bjoernager/rust
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Improve heuristics for match arm body placement

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This commit is contained in:
Marcus Klaas 2015-09-26 18:16:07 +02:00
parent fd057ab595
commit 078fff068a
6 changed files with 386 additions and 273 deletions
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68
src/expr.rs
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@ -15,7 +15,7 @@ use Indent;
use rewrite::{Rewrite, RewriteContext};
use lists::{write_list, itemize_list, ListFormatting, SeparatorTactic, ListTactic};
use string::{StringFormat, rewrite_string};
use utils::{span_after, extra_offset, first_line_width, last_line_width, wrap_str, binary_search};
use utils::{span_after, extra_offset, last_line_width, wrap_str, binary_search};
use visitor::FmtVisitor;
use config::{StructLitStyle, MultilineStyle};
use comment::{FindUncommented, rewrite_comment, contains_comment};
@ -352,9 +352,9 @@ fn rewrite_closure(capture: ast::CaptureClause,
Some(format!("{} {}", prefix, try_opt!(body_rewrite)))
}
fn nop_block_collapse(block_str: Option<String>) -> Option<String> {
fn nop_block_collapse(block_str: Option<String>, budget: usize) -> Option<String> {
block_str.map(|block_str| {
if block_str.starts_with("{") &&
if block_str.starts_with("{") && budget >= 2 &&
(block_str[1..].find(|c: char| !c.is_whitespace()).unwrap() == block_str.len() - 2) {
"{}".to_owned()
} else {
@ -889,36 +889,64 @@ impl Rewrite for ast::Arm {
// Let's try and get the arm body on the same line as the condition.
// 4 = ` => `.len()
if context.config.max_width > line_start + comma.len() + 4 {
let same_line_body = if context.config.max_width > line_start + comma.len() + 4 {
let budget = context.config.max_width - line_start - comma.len() - 4;
if let Some(ref body_str) = nop_block_collapse(body.rewrite(context,
budget,
line_indent + 4)) {
if first_line_width(body_str) <= budget {
let rewrite = nop_block_collapse(body.rewrite(context, budget, line_indent + 4),
budget);
match rewrite {
Some(ref body_str) if body_str.len() <= budget || comma.is_empty() =>
return Some(format!("{}{} => {}{}",
attr_str.trim_left(),
pats_str,
body_str,
comma));
}
comma)),
_ => rewrite,
}
}
} else {
None
};
// We have to push the body to the next line.
if comma.is_empty() {
if let ast::ExprBlock(_) = body.node {
// We're trying to fit a block in, but it still failed, give up.
return None;
}
let body_budget = try_opt!(width.checked_sub(context.config.tab_spaces));
let body_str = try_opt!(nop_block_collapse(body.rewrite(context,
body_budget,
context.block_indent)));
Some(format!("{}{} =>\n{}{},",
attr_str.trim_left(),
pats_str,
offset.block_indent(context.config).to_string(context.config),
body_str))
let next_line_body = nop_block_collapse(body.rewrite(context,
body_budget,
context.block_indent
.block_indent(context.config)),
body_budget);
let (body_str, break_line) = try_opt!(match_arm_heuristic(same_line_body.as_ref()
.map(|x| &x[..]),
next_line_body.as_ref()
.map(|x| &x[..])));
let spacer = if break_line {
format!("\n{}", offset.block_indent(context.config).to_string(context.config))
} else {
" ".to_owned()
};
Some(format!("{}{} =>{}{},", attr_str.trim_left(), pats_str, spacer, body_str))
}
}
// Takes two possible rewrites for the match arm body and chooses the "nicest".
// Bool marks break line or no.
fn match_arm_heuristic<'a>(former: Option<&'a str>,
latter: Option<&'a str>)
-> Option<(&'a str, bool)> {
match (former, latter) {
(Some(f), None) => Some((f, false)),
(Some(f), Some(l)) if f.chars().filter(|&c| c == '\n').count() <=
l.chars().filter(|&c| c == '\n').count() => {
Some((f, false))
}
(_, l) => l.map(|s| (s, true)),
}
}