blob: 4c37116f120bce8b8011f1377dc8349237a63c49 [file] [log] [blame]
//! Format match expression.
use std::iter::repeat;
use rustc_ast::{ast, ptr};
use rustc_span::{BytePos, Span};
use crate::comment::{combine_strs_with_missing_comments, rewrite_comment};
use crate::config::lists::*;
use crate::config::{Config, ControlBraceStyle, IndentStyle, MatchArmLeadingPipe, Version};
use crate::expr::{
format_expr, is_empty_block, is_simple_block, is_unsafe_block, prefer_next_line, rewrite_cond,
ExprType, RhsTactics,
};
use crate::lists::{itemize_list, write_list, ListFormatting};
use crate::rewrite::{Rewrite, RewriteContext};
use crate::shape::Shape;
use crate::source_map::SpanUtils;
use crate::spanned::Spanned;
use crate::utils::{
contains_skip, extra_offset, first_line_width, inner_attributes, last_line_extendable, mk_sp,
semicolon_for_expr, trimmed_last_line_width, unicode_str_width,
};
/// A simple wrapper type against `ast::Arm`. Used inside `write_list()`.
struct ArmWrapper<'a> {
arm: &'a ast::Arm,
/// `true` if the arm is the last one in match expression. Used to decide on whether we should
/// add trailing comma to the match arm when `config.trailing_comma() == Never`.
is_last: bool,
/// Holds a byte position of `|` at the beginning of the arm pattern, if available.
beginning_vert: Option<BytePos>,
}
impl<'a> ArmWrapper<'a> {
fn new(arm: &'a ast::Arm, is_last: bool, beginning_vert: Option<BytePos>) -> ArmWrapper<'a> {
ArmWrapper {
arm,
is_last,
beginning_vert,
}
}
}
impl<'a> Spanned for ArmWrapper<'a> {
fn span(&self) -> Span {
if let Some(lo) = self.beginning_vert {
let lo = std::cmp::min(lo, self.arm.span().lo());
mk_sp(lo, self.arm.span().hi())
} else {
self.arm.span()
}
}
}
impl<'a> Rewrite for ArmWrapper<'a> {
fn rewrite(&self, context: &RewriteContext<'_>, shape: Shape) -> Option<String> {
rewrite_match_arm(
context,
self.arm,
shape,
self.is_last,
self.beginning_vert.is_some(),
)
}
}
pub(crate) fn rewrite_match(
context: &RewriteContext<'_>,
cond: &ast::Expr,
arms: &[ast::Arm],
shape: Shape,
span: Span,
attrs: &[ast::Attribute],
) -> Option<String> {
// Do not take the rhs overhead from the upper expressions into account
// when rewriting match condition.
let cond_shape = Shape {
width: context.budget(shape.used_width()),
..shape
};
// 6 = `match `
let cond_shape = match context.config.indent_style() {
IndentStyle::Visual => cond_shape.shrink_left(6)?,
IndentStyle::Block => cond_shape.offset_left(6)?,
};
let cond_str = cond.rewrite(context, cond_shape)?;
let alt_block_sep = &shape.indent.to_string_with_newline(context.config);
let block_sep = match context.config.control_brace_style() {
ControlBraceStyle::AlwaysNextLine => alt_block_sep,
_ if last_line_extendable(&cond_str) => " ",
// 2 = ` {`
_ if cond_str.contains('\n') || cond_str.len() + 2 > cond_shape.width => alt_block_sep,
_ => " ",
};
let nested_indent_str = shape
.indent
.block_indent(context.config)
.to_string(context.config);
// Inner attributes.
let inner_attrs = &inner_attributes(attrs);
let inner_attrs_str = if inner_attrs.is_empty() {
String::new()
} else {
inner_attrs
.rewrite(context, shape)
.map(|s| format!("{}{}\n", nested_indent_str, s))?
