src/patterns.rs

   1 // Copyright 2015 The Rust Project Developers. See the COPYRIGHT
   2 // file at the top-level directory of this distribution and at
   3 // http://rust-lang.org/COPYRIGHT.
   4 //
   5 // Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
   6 // http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
   7 // <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
   8 // option. This file may not be copied, modified, or distributed
   9 // except according to those terms.
  10
  11 use config::lists::*;
  12 use syntax::ast::{self, BindingMode, FieldPat, Pat, PatKind, RangeEnd, RangeSyntax};
  13 use syntax::codemap::{self, BytePos, Span};
  14 use syntax::ptr;
  15
  16 use codemap::SpanUtils;
  17 use comment::FindUncommented;
  18 use expr::{can_be_overflowed_expr, rewrite_unary_prefix, wrap_struct_field};
  19 use lists::{
  20     itemize_list, shape_for_tactic, struct_lit_formatting, struct_lit_shape, struct_lit_tactic,
  21     write_list,
  22 };
  23 use macros::{rewrite_macro, MacroPosition};
  24 use overflow;
  25 use pairs::{rewrite_pair, PairParts};
  26 use rewrite::{Rewrite, RewriteContext};
  27 use shape::Shape;
  28 use spanned::Spanned;
  29 use types::{rewrite_path, PathContext};
  30 use utils::{format_mutability, mk_sp, rewrite_ident};
  31
  32 /// Returns true if the given pattern is short. A short pattern is defined by the following grammer:
  33 ///
  34 /// [small, ntp]:
  35 ///     - single token
  36 ///     - `&[single-line, ntp]`
  37 ///
  38 /// [small]:
  39 ///     - `[small, ntp]`
  40 ///     - unary tuple constructor `([small, ntp])`
  41 ///     - `&[small]`
  42 pub fn is_short_pattern(pat: &ast::Pat, pat_str: &str) -> bool {
  43     // We also require that the pattern is reasonably 'small' with its literal width.
  44     pat_str.len() <= 20 && !pat_str.contains('\n') && is_short_pattern_inner(pat)
  45 }
  46
  47 fn is_short_pattern_inner(pat: &ast::Pat) -> bool {
  48     match pat.node {
  49         ast::PatKind::Wild | ast::PatKind::Lit(_) => true,
  50         ast::PatKind::Ident(_, _, ref pat) => pat.is_none(),
  51         ast::PatKind::Struct(..)
  52         | ast::PatKind::Mac(..)
  53         | ast::PatKind::Slice(..)
  54         | ast::PatKind::Path(..)
  55         | ast::PatKind::Range(..) => false,
  56         ast::PatKind::Tuple(ref subpats, _) => subpats.len() <= 1,
  57         ast::PatKind::TupleStruct(ref path, ref subpats, _) => {
  58             path.segments.len() <= 1 && subpats.len() <= 1
  59         }
  60         ast::PatKind::Box(ref p) | ast::PatKind::Ref(ref p, _) | ast::PatKind::Paren(ref p) => {
  61             is_short_pattern_inner(&*p)
  62         }
  63     }
  64 }
  65
  66 impl Rewrite for Pat {
  67     fn rewrite(&self, context: &RewriteContext, shape: Shape) -> Option<String> {
  68         match self.node {
  69             PatKind::Box(ref pat) => rewrite_unary_prefix(context, "box ", &**pat, shape),
  70             PatKind::Ident(binding_mode, ident, ref sub_pat) => {
  71                 let (prefix, mutability) = match binding_mode {
  72                     BindingMode::ByRef(mutability) => ("ref ", mutability),
  73                     BindingMode::ByValue(mutability) => ("", mutability),
  74                 };
  75                 let mut_infix = format_mutability(mutability);
  76                 let id_str = rewrite_ident(context, ident);
  77                 let sub_pat = match *sub_pat {
  78                     Some(ref p) => {
  79                         // 3 - ` @ `.
  80                         let width = shape
  81                             .width
  82                             .checked_sub(prefix.len() + mut_infix.len() + id_str.len() + 3)?;
  83                         format!(
  84                             " @ {}",
  85                             p.rewrite(context, Shape::legacy(width, shape.indent))?
