599 lines
20 KiB
Rust
599 lines
20 KiB
Rust
//! Format match expression.
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use std::iter::repeat;
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use rustc_ast::{ast, ptr};
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use rustc_span::{BytePos, Span};
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use crate::comment::{combine_strs_with_missing_comments, rewrite_comment};
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use crate::config::lists::*;
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use crate::config::{Config, ControlBraceStyle, IndentStyle, MatchArmLeadingPipe, Version};
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use crate::expr::{
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format_expr, is_empty_block, is_simple_block, is_unsafe_block, prefer_next_line, rewrite_cond,
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ExprType, RhsTactics,
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};
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use crate::lists::{itemize_list, write_list, ListFormatting};
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use crate::rewrite::{Rewrite, RewriteContext};
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use crate::shape::Shape;
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use crate::source_map::SpanUtils;
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use crate::spanned::Spanned;
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use crate::utils::{
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contains_skip, extra_offset, first_line_width, inner_attributes, last_line_extendable, mk_sp,
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semicolon_for_expr, trimmed_last_line_width, unicode_str_width,
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};
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/// A simple wrapper type against `ast::Arm`. Used inside `write_list()`.
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struct ArmWrapper<'a> {
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arm: &'a ast::Arm,
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/// `true` if the arm is the last one in match expression. Used to decide on whether we should
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/// add trailing comma to the match arm when `config.trailing_comma() == Never`.
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is_last: bool,
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/// Holds a byte position of `|` at the beginning of the arm pattern, if available.
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beginning_vert: Option<BytePos>,
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}
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impl<'a> ArmWrapper<'a> {
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fn new(arm: &'a ast::Arm, is_last: bool, beginning_vert: Option<BytePos>) -> ArmWrapper<'a> {
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ArmWrapper {
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arm,
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is_last,
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beginning_vert,
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}
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}
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}
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impl<'a> Spanned for ArmWrapper<'a> {
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fn span(&self) -> Span {
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if let Some(lo) = self.beginning_vert {
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let lo = std::cmp::min(lo, self.arm.span().lo());
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mk_sp(lo, self.arm.span().hi())
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} else {
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self.arm.span()
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}
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}
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}
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impl<'a> Rewrite for ArmWrapper<'a> {
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fn rewrite(&self, context: &RewriteContext<'_>, shape: Shape) -> Option<String> {
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rewrite_match_arm(
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context,
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self.arm,
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shape,
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self.is_last,
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self.beginning_vert.is_some(),
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)
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}
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}
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pub(crate) fn rewrite_match(
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context: &RewriteContext<'_>,
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cond: &ast::Expr,
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arms: &[ast::Arm],
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shape: Shape,
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span: Span,
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attrs: &[ast::Attribute],
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) -> Option<String> {
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// Do not take the rhs overhead from the upper expressions into account
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// when rewriting match condition.
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let cond_shape = Shape {
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width: context.budget(shape.used_width()),
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..shape
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};
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// 6 = `match `
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let cond_shape = match context.config.indent_style() {
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IndentStyle::Visual => cond_shape.shrink_left(6)?,
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IndentStyle::Block => cond_shape.offset_left(6)?,
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};
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let cond_str = cond.rewrite(context, cond_shape)?;
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let alt_block_sep = &shape.indent.to_string_with_newline(context.config);
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let block_sep = match context.config.control_brace_style() {
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ControlBraceStyle::AlwaysNextLine => alt_block_sep,
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_ if last_line_extendable(&cond_str) => " ",
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// 2 = ` {`
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_ if cond_str.contains('\n') || cond_str.len() + 2 > cond_shape.width => alt_block_sep,
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_ => " ",
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};
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let nested_indent_str = shape
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.indent
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.block_indent(context.config)
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.to_string(context.config);
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// Inner attributes.
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let inner_attrs = &inner_attributes(attrs);
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let inner_attrs_str = if inner_attrs.is_empty() {
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String::new()
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} else {
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inner_attrs
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.rewrite(context, shape)
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.map(|s| format!("{}{}\n", nested_indent_str, s))?