};
let open_brace_pos = if inner_attrs.is_empty() {
let hi = if arms.is_empty() {
span.hi()
} else {
arms[0].span().lo()
};
context
.snippet_provider
.span_after(mk_sp(cond.span.hi(), hi), "{")
} else {
inner_attrs[inner_attrs.len() - 1].span.hi()
};
if arms.is_empty() {
let snippet = context.snippet(mk_sp(open_brace_pos, span.hi() - BytePos(1)));
if snippet.trim().is_empty() {
Some(format!("match {} {{}}", cond_str))
} else {
// Empty match with comments or inner attributes? We are not going to bother, sorry ;)
Some(context.snippet(span).to_owned())
}
} else {
let span_after_cond = mk_sp(cond.span.hi(), span.hi());
Some(format!(
"match {}{}{{\n{}{}{}\n{}}}",
cond_str,
block_sep,
inner_attrs_str,
nested_indent_str,
rewrite_match_arms(context, arms, shape, span_after_cond, open_brace_pos)?,
shape.indent.to_string(context.config),
))
}
}
fn arm_comma(config: &Config, body: &ast::Expr, is_last: bool) -> &'static str {
if is_last && config.trailing_comma() == SeparatorTactic::Never {
""
} else if config.match_block_trailing_comma() {
","
} else if let ast::ExprKind::Block(ref block, _) = body.kind {
if let ast::BlockCheckMode::Default = block.rules {
""
} else {
","
}
} else {
","
}
}
/// Collect a byte position of the beginning `|` for each arm, if available.
fn collect_beginning_verts(
context: &RewriteContext<'_>,
arms: &[ast::Arm],
) -> Vec<Option<BytePos>> {
arms.iter()
.map(|a| {
context
.snippet(a.pat.span)
.starts_with('|')
.then(|| a.pat.span().lo())
})
.collect()
}
fn rewrite_match_arms(
context: &RewriteContext<'_>,
arms: &[ast::Arm],
shape: Shape,
span: Span,
open_brace_pos: BytePos,
) -> Option<String> {
let arm_shape = shape
.block_indent(context.config.tab_spaces())
.with_max_width(context.config);
let arm_len = arms.len();
let is_last_iter = repeat(false)
.take(arm_len.saturating_sub(1))
.chain(repeat(true));
let beginning_verts = collect_beginning_verts(context, arms);
let items = itemize_list(
context.snippet_provider,
arms.iter()
.zip(is_last_iter)
.zip(beginning_verts.into_iter())
.map(|((arm, is_last), beginning_vert)| ArmWrapper::new(arm, is_last, beginning_vert)),
"}",
"|",
|arm| arm.span().lo(),
|arm| arm.span().hi(),
|arm| arm.rewrite(context, arm_shape),
open_brace_pos,
span.hi(),
false,
);
let arms_vec: Vec<_> = items.collect();
// We will add/remove commas inside `arm.rewrite()`, and hence no separator here.
let fmt = ListFormatting::new(arm_shape, context.config)
.separator("")
.preserve_newline(true);
write_list(&arms_vec, &fmt)
}
fn rewrite_match_arm(
context: &RewriteContext<'_>,
arm: &ast::Arm,
shape: Shape,
is_last: bool,
has_leading_pipe: bool,
) -> Option<String> {
let (missing_span, attrs_str) = if !arm.attrs.is_empty() {
if contains_skip(&arm.attrs) {
let (_, body) = flatten_arm_body(context, &arm.body, None);
// `arm.span()` does not include trailing comma, add it manually.
return Some(format!(
"{}{}",
context.snippet(arm.span()),
arm_comma(context.config, body, is_last),
));
}
let missing_span = mk_sp(arm.attrs[arm.attrs.len() - 1].span.hi(), arm.pat.span.lo());
(missing_span, arm.attrs.rewrite(context, shape)?)
