src/functions.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 {ReturnIndent, MAX_WIDTH, BraceStyle,
  12      IDEAL_WIDTH, LEEWAY, FN_BRACE_STYLE, FN_RETURN_INDENT};
  13 use utils::make_indent;
  14 use lists::{write_list, ListFormatting, SeparatorTactic, ListTactic};
  15 use visitor::FmtVisitor;
  16 use syntax::{ast, abi};
  17 use syntax::codemap::{self, Span, BytePos};
  18 use syntax::print::pprust;
  19 use syntax::parse::token;
  20
  21 impl<'a> FmtVisitor<'a> {
  22     pub fn rewrite_fn(&mut self,
  23                       indent: usize,
  24                       ident: ast::Ident,
  25                       fd: &ast::FnDecl,
  26                       explicit_self: Option<&ast::ExplicitSelf>,
  27                       generics: &ast::Generics,
  28                       unsafety: &ast::Unsafety,
  29                       abi: &abi::Abi,
  30                       vis: ast::Visibility,
  31                       next_span: Span) // next_span is a nasty hack, its a loose upper
  32                                        // bound on any comments after the where clause.
  33         -> String
  34     {
  35         // FIXME we'll lose any comments in between parts of the function decl, but anyone
  36         // who comments there probably deserves what they get.
  37
  38         let where_clause = &generics.where_clause;
  39         let newline_brace = self.newline_for_brace(where_clause);
  40
  41         let mut result = String::with_capacity(1024);
  42         // Vis unsafety abi.
  43         if vis == ast::Visibility::Public {
  44             result.push_str("pub ");
  45         }
  46         if let &ast::Unsafety::Unsafe = unsafety {
  47             result.push_str("unsafe ");
  48         }
  49         if *abi != abi::Rust {
  50             result.push_str("extern ");
  51             result.push_str(&abi.to_string());
  52             result.push(' ');
  53         }
  54
  55         // fn foo
  56         result.push_str("fn ");
  57         result.push_str(&token::get_ident(ident));
  58
  59         // Generics.
  60         let generics_indent = indent + result.len();
  61         result.push_str(&self.rewrite_generics(generics,
  62                                                generics_indent,
  63                                                span_for_return(&fd.output)));
  64
  65         let ret_str = self.rewrite_return(&fd.output);
  66
  67         // Args.
  68         let (one_line_budget, multi_line_budget, arg_indent) =
  69             self.compute_budgets_for_args(&mut result, indent, ret_str.len(), newline_brace);
  70
  71         debug!("rewrite_fn: one_line_budget: {}, multi_line_budget: {}, arg_indent: {}",
  72                one_line_budget, multi_line_budget, arg_indent);
  73
  74         result.push('(');
  75         result.push_str(&self.rewrite_args(&fd.inputs,
  76                                            explicit_self,
  77                                            one_line_budget,
  78                                            multi_line_budget,
  79                                            arg_indent,
  80                                            span_for_return(&fd.output)));
  81         result.push(')');
  82
  83         // Return type.
  84         if ret_str.len() > 0 {
  85             // If we've already gone multi-line, or the return type would push
  86             // over the max width, then put the return type on a new line.
  87             if result.contains("\n") ||
  88                result.len() + indent + ret_str.len() > MAX_WIDTH {
  89                 let indent = match FN_RETURN_INDENT {
  90                     ReturnIndent::WithWhereClause => indent + 4,
  91                     // TODO we might want to check that using the arg indent doesn't
  92                     // blow our budget, and if it does, then fallback to the where
  93                     // clause indent.
  94                     _ => arg_indent,
  95                 };
  96
  97                 result.push('\n');
  98                 result.push_str(&make_indent(indent));
  99             } else {
 100                 result.push(' ');
 101             }
 102             result.push_str(&ret_str);
 103
 104             // Comment between return type and the end of the decl.
 105             let snippet_lo = fd.output.span().hi;
 106             if where_clause.predicates.len() == 0 {
 107                 let snippet_hi = next_span.lo;
 108                 let snippet = self.snippet(codemap::mk_sp(snippet_lo, snippet_hi));
 109                 let snippet = snippet.trim();
 110                 if snippet.len() > 0 {
 111                     result.push(' ');
 112                     result.push_str(snippet);
 113                 }
 114             } else {
 115                 // FIXME it would be nice to catch comments between the return type
 116                 // and the where clause, but we don't have a span for the where
 117                 // clause.
 118             }
 119         }
 120
 121         // Where clause.
 122         result.push_str(&self.rewrite_where_clause(where_clause, indent, next_span));
 123
 124         // Prepare for the function body by possibly adding a newline and indent.