  86                         )
  87                     }
  88                     None => "".to_owned(),
  89                 };
  90
  91                 Some(format!("{}{}{}{}", prefix, mut_infix, id_str, sub_pat))
  92             }
  93             PatKind::Wild => {
  94                 if 1 <= shape.width {
  95                     Some("_".to_owned())
  96                 } else {
  97                     None
  98                 }
  99             }
 100             PatKind::Range(ref lhs, ref rhs, ref end_kind) => {
 101                 let infix = match end_kind.node {
 102                     RangeEnd::Included(RangeSyntax::DotDotDot) => "...",
 103                     RangeEnd::Included(RangeSyntax::DotDotEq) => "..=",
 104                     RangeEnd::Excluded => "..",
 105                 };
 106                 let infix = if context.config.spaces_around_ranges() {
 107                     format!(" {} ", infix)
 108                 } else {
 109                     infix.to_owned()
 110                 };
 111                 rewrite_pair(
 112                     &**lhs,
 113                     &**rhs,
 114                     PairParts::infix(&infix),
 115                     context,
 116                     shape,
 117                     SeparatorPlace::Front,
 118                 )
 119             }
 120             PatKind::Ref(ref pat, mutability) => {
 121                 let prefix = format!("&{}", format_mutability(mutability));
 122                 rewrite_unary_prefix(context, &prefix, &**pat, shape)
 123             }
 124             PatKind::Tuple(ref items, dotdot_pos) => {
 125                 rewrite_tuple_pat(items, dotdot_pos, None, self.span, context, shape)
 126             }
 127             PatKind::Path(ref q_self, ref path) => {
 128                 rewrite_path(context, PathContext::Expr, q_self.as_ref(), path, shape)
 129             }
 130             PatKind::TupleStruct(ref path, ref pat_vec, dotdot_pos) => {
 131                 let path_str = rewrite_path(context, PathContext::Expr, None, path, shape)?;
 132                 rewrite_tuple_pat(
 133                     pat_vec,
 134                     dotdot_pos,
 135                     Some(path_str),
 136                     self.span,
 137                     context,
 138                     shape,
 139                 )
 140             }
 141             PatKind::Lit(ref expr) => expr.rewrite(context, shape),
 142             PatKind::Slice(ref prefix, ref slice_pat, ref suffix) => {
 143                 // Rewrite all the sub-patterns.
 144                 let prefix = prefix.iter().map(|p| p.rewrite(context, shape));
 145                 let slice_pat = slice_pat
 146                     .as_ref()
 147                     .map(|p| Some(format!("{}..", p.rewrite(context, shape)?)));
 148                 let suffix = suffix.iter().map(|p| p.rewrite(context, shape));
 149
 150                 // Munge them together.
 151                 let pats: Option<Vec<String>> =
 152                     prefix.chain(slice_pat.into_iter()).chain(suffix).collect();
 153
 154                 // Check that all the rewrites succeeded, and if not return None.
 155                 let pats = pats?;
 156
 157                 // Unwrap all the sub-strings and join them with commas.
 158                 Some(format!("[{}]", pats.join(", ")))
 159             }
 160             PatKind::Struct(ref path, ref fields, ellipsis) => {
 161                 rewrite_struct_pat(path, fields, ellipsis, self.span, context, shape)
 162             }
 163             PatKind::Mac(ref mac) => rewrite_macro(mac, None, context, shape, MacroPosition::Pat),
 164             PatKind::Paren(ref pat) => pat
 165                 .rewrite(context, shape.offset_left(1)?.sub_width(1)?)
 166                 .map(|inner_pat| format!("({})", inner_pat)),
 167         }
 168     }
 169 }
 170
 171 fn rewrite_struct_pat(
 172     path: &ast::Path,
 173     fields: &[codemap::Spanned<ast::FieldPat>],
 174     ellipsis: bool,
 175     span: Span,
 176     context: &RewriteContext,
 177     shape: Shape,
 178 ) -> Option<String> {
 179     // 2 =  ` {`
 180     let path_shape = shape.sub_width(2)?;
 181     let path_str = rewrite_path(context, PathContext::Expr, None, path, path_shape)?;
 182
 183     if fields.is_empty() && !ellipsis {
 184         return Some(format!("{} {{}}", path_str));
 185     }
 186
 187     let (ellipsis_str, terminator) = if ellipsis { (", ..", "..") } else { ("", "}") };
 188
 189     // 3 = ` { `, 2 = ` }`.