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};
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let open_brace_pos = if inner_attrs.is_empty() {
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let hi = if arms.is_empty() {
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span.hi()
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} else {
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arms[0].span().lo()
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};
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context
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.snippet_provider
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.span_after(mk_sp(cond.span.hi(), hi), "{")
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} else {
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inner_attrs[inner_attrs.len() - 1].span.hi()
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};
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if arms.is_empty() {
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let snippet = context.snippet(mk_sp(open_brace_pos, span.hi() - BytePos(1)));
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if snippet.trim().is_empty() {
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Some(format!("match {} {{}}", cond_str))
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} else {
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// Empty match with comments or inner attributes? We are not going to bother, sorry ;)
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Some(context.snippet(span).to_owned())
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}
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} else {
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let span_after_cond = mk_sp(cond.span.hi(), span.hi());
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Some(format!(
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"match {}{}{{\n{}{}{}\n{}}}",
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cond_str,
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block_sep,
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inner_attrs_str,
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nested_indent_str,
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rewrite_match_arms(context, arms, shape, span_after_cond, open_brace_pos)?,
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shape.indent.to_string(context.config),
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))
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}
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}
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fn arm_comma(config: &Config, body: &ast::Expr, is_last: bool) -> &'static str {
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if is_last && config.trailing_comma() == SeparatorTactic::Never {
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""
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} else if config.match_block_trailing_comma() {
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","
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} else if let ast::ExprKind::Block(ref block, _) = body.kind {
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if let ast::BlockCheckMode::Default = block.rules {
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""
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} else {
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","
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}
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} else {
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","
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}
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}
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/// Collect a byte position of the beginning `|` for each arm, if available.
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fn collect_beginning_verts(
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context: &RewriteContext<'_>,
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arms: &[ast::Arm],
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) -> Vec<Option<BytePos>> {
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arms.iter()
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.map(|a| {
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context
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.snippet(a.pat.span)
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.starts_with('|')
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.then(|| a.pat.span().lo())
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})
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.collect()
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}
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fn rewrite_match_arms(
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context: &RewriteContext<'_>,
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arms: &[ast::Arm],
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shape: Shape,
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span: Span,
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open_brace_pos: BytePos,
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) -> Option<String> {
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let arm_shape = shape
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.block_indent(context.config.tab_spaces())
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.with_max_width(context.config);
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let arm_len = arms.len();
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let is_last_iter = repeat(false)
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.take(arm_len.saturating_sub(1))
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.chain(repeat(true));
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let beginning_verts = collect_beginning_verts(context, arms);
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let items = itemize_list(
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context.snippet_provider,
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arms.iter()
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.zip(is_last_iter)
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.zip(beginning_verts.into_iter())
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.map(|((arm, is_last), beginning_vert)| ArmWrapper::new(arm, is_last, beginning_vert)),
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"}",
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"|",
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|arm| arm.span().lo(),
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|arm| arm.span().hi(),
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|arm| arm.rewrite(context, arm_shape),
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open_brace_pos,
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span.hi(),
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false,
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);
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let arms_vec: Vec<_> = items.collect();
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// We will add/remove commas inside `arm.rewrite()`, and hence no separator here.
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let fmt = ListFormatting::new(arm_shape, context.config)
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.separator("")
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.preserve_newline(true);
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write_list(&arms_vec, &fmt)
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}
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fn rewrite_match_arm(
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context: &RewriteContext<'_>,
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arm: &ast::Arm,
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shape: Shape,
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is_last: bool,
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has_leading_pipe: bool,
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) -> Option<String> {
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let (missing_span, attrs_str) = if !arm.attrs.is_empty() {
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if contains_skip(&arm.attrs) {
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let (_, body) = flatten_arm_body(context, &arm.body, None);
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// `arm.span()` does not include trailing comma, add it manually.
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return Some(format!(
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"{}{}",
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context.snippet(arm.span()),
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arm_comma(context.config, body, is_last),
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));
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}
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let missing_span = mk_sp(arm.attrs[arm.attrs.len() - 1].span.hi(), arm.pat.span.lo());
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(missing_span, arm.attrs.rewrite(context, shape)?)
