--- /dev/null
+//! 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],
+ span: Span,
+) -> Vec<Option<BytePos>> {
+ let mut beginning_verts = Vec::with_capacity(arms.len());
+ let mut lo = context.snippet_provider.span_after(span, "{");
+ for arm in arms {
+ let hi = arm.pat.span.lo();
+ let missing_span = mk_sp(lo, hi);
+ beginning_verts.push(context.snippet_provider.opt_span_before(missing_span, "|"));
+ lo = arm.span().hi();
+ }
+ beginning_verts
+}
+
+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, span);
+ 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(ref 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 {
+ flatten_arm_body(context, expr, None)
+ } 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);
+ 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::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,
+ }
+}
projects / rustc.git / blobdiff