();
907    for piece in pieces {
908        match piece {
909            FormatArgsPiece::Literal(s) => {
910                for c in s.as_str().chars() {
911                    template.extend(c.escape_debug());
912                    if let '{' | '}' = c {
913                        template.push(c);
914                    }
915                }
916            }
917            FormatArgsPiece::Placeholder(p) => {
918                template.push('{');
919                let (Ok(n) | Err(n)) = p.argument.index;
920                write!(template, "{n}").unwrap();
921                if p.format_options != Default::default() || p.format_trait != FormatTrait::Display
922                {
923                    template.push(':');
924                }
925                if let Some(fill) = p.format_options.fill {
926                    template.push(fill);
927                }
928                match p.format_options.alignment {
929                    Some(FormatAlignment::Left) => template.push('<'),
930                    Some(FormatAlignment::Right) => template.push('>'),
931                    Some(FormatAlignment::Center) => template.push('^'),
932                    None => {}
933                }
934                match p.format_options.sign {
935                    Some(FormatSign::Plus) => template.push('+'),
936                    Some(FormatSign::Minus) => template.push('-'),
937                    None => {}
938                }
939                if p.format_options.alternate {
940                    template.push('#');
941                }
942                if p.format_options.zero_pad {
943                    template.push('0');
944                }
945                if let Some(width) = &p.format_options.width {
946                    match width {
947                        FormatCount::Literal(n) => write!(template, "{n}").unwrap(),
948                        FormatCount::Argument(FormatArgPosition {
949                            index: Ok(n) | Err(n), ..
950                        }) => {
951                            write!(template, "{n}$").unwrap();
952                        }
953                    }
954                }
955                if let Some(precision) = &p.format_options.precision {
956                    template.push('.');
957                    match precision {
958                        FormatCount::Literal(n) => write!(template, "{n}").unwrap(),
959                        FormatCount::Argument(FormatArgPosition {
960                            index: Ok(n) | Err(n), ..
961                        }) => {
962                            write!(template, "{n}$").unwrap();
963                        }
964                    }
965                }
966                match p.format_options.debug_hex {
967                    Some(FormatDebugHex::Lower) => template.push('x'),
968                    Some(FormatDebugHex::Upper) => template.push('X'),
969                    None => {}
970                }
971                template.push_str(match p.format_trait {
972                    FormatTrait::Display => "",
973                    FormatTrait::Debug => "?",
974                    FormatTrait::LowerExp => "e",
975                    FormatTrait::UpperExp => "E",
976                    FormatTrait::Octal => "o",
977                    FormatTrait::Pointer => "p",
978                    FormatTrait::Binary => "b",
979                    FormatTrait::LowerHex => "x",
980                    FormatTrait::UpperHex => "X",
981                });
982                template.push('}');
983            }
984        }
985    }
986    template.push('"');
987    template
988}