 190     let (h_shape, v_shape) =
 191         struct_lit_shape(shape, context, path_str.len() + 3, ellipsis_str.len() + 2)?;
 192
 193     let items = itemize_list(
 194         context.snippet_provider,
 195         fields.iter(),
 196         terminator,
 197         ",",
 198         |f| f.span.lo(),
 199         |f| f.span.hi(),
 200         |f| f.node.rewrite(context, v_shape),
 201         context.snippet_provider.span_after(span, "{"),
 202         span.hi(),
 203         false,
 204     );
 205     let item_vec = items.collect::<Vec<_>>();
 206
 207     let tactic = struct_lit_tactic(h_shape, context, &item_vec);
 208     let nested_shape = shape_for_tactic(tactic, h_shape, v_shape);
 209     let fmt = struct_lit_formatting(nested_shape, tactic, context, false);
 210
 211     let mut fields_str = write_list(&item_vec, &fmt)?;
 212     let one_line_width = h_shape.map_or(0, |shape| shape.width);
 213
 214     if ellipsis {
 215         if fields_str.contains('\n') || fields_str.len() > one_line_width {
 216             // Add a missing trailing comma.
 217             if fmt.trailing_separator == SeparatorTactic::Never {
 218                 fields_str.push_str(",");
 219             }
 220             fields_str.push_str("\n");
 221             fields_str.push_str(&nested_shape.indent.to_string(context.config));
 222             fields_str.push_str("..");
 223         } else {
 224             if !fields_str.is_empty() {
 225                 // there are preceding struct fields being matched on
 226                 if fmt.tactic == DefinitiveListTactic::Vertical {
 227                     // if the tactic is Vertical, write_list already added a trailing ,
 228                     fields_str.push_str(" ");
 229                 } else {
 230                     fields_str.push_str(", ");
 231                 }
 232             }
 233             fields_str.push_str("..");
 234         }
 235     }
 236
 237     let fields_str = wrap_struct_field(context, &fields_str, shape, v_shape, one_line_width);
 238     Some(format!("{} {{{}}}", path_str, fields_str))
 239 }
 240
 241 impl Rewrite for FieldPat {
 242     fn rewrite(&self, context: &RewriteContext, shape: Shape) -> Option<String> {
 243         let pat = self.pat.rewrite(context, shape);
 244         if self.is_shorthand {
 245             pat
 246         } else {
 247             let pat_str = pat?;
 248             let id_str = rewrite_ident(context, self.ident);
 249             let one_line_width = id_str.len() + 2 + pat_str.len();
 250             if one_line_width <= shape.width {
 251                 Some(format!("{}: {}", id_str, pat_str))
 252             } else {
 253                 let nested_shape = shape.block_indent(context.config.tab_spaces());
 254                 let pat_str = self.pat.rewrite(context, nested_shape)?;
 255                 Some(format!(
 256                     "{}:\n{}{}",
 257                     id_str,
 258                     nested_shape.indent.to_string(context.config),
 259                     pat_str,
 260                 ))
 261             }
 262         }
 263     }
 264 }
 265
 266 pub enum TuplePatField<'a> {
 267     Pat(&'a ptr::P<ast::Pat>),
 268     Dotdot(Span),
 269 }
 270
 271 impl<'a> Rewrite for TuplePatField<'a> {
 272     fn rewrite(&self, context: &RewriteContext, shape: Shape) -> Option<String> {
 273         match *self {
 274             TuplePatField::Pat(p) => p.rewrite(context, shape),
 275             TuplePatField::Dotdot(_) => Some("..".to_string()),
 276         }
 277     }
 278 }
 279
 280 impl<'a> Spanned for TuplePatField<'a> {
 281     fn span(&self) -> Span {
 282         match *self {
 283             TuplePatField::Pat(p) => p.span(),
 284             TuplePatField::Dotdot(span) => span,
 285         }
 286     }
 287 }
 288
 289 pub fn can_be_overflowed_pat(context: &RewriteContext, pat: &TuplePatField, len: usize) -> bool {
 290     match *pat {
 291         TuplePatField::Pat(pat) => match pat.node {
 292             ast::PatKind::Path(..)
 293             | ast::PatKind::Tuple(..)
 294             | ast::PatKind::Struct(..)