 125         // FIXME we'll miss anything between the end of the signature and the start
 126         // of the body, but we need more spans from the compiler to solve this.
 127         if newline_brace {
 128             result.push('\n');
 129             result.push_str(&make_indent(self.block_indent));
 130         } else {
 131             result.push(' ');
 132         }
 133
 134         result
 135     }
 136
 137     fn rewrite_args(&self,
 138                     args: &[ast::Arg],
 139                     explicit_self: Option<&ast::ExplicitSelf>,
 140                     one_line_budget: usize,
 141                     multi_line_budget: usize,
 142                     arg_indent: usize,
 143                     ret_span: Span)
 144         -> String
 145     {
 146         let mut arg_item_strs: Vec<_> = args.iter().map(|a| self.rewrite_fn_input(a)).collect();
 147         // Account for sugary self.
 148         let mut min_args = 1;
 149         if let Some(explicit_self) = explicit_self {
 150             match explicit_self.node {
 151                 ast::ExplicitSelf_::SelfRegion(ref lt, ref m, _) => {
 152                     let lt_str = match lt {
 153                         &Some(ref l) => format!("{} ", pprust::lifetime_to_string(l)),
 154                         &None => String::new(),
 155                     };
 156                     let mut_str = match m {
 157                         &ast::Mutability::MutMutable => "mut ".to_owned(),
 158                         &ast::Mutability::MutImmutable => String::new(),
 159                     };
 160                     arg_item_strs[0] = format!("&{}{}self", lt_str, mut_str);
 161                     min_args = 2;
 162                 }
 163                 ast::ExplicitSelf_::SelfExplicit(ref ty, _) => {
 164                     arg_item_strs[0] = format!("self: {}", pprust::ty_to_string(ty));
 165                 }
 166                 ast::ExplicitSelf_::SelfValue(_) => {
 167                     arg_item_strs[0] = "self".to_owned();
 168                     min_args = 2;
 169                 }
 170                 _ => {}
 171             }
 172         }
 173
 174         // Comments between args
 175         let mut arg_comments = Vec::new();
 176         if min_args == 2 {
 177             arg_comments.push("".to_owned());
 178         }
 179         // TODO if there are no args, there might still be a comment, but without
 180         // spans for the comment or parens, there is no chance of getting it right.
 181         // You also don't get to put a comment on self, unless it is explicit.
 182         if args.len() >= min_args {
 183             arg_comments = self.make_comments_for_list(arg_comments,
 184                                                        args[min_args-1..].iter(),
 185                                                        ",",
 186                                                        ")",
 187                                                        |arg| arg.pat.span.lo,
 188                                                        |arg| arg.ty.span.hi,
 189                                                        ret_span.lo);
 190         }
 191
 192         debug!("comments: {:?}", arg_comments);
 193
 194         // If there are // comments, keep them multi-line.
 195         let mut list_tactic = ListTactic::HorizontalVertical;
 196         if arg_comments.iter().any(|c| c.contains("//")) {
 197             list_tactic = ListTactic::Vertical;
 198         }
 199
 200         assert_eq!(arg_item_strs.len(), arg_comments.len());
 201         let arg_strs: Vec<_> = arg_item_strs.into_iter().zip(arg_comments.into_iter()).collect();
 202
 203         let fmt = ListFormatting {
 204             tactic: list_tactic,
 205             separator: ",",
 206             trailing_separator: SeparatorTactic::Never,
 207             indent: arg_indent,
 208             h_width: one_line_budget,
 209             v_width: multi_line_budget,
 210         };
 211
 212         write_list(&arg_strs, &fmt)
 213     }
 214
 215     // Gets comments in between items of a list.
 216     fn make_comments_for_list<T, I, F1, F2>(&self,
 217                                             prefix: Vec<String>,
 218                                             mut it: I,
 219                                             separator: &str,
 220                                             terminator: &str,
 221                                             get_lo: F1,
 222                                             get_hi: F2,
 223                                             next_span_start: BytePos)
 224         -> Vec<String>
 225         where I: Iterator<Item=T>,
 226               F1: Fn(&T) -> BytePos,
 227               F2: Fn(&T) -> BytePos
 228     {
 229         let mut result = prefix;
 230
 231         let mut prev_end = get_hi(&it.next().unwrap());
 232         for item in it {
 233             let cur_start = get_lo(&item);
 234             let snippet = self.snippet(codemap::mk_sp(prev_end, cur_start));
 235             let mut snippet = snippet.trim();
 236             let white_space: &[_] = &[' ', '\t'];
 237             if snippet.starts_with(separator) {
 238                 snippet = snippet[separator.len()..].trim_matches(white_space);
 239             } else if snippet.ends_with(separator) {
 240                 snippet = snippet[..snippet.len()-separator.len()].trim_matches(white_space);
 241             }
 242             result.push(snippet.to_owned());
 243             prev_end = get_hi(&item);
 244         }
 245         // Get the last commment.
