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::ptr;
  14 use syntax::source_map::{self, BytePos, Span};
  15
  16 use comment::FindUncommented;
  17 use expr::{can_be_overflowed_expr, rewrite_unary_prefix, wrap_struct_field};
  18 use lists::{
  19     itemize_list, shape_for_tactic, struct_lit_formatting, struct_lit_shape, struct_lit_tactic,
  20     write_list,
  21 };
  22 use macros::{rewrite_macro, MacroPosition};
  23 use overflow;
  24 use pairs::{rewrite_pair, PairParts};
  25 use rewrite::{Rewrite, RewriteContext};
  26 use shape::Shape;
  27 use source_map::SpanUtils;
  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                     .and_then(|p| p.rewrite(context, shape))
 148                     .map(|rw| Some(format!("{}..", if rw == "_" { "" } else { &rw })));
 149                 let suffix = suffix.iter().map(|p| p.rewrite(context, shape));
 150
 151                 // Munge them together.
 152                 let pats: Option<Vec<String>> =
 153                     prefix.chain(slice_pat.into_iter()).chain(suffix).collect();
 154
 155                 // Check that all the rewrites succeeded, and if not return None.
 156                 let pats = pats?;
 157
 158                 // Unwrap all the sub-strings and join them with commas.
 159                 Some(format!("[{}]", pats.join(", ")))
 160             }
 161             PatKind::Struct(ref path, ref fields, ellipsis) => {
 162                 rewrite_struct_pat(path, fields, ellipsis, self.span, context, shape)
 163             }
 164             PatKind::Mac(ref mac) => rewrite_macro(mac, None, context, shape, MacroPosition::Pat),
 165             PatKind::Paren(ref pat) => pat
 166                 .rewrite(context, shape.offset_left(1)?.sub_width(1)?)
 167                 .map(|inner_pat| format!("({})", inner_pat)),
 168         }
 169     }
 170 }
 171
 172 fn rewrite_struct_pat(
 173     path: &ast::Path,
 174     fields: &[source_map::Spanned<ast::FieldPat>],
 175     ellipsis: bool,
 176     span: Span,
 177     context: &RewriteContext,
 178     shape: Shape,
 179 ) -> Option<String> {
 180     // 2 =  ` {`
 181     let path_shape = shape.sub_width(2)?;
 182     let path_str = rewrite_path(context, PathContext::Expr, None, path, path_shape)?;
 183
 184     if fields.is_empty() && !ellipsis {
 185         return Some(format!("{} {{}}", path_str));
 186     }
 187
 188     let (ellipsis_str, terminator) = if ellipsis { (", ..", "..") } else { ("", "}") };
 189
 190     // 3 = ` { `, 2 = ` }`.
 191     let (h_shape, v_shape) =
 192         struct_lit_shape(shape, context, path_str.len() + 3, ellipsis_str.len() + 2)?;
 193
 194     let items = itemize_list(
 195         context.snippet_provider,
 196         fields.iter(),
 197         terminator,
 198         ",",
 199         |f| f.span.lo(),
 200         |f| f.span.hi(),
 201         |f| f.node.rewrite(context, v_shape),
 202         context.snippet_provider.span_after(span, "{"),
 203         span.hi(),
 204         false,
 205     );
 206     let item_vec = items.collect::<Vec<_>>();
 207
 208     let tactic = struct_lit_tactic(h_shape, context, &item_vec);
 209     let nested_shape = shape_for_tactic(tactic, h_shape, v_shape);
 210     let fmt = struct_lit_formatting(nested_shape, tactic, context, false);
 211
 212     let mut fields_str = write_list(&item_vec, &fmt)?;
 213     let one_line_width = h_shape.map_or(0, |shape| shape.width);
 214
 215     if ellipsis {
 216         if fields_str.contains('\n') || fields_str.len() > one_line_width {
 217             // Add a missing trailing comma.
 218             if context.config.trailing_comma() == SeparatorTactic::Never {
 219                 fields_str.push_str(",");
 220             }
 221             fields_str.push_str("\n");
 222             fields_str.push_str(&nested_shape.indent.to_string(context.config));
 223             fields_str.push_str("..");
 224         } else {
 225             if !fields_str.is_empty() {
 226                 // there are preceding struct fields being matched on
 227                 if tactic == DefinitiveListTactic::Vertical {
 228                     // if the tactic is Vertical, write_list already added a trailing ,
 229                     fields_str.push_str(" ");
 230                 } else {
 231                     fields_str.push_str(", ");
 232                 }
 233             }
 234             fields_str.push_str("..");
 235         }
 236     }
 237
 238     let fields_str = wrap_struct_field(context, &fields_str, shape, v_shape, one_line_width);
 239     Some(format!("{} {{{}}}", path_str, fields_str))
 240 }
 241
 242 impl Rewrite for FieldPat {
 243     fn rewrite(&self, context: &RewriteContext, shape: Shape) -> Option<String> {
 244         let pat = self.pat.rewrite(context, shape);
 245         if self.is_shorthand {
 246             pat
 247         } else {
 248             let pat_str = pat?;
 249             let id_str = rewrite_ident(context, self.ident);
 250             let one_line_width = id_str.len() + 2 + pat_str.len();
 251             if one_line_width <= shape.width {
 252                 Some(format!("{}: {}", id_str, pat_str))
 253             } else {
 254                 let nested_shape = shape.block_indent(context.config.tab_spaces());
 255                 let pat_str = self.pat.rewrite(context, nested_shape)?;
 256                 Some(format!(
 257                     "{}:\n{}{}",
 258                     id_str,
 259                     nested_shape.indent.to_string(context.config),
 260                     pat_str,
 261                 ))
 262             }
 263         }
 264     }
 265 }
 266
 267 pub enum TuplePatField<'a> {
 268     Pat(&'a ptr::P<ast::Pat>),
 269     Dotdot(Span),
 270 }
 271
 272 impl<'a> Rewrite for TuplePatField<'a> {
 273     fn rewrite(&self, context: &RewriteContext, shape: Shape) -> Option<String> {
 274         match *self {
 275             TuplePatField::Pat(p) => p.rewrite(context, shape),
 276             TuplePatField::Dotdot(_) => Some("..".to_string()),
 277         }
 278     }
 279 }
 280
 281 impl<'a> Spanned for TuplePatField<'a> {
 282     fn span(&self) -> Span {
 283         match *self {
 284             TuplePatField::Pat(p) => p.span(),
 285             TuplePatField::Dotdot(span) => span,
 286         }
 287     }
 288 }
 289
 290 pub fn can_be_overflowed_pat(context: &RewriteContext, pat: &TuplePatField, len: usize) -> bool {
 291     match *pat {
 292         TuplePatField::Pat(pat) => match pat.node {
 293             ast::PatKind::Path(..)
