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> {
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 mk_sp(lo, self.arm.span().hi())
55 impl<'a> Rewrite for ArmWrapper<'a> {
56 fn rewrite(&self, context: &RewriteContext<'_>, shape: Shape) -> Option<String> {
57 rewrite_match_arm(context, self.arm, shape, self.is_last)
61 pub(crate) fn rewrite_match(
62 context: &RewriteContext<'_>,
67 attrs: &[ast::Attribute],
69 // Do not take the rhs overhead from the upper expressions into account
70 // when rewriting match condition.
71 let cond_shape = Shape {
72 width: context.budget(shape.used_width()),
76 let cond_shape = match context.config.indent_style() {
77 IndentStyle::Visual => cond_shape.shrink_left(6)?,
78 IndentStyle::Block => cond_shape.offset_left(6)?,
80 let cond_str = cond.rewrite(context, cond_shape)?;
81 let alt_block_sep = &shape.indent.to_string_with_newline(context.config);
82 let block_sep = match context.config.control_brace_style() {
83 ControlBraceStyle::AlwaysNextLine => alt_block_sep,
84 _ if last_line_extendable(&cond_str) => " ",
86 _ if cond_str.contains('\n') || cond_str.len() + 2 > cond_shape.width => alt_block_sep,
90 let nested_indent_str = shape
92 .block_indent(context.config)
93 .to_string(context.config);
95 let inner_attrs = &inner_attributes(attrs);
96 let inner_attrs_str = if inner_attrs.is_empty() {
100 .rewrite(context, shape)
101 .map(|s| format!("{}{}\n", nested_indent_str, s))?
104 let open_brace_pos = if inner_attrs.is_empty() {
105 let hi = if arms.is_empty() {
112 .span_after(mk_sp(cond.span.hi(), hi), "{")
114 inner_attrs[inner_attrs.len() - 1].span.hi()
118 let snippet = context.snippet(mk_sp(open_brace_pos, span.hi() - BytePos(1)));
119 if snippet.trim().is_empty() {
120 Some(format!("match {} {{}}", cond_str))
122 // Empty match with comments or inner attributes? We are not going to bother, sorry ;)
123 Some(context.snippet(span).to_owned())
126 let span_after_cond = mk_sp(cond.span.hi(), span.hi());
128 "match {}{}{{\n{}{}{}\n{}}}",
133 rewrite_match_arms(context, arms, shape, span_after_cond, open_brace_pos)?,
134 shape.indent.to_string(context.config),
139 fn arm_comma(config: &Config, body: &ast::Expr, is_last: bool) -> &'static str {
140 if is_last && config.trailing_comma() == SeparatorTactic::Never {
142 } else if config.match_block_trailing_comma() {
144 } else if let ast::ExprKind::Block(ref block, _) = body.node {
145 if let ast::BlockCheckMode::Default = block.rules {
155 /// Collect a byte position of the beginning `|` for each arm, if available.
156 fn collect_beginning_verts(
157 context: &RewriteContext<'_>,
160 ) -> Vec<Option<BytePos>> {
161 let mut beginning_verts = Vec::with_capacity(arms.len());
162 let mut lo = context.snippet_provider.span_after(span, "{");
164 let hi = arm.pats[0].span.lo();
165 let missing_span = mk_sp(lo, hi);
166 beginning_verts.push(context.snippet_provider.opt_span_before(missing_span, "|"));
167 lo = arm.span().hi();
172 fn rewrite_match_arms(
173 context: &RewriteContext<'_>,
177 open_brace_pos: BytePos,
178 ) -> Option<String> {
179 let arm_shape = shape
180 .block_indent(context.config.tab_spaces())
181 .with_max_width(context.config);
183 let arm_len = arms.len();
184 let is_last_iter = repeat(false)
185 .take(arm_len.saturating_sub(1))
186 .chain(repeat(true));
187 let beginning_verts = collect_beginning_verts(context, arms, span);
188 let items = itemize_list(
189 context.snippet_provider,
192 .zip(beginning_verts.into_iter())
193 .map(|((arm, is_last), beginning_vert)| ArmWrapper::new(arm, is_last, beginning_vert)),
196 |arm| arm.span().lo(),
197 |arm| arm.span().hi(),
198 |arm| arm.rewrite(context, arm_shape),
203 let arms_vec: Vec<_> = items.collect();
204 // We will add/remove commas inside `arm.rewrite()`, and hence no separator here.
