1 //! Format match expression.
5 use syntax::source_map::{BytePos, Span};
6 use syntax::{ast, ptr};
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,
13 rewrite_multiple_patterns, ExprType, RhsTactics,
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 ptr_vec_to_ref_vec, semicolon_for_expr, trimmed_last_line_width,
25 /// A simple wrapper type against `ast::Arm`. Used inside `write_list()`.
26 struct ArmWrapper<'a> {
27 pub arm: &'a ast::Arm,
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 pub beginning_vert: Option<BytePos>,
35 impl<'a> ArmWrapper<'a> {
39 beginning_vert: Option<BytePos>,
49 impl<'a> Spanned for ArmWrapper<'a> {
50 fn span(&self) -> Span {
51 if let Some(lo) = self.beginning_vert {
52 mk_sp(lo, self.arm.span().hi())
59 impl<'a> Rewrite for ArmWrapper<'a> {
60 fn rewrite(&self, context: &RewriteContext<'_>, shape: Shape) -> Option<String> {
61 rewrite_match_arm(context, self.arm, shape, self.is_last)
66 context: &RewriteContext<'_>,
71 attrs: &[ast::Attribute],
73 // Do not take the rhs overhead from the upper expressions into account
74 // when rewriting match condition.
75 let cond_shape = Shape {
76 width: context.budget(shape.used_width()),
80 let cond_shape = match context.config.indent_style() {
81 IndentStyle::Visual => cond_shape.shrink_left(6)?,
82 IndentStyle::Block => cond_shape.offset_left(6)?,
84 let cond_str = cond.rewrite(context, cond_shape)?;
85 let alt_block_sep = &shape.indent.to_string_with_newline(context.config);
86 let block_sep = match context.config.control_brace_style() {
87 ControlBraceStyle::AlwaysNextLine => alt_block_sep,
88 _ if last_line_extendable(&cond_str) => " ",
90 _ if cond_str.contains('\n') || cond_str.len() + 2 > cond_shape.width => alt_block_sep,
94 let nested_indent_str = shape
96 .block_indent(context.config)
97 .to_string(context.config);
99 let inner_attrs = &inner_attributes(attrs);
100 let inner_attrs_str = if inner_attrs.is_empty() {
104 .rewrite(context, shape)
105 .map(|s| format!("{}{}\n", nested_indent_str, s))?
108 let open_brace_pos = if inner_attrs.is_empty() {
109 let hi = if arms.is_empty() {
116 .span_after(mk_sp(cond.span.hi(), hi), "{")
118 inner_attrs[inner_attrs.len() - 1].span().hi()
122 let snippet = context.snippet(mk_sp(open_brace_pos, span.hi() - BytePos(1)));
123 if snippet.trim().is_empty() {
124 Some(format!("match {} {{}}", cond_str))
126 // Empty match with comments or inner attributes? We are not going to bother, sorry ;)
127 Some(context.snippet(span).to_owned())
130 let span_after_cond = mk_sp(cond.span.hi(), span.hi());
132 "match {}{}{{\n{}{}{}\n{}}}",
137 rewrite_match_arms(context, arms, shape, span_after_cond, open_brace_pos)?,
138 shape.indent.to_string(context.config),
143 fn arm_comma(config: &Config, body: &ast::Expr, is_last: bool) -> &'static str {
144 if is_last && config.trailing_comma() == SeparatorTactic::Never {
146 } else if config.match_block_trailing_comma() {
148 } else if let ast::ExprKind::Block(ref block, _) = body.node {
149 if let ast::BlockCheckMode::Default = block.rules {
159 /// Collect a byte position of the beginning `|` for each arm, if available.
