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_pair, rewrite_unary_prefix, wrap_struct_field,
  19            PairParts};
  20 use lists::{itemize_list, shape_for_tactic, struct_lit_formatting, struct_lit_shape,
  21             struct_lit_tactic, write_list};
  22 use macros::{rewrite_macro, MacroPosition};
  23 use overflow;
  24 use rewrite::{Rewrite, RewriteContext};
  25 use shape::Shape;
  26 use spanned::Spanned;
  27 use types::{rewrite_path, PathContext};
  28 use utils::{format_mutability, mk_sp};
  29
  30 /// Returns true if the given pattern is short. A short pattern is defined by the following grammer:
  31 ///
  32 /// [small, ntp]:
  33 ///     - single token
  34 ///     - `&[single-line, ntp]`
  35 ///
  36 /// [small]:
  37 ///     - `[small, ntp]`
  38 ///     - unary tuple constructor `([small, ntp])`
  39 ///     - `&[small]`
  40 pub fn is_short_pattern(pat: &ast::Pat, pat_str: &str) -> bool {
  41     // We also require that the pattern is reasonably 'small' with its literal width.
  42     pat_str.len() <= 20 && !pat_str.contains('\n') && is_short_pattern_inner(pat)
  43 }
  44
  45 fn is_short_pattern_inner(pat: &ast::Pat) -> bool {
  46     match pat.node {
  47         ast::PatKind::Wild | ast::PatKind::Lit(_) => true,
  48         ast::PatKind::Ident(_, _, ref pat) => pat.is_none(),
  49         ast::PatKind::Struct(..)
  50         | ast::PatKind::Mac(..)
  51         | ast::PatKind::Slice(..)
  52         | ast::PatKind::Path(..)
  53         | ast::PatKind::Range(..) => false,
  54         ast::PatKind::Tuple(ref subpats, _) => subpats.len() <= 1,
  55         ast::PatKind::TupleStruct(ref path, ref subpats, _) => {
  56             path.segments.len() <= 1 && subpats.len() <= 1
  57         }
  58         ast::PatKind::Box(ref p) | ast::PatKind::Ref(ref p, _) | ast::PatKind::Paren(ref p) => {
  59             is_short_pattern_inner(&*p)
  60         }
  61     }
  62 }
  63
  64 impl Rewrite for Pat {
  65     fn rewrite(&self, context: &RewriteContext, shape: Shape) -> Option<String> {
  66         match self.node {
  67             PatKind::Box(ref pat) => rewrite_unary_prefix(context, "box ", &**pat, shape),
  68             PatKind::Ident(binding_mode, ident, ref sub_pat) => {
  69                 let (prefix, mutability) = match binding_mode {
  70                     BindingMode::ByRef(mutability) => ("ref ", mutability),
  71                     BindingMode::ByValue(mutability) => ("", mutability),
  72                 };
  73                 let mut_infix = format_mutability(mutability);
  74                 let id_str = ident.node.to_string();
  75                 let sub_pat = match *sub_pat {
  76                     Some(ref p) => {
  77                         // 3 - ` @ `.
  78                         let width = shape
  79                             .width
  80                             .checked_sub(prefix.len() + mut_infix.len() + id_str.len() + 3)?;
  81                         format!(
  82                             " @ {}",
  83                             p.rewrite(context, Shape::legacy(width, shape.indent))?