} else {
(mk_sp(arm.span().lo(), arm.span().lo()), String::new())
};
// Leading pipe offset
// 2 = `| `
let (pipe_offset, pipe_str) = match context.config.match_arm_leading_pipes() {
MatchArmLeadingPipe::Never => (0, ""),
MatchArmLeadingPipe::Preserve if !has_leading_pipe => (0, ""),
MatchArmLeadingPipe::Preserve | MatchArmLeadingPipe::Always => (2, "| "),
};
// Patterns
// 5 = ` => {`
let pat_shape = shape.sub_width(5)?.offset_left(pipe_offset)?;
let pats_str = arm.pat.rewrite(context, pat_shape)?;
// Guard
let block_like_pat = trimmed_last_line_width(&pats_str) <= context.config.tab_spaces();
let new_line_guard = pats_str.contains('\n') && !block_like_pat;
let guard_str = rewrite_guard(
context,
&arm.guard,
shape,
trimmed_last_line_width(&pats_str),
new_line_guard,
)?;
let lhs_str = combine_strs_with_missing_comments(
context,
&attrs_str,
&format!("{}{}{}", pipe_str, pats_str, guard_str),
missing_span,
shape,
false,
)?;
let arrow_span = mk_sp(arm.pat.span.hi(), arm.body.span().lo());
rewrite_match_body(
context,
&arm.body,
&lhs_str,
shape,
guard_str.contains('\n'),
arrow_span,
is_last,
)
}
fn stmt_is_expr_mac(stmt: &ast::Stmt) -> bool {
if let ast::StmtKind::Expr(expr) = &stmt.kind {
if let ast::ExprKind::MacCall(_) = &expr.kind {
return true;
}
}
false
}
fn block_can_be_flattened<'a>(
context: &RewriteContext<'_>,
expr: &'a ast::Expr,
) -> Option<&'a ast::Block> {
match expr.kind {
ast::ExprKind::Block(ref block, _)
if !is_unsafe_block(block)
&& !context.inside_macro()
&& is_simple_block(context, block, Some(&expr.attrs))
&& !stmt_is_expr_mac(&block.stmts[0]) =>
{
Some(&*block)
}
_ => None,
}
}
// (extend, body)
// @extend: true if the arm body can be put next to `=>`
// @body: flattened body, if the body is block with a single expression
fn flatten_arm_body<'a>(
context: &'a RewriteContext<'_>,
body: &'a ast::Expr,
opt_shape: Option<Shape>,
) -> (bool, &'a ast::Expr) {
let can_extend =
|expr| !context.config.force_multiline_blocks() && can_flatten_block_around_this(expr);
if let Some(block) = block_can_be_flattened(context, body) {
if let ast::StmtKind::Expr(ref expr) = block.stmts[0].kind {
if let ast::ExprKind::Block(..) = expr.kind {
if expr.attrs.is_empty() {
flatten_arm_body(context, expr, None)
} else {
(true, body)
}
} else {
let cond_becomes_muti_line = opt_shape
.and_then(|shape| rewrite_cond(context, expr, shape))
.map_or(false, |cond| cond.contains('\n'));
if cond_becomes_muti_line {
(false, &*body)
} else {
(can_extend(expr), &*expr)
}
}
} else {
(false, &*body)
}
} else {
(can_extend(body), &*body)
}
}
fn rewrite_match_body(
context: &RewriteContext<'_>,
body: &ptr::P<ast::Expr>,
pats_str: &str,
shape: Shape,
has_guard: bool,
arrow_span: Span,
is_last: bool,
) -> Option<String> {
let (extend, body) = flatten_arm_body(
context,
body,
shape.offset_left(extra_offset(pats_str, shape) + 4),
);
let (is_block, is_empty_block) = if let ast::ExprKind::Block(ref block, _) = body.kind {
(true, is_empty_block(context, block, Some(&body.attrs)))
} else {
(false, false)
};
let comma = arm_comma(context.config, body, is_last);
let alt_block_sep = &shape.indent.to_string_with_newline(context.config);
let combine_orig_body = |body_str: &str| {
let block_sep = match context.config.control_brace_style() {
ControlBraceStyle::AlwaysNextLine if is_block => alt_block_sep,
_ => " ",
};
Some(format!("{} =>{}{}{}", pats_str, block_sep, body_str, comma))
};
let next_line_indent = if !is_block || is_empty_block {
shape.indent.block_indent(context.config)
} else {
shape.indent
};
let forbid_same_line =
(has_guard && pats_str.contains('\n') && !is_empty_block) || !body.attrs.is_empty();
// Look for comments between `=>` and the start of the body.