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} else {
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(mk_sp(arm.span().lo(), arm.span().lo()), String::new())
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};
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// Leading pipe offset
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// 2 = `| `
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let (pipe_offset, pipe_str) = match context.config.match_arm_leading_pipes() {
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MatchArmLeadingPipe::Never => (0, ""),
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MatchArmLeadingPipe::Preserve if !has_leading_pipe => (0, ""),
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MatchArmLeadingPipe::Preserve | MatchArmLeadingPipe::Always => (2, "| "),
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};
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// Patterns
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// 5 = ` => {`
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let pat_shape = shape.sub_width(5)?.offset_left(pipe_offset)?;
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let pats_str = arm.pat.rewrite(context, pat_shape)?;
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// Guard
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let block_like_pat = trimmed_last_line_width(&pats_str) <= context.config.tab_spaces();
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let new_line_guard = pats_str.contains('\n') && !block_like_pat;
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let guard_str = rewrite_guard(
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context,
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&arm.guard,
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shape,
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trimmed_last_line_width(&pats_str),
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new_line_guard,
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)?;
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let lhs_str = combine_strs_with_missing_comments(
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context,
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&attrs_str,
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&format!("{}{}{}", pipe_str, pats_str, guard_str),
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missing_span,
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shape,
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false,
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)?;
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let arrow_span = mk_sp(arm.pat.span.hi(), arm.body.span().lo());
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rewrite_match_body(
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context,
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&arm.body,
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&lhs_str,
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shape,
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guard_str.contains('\n'),
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arrow_span,
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is_last,
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)
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}
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fn stmt_is_expr_mac(stmt: &ast::Stmt) -> bool {
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if let ast::StmtKind::Expr(expr) = &stmt.kind {
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if let ast::ExprKind::MacCall(_) = &expr.kind {
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return true;
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}
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}
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false
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}
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fn block_can_be_flattened<'a>(
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context: &RewriteContext<'_>,
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expr: &'a ast::Expr,
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) -> Option<&'a ast::Block> {
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match expr.kind {
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ast::ExprKind::Block(ref block, _)
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if !is_unsafe_block(block)
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&& !context.inside_macro()
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&& is_simple_block(context, block, Some(&expr.attrs))
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&& !stmt_is_expr_mac(&block.stmts[0]) =>
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{
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Some(&*block)
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}
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_ => None,
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}
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}
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// (extend, body)
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// @extend: true if the arm body can be put next to `=>`
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// @body: flattened body, if the body is block with a single expression
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fn flatten_arm_body<'a>(
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context: &'a RewriteContext<'_>,
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body: &'a ast::Expr,
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opt_shape: Option<Shape>,
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) -> (bool, &'a ast::Expr) {
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let can_extend =
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|expr| !context.config.force_multiline_blocks() && can_flatten_block_around_this(expr);
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if let Some(block) = block_can_be_flattened(context, body) {
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if let ast::StmtKind::Expr(ref expr) = block.stmts[0].kind {
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if let ast::ExprKind::Block(..) = expr.kind {
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flatten_arm_body(context, expr, None)
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} else {
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let cond_becomes_muti_line = opt_shape
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.and_then(|shape| rewrite_cond(context, expr, shape))
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.map_or(false, |cond| cond.contains('\n'));
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if cond_becomes_muti_line {
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(false, &*body)
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} else {
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(can_extend(expr), &*expr)
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}
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}
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} else {
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(false, &*body)
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}
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} else {
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(can_extend(body), &*body)
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}
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}
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fn rewrite_match_body(
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context: &RewriteContext<'_>,
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body: &ptr::P<ast::Expr>,
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pats_str: &str,
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shape: Shape,
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has_guard: bool,
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arrow_span: Span,
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is_last: bool,
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) -> Option<String> {
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let (extend, body) = flatten_arm_body(
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context,
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body,
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shape.offset_left(extra_offset(pats_str, shape) + 4),
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);
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let (is_block, is_empty_block) = if let ast::ExprKind::Block(ref block, _) = body.kind {
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(true, is_empty_block(context, block, Some(&body.attrs)))
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} else {
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(false, false)
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};
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let comma = arm_comma(context.config, body, is_last);
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let alt_block_sep = &shape.indent.to_string_with_newline(context.config);
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let combine_orig_body = |body_str: &str| {
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let block_sep = match context.config.control_brace_style() {
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ControlBraceStyle::AlwaysNextLine if is_block => alt_block_sep,
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_ => " ",
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};
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Some(format!("{} =>{}{}{}", pats_str, block_sep, body_str, comma))
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};
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let next_line_indent = if !is_block || is_empty_block {
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shape.indent.block_indent(context.config)
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} else {
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shape.indent
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};
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let forbid_same_line =
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(has_guard && pats_str.contains('\n') && !is_empty_block) || !body.attrs.is_empty();
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// Look for comments between `=>` and the start of the body.