205 let fmt = ListFormatting::new(arm_shape, context.config)
207 .preserve_newline(true);
209 write_list(&arms_vec, &fmt)
212 fn rewrite_match_arm(
213 context: &RewriteContext<'_>,
217 ) -> Option<String> {
218 let (missing_span, attrs_str) = if !arm.attrs.is_empty() {
219 if contains_skip(&arm.attrs) {
220 let (_, body) = flatten_arm_body(context, &arm.body, None);
221 // `arm.span()` does not include trailing comma, add it manually.
224 context.snippet(arm.span()),
225 arm_comma(context.config, body, is_last),
228 let missing_span = mk_sp(
229 arm.attrs[arm.attrs.len() - 1].span.hi(),
230 arm.pats[0].span.lo(),
232 (missing_span, arm.attrs.rewrite(context, shape)?)
234 (mk_sp(arm.span().lo(), arm.span().lo()), String::new())
239 let pat_shape = shape.sub_width(5)?;
240 let pats_str = rewrite_multiple_patterns(context, &ptr_vec_to_ref_vec(&arm.pats), pat_shape)?;
243 let block_like_pat = trimmed_last_line_width(&pats_str) <= context.config.tab_spaces();
244 let new_line_guard = pats_str.contains('\n') && !block_like_pat;
245 let guard_str = rewrite_guard(
249 trimmed_last_line_width(&pats_str),
253 let lhs_str = combine_strs_with_missing_comments(
256 &format!("{}{}", pats_str, guard_str),
262 let arrow_span = mk_sp(arm.pats.last().unwrap().span.hi(), arm.body.span().lo());
268 guard_str.contains('\n'),
274 fn block_can_be_flattened<'a>(
275 context: &RewriteContext<'_>,
277 ) -> Option<&'a ast::Block> {
279 ast::ExprKind::Block(ref block, _)
280 if !is_unsafe_block(block)
281 && is_simple_block(block, Some(&expr.attrs), context.source_map) =>
290 // @extend: true if the arm body can be put next to `=>`
291 // @body: flattened body, if the body is block with a single expression
292 fn flatten_arm_body<'a>(
293 context: &'a RewriteContext<'_>,
295 opt_shape: Option<Shape>,
296 ) -> (bool, &'a ast::Expr) {
298 |expr| !context.config.force_multiline_blocks() && can_flatten_block_around_this(expr);
300 if let Some(ref block) = block_can_be_flattened(context, body) {
301 if let ast::StmtKind::Expr(ref expr) = block.stmts[0].node {
302 if let ast::ExprKind::Block(..) = expr.node {
303 flatten_arm_body(context, expr, None)
305 let cond_becomes_muti_line = opt_shape
306 .and_then(|shape| rewrite_cond(context, expr, shape))
307 .map_or(false, |cond| cond.contains('\n'));
308 if cond_becomes_muti_line {
311 (can_extend(expr), &*expr)
318 (can_extend(body), &*body)
322 fn rewrite_match_body(
323 context: &RewriteContext<'_>,
324 body: &ptr::P<ast::Expr>,
330 ) -> Option<String> {
331 let (extend, body) = flatten_arm_body(
334 shape.offset_left(extra_offset(pats_str, shape) + 4),
336 let (is_block, is_empty_block) = if let ast::ExprKind::Block(ref block, _) = body.node {
339 is_empty_block(block, Some(&body.attrs), context.source_map),
345 let comma = arm_comma(context.config, body, is_last);
346 let alt_block_sep = &shape.indent.to_string_with_newline(context.config);
348 let combine_orig_body = |body_str: &str| {
349 let block_sep = match context.config.control_brace_style() {
350 ControlBraceStyle::AlwaysNextLine if is_block => alt_block_sep,
354 Some(format!("{} =>{}{}{}", pats_str, block_sep, body_str, comma))
357 let next_line_indent = if !is_block || is_empty_block {
358 shape.indent.block_indent(context.config)
363 let forbid_same_line =
364 (has_guard && pats_str.contains('\n') && !is_empty_block) || !body.attrs.is_empty();
366 // Look for comments between `=>` and the start of the body.