 295             | ast::PatKind::TupleStruct(..) => context.use_block_indent() && len == 1,
 296             ast::PatKind::Ref(ref p, _) | ast::PatKind::Box(ref p) => {
 297                 can_be_overflowed_pat(context, &TuplePatField::Pat(p), len)
 298             }
 299             ast::PatKind::Lit(ref expr) => can_be_overflowed_expr(context, expr, len),
 300             _ => false,
 301         },
 302         TuplePatField::Dotdot(..) => false,
 303     }
 304 }
 305
 306 fn rewrite_tuple_pat(
 307     pats: &[ptr::P<ast::Pat>],
 308     dotdot_pos: Option<usize>,
 309     path_str: Option<String>,
 310     span: Span,
 311     context: &RewriteContext,
 312     shape: Shape,
 313 ) -> Option<String> {
 314     let mut pat_vec: Vec<_> = pats.into_iter().map(|x| TuplePatField::Pat(x)).collect();
 315
 316     if let Some(pos) = dotdot_pos {
 317         let prev = if pos == 0 {
 318             span.lo()
 319         } else {
 320             pats[pos - 1].span().hi()
 321         };
 322         let next = if pos + 1 >= pats.len() {
 323             span.hi()
 324         } else {
 325             pats[pos + 1].span().lo()
 326         };
 327         let dot_span = mk_sp(prev, next);
 328         let snippet = context.snippet(dot_span);
 329         let lo = dot_span.lo() + BytePos(snippet.find_uncommented("..").unwrap() as u32);
 330         let dotdot = TuplePatField::Dotdot(Span::new(
 331             lo,
 332             // 2 == "..".len()
 333             lo + BytePos(2),
 334             codemap::NO_EXPANSION,
 335         ));
 336         pat_vec.insert(pos, dotdot);
 337     }
 338
 339     if pat_vec.is_empty() {
 340         return Some(format!("{}()", path_str.unwrap_or_default()));
 341     }
 342
 343     let wildcard_suffix_len = count_wildcard_suffix_len(context, &pat_vec, span, shape);
 344     let (pat_vec, span) = if context.config.condense_wildcard_suffixes() && wildcard_suffix_len >= 2
 345     {
 346         let new_item_count = 1 + pat_vec.len() - wildcard_suffix_len;
 347         let sp = pat_vec[new_item_count - 1].span();
 348         let snippet = context.snippet(sp);
 349         let lo = sp.lo() + BytePos(snippet.find_uncommented("_").unwrap() as u32);
 350         pat_vec[new_item_count - 1] = TuplePatField::Dotdot(mk_sp(lo, lo + BytePos(1)));
 351         (
 352             &pat_vec[..new_item_count],
 353             mk_sp(span.lo(), lo + BytePos(1)),
 354         )
 355     } else {
 356         (&pat_vec[..], span)
 357     };
 358
 359     // add comma if `(x,)`
 360     let add_comma = path_str.is_none() && pat_vec.len() == 1 && dotdot_pos.is_none();
 361     let path_str = path_str.unwrap_or_default();
 362     let pat_ref_vec = pat_vec.iter().collect::<Vec<_>>();
 363
 364     overflow::rewrite_with_parens(
 365         &context,
 366         &path_str,
 367         &pat_ref_vec,
 368         shape,
 369         span,
 370         context.config.max_width(),
 371         if add_comma {
 372             Some(SeparatorTactic::Always)
 373         } else {
 374             None
 375         },
 376     )
 377 }
 378
 379 fn count_wildcard_suffix_len(
 380     context: &RewriteContext,
 381     patterns: &[TuplePatField],
 382     span: Span,
 383     shape: Shape,
 384 ) -> usize {
 385     let mut suffix_len = 0;
 386
 387     let items: Vec<_> = itemize_list(
 388         context.snippet_provider,
 389         patterns.iter(),
 390         ")",
 391         ",",
 392         |item| item.span().lo(),
 393         |item| item.span().hi(),
 394         |item| item.rewrite(context, shape),
 395         context.snippet_provider.span_after(span, "("),
 396         span.hi() - BytePos(1),
 397         false,
 398     ).collect();
 399
 400     for item in items.iter().rev().take_while(|i| match i.item {
 401         Some(ref internal_string) if internal_string == "_" => true,
 402         _ => false,
 403     }) {
 404         suffix_len += 1;
 405
 406         if item.has_comment() {
 407             break;
 408         }
 409     }
 410
 411     suffix_len
 412 }