  84                         )
  85                     }
  86                     None => "".to_owned(),
  87                 };
  88
  89                 Some(format!("{}{}{}{}", prefix, mut_infix, id_str, sub_pat))
  90             }
  91             PatKind::Wild => {
  92                 if 1 <= shape.width {
  93                     Some("_".to_owned())
  94                 } else {
  95                     None
  96                 }
  97             }
  98             PatKind::Range(ref lhs, ref rhs, ref end_kind) => {
  99                 let infix = match *end_kind {
 100                     RangeEnd::Included(RangeSyntax::DotDotDot) => "...",
 101                     RangeEnd::Included(RangeSyntax::DotDotEq) => "..=",
 102                     RangeEnd::Excluded => "..",
 103                 };
 104                 let infix = if context.config.spaces_around_ranges() {
 105                     format!(" {} ", infix)
 106                 } else {
 107                     infix.to_owned()
 108                 };
 109                 rewrite_pair(
 110                     &**lhs,
 111                     &**rhs,
 112                     PairParts::new("", &infix, ""),
 113                     context,
 114                     shape,
 115                     SeparatorPlace::Front,
 116                 )
 117             }
 118             PatKind::Ref(ref pat, mutability) => {
 119                 let prefix = format!("&{}", format_mutability(mutability));
 120                 rewrite_unary_prefix(context, &prefix, &**pat, shape)
 121             }
 122             PatKind::Tuple(ref items, dotdot_pos) => {
 123                 rewrite_tuple_pat(items, dotdot_pos, None, self.span, context, shape)
 124             }
 125             PatKind::Path(ref q_self, ref path) => {
 126                 rewrite_path(context, PathContext::Expr, q_self.as_ref(), path, shape)
 127             }
 128             PatKind::TupleStruct(ref path, ref pat_vec, dotdot_pos) => {
 129                 let path_str = rewrite_path(context, PathContext::Expr, None, path, shape)?;
 130                 rewrite_tuple_pat(
 131                     pat_vec,
 132                     dotdot_pos,
 133                     Some(path_str),
 134                     self.span,
 135                     context,
 136                     shape,
 137                 )
 138             }
 139             PatKind::Lit(ref expr) => expr.rewrite(context, shape),
 140             PatKind::Slice(ref prefix, ref slice_pat, ref suffix) => {
 141                 // Rewrite all the sub-patterns.
 142                 let prefix = prefix.iter().map(|p| p.rewrite(context, shape));
 143                 let slice_pat = slice_pat
 144                     .as_ref()
 145                     .map(|p| Some(format!("{}..", p.rewrite(context, shape)?)));
 146                 let suffix = suffix.iter().map(|p| p.rewrite(context, shape));
 147
 148                 // Munge them together.
 149                 let pats: Option<Vec<String>> =
 150                     prefix.chain(slice_pat.into_iter()).chain(suffix).collect();
 151
 152                 // Check that all the rewrites succeeded, and if not return None.
 153                 let pats = pats?;
 154
 155                 // Unwrap all the sub-strings and join them with commas.
 156                 let result = if context.config.spaces_within_parens_and_brackets() {
 157                     format!("[ {} ]", pats.join(", "))
 158                 } else {
 159                     format!("[{}]", pats.join(", "))
 160                 };
 161                 Some(result)
 162             }
 163             PatKind::Struct(ref path, ref fields, ellipsis) => {
 164                 rewrite_struct_pat(path, fields, ellipsis, self.span, context, shape)
 165             }
 166             PatKind::Mac(ref mac) => rewrite_macro(mac, None, context, shape, MacroPosition::Pat),
 167             PatKind::Paren(ref pat) => pat.rewrite(context, shape.offset_left(1)?.sub_width(1)?)
 168                 .map(|inner_pat| format!("({})", inner_pat)),
 169         }
 170     }
 171 }
 172
 173 fn rewrite_struct_pat(
 174     path: &ast::Path,
 175     fields: &[codemap::Spanned<ast::FieldPat>],
 176     ellipsis: bool,
 177     span: Span,
 178     context: &RewriteContext,
 179     shape: Shape,
 180 ) -> Option<String> {
 181     // 2 =  ` {`
 182     let path_shape = shape.sub_width(2)?;
 183     let path_str = rewrite_path(context, PathContext::Expr, None, path, path_shape)?;
 184
 185     if fields.is_empty() && !ellipsis {
 186         return Some(format!("{} {{}}", path_str));
 187     }
 188
 189     let (ellipsis_str, terminator) = if ellipsis { (", ..", "..") } else { ("", "}") };
 190
 191     // 3 = ` { `, 2 = ` }`.
