1 //! Format match expression.
5 use rustc_ast::{ast, ptr};
6 use rustc_span::{BytePos, Span};
8 use crate::comment::{combine_strs_with_missing_comments, rewrite_comment};
9 use crate::config::lists::*;
10 use crate::config::{Config, ControlBraceStyle, IndentStyle, Version};
12 format_expr, is_empty_block, is_simple_block, is_unsafe_block, prefer_next_line, rewrite_cond,
15 use crate::lists::{itemize_list, write_list, ListFormatting};
16 use crate::rewrite::{Rewrite, RewriteContext};
17 use crate::shape::Shape;
18 use crate::source_map::SpanUtils;
19 use crate::spanned::Spanned;
21 contains_skip, extra_offset, first_line_width, inner_attributes, last_line_extendable, mk_sp,
22 semicolon_for_expr, trimmed_last_line_width, unicode_str_width,
25 /// A simple wrapper type against `ast::Arm`. Used inside `write_list()`.
26 struct ArmWrapper<'a> {
28 /// `true` if the arm is the last one in match expression. Used to decide on whether we should
29 /// add trailing comma to the match arm when `config.trailing_comma() == Never`.
31 /// Holds a byte position of `|` at the beginning of the arm pattern, if available.
32 beginning_vert: Option<BytePos>,
35 impl<'a> ArmWrapper<'a> {
36 fn new(arm: &'a ast::Arm, is_last: bool, beginning_vert: Option<BytePos>) -> ArmWrapper<'a> {
45 impl<'a> Spanned for ArmWrapper<'a> {
46 fn span(&self) -> Span {
47 if let Some(lo) = self.beginning_vert {
48 let lo = std::cmp::min(lo, self.arm.span().lo());
49 mk_sp(lo, self.arm.span().hi())
56 impl<'a> Rewrite for ArmWrapper<'a> {
57 fn rewrite(&self, context: &RewriteContext<'_>, shape: Shape) -> Option<String> {
58 rewrite_match_arm(context, self.arm, shape, self.is_last)
62 pub(crate) fn rewrite_match(
63 context: &RewriteContext<'_>,
68 attrs: &[ast::Attribute],
70 // Do not take the rhs overhead from the upper expressions into account
71 // when rewriting match condition.
72 let cond_shape = Shape {
73 width: context.budget(shape.used_width()),
77 let cond_shape = match context.config.indent_style() {
78 IndentStyle::Visual => cond_shape.shrink_left(6)?,
79 IndentStyle::Block => cond_shape.offset_left(6)?,
81 let cond_str = cond.rewrite(context, cond_shape)?;
82 let alt_block_sep = &shape.indent.to_string_with_newline(context.config);
83 let block_sep = match context.config.control_brace_style() {
84 ControlBraceStyle::AlwaysNextLine => alt_block_sep,
85 _ if last_line_extendable(&cond_str) => " ",
87 _ if cond_str.contains('\n') || cond_str.len() + 2 > cond_shape.width => alt_block_sep,
91 let nested_indent_str = shape
93 .block_indent(context.config)
94 .to_string(context.config);
96 let inner_attrs = &inner_attributes(attrs);
97 let inner_attrs_str = if inner_attrs.is_empty() {
101 .rewrite(context, shape)
102 .map(|s| format!("{}{}\n", nested_indent_str, s))?
105 let open_brace_pos = if inner_attrs.is_empty() {
106 let hi = if arms.is_empty() {
113 .span_after(mk_sp(cond.span.hi(), hi), "{")
115 inner_attrs[inner_attrs.len() - 1].span.hi()
119 let snippet = context.snippet(mk_sp(open_brace_pos, span.hi() - BytePos(1)));
120 if snippet.trim().is_empty() {
121 Some(format!("match {} {{}}", cond_str))
123 // Empty match with comments or inner attributes? We are not going to bother, sorry ;)
124 Some(context.snippet(span).to_owned())
127 let span_after_cond = mk_sp(cond.span.hi(), span.hi());
129 "match {}{}{{\n{}{}{}\n{}}}",
134 rewrite_match_arms(context, arms, shape, span_after_cond, open_brace_pos)?,
135 shape.indent.to_string(context.config),
140 fn arm_comma(config: &Config, body: &ast::Expr, is_last: bool) -> &'static str {
141 if is_last && config.trailing_comma() == SeparatorTactic::Never {
143 } else if config.match_block_trailing_comma() {
145 } else if let ast::ExprKind::Block(ref block, _) = body.kind {
146 if let ast::BlockCheckMode::Default = block.rules {
156 /// Collect a byte position of the beginning `|` for each arm, if available.