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let arrow_comment = {
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let arrow_snippet = context.snippet(arrow_span).trim();
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// search for the arrow starting from the end of the snippet since there may be a match
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// expression within the guard
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let arrow_index = arrow_snippet.rfind("=>").unwrap();
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// 2 = `=>`
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let comment_str = arrow_snippet[arrow_index + 2..].trim();
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if comment_str.is_empty() {
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String::new()
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} else {
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rewrite_comment(comment_str, false, shape, context.config)?
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}
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};
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let combine_next_line_body = |body_str: &str| {
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let nested_indent_str = next_line_indent.to_string_with_newline(context.config);
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if is_block {
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let mut result = pats_str.to_owned();
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result.push_str(" =>");
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if !arrow_comment.is_empty() {
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result.push_str(&nested_indent_str);
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result.push_str(&arrow_comment);
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}
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result.push_str(&nested_indent_str);
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result.push_str(body_str);
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result.push_str(comma);
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return Some(result);
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}
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let indent_str = shape.indent.to_string_with_newline(context.config);
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let (body_prefix, body_suffix) =
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if context.config.match_arm_blocks() && !context.inside_macro() {
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let comma = if context.config.match_block_trailing_comma() {
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","
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} else {
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""
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};
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let semicolon = if context.config.version() == Version::One {
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""
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} else {
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if semicolon_for_expr(context, body) {
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";"
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} else {
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""
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}
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};
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("{", format!("{}{}}}{}", semicolon, indent_str, comma))
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} else {
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("", String::from(","))
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};
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let block_sep = match context.config.control_brace_style() {
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ControlBraceStyle::AlwaysNextLine => format!("{}{}", alt_block_sep, body_prefix),
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_ if body_prefix.is_empty() => "".to_owned(),
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_ if forbid_same_line || !arrow_comment.is_empty() => {
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format!("{}{}", alt_block_sep, body_prefix)
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}
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_ => format!(" {}", body_prefix),
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} + &nested_indent_str;
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let mut result = pats_str.to_owned();
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result.push_str(" =>");
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if !arrow_comment.is_empty() {
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result.push_str(&indent_str);
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result.push_str(&arrow_comment);
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}
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result.push_str(&block_sep);
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result.push_str(body_str);
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result.push_str(&body_suffix);
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Some(result)
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};
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// Let's try and get the arm body on the same line as the condition.
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// 4 = ` => `.len()
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let orig_body_shape = shape
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.offset_left(extra_offset(pats_str, shape) + 4)
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.and_then(|shape| shape.sub_width(comma.len()));
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let orig_body = if forbid_same_line || !arrow_comment.is_empty() {
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None
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} else if let Some(body_shape) = orig_body_shape {
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let rewrite = nop_block_collapse(
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format_expr(body, ExprType::Statement, context, body_shape),
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body_shape.width,
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);
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match rewrite {
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Some(ref body_str)
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if is_block
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|| (!body_str.contains('\n')
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&& unicode_str_width(body_str) <= body_shape.width) =>
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{
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return combine_orig_body(body_str);
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}
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_ => rewrite,
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}
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} else {
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None
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};
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let orig_budget = orig_body_shape.map_or(0, |shape| shape.width);
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// Try putting body on the next line and see if it looks better.
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let next_line_body_shape = Shape::indented(next_line_indent, context.config);
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let next_line_body = nop_block_collapse(
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format_expr(body, ExprType::Statement, context, next_line_body_shape),
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next_line_body_shape.width,
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);
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match (orig_body, next_line_body) {
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(Some(ref orig_str), Some(ref next_line_str))
|
|
if prefer_next_line(orig_str, next_line_str, RhsTactics::Default) =>
|
|
{
|
|
combine_next_line_body(next_line_str)
|
|
}
|
|
(Some(ref orig_str), _) if extend && first_line_width(orig_str) <= orig_budget => {
|
|
combine_orig_body(orig_str)
|
|
}
|
|
(Some(ref orig_str), Some(ref next_line_str)) if orig_str.contains('\n') => {
|
|
combine_next_line_body(next_line_str)
|
|
}
|
|
(None, Some(ref next_line_str)) => combine_next_line_body(next_line_str),
|
|
(None, None) => None,
|
|
(Some(ref orig_str), _) => combine_orig_body(orig_str),
|
|
}
|
|
}
|
|
|
|
// The `if ...` guard on a match arm.