 192     let (h_shape, v_shape) =
 193         struct_lit_shape(shape, context, path_str.len() + 3, ellipsis_str.len() + 2)?;
 194
 195     let items = itemize_list(
 196         context.snippet_provider,
 197         fields.iter(),
 198         terminator,
 199         ",",
 200         |f| f.span.lo(),
 201         |f| f.span.hi(),
 202         |f| f.node.rewrite(context, v_shape),
 203         context.snippet_provider.span_after(span, "{"),
 204         span.hi(),
 205         false,
 206     );
 207     let item_vec = items.collect::<Vec<_>>();
 208
 209     let tactic = struct_lit_tactic(h_shape, context, &item_vec);
 210     let nested_shape = shape_for_tactic(tactic, h_shape, v_shape);
 211     let fmt = struct_lit_formatting(nested_shape, tactic, context, false);
 212
 213     let mut fields_str = write_list(&item_vec, &fmt)?;
 214     let one_line_width = h_shape.map_or(0, |shape| shape.width);
 215
 216     if ellipsis {
 217         if fields_str.contains('\n') || fields_str.len() > one_line_width {
 218             // Add a missing trailing comma.
 219             if fmt.trailing_separator == SeparatorTactic::Never {
 220                 fields_str.push_str(",");
 221             }
 222             fields_str.push_str("\n");
 223             fields_str.push_str(&nested_shape.indent.to_string(context.config));
 224             fields_str.push_str("..");
 225         } else {
 226             if !fields_str.is_empty() {
 227                 // there are preceding struct fields being matched on
 228                 if fmt.tactic == DefinitiveListTactic::Vertical {
 229                     // if the tactic is Vertical, write_list already added a trailing ,
 230                     fields_str.push_str(" ");
 231                 } else {
 232                     fields_str.push_str(", ");
 233                 }
 234             }
 235             fields_str.push_str("..");
 236         }
 237     }
 238
 239     let fields_str = wrap_struct_field(context, &fields_str, shape, v_shape, one_line_width);
 240     Some(format!("{} {{{}}}", path_str, fields_str))
 241 }
 242
 243 impl Rewrite for FieldPat {
 244     fn rewrite(&self, context: &RewriteContext, shape: Shape) -> Option<String> {
 245         let pat = self.pat.rewrite(context, shape);
 246         if self.is_shorthand {
 247             pat
 248         } else {
 249             let pat_str = pat?;
 250             let id_str = self.ident.to_string();
 251             let one_line_width = id_str.len() + 2 + pat_str.len();
 252             if one_line_width <= shape.width {
 253                 Some(format!("{}: {}", id_str, pat_str))
 254             } else {
 255                 let nested_shape = shape.block_indent(context.config.tab_spaces());
 256                 let pat_str = self.pat.rewrite(context, nested_shape)?;
 257                 Some(format!(
 258                     "{}:\n{}{}",
 259                     id_str,
 260                     nested_shape.indent.to_string(context.config),
 261                     pat_str,
 262                 ))
 263             }
 264         }
 265     }
 266 }
 267
 268 pub enum TuplePatField<'a> {
 269     Pat(&'a ptr::P<ast::Pat>),
 270     Dotdot(Span),
 271 }
 272
 273 impl<'a> Rewrite for TuplePatField<'a> {
 274     fn rewrite(&self, context: &RewriteContext, shape: Shape) -> Option<String> {
 275         match *self {
 276             TuplePatField::Pat(p) => p.rewrite(context, shape),
 277             TuplePatField::Dotdot(_) => Some("..".to_string()),
 278         }
 279     }
 280 }
 281
 282 impl<'a> Spanned for TuplePatField<'a> {
 283     fn span(&self) -> Span {
 284         match *self {
 285             TuplePatField::Pat(p) => p.span(),
 286             TuplePatField::Dotdot(span) => span,
 287         }
 288     }
 289 }
 290
 291 pub fn can_be_overflowed_pat(context: &RewriteContext, pat: &TuplePatField, len: usize) -> bool {
 292     match *pat {
 293         TuplePatField::Pat(pat) => match pat.node {
 294             ast::PatKind::Path(..)
 295             | ast::PatKind::Tuple(..)
 296             | ast::PatKind::Struct(..)