160 fn collect_beginning_verts(
161 context: &RewriteContext<'_>,
164 ) -> Vec<Option<BytePos>> {
165 let mut beginning_verts = Vec::with_capacity(arms.len());
166 let mut lo = context.snippet_provider.span_after(span, "{");
168 let hi = arm.pats[0].span.lo();
169 let missing_span = mk_sp(lo, hi);
170 beginning_verts.push(context.snippet_provider.opt_span_before(missing_span, "|"));
171 lo = arm.span().hi();
176 fn rewrite_match_arms(
177 context: &RewriteContext<'_>,
181 open_brace_pos: BytePos,
182 ) -> Option<String> {
183 let arm_shape = shape
184 .block_indent(context.config.tab_spaces())
185 .with_max_width(context.config);
187 let arm_len = arms.len();
188 let is_last_iter = repeat(false)
189 .take(arm_len.saturating_sub(1))
190 .chain(repeat(true));
191 let beginning_verts = collect_beginning_verts(context, arms, span);
192 let items = itemize_list(
193 context.snippet_provider,
196 .zip(beginning_verts.into_iter())
197 .map(|((arm, is_last), beginning_vert)| ArmWrapper::new(arm, is_last, beginning_vert)),
200 |arm| arm.span().lo(),
201 |arm| arm.span().hi(),
202 |arm| arm.rewrite(context, arm_shape),
207 let arms_vec: Vec<_> = items.collect();
208 // We will add/remove commas inside `arm.rewrite()`, and hence no separator here.
209 let fmt = ListFormatting::new(arm_shape, context.config)
211 .preserve_newline(true);
213 write_list(&arms_vec, &fmt)
216 fn rewrite_match_arm(
217 context: &RewriteContext<'_>,
221 ) -> Option<String> {
222 let (missing_span, attrs_str) = if !arm.attrs.is_empty() {
223 if contains_skip(&arm.attrs) {
224 let (_, body) = flatten_arm_body(context, &arm.body, None);
225 // `arm.span()` does not include trailing comma, add it manually.
228 context.snippet(arm.span()),
229 arm_comma(context.config, body, is_last),
232 let missing_span = mk_sp(
233 arm.attrs[arm.attrs.len() - 1].span.hi(),
234 arm.pats[0].span.lo(),
236 (missing_span, arm.attrs.rewrite(context, shape)?)
238 (mk_sp(arm.span().lo(), arm.span().lo()), String::new())
243 let pat_shape = shape.sub_width(5)?;
244 let pats_str = rewrite_multiple_patterns(context, &ptr_vec_to_ref_vec(&arm.pats), pat_shape)?;
247 let block_like_pat = trimmed_last_line_width(&pats_str) <= context.config.tab_spaces();
248 let new_line_guard = pats_str.contains('\n') && !block_like_pat;
249 let guard_str = rewrite_guard(
253 trimmed_last_line_width(&pats_str),
257 let lhs_str = combine_strs_with_missing_comments(
260 &format!("{}{}", pats_str, guard_str),
266 let arrow_span = mk_sp(arm.pats.last().unwrap().span.hi(), arm.body.span().lo());
272 guard_str.contains('\n'),
278 fn block_can_be_flattened<'a>(
279 context: &RewriteContext<'_>,
281 ) -> Option<&'a ast::Block> {
283 ast::ExprKind::Block(ref block, _)
284 if !is_unsafe_block(block)
285 && is_simple_block(block, Some(&expr.attrs), context.source_map) =>
294 // @extend: true if the arm body can be put next to `=>`
295 // @body: flattened body, if the body is block with a single expression
296 fn flatten_arm_body<'a>(
297 context: &'a RewriteContext<'_>,
299 opt_shape: Option<Shape>,
300 ) -> (bool, &'a ast::Expr) {
302 |expr| !context.config.force_multiline_blocks() && can_flatten_block_around_this(expr);
304 if let Some(ref block) = block_can_be_flattened(context, body) {
305 if let ast::StmtKind::Expr(ref expr) = block.stmts[0].node {
306 if let ast::ExprKind::Block(..) = expr.node {
307 flatten_arm_body(context, expr, None)
309 let cond_becomes_muti_line = opt_shape
310 .and_then(|shape| rewrite_cond(context, expr, shape))
311 .map_or(false, |cond| cond.contains('\n'));
312 if cond_becomes_muti_line {
315 (can_extend(expr), &*expr)
322 (can_extend(body), &*body)
326 fn rewrite_match_body(
327 context: &RewriteContext<'_>,
328 body: &ptr::P<ast::Expr>,
334 ) -> Option<String> {
335 let (extend, body) = flatten_arm_body(
338 shape.offset_left(extra_offset(pats_str, shape) + 4),
340 let (is_block, is_empty_block) = if let ast::ExprKind::Block(ref block, _) = body.node {
343 is_empty_block(block, Some(&body.attrs), context.source_map),
349 let comma = arm_comma(context.config, body, is_last);
350 let alt_block_sep = &shape.indent.to_string_with_newline(context.config);
352 let combine_orig_body = |body_str: &str| {
353 let block_sep = match context.config.control_brace_style() {
354 ControlBraceStyle::AlwaysNextLine if is_block => alt_block_sep,
358 Some(format!("{} =>{}{}{}", pats_str, block_sep, body_str, comma))
361 let next_line_indent = if !is_block || is_empty_block {
362 shape.indent.block_indent(context.config)
367 let forbid_same_line =
368 (has_guard && pats_str.contains('\n') && !is_empty_block) || !body.attrs.is_empty();
370 // Look for comments between `=>` and the start of the body.