367 let arrow_comment = {
368 let arrow_snippet = context.snippet(arrow_span).trim();
369 // search for the arrow starting from the end of the snippet since there may be a match
370 // expression within the guard
371 let arrow_index = arrow_snippet.rfind("=>").unwrap();
373 let comment_str = arrow_snippet[arrow_index + 2..].trim();
374 if comment_str.is_empty() {
377 rewrite_comment(comment_str, false, shape, &context.config)?
381 let combine_next_line_body = |body_str: &str| {
382 let nested_indent_str = next_line_indent.to_string_with_newline(context.config);
385 let mut result = pats_str.to_owned();
386 result.push_str(" =>");
387 if !arrow_comment.is_empty() {
388 result.push_str(&nested_indent_str);
389 result.push_str(&arrow_comment);
391 result.push_str(&nested_indent_str);
392 result.push_str(&body_str);
396 let indent_str = shape.indent.to_string_with_newline(context.config);
397 let (body_prefix, body_suffix) = if context.config.match_arm_blocks() {
398 let comma = if context.config.match_block_trailing_comma() {
403 let semicolon = if context.config.version() == Version::One {
406 if semicolon_for_expr(context, body) {
412 ("{", format!("{}{}}}{}", semicolon, indent_str, comma))
414 ("", String::from(","))
417 let block_sep = match context.config.control_brace_style() {
418 ControlBraceStyle::AlwaysNextLine => format!("{}{}", alt_block_sep, body_prefix),
419 _ if body_prefix.is_empty() => "".to_owned(),
420 _ if forbid_same_line || !arrow_comment.is_empty() => {
421 format!("{}{}", alt_block_sep, body_prefix)
423 _ => format!(" {}", body_prefix),
424 } + &nested_indent_str;
426 let mut result = pats_str.to_owned();
427 result.push_str(" =>");
428 if !arrow_comment.is_empty() {
429 result.push_str(&indent_str);
430 result.push_str(&arrow_comment);
432 result.push_str(&block_sep);
433 result.push_str(&body_str);
434 result.push_str(&body_suffix);
438 // Let's try and get the arm body on the same line as the condition.
440 let orig_body_shape = shape
441 .offset_left(extra_offset(pats_str, shape) + 4)
442 .and_then(|shape| shape.sub_width(comma.len()));
443 let orig_body = if forbid_same_line || !arrow_comment.is_empty() {
445 } else if let Some(body_shape) = orig_body_shape {
446 let rewrite = nop_block_collapse(
447 format_expr(body, ExprType::Statement, context, body_shape),
453 if is_block || (!body_str.contains('\n') && body_str.len() <= body_shape.width) =>
455 return combine_orig_body(body_str);
462 let orig_budget = orig_body_shape.map_or(0, |shape| shape.width);
464 // Try putting body on the next line and see if it looks better.