 297             | ast::PatKind::TupleStruct(..) => context.use_block_indent() && len == 1,
 298             ast::PatKind::Ref(ref p, _) | ast::PatKind::Box(ref p) => {
 299                 can_be_overflowed_pat(context, &TuplePatField::Pat(p), len)
 300             }
 301             ast::PatKind::Lit(ref expr) => can_be_overflowed_expr(context, expr, len),
 302             _ => false,
 303         },
 304         TuplePatField::Dotdot(..) => false,
 305     }
 306 }
 307
 308 fn rewrite_tuple_pat(
 309     pats: &[ptr::P<ast::Pat>],
 310     dotdot_pos: Option<usize>,
 311     path_str: Option<String>,
 312     span: Span,
 313     context: &RewriteContext,
 314     shape: Shape,
 315 ) -> Option<String> {
 316     let mut pat_vec: Vec<_> = pats.into_iter().map(|x| TuplePatField::Pat(x)).collect();
 317
 318     if let Some(pos) = dotdot_pos {
 319         let prev = if pos == 0 {
 320             span.lo()
 321         } else {
 322             pats[pos - 1].span().hi()
 323         };
 324         let next = if pos + 1 >= pats.len() {
 325             span.hi()
 326         } else {
 327             pats[pos + 1].span().lo()
 328         };
 329         let dot_span = mk_sp(prev, next);
 330         let snippet = context.snippet(dot_span);
 331         let lo = dot_span.lo() + BytePos(snippet.find_uncommented("..").unwrap() as u32);
 332         let dotdot = TuplePatField::Dotdot(Span::new(
 333             lo,
 334             // 2 == "..".len()
 335             lo + BytePos(2),
 336             codemap::NO_EXPANSION,
 337         ));
 338         pat_vec.insert(pos, dotdot);
 339     }
 340
 341     if pat_vec.is_empty() {
 342         return Some(format!("{}()", path_str.unwrap_or_default()));
 343     }
 344
 345     let wildcard_suffix_len = count_wildcard_suffix_len(context, &pat_vec, span, shape);
 346     let (pat_vec, span) = if context.config.condense_wildcard_suffixes() && wildcard_suffix_len >= 2
 347     {
 348         let new_item_count = 1 + pat_vec.len() - wildcard_suffix_len;
 349         let sp = pat_vec[new_item_count - 1].span();
 350         let snippet = context.snippet(sp);
 351         let lo = sp.lo() + BytePos(snippet.find_uncommented("_").unwrap() as u32);
 352         pat_vec[new_item_count - 1] = TuplePatField::Dotdot(mk_sp(lo, lo + BytePos(1)));
 353         (
 354             &pat_vec[..new_item_count],
 355             mk_sp(span.lo(), lo + BytePos(1)),
 356         )
 357     } else {
 358         (&pat_vec[..], span)
 359     };
 360
 361     // add comma if `(x,)`
 362     let add_comma = path_str.is_none() && pat_vec.len() == 1 && dotdot_pos.is_none();
 363     let path_str = path_str.unwrap_or_default();
 364     let pat_ref_vec = pat_vec.iter().collect::<Vec<_>>();
 365
 366     overflow::rewrite_with_parens(
 367         &context,
 368         &path_str,
 369         &pat_ref_vec,
 370         shape,
 371         span,
 372         context.config.max_width(),
 373         if add_comma {
 374             Some(SeparatorTactic::Always)
 375         } else {
 376             None
 377         },
 378     )
 379 }
 380
 381 fn count_wildcard_suffix_len(
 382     context: &RewriteContext,
 383     patterns: &[TuplePatField],
 384     span: Span,
 385     shape: Shape,
 386 ) -> usize {
 387     let mut suffix_len = 0;
 388
 389     let items: Vec<_> = itemize_list(
 390         context.snippet_provider,
 391         patterns.iter(),
 392         ")",
 393         ",",
 394         |item| item.span().lo(),
 395         |item| item.span().hi(),
 396         |item| item.rewrite(context, shape),
 397         context.snippet_provider.span_after(span, "("),
 398         span.hi() - BytePos(1),
 399         false,
 400     ).collect();
 401
 402     for item in items.iter().rev().take_while(|i| match i.item {
 403         Some(ref internal_string) if internal_string == "_" => true,
 404         _ => false,
 405     }) {
 406         suffix_len += 1;
 407
 408         if item.has_comment() {
 409             break;
 410         }
 411     }
 412
 413     suffix_len
 414 }