 294             | ast::PatKind::Tuple(..)
 295             | ast::PatKind::Struct(..)
 296             | ast::PatKind::TupleStruct(..) => context.use_block_indent() && len == 1,
 297             ast::PatKind::Ref(ref p, _) | ast::PatKind::Box(ref p) => {
 298                 can_be_overflowed_pat(context, &TuplePatField::Pat(p), len)
 299             }
 300             ast::PatKind::Lit(ref expr) => can_be_overflowed_expr(context, expr, len),
 301             _ => false,
 302         },
 303         TuplePatField::Dotdot(..) => false,
 304     }
 305 }
 306
 307 fn rewrite_tuple_pat(
 308     pats: &[ptr::P<ast::Pat>],
 309     dotdot_pos: Option<usize>,
 310     path_str: Option<String>,
 311     span: Span,
 312     context: &RewriteContext,
 313     shape: Shape,
 314 ) -> Option<String> {
 315     let mut pat_vec: Vec<_> = pats.into_iter().map(|x| TuplePatField::Pat(x)).collect();
 316
 317     if let Some(pos) = dotdot_pos {
 318         let prev = if pos == 0 {
 319             span.lo()
 320         } else {
 321             pats[pos - 1].span().hi()
 322         };
 323         let next = if pos + 1 >= pats.len() {
 324             span.hi()
 325         } else {
 326             pats[pos + 1].span().lo()
 327         };
 328         let dot_span = mk_sp(prev, next);
 329         let snippet = context.snippet(dot_span);
 330         let lo = dot_span.lo() + BytePos(snippet.find_uncommented("..").unwrap() as u32);
 331         let dotdot = TuplePatField::Dotdot(Span::new(
 332             lo,
 333             // 2 == "..".len()
 334             lo + BytePos(2),
 335             source_map::NO_EXPANSION,
 336         ));
 337         pat_vec.insert(pos, dotdot);
 338     }
 339
 340     if pat_vec.is_empty() {
 341         return Some(format!("{}()", path_str.unwrap_or_default()));
 342     }
 343
 344     let wildcard_suffix_len = count_wildcard_suffix_len(context, &pat_vec, span, shape);
 345     let (pat_vec, span) = if context.config.condense_wildcard_suffixes() && wildcard_suffix_len >= 2
 346     {
 347         let new_item_count = 1 + pat_vec.len() - wildcard_suffix_len;
 348         let sp = pat_vec[new_item_count - 1].span();
 349         let snippet = context.snippet(sp);
 350         let lo = sp.lo() + BytePos(snippet.find_uncommented("_").unwrap() as u32);
 351         pat_vec[new_item_count - 1] = TuplePatField::Dotdot(mk_sp(lo, lo + BytePos(1)));
 352         (
 353             &pat_vec[..new_item_count],
 354             mk_sp(span.lo(), lo + BytePos(1)),
 355         )
 356     } else {
 357         (&pat_vec[..], span)
 358     };
 359
 360     // add comma if `(x,)`
 361     let add_comma = path_str.is_none() && pat_vec.len() == 1 && dotdot_pos.is_none();
 362     let path_str = path_str.unwrap_or_default();
 363     let pat_ref_vec = pat_vec.iter().collect::<Vec<_>>();
 364
 365     overflow::rewrite_with_parens(
 366         &context,
 367         &path_str,
 368         &pat_ref_vec,
 369         shape,
 370         span,
 371         context.config.max_width(),
 372         if dotdot_pos.is_some() {
 373             Some(SeparatorTactic::Never)
 374         } else if add_comma {
 375             Some(SeparatorTactic::Always)
 376         } else {
 377             None
 378         },
 379     )
 380 }
 381
 382 fn count_wildcard_suffix_len(
 383     context: &RewriteContext,
 384     patterns: &[TuplePatField],
 385     span: Span,
 386     shape: Shape,
 387 ) -> usize {
 388     let mut suffix_len = 0;
 389
 390     let items: Vec<_> = itemize_list(
 391         context.snippet_provider,
 392         patterns.iter(),
 393         ")",
 394         ",",
 395         |item| item.span().lo(),
 396         |item| item.span().hi(),
 397         |item| item.rewrite(context, shape),
 398         context.snippet_provider.span_after(span, "("),
 399         span.hi() - BytePos(1),
 400         false,
 401     ).collect();
 402
 403     for item in items.iter().rev().take_while(|i| match i.item {
 404         Some(ref internal_string) if internal_string == "_" => true,
 405         _ => false,
 406     }) {
 407         suffix_len += 1;
 408
 409         if item.has_comment() {
 410             break;
 411         }
 412     }
 413
 414     suffix_len
 415 }