465 let next_line_body_shape = Shape::indented(next_line_indent, context.config);
466 let next_line_body = nop_block_collapse(
467 format_expr(body, ExprType::Statement, context, next_line_body_shape),
468 next_line_body_shape.width,
470 match (orig_body, next_line_body) {
471 (Some(ref orig_str), Some(ref next_line_str))
472 if prefer_next_line(orig_str, next_line_str, RhsTactics::Default) =>
474 combine_next_line_body(next_line_str)
476 (Some(ref orig_str), _) if extend && first_line_width(orig_str) <= orig_budget => {
477 combine_orig_body(orig_str)
479 (Some(ref orig_str), Some(ref next_line_str)) if orig_str.contains('\n') => {
480 combine_next_line_body(next_line_str)
482 (None, Some(ref next_line_str)) => combine_next_line_body(next_line_str),
483 (None, None) => None,
484 (Some(ref orig_str), _) => combine_orig_body(orig_str),
488 impl Rewrite for ast::Guard {
489 fn rewrite(&self, context: &RewriteContext<'_>, shape: Shape) -> Option<String> {
491 ast::Guard::If(ref expr) => expr.rewrite(context, shape),
496 // The `if ...` guard on a match arm.
498 context: &RewriteContext<'_>,
499 guard: &Option<ast::Guard>,
501 // The amount of space used up on this line for the pattern in
502 // the arm (excludes offset).
503 pattern_width: usize,
504 multiline_pattern: bool,
505 ) -> Option<String> {
506 if let Some(ref guard) = *guard {
507 // First try to fit the guard string on the same line as the pattern.
508 // 4 = ` if `, 5 = ` => {`
509 let cond_shape = shape
510 .offset_left(pattern_width + 4)
511 .and_then(|s| s.sub_width(5));
512 if !multiline_pattern {
513 if let Some(cond_shape) = cond_shape {
514 if let Some(cond_str) = guard.rewrite(context, cond_shape) {
515 if !cond_str.contains('\n') || pattern_width <= context.config.tab_spaces() {
516 return Some(format!(" if {}", cond_str));
522 // Not enough space to put the guard after the pattern, try a newline.
523 // 3 = `if `, 5 = ` => {`
524 let cond_shape = Shape::indented(shape.indent.block_indent(context.config), context.config)
526 .and_then(|s| s.sub_width(5));
527 if let Some(cond_shape) = cond_shape {
528 if let Some(cond_str) = guard.rewrite(context, cond_shape) {
531 cond_shape.indent.to_string_with_newline(context.config),
543 fn nop_block_collapse(block_str: Option<String>, budget: usize) -> Option<String> {
544 debug!("nop_block_collapse {:?} {}", block_str, budget);
545 block_str.map(|block_str| {
546 if block_str.starts_with('{')
548 && (block_str[1..].find(|c: char| !c.is_whitespace()).unwrap() == block_str.len() - 2)
557 fn can_flatten_block_around_this(body: &ast::Expr) -> bool {
559 // We do not allow `if` to stay on the same line, since we could easily mistake
560 // `pat => if cond { ... }` and `pat if cond => { ... }`.
561 ast::ExprKind::If(..) | ast::ExprKind::IfLet(..) => false,
562 // We do not allow collapsing a block around expression with condition
563 // to avoid it being cluttered with match arm.
564 ast::ExprKind::ForLoop(..) | ast::ExprKind::While(..) | ast::ExprKind::WhileLet(..) => {
567 ast::ExprKind::Loop(..)
568 | ast::ExprKind::Match(..)
569 | ast::ExprKind::Block(..)
570 | ast::ExprKind::Closure(..)
571 | ast::ExprKind::Array(..)
572 | ast::ExprKind::Call(..)
573 | ast::ExprKind::MethodCall(..)
574 | ast::ExprKind::Mac(..)
575 | ast::ExprKind::Struct(..)
576 | ast::ExprKind::Tup(..) => true,
577 ast::ExprKind::AddrOf(_, ref expr)
578 | ast::ExprKind::Box(ref expr)
579 | ast::ExprKind::Try(ref expr)
580 | ast::ExprKind::Unary(_, ref expr)
581 | ast::ExprKind::Cast(ref expr, _) => can_flatten_block_around_this(expr),