157 fn collect_beginning_verts(
158 context: &RewriteContext<'_>,
161 ) -> Vec<Option<BytePos>> {
162 let mut beginning_verts = Vec::with_capacity(arms.len());
163 let mut lo = context.snippet_provider.span_after(span, "{");
165 let hi = arm.pat.span.lo();
166 let missing_span = mk_sp(lo, hi);
167 beginning_verts.push(context.snippet_provider.opt_span_before(missing_span, "|"));
168 lo = arm.span().hi();
173 fn rewrite_match_arms(
174 context: &RewriteContext<'_>,
178 open_brace_pos: BytePos,
179 ) -> Option<String> {
180 let arm_shape = shape
181 .block_indent(context.config.tab_spaces())
182 .with_max_width(context.config);
184 let arm_len = arms.len();
185 let is_last_iter = repeat(false)
186 .take(arm_len.saturating_sub(1))
187 .chain(repeat(true));
188 let beginning_verts = collect_beginning_verts(context, arms, span);
189 let items = itemize_list(
190 context.snippet_provider,
193 .zip(beginning_verts.into_iter())
194 .map(|((arm, is_last), beginning_vert)| ArmWrapper::new(arm, is_last, beginning_vert)),
197 |arm| arm.span().lo(),
198 |arm| arm.span().hi(),
199 |arm| arm.rewrite(context, arm_shape),
204 let arms_vec: Vec<_> = items.collect();
205 // We will add/remove commas inside `arm.rewrite()`, and hence no separator here.
206 let fmt = ListFormatting::new(arm_shape, context.config)
208 .preserve_newline(true);
210 write_list(&arms_vec, &fmt)
213 fn rewrite_match_arm(
214 context: &RewriteContext<'_>,
218 ) -> Option<String> {
219 let (missing_span, attrs_str) = if !arm.attrs.is_empty() {
220 if contains_skip(&arm.attrs) {
221 let (_, body) = flatten_arm_body(context, &arm.body, None);
222 // `arm.span()` does not include trailing comma, add it manually.
225 context.snippet(arm.span()),
226 arm_comma(context.config, body, is_last),
229 let missing_span = mk_sp(arm.attrs[arm.attrs.len() - 1].span.hi(), arm.pat.span.lo());
230 (missing_span, arm.attrs.rewrite(context, shape)?)
232 (mk_sp(arm.span().lo(), arm.span().lo()), String::new())
237 let pat_shape = shape.sub_width(5)?;
238 let pats_str = arm.pat.rewrite(context, pat_shape)?;
241 let block_like_pat = trimmed_last_line_width(&pats_str) <= context.config.tab_spaces();
242 let new_line_guard = pats_str.contains('\n') && !block_like_pat;
243 let guard_str = rewrite_guard(
247 trimmed_last_line_width(&pats_str),
251 let lhs_str = combine_strs_with_missing_comments(
254 &format!("{}{}", pats_str, guard_str),
260 let arrow_span = mk_sp(arm.pat.span.hi(), arm.body.span().lo());
266 guard_str.contains('\n'),
272 fn block_can_be_flattened<'a>(
273 context: &RewriteContext<'_>,
275 ) -> Option<&'a ast::Block> {
277 ast::ExprKind::Block(ref block, _)
278 if !is_unsafe_block(block)
279 && !context.inside_macro()
280 && is_simple_block(context, block, Some(&expr.attrs)) =>
289 // @extend: true if the arm body can be put next to `=>`
290 // @body: flattened body, if the body is block with a single expression
291 fn flatten_arm_body<'a>(
292 context: &'a RewriteContext<'_>,
294 opt_shape: Option<Shape>,
295 ) -> (bool, &'a ast::Expr) {
297 |expr| !context.config.force_multiline_blocks() && can_flatten_block_around_this(expr);
299 if let Some(ref block) = block_can_be_flattened(context, body) {
300 if let ast::StmtKind::Expr(ref expr) = block.stmts[0].kind {
301 if let ast::ExprKind::Block(..) = expr.kind {
302 flatten_arm_body(context, expr, None)
304 let cond_becomes_muti_line = opt_shape
305 .and_then(|shape| rewrite_cond(context, expr, shape))
306 .map_or(false, |cond| cond.contains('\n'));
307 if cond_becomes_muti_line {
310 (can_extend(expr), &*expr)
317 (can_extend(body), &*body)
321 fn rewrite_match_body(