|
|
fn rewrite_guard(
|
|
context: &RewriteContext<'_>,
|
|
guard: &Option<ptr::P<ast::Expr>>,
|
|
shape: Shape,
|
|
// The amount of space used up on this line for the pattern in
|
|
// the arm (excludes offset).
|
|
pattern_width: usize,
|
|
multiline_pattern: bool,
|
|
) -> Option<String> {
|
|
if let Some(ref guard) = *guard {
|
|
// First try to fit the guard string on the same line as the pattern.
|
|
// 4 = ` if `, 5 = ` => {`
|
|
let cond_shape = shape
|
|
.offset_left(pattern_width + 4)
|
|
.and_then(|s| s.sub_width(5));
|
|
if !multiline_pattern {
|
|
if let Some(cond_shape) = cond_shape {
|
|
if let Some(cond_str) = guard.rewrite(context, cond_shape) {
|
|
if !cond_str.contains('\n') || pattern_width <= context.config.tab_spaces() {
|
|
return Some(format!(" if {}", cond_str));
|
|
}
|
|
}
|
|
}
|
|
}
|
|
|
|
// Not enough space to put the guard after the pattern, try a newline.
|
|
// 3 = `if `, 5 = ` => {`
|
|
let cond_shape = Shape::indented(shape.indent.block_indent(context.config), context.config)
|
|
.offset_left(3)
|
|
.and_then(|s| s.sub_width(5));
|
|
if let Some(cond_shape) = cond_shape {
|
|
if let Some(cond_str) = guard.rewrite(context, cond_shape) {
|
|
return Some(format!(
|
|
"{}if {}",
|
|
cond_shape.indent.to_string_with_newline(context.config),
|
|
cond_str
|
|
));
|
|
}
|
|
}
|
|
|
|
None
|
|
} else {
|
|
Some(String::new())
|
|
}
|
|
}
|
|
|
|
fn nop_block_collapse(block_str: Option<String>, budget: usize) -> Option<String> {
|
|
debug!("nop_block_collapse {:?} {}", block_str, budget);
|
|
block_str.map(|block_str| {
|
|
if block_str.starts_with('{')
|
|
&& budget >= 2
|
|
&& (block_str[1..].find(|c: char| !c.is_whitespace()).unwrap() == block_str.len() - 2)
|
|
{
|
|
String::from("{}")
|
|
} else {
|
|
block_str
|
|
}
|
|
})
|
|
}
|
|
|
|
fn can_flatten_block_around_this(body: &ast::Expr) -> bool {
|
|
match body.kind {
|
|
// We do not allow `if` to stay on the same line, since we could easily mistake
|
|
// `pat => if cond { ... }` and `pat if cond => { ... }`.
|
|
ast::ExprKind::If(..) => false,
|
|
// We do not allow collapsing a block around expression with condition
|
|
// to avoid it being cluttered with match arm.
|
|
ast::ExprKind::ForLoop(..) | ast::ExprKind::While(..) => false,
|
|
ast::ExprKind::Loop(..)
|
|
| ast::ExprKind::Match(..)
|
|
| ast::ExprKind::Block(..)
|
|
| ast::ExprKind::Closure(..)
|
|
| ast::ExprKind::Array(..)
|
|
| ast::ExprKind::Call(..)
|
|
| ast::ExprKind::MethodCall(..)
|
|
| ast::ExprKind::MacCall(..)
|
|
| ast::ExprKind::Struct(..)
|
|
| ast::ExprKind::Tup(..) => true,
|
|
ast::ExprKind::AddrOf(_, _, ref expr)
|
|
| ast::ExprKind::Box(ref expr)
|
|
| ast::ExprKind::Try(ref expr)
|
|
| ast::ExprKind::Unary(_, ref expr)
|
|
| ast::ExprKind::Index(ref expr, _)
|
|
| ast::ExprKind::Cast(ref expr, _) => can_flatten_block_around_this(expr),
|
|
_ => false,
|
|
}
|
|
}
|