371 let arrow_comment = {
372 let arrow_snippet = context.snippet(arrow_span).trim();
373 // search for the arrow starting from the end of the snippet since there may be a match
374 // expression within the guard
375 let arrow_index = arrow_snippet.rfind("=>").unwrap();
377 let comment_str = arrow_snippet[arrow_index + 2..].trim();
378 if comment_str.is_empty() {
381 rewrite_comment(comment_str, false, shape, &context.config)?
385 let combine_next_line_body = |body_str: &str| {
386 let nested_indent_str = next_line_indent.to_string_with_newline(context.config);
389 let mut result = pats_str.to_owned();
390 result.push_str(" =>");
391 if !arrow_comment.is_empty() {
392 result.push_str(&nested_indent_str);
393 result.push_str(&arrow_comment);
395 result.push_str(&nested_indent_str);
396 result.push_str(&body_str);
400 let indent_str = shape.indent.to_string_with_newline(context.config);
401 let (body_prefix, body_suffix) = if context.config.match_arm_blocks() {
402 let comma = if context.config.match_block_trailing_comma() {
407 let semicolon = if context.config.version() == Version::One {
410 if semicolon_for_expr(context, body) {
416 ("{", format!("{}{}}}{}", semicolon, indent_str, comma))
418 ("", String::from(","))
421 let block_sep = match context.config.control_brace_style() {
422 ControlBraceStyle::AlwaysNextLine => format!("{}{}", alt_block_sep, body_prefix),
423 _ if body_prefix.is_empty() => "".to_owned(),
424 _ if forbid_same_line || !arrow_comment.is_empty() => {
425 format!("{}{}", alt_block_sep, body_prefix)
427 _ => format!(" {}", body_prefix),
428 } + &nested_indent_str;
430 let mut result = pats_str.to_owned();
431 result.push_str(" =>");
432 if !arrow_comment.is_empty() {
433 result.push_str(&indent_str);
434 result.push_str(&arrow_comment);
436 result.push_str(&block_sep);
437 result.push_str(&body_str);
438 result.push_str(&body_suffix);
442 // Let's try and get the arm body on the same line as the condition.
444 let orig_body_shape = shape
445 .offset_left(extra_offset(pats_str, shape) + 4)
446 .and_then(|shape| shape.sub_width(comma.len()));
447 let orig_body = if forbid_same_line || !arrow_comment.is_empty() {
449 } else if let Some(body_shape) = orig_body_shape {
450 let rewrite = nop_block_collapse(
451 format_expr(body, ExprType::Statement, context, body_shape),
457 if is_block || (!body_str.contains('\n') && body_str.len() <= body_shape.width) =>
459 return combine_orig_body(body_str);
466 let orig_budget = orig_body_shape.map_or(0, |shape| shape.width);
468 // Try putting body on the next line and see if it looks better.