322 context: &RewriteContext<'_>,
323 body: &ptr::P<ast::Expr>,
329 ) -> Option<String> {
330 let (extend, body) = flatten_arm_body(
333 shape.offset_left(extra_offset(pats_str, shape) + 4),
335 let (is_block, is_empty_block) = if let ast::ExprKind::Block(ref block, _) = body.kind {
336 (true, is_empty_block(context, block, Some(&body.attrs)))
341 let comma = arm_comma(context.config, body, is_last);
342 let alt_block_sep = &shape.indent.to_string_with_newline(context.config);
344 let combine_orig_body = |body_str: &str| {
345 let block_sep = match context.config.control_brace_style() {
346 ControlBraceStyle::AlwaysNextLine if is_block => alt_block_sep,
350 Some(format!("{} =>{}{}{}", pats_str, block_sep, body_str, comma))
353 let next_line_indent = if !is_block || is_empty_block {
354 shape.indent.block_indent(context.config)
359 let forbid_same_line =
360 (has_guard && pats_str.contains('\n') && !is_empty_block) || !body.attrs.is_empty();
362 // Look for comments between `=>` and the start of the body.
363 let arrow_comment = {
364 let arrow_snippet = context.snippet(arrow_span).trim();
365 // search for the arrow starting from the end of the snippet since there may be a match
366 // expression within the guard
367 let arrow_index = arrow_snippet.rfind("=>").unwrap();
369 let comment_str = arrow_snippet[arrow_index + 2..].trim();
370 if comment_str.is_empty() {
373 rewrite_comment(comment_str, false, shape, &context.config)?
377 let combine_next_line_body = |body_str: &str| {
378 let nested_indent_str = next_line_indent.to_string_with_newline(context.config);
381 let mut result = pats_str.to_owned();
382 result.push_str(" =>");
383 if !arrow_comment.is_empty() {
384 result.push_str(&nested_indent_str);
385 result.push_str(&arrow_comment);
387 result.push_str(&nested_indent_str);
388 result.push_str(&body_str);
392 let indent_str = shape.indent.to_string_with_newline(context.config);
393 let (body_prefix, body_suffix) =
394 if context.config.match_arm_blocks() && !context.inside_macro() {
395 let comma = if context.config.match_block_trailing_comma() {
400 let semicolon = if context.config.version() == Version::One {
403 if semicolon_for_expr(context, body) {
409 ("{", format!("{}{}}}{}", semicolon, indent_str, comma))
411 ("", String::from(","))
414 let block_sep = match context.config.control_brace_style() {
415 ControlBraceStyle::AlwaysNextLine => format!("{}{}", alt_block_sep, body_prefix),
416 _ if body_prefix.is_empty() => "".to_owned(),
417 _ if forbid_same_line || !arrow_comment.is_empty() => {
418 format!("{}{}", alt_block_sep, body_prefix)
420 _ => format!(" {}", body_prefix),
421 } + &nested_indent_str;
423 let mut result = pats_str.to_owned();
424 result.push_str(" =>");
425 if !arrow_comment.is_empty() {
426 result.push_str(&indent_str);
427 result.push_str(&arrow_comment);
429 result.push_str(&block_sep);
430 result.push_str(&body_str);
431 result.push_str(&body_suffix);
435 // Let's try and get the arm body on the same line as the condition.
437 let orig_body_shape = shape
438 .offset_left(extra_offset(pats_str, shape) + 4)
439 .and_then(|shape| shape.sub_width(comma.len()));
440 let orig_body = if forbid_same_line || !arrow_comment.is_empty() {
442 } else if let Some(body_shape) = orig_body_shape {
443 let rewrite = nop_block_collapse(
444 format_expr(body, ExprType::Statement, context, body_shape),
451 || (!body_str.contains('\n')
452 && unicode_str_width(body_str) <= body_shape.width) =>
454 return combine_orig_body(body_str);
461 let orig_budget = orig_body_shape.map_or(0, |shape| shape.width);
463 // Try putting body on the next line and see if it looks better.