 246         // FIXME If you thought the crap with the commas was ugly, just wait.
 247         // This is awful. We're going to look from the last item span to the
 248         // start of the return type span, then we drop everything after the
 249         // first closing paren. Obviously, this will break if there is a
 250         // closing paren in the comment.
 251         // The fix is comments in the AST or a span for the closing paren.
 252         let snippet = self.snippet(codemap::mk_sp(prev_end, next_span_start));
 253         let snippet = snippet.trim();
 254         let snippet = &snippet[..snippet.find(terminator)
 255                                     .unwrap_or(snippet.find(separator).unwrap_or(snippet.len()))];
 256         let snippet = snippet.trim();
 257         result.push(snippet.to_owned());
 258
 259         result
 260     }
 261
 262     fn compute_budgets_for_args(&self,
 263                                 result: &mut String,
 264                                 indent: usize,
 265                                 ret_str_len: usize,
 266                                 newline_brace: bool)
 267         -> (usize, usize, usize)
 268     {
 269         let mut budgets = None;
 270
 271         // Try keeping everything on the same line
 272         if !result.contains("\n") {
 273             // 3 = `() `, space is before ret_string
 274             let mut used_space = indent + result.len() + ret_str_len + 3;
 275             if !newline_brace {
 276                 used_space += 2;
 277             }
 278             let one_line_budget = if used_space > MAX_WIDTH {
 279                 0
 280             } else {
 281                 MAX_WIDTH - used_space
 282             };
 283
 284             // 2 = `()`
 285             let used_space = indent + result.len() + 2;
 286             let max_space = IDEAL_WIDTH + LEEWAY;
 287             debug!("compute_budgets_for_args: used_space: {}, max_space: {}",
 288                    used_space, max_space);
 289             if used_space < max_space {
 290                 budgets = Some((one_line_budget,
 291                                 max_space - used_space,
 292                                 indent + result.len() + 1));
 293             }
 294         }
 295
 296         // Didn't work. we must force vertical layout and put args on a newline.
 297         if let None = budgets {
 298             result.push('\n');
 299             result.push_str(&make_indent(indent + 4));
 300             // 6 = new indent + `()`
 301             let used_space = indent + 6;
 302             let max_space = IDEAL_WIDTH + LEEWAY;
 303             if used_space > max_space {
 304                 // Whoops! bankrupt.
 305                 // TODO take evasive action, perhaps kill the indent or something.
 306             } else {
 307                 // 5 = new indent + `(`
 308                 budgets = Some((0, max_space - used_space, indent + 5));
 309             }
 310         }
 311
 312         budgets.unwrap()
 313     }
 314
 315     fn newline_for_brace(&self, where_clause: &ast::WhereClause) -> bool {
 316         match FN_BRACE_STYLE {
 317             BraceStyle::AlwaysNextLine => true,
 318             BraceStyle::SameLineWhere if where_clause.predicates.len() > 0 => true,
 319             _ => false,
 320         }
 321     }
 322
 323     fn rewrite_generics(&self, generics: &ast::Generics, indent: usize, ret_span: Span) -> String {
 324         // FIXME convert bounds to where clauses where they get too big or if
 325         // there is a where clause at all.
 326         let mut result = String::new();
 327         let lifetimes: &[_] = &generics.lifetimes;
 328         let tys: &[_] = &generics.ty_params;
 329         if lifetimes.len() + tys.len() == 0 {
 330             return result;
 331         }
 332
 333         let budget = MAX_WIDTH - indent - 2;
 334         // TODO might need to insert a newline if the generics are really long
 335         result.push('<');
 336
 337         // Strings for the generics.
 338         let lt_strs = lifetimes.iter().map(|l| self.rewrite_lifetime_def(l));
 339         let ty_strs = tys.iter().map(|ty| self.rewrite_ty_param(ty));
 340
 341         // Extract comments between generics.
 342         let lt_spans = lifetimes.iter().map(|l| {
 343             let hi = if l.bounds.len() == 0 {
 344                 l.lifetime.span.hi
 345             } else {
 346                 l.bounds[l.bounds.len() - 1].span.hi
 347             };
 348             codemap::mk_sp(l.lifetime.span.lo, hi)
 349         });
 350         let ty_spans = tys.iter().map(span_for_ty_param);
 351         let comments = self.make_comments_for_list(Vec::new(),
 352                                                    lt_spans.chain(ty_spans),
 353                                                    ",",
 354                                                    ">",
 355                                                    |sp| sp.lo,
 356                                                    |sp| sp.hi,
 357                                                    ret_span.lo);
 358
 359         // If there are // comments, keep them multi-line.