let arrow_comment = {
let arrow_snippet = context.snippet(arrow_span).trim();
// search for the arrow starting from the end of the snippet since there may be a match
// expression within the guard
let arrow_index = arrow_snippet.rfind("=>").unwrap();
// 2 = `=>`
let comment_str = arrow_snippet[arrow_index + 2..].trim();
if comment_str.is_empty() {
String::new()
} else {
rewrite_comment(comment_str, false, shape, context.config)?
}
};
let combine_next_line_body = |body_str: &str| {
let nested_indent_str = next_line_indent.to_string_with_newline(context.config);
if is_block {
let mut result = pats_str.to_owned();
result.push_str(" =>");
if !arrow_comment.is_empty() {
result.push_str(&nested_indent_str);
result.push_str(&arrow_comment);
}
result.push_str(&nested_indent_str);
result.push_str(body_str);
result.push_str(comma);
return Some(result);
}
let indent_str = shape.indent.to_string_with_newline(context.config);
let (body_prefix, body_suffix) =
if context.config.match_arm_blocks() && !context.inside_macro() {
let comma = if context.config.match_block_trailing_comma() {
","
} else {
""
};
let semicolon = if context.config.version() == Version::One {
""
} else {
if semicolon_for_expr(context, body) {
";"
} else {
""
}
};
("{", format!("{}{}}}{}", semicolon, indent_str, comma))
} else {
("", String::from(","))
};
let block_sep = match context.config.control_brace_style() {
ControlBraceStyle::AlwaysNextLine => format!("{}{}", alt_block_sep, body_prefix),
_ if body_prefix.is_empty() => "".to_owned(),
_ if forbid_same_line || !arrow_comment.is_empty() => {
format!("{}{}", alt_block_sep, body_prefix)
}
_ => format!(" {}", body_prefix),
} + &nested_indent_str;
let mut result = pats_str.to_owned();
result.push_str(" =>");
if !arrow_comment.is_empty() {
result.push_str(&indent_str);
result.push_str(&arrow_comment);
}
result.push_str(&block_sep);
result.push_str(body_str);
result.push_str(&body_suffix);
Some(result)
};
// Let's try and get the arm body on the same line as the condition.
// 4 = ` => `.len()
let orig_body_shape = shape
.offset_left(extra_offset(pats_str, shape) + 4)
.and_then(|shape| shape.sub_width(comma.len()));
let orig_body = if forbid_same_line || !arrow_comment.is_empty() {
None
} else if let Some(body_shape) = orig_body_shape {
let rewrite = nop_block_collapse(
format_expr(body, ExprType::Statement, context, body_shape),
body_shape.width,
);
match rewrite {
Some(ref body_str)
if is_block
|| (!body_str.contains('\n')
&& unicode_str_width(body_str) <= body_shape.width) =>
{
return combine_orig_body(body_str);
}
_ => rewrite,
}
} else {
None
};
let orig_budget = orig_body_shape.map_or(0, |shape| shape.width);
// Try putting body on the next line and see if it looks better.
let next_line_body_shape = Shape::indented(next_line_indent, context.config);
let next_line_body = nop_block_collapse(
format_expr(body, ExprType::Statement, context, next_line_body_shape),
next_line_body_shape.width,
);
match (orig_body, next_line_body) {
(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::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,
}
}