464 let next_line_body_shape = Shape::indented(next_line_indent, context.config);
465 let next_line_body = nop_block_collapse(
466 format_expr(body, ExprType::Statement, context, next_line_body_shape),
467 next_line_body_shape.width,
469 match (orig_body, next_line_body) {
470 (Some(ref orig_str), Some(ref next_line_str))
471 if prefer_next_line(orig_str, next_line_str, RhsTactics::Default) =>
473 combine_next_line_body(next_line_str)
475 (Some(ref orig_str), _) if extend && first_line_width(orig_str) <= orig_budget => {
476 combine_orig_body(orig_str)
478 (Some(ref orig_str), Some(ref next_line_str)) if orig_str.contains('\n') => {
479 combine_next_line_body(next_line_str)
481 (None, Some(ref next_line_str)) => combine_next_line_body(next_line_str),
482 (None, None) => None,
483 (Some(ref orig_str), _) => combine_orig_body(orig_str),
487 // The `if ...` guard on a match arm.
489 context: &RewriteContext<'_>,
490 guard: &Option<ptr::P<ast::Expr>>,
492 // The amount of space used up on this line for the pattern in
493 // the arm (excludes offset).
494 pattern_width: usize,
495 multiline_pattern: bool,
496 ) -> Option<String> {
497 if let Some(ref guard) = *guard {
498 // First try to fit the guard string on the same line as the pattern.
499 // 4 = ` if `, 5 = ` => {`
500 let cond_shape = shape
501 .offset_left(pattern_width + 4)
502 .and_then(|s| s.sub_width(5));
503 if !multiline_pattern {
504 if let Some(cond_shape) = cond_shape {
505 if let Some(cond_str) = guard.rewrite(context, cond_shape) {
506 if !cond_str.contains('\n') || pattern_width <= context.config.tab_spaces() {
507 return Some(format!(" if {}", cond_str));
513 // Not enough space to put the guard after the pattern, try a newline.
514 // 3 = `if `, 5 = ` => {`
515 let cond_shape = Shape::indented(shape.indent.block_indent(context.config), context.config)
517 .and_then(|s| s.sub_width(5));
518 if let Some(cond_shape) = cond_shape {
519 if let Some(cond_str) = guard.rewrite(context, cond_shape) {
522 cond_shape.indent.to_string_with_newline(context.config),
534 fn nop_block_collapse(block_str: Option<String>, budget: usize) -> Option<String> {
535 debug!("nop_block_collapse {:?} {}", block_str, budget);
536 block_str.map(|block_str| {
537 if block_str.starts_with('{')
539 && (block_str[1..].find(|c: char| !c.is_whitespace()).unwrap() == block_str.len() - 2)
548 fn can_flatten_block_around_this(body: &ast::Expr) -> bool {
550 // We do not allow `if` to stay on the same line, since we could easily mistake
551 // `pat => if cond { ... }` and `pat if cond => { ... }`.
552 ast::ExprKind::If(..) => false,
553 // We do not allow collapsing a block around expression with condition
554 // to avoid it being cluttered with match arm.
555 ast::ExprKind::ForLoop(..) | ast::ExprKind::While(..) => false,
556 ast::ExprKind::Loop(..)
557 | ast::ExprKind::Match(..)
558 | ast::ExprKind::Block(..)
559 | ast::ExprKind::Closure(..)
560 | ast::ExprKind::Array(..)
561 | ast::ExprKind::Call(..)
562 | ast::ExprKind::MethodCall(..)
563 | ast::ExprKind::MacCall(..)
564 | ast::ExprKind::Struct(..)
565 | ast::ExprKind::Tup(..) => true,
566 ast::ExprKind::AddrOf(_, _, ref expr)
567 | ast::ExprKind::Box(ref expr)
568 | ast::ExprKind::Try(ref expr)
569 | ast::ExprKind::Unary(_, ref expr)
570 | ast::ExprKind::Index(ref expr, _)
571 | ast::ExprKind::Cast(ref expr, _) => can_flatten_block_around_this(expr),