 360         let mut list_tactic = ListTactic::HorizontalVertical;
 361         if comments.iter().any(|c| c.contains("//")) {
 362             list_tactic = ListTactic::Vertical;
 363         }
 364
 365         let generics_strs: Vec<_> = lt_strs.chain(ty_strs).zip(comments.into_iter()).collect();
 366         let fmt = ListFormatting {
 367             tactic: list_tactic,
 368             separator: ",",
 369             trailing_separator: SeparatorTactic::Never,
 370             indent: indent + 1,
 371             h_width: budget,
 372             v_width: budget,
 373         };
 374         result.push_str(&write_list(&generics_strs, &fmt));
 375
 376         result.push('>');
 377
 378         result
 379     }
 380
 381     fn rewrite_where_clause(&self,
 382                             where_clause: &ast::WhereClause,
 383                             indent: usize,
 384                             next_span: Span)
 385         -> String
 386     {
 387         let mut result = String::new();
 388         if where_clause.predicates.len() == 0 {
 389             return result;
 390         }
 391
 392         result.push('\n');
 393         result.push_str(&make_indent(indent + 4));
 394         result.push_str("where ");
 395
 396         let comments = self.make_comments_for_list(Vec::new(),
 397                                                    where_clause.predicates.iter(),
 398                                                    ",",
 399                                                    "{",
 400                                                    |pred| span_for_where_pred(pred).lo,
 401                                                    |pred| span_for_where_pred(pred).hi,
 402                                                    next_span.lo);
 403         let where_strs: Vec<_> = where_clause.predicates.iter()
 404                                                         .map(|p| (self.rewrite_pred(p)))
 405                                                         .zip(comments.into_iter())
 406                                                         .collect();
 407
 408         let budget = IDEAL_WIDTH + LEEWAY - indent - 10;
 409         let fmt = ListFormatting {
 410             tactic: ListTactic::Vertical,
 411             separator: ",",
 412             trailing_separator: SeparatorTactic::Never,
 413             indent: indent + 10,
 414             h_width: budget,
 415             v_width: budget,
 416         };
 417         result.push_str(&write_list(&where_strs, &fmt));
 418
 419         result
 420     }
 421
 422     fn rewrite_return(&self, ret: &ast::FunctionRetTy) -> String {
 423         match *ret {
 424             ast::FunctionRetTy::DefaultReturn(_) => String::new(),
 425             ast::FunctionRetTy::NoReturn(_) => "-> !".to_owned(),
 426             ast::FunctionRetTy::Return(ref ty) => "-> ".to_owned() + &pprust::ty_to_string(ty),
 427         }
 428     }
 429
 430     // TODO we farm this out, but this could spill over the column limit, so we ought to handle it properly
 431     fn rewrite_fn_input(&self, arg: &ast::Arg) -> String {
 432         format!("{}: {}",
 433                 pprust::pat_to_string(&arg.pat),
 434                 pprust::ty_to_string(&arg.ty))
 435     }
 436 }
 437
 438 fn span_for_return(ret: &ast::FunctionRetTy) -> Span {
 439     match *ret {
 440         ast::FunctionRetTy::NoReturn(ref span) |
 441         ast::FunctionRetTy::DefaultReturn(ref span) => span.clone(),
 442         ast::FunctionRetTy::Return(ref ty) => ty.span,
 443     }
 444 }
 445
 446 fn span_for_ty_param(ty: &ast::TyParam) -> Span {
 447     // Note that ty.span is the span for ty.ident, not the whole item.
 448     let lo = ty.span.lo;
 449     if let Some(ref def) = ty.default {
 450         return codemap::mk_sp(lo, def.span.hi);
 451     }
 452     if ty.bounds.len() == 0 {
 453         return ty.span;
 454     }
 455     let hi = match ty.bounds[ty.bounds.len() - 1] {
 456         ast::TyParamBound::TraitTyParamBound(ref ptr, _) => ptr.span.hi,
 457         ast::TyParamBound::RegionTyParamBound(ref l) => l.span.hi,
 458     };
 459     codemap::mk_sp(lo, hi)
 460 }
 461
 462 fn span_for_where_pred(pred: &ast::WherePredicate) -> Span {
 463     match *pred {
 464         ast::WherePredicate::BoundPredicate(ref p) => p.span,
 465         ast::WherePredicate::RegionPredicate(ref p) => p.span,
 466         ast::WherePredicate::EqPredicate(ref p) => p.span,
 467     }
 468 }