469 let next_line_body_shape = Shape::indented(next_line_indent, context.config);
470 let next_line_body = nop_block_collapse(
471 format_expr(body, ExprType::Statement, context, next_line_body_shape),
472 next_line_body_shape.width,
474 match (orig_body, next_line_body) {
475 (Some(ref orig_str), Some(ref next_line_str))
476 if prefer_next_line(orig_str, next_line_str, RhsTactics::Default) =>
478 combine_next_line_body(next_line_str)
480 (Some(ref orig_str), _) if extend && first_line_width(orig_str) <= orig_budget => {
481 combine_orig_body(orig_str)
483 (Some(ref orig_str), Some(ref next_line_str)) if orig_str.contains('\n') => {
484 combine_next_line_body(next_line_str)
486 (None, Some(ref next_line_str)) => combine_next_line_body(next_line_str),
487 (None, None) => None,
488 (Some(ref orig_str), _) => combine_orig_body(orig_str),
492 impl Rewrite for ast::Guard {
493 fn rewrite(&self, context: &RewriteContext<'_>, shape: Shape) -> Option<String> {
495 ast::Guard::If(ref expr) => expr.rewrite(context, shape),
500 // The `if ...` guard on a match arm.
502 context: &RewriteContext<'_>,
503 guard: &Option<ast::Guard>,
505 // The amount of space used up on this line for the pattern in
506 // the arm (excludes offset).
507 pattern_width: usize,
508 multiline_pattern: bool,
509 ) -> Option<String> {
510 if let Some(ref guard) = *guard {
511 // First try to fit the guard string on the same line as the pattern.
512 // 4 = ` if `, 5 = ` => {`
513 let cond_shape = shape
514 .offset_left(pattern_width + 4)
515 .and_then(|s| s.sub_width(5));
516 if !multiline_pattern {
517 if let Some(cond_shape) = cond_shape {
518 if let Some(cond_str) = guard.rewrite(context, cond_shape) {
519 if !cond_str.contains('\n') || pattern_width <= context.config.tab_spaces() {
520 return Some(format!(" if {}", cond_str));
526 // Not enough space to put the guard after the pattern, try a newline.
527 // 3 = `if `, 5 = ` => {`
528 let cond_shape = Shape::indented(shape.indent.block_indent(context.config), context.config)
530 .and_then(|s| s.sub_width(5));
531 if let Some(cond_shape) = cond_shape {
532 if let Some(cond_str) = guard.rewrite(context, cond_shape) {
535 cond_shape.indent.to_string_with_newline(context.config),
547 fn nop_block_collapse(block_str: Option<String>, budget: usize) -> Option<String> {
548 debug!("nop_block_collapse {:?} {}", block_str, budget);
549 block_str.map(|block_str| {
550 if block_str.starts_with('{')
552 && (block_str[1..].find(|c: char| !c.is_whitespace()).unwrap() == block_str.len() - 2)
561 fn can_flatten_block_around_this(body: &ast::Expr) -> bool {
563 // We do not allow `if` to stay on the same line, since we could easily mistake
564 // `pat => if cond { ... }` and `pat if cond => { ... }`.
565 ast::ExprKind::If(..) | ast::ExprKind::IfLet(..) => false,
566 // We do not allow collapsing a block around expression with condition
567 // to avoid it being cluttered with match arm.
568 ast::ExprKind::ForLoop(..) | ast::ExprKind::While(..) | ast::ExprKind::WhileLet(..) => {
571 ast::ExprKind::Loop(..)
572 | ast::ExprKind::Match(..)
573 | ast::ExprKind::Block(..)
574 | ast::ExprKind::Closure(..)
575 | ast::ExprKind::Array(..)
576 | ast::ExprKind::Call(..)
577 | ast::ExprKind::MethodCall(..)
578 | ast::ExprKind::Mac(..)
579 | ast::ExprKind::Struct(..)
580 | ast::ExprKind::Tup(..) => true,
581 ast::ExprKind::AddrOf(_, ref expr)
582 | ast::ExprKind::Box(ref expr)
583 | ast::ExprKind::Try(ref expr)
584 | ast::ExprKind::Unary(_, ref expr)
585 | ast::ExprKind::Cast(ref expr, _) => can_flatten_block_around_this(expr),