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         result.push('(');
  72         result.push_str(&self.rewrite_args(&fd.inputs,
  73                                            explicit_self,
  74                                            one_line_budget,
  75                                            multi_line_budget,
  76                                            arg_indent,
  77                                            span_for_return(&fd.output)));
  78         result.push(')');
  79
  80         // Where clause.
  81         result.push_str(&self.rewrite_where_clause(where_clause, indent, next_span));
  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                     ReturnIndent::WithArgs => 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
 105         // TODO any comments here?
 106
 107         // Prepare for the function body by possibly adding a newline and indent.
 108         // FIXME we'll miss anything between the end of the signature and the start
 109         // of the body, but we need more spans from the compiler to solve this.
 110         if newline_brace {
 111             result.push('\n');
 112             result.push_str(&make_indent(self.block_indent));
 113         } else {
 114             result.push(' ');
 115         }
 116
 117         result
 118     }
 119
 120     fn rewrite_args(&self,
 121                     args: &[ast::Arg],
 122                     explicit_self: Option<&ast::ExplicitSelf>,
 123                     one_line_budget: usize,
 124                     multi_line_budget: usize,
 125                     arg_indent: usize,
 126                     ret_span: Span)
 127         -> String
 128     {
 129         let mut arg_item_strs: Vec<_> = args.iter().map(|a| self.rewrite_fn_input(a)).collect();
 130         // Account for sugary self.
 131         let mut min_args = 1;
 132         if let Some(explicit_self) = explicit_self {
 133             match explicit_self.node {
 134                 ast::ExplicitSelf_::SelfRegion(ref lt, ref m, _) => {
 135                     let lt_str = match lt {
 136                         &Some(ref l) => format!("{} ", pprust::lifetime_to_string(l)),
 137                         &None => String::new(),
 138                     };
 139                     let mut_str = match m {
 140                         &ast::Mutability::MutMutable => "mut ".to_string(),
 141                         &ast::Mutability::MutImmutable => String::new(),
 142                     };
 143                     arg_item_strs[0] = format!("&{}{}self", lt_str, mut_str);
 144                     min_args = 2;
 145                 }
 146                 ast::ExplicitSelf_::SelfExplicit(ref ty, _) => {
 147                     arg_item_strs[0] = format!("self: {}", pprust::ty_to_string(ty));
 148                 }
 149                 ast::ExplicitSelf_::SelfValue(_) => {
 150                     arg_item_strs[0] = "self".to_string();
 151                     min_args = 2;
 152                 }
 153                 _ => {}
 154             }
 155         }
 156
 157         // Comments between args
 158         let mut arg_comments = Vec::new();
 159         if min_args == 2 {
 160             arg_comments.push("".to_string());
 161         }
 162         // TODO if there are no args, there might still be a comment, but without
 163         // spans for the comment or parens, there is no chance of getting it right.
 164         // You also don't get to put a comment on self, unless it is explicit.
 165         if args.len() >= min_args {
 166             arg_comments = self.make_comments_for_list(arg_comments,
 167                                                        args[min_args-1..].iter(),
 168                                                        ",",
 169                                                        ")",
 170                                                        |arg| arg.pat.span.lo,
 171                                                        |arg| arg.ty.span.hi,
 172                                                        ret_span.lo);
 173         }
 174
 175         debug!("comments: {:?}", arg_comments);
 176
 177         // If there are // comments, keep them multi-line.
 178         let mut list_tactic = ListTactic::HorizontalVertical;
 179         if arg_comments.iter().any(|c| c.contains("//")) {
 180             list_tactic = ListTactic::Vertical;
 181         }
 182
 183         assert_eq!(arg_item_strs.len(), arg_comments.len());
 184         let arg_strs: Vec<_> = arg_item_strs.into_iter().zip(arg_comments.into_iter()).collect();
 185
 186         let fmt = ListFormatting {
 187             tactic: list_tactic,
 188             separator: ",",
 189             trailing_separator: SeparatorTactic::Never,
 190             indent: arg_indent,
 191             h_width: one_line_budget,
 192             v_width: multi_line_budget,
 193         };
 194
 195         write_list(&arg_strs, &fmt)
 196     }
 197
 198     // Gets comments in between items of a list.
 199     fn make_comments_for_list<T, I, F1, F2>(&self,
 200                                             prefix: Vec<String>,
 201                                             mut it: I,
 202                                             separator: &str,
 203                                             terminator: &str,
 204                                             get_lo: F1,
 205                                             get_hi: F2,
 206                                             next_span_start: BytePos)
 207         -> Vec<String>
 208         where I: Iterator<Item=T>,
 209               F1: Fn(&T) -> BytePos,
 210               F2: Fn(&T) -> BytePos
 211     {
 212         let mut result = prefix;
 213
 214         let mut prev_end = get_hi(&it.next().unwrap());
 215         for item in it {
 216             let cur_start = get_lo(&item);
 217             let snippet = self.snippet(codemap::mk_sp(prev_end, cur_start));
 218             let mut snippet = snippet.trim();
 219             if snippet.starts_with(separator) {
 220                 snippet = snippet[1..].trim();
 221             } else if snippet.ends_with(separator) {
 222                 snippet = snippet[..snippet.len()-1].trim();
 223             }
 224             result.push(snippet.to_string());
 225             prev_end = get_hi(&item);
 226         }
 227         // Get the last commment.
 228         // FIXME If you thought the crap with the commas was ugly, just wait.
 229         // This is awful. We're going to look from the last item span to the
 230         // start of the return type span, then we drop everything after the
 231         // first closing paren. Obviously, this will break if there is a
 232         // closing paren in the comment.
 233         // The fix is comments in the AST or a span for the closing paren.
 234         let snippet = self.snippet(codemap::mk_sp(prev_end, next_span_start));
 235         let snippet = snippet.trim();
 236         let snippet = &snippet[..snippet.find(terminator).unwrap()];
 237         let snippet = snippet.trim();
 238         result.push(snippet.to_string());
 239
 240         result
 241     }
 242
 243     fn compute_budgets_for_args(&self,
 244                                 result: &mut String,
 245                                 indent: usize,
 246                                 ret_str_len: usize,
 247                                 newline_brace: bool)
 248         -> (usize, usize, usize)
 249     {
 250         let mut budgets = None;
 251
 252         // Try keeping everything on the same line
 253         if !result.contains("\n") {
 254             // 3 = `() `, space is before ret_string
 255             let mut used_space = indent + result.len() + 3 + ret_str_len;
 256             if newline_brace {
 257                 used_space += 2;
 258             }
 259             let one_line_budget = if used_space > MAX_WIDTH {
 260                 0
 261             } else {
 262                 MAX_WIDTH - used_space
 263             };
 264
 265             let used_space = indent + result.len() + 2;
 266             let max_space = IDEAL_WIDTH + LEEWAY;
 267             if used_space < max_space {
 268                 budgets = Some((one_line_budget,
 269                                 // 2 = `()`
 270                                 max_space - used_space,
 271                                 indent + result.len() + 1));
 272             }
 273         }
 274
 275         // Didn't work. we must force vertical layout and put args on a newline.
 276         if let None = budgets {
 277             result.push('\n');
 278             result.push_str(&make_indent(indent + 4));
 279             // 6 = new indent + `()`
 280             let used_space = indent + 6;
 281             let max_space = IDEAL_WIDTH + LEEWAY;
 282             if used_space > max_space {
 283                 // Whoops! bankrupt.
 284                 // TODO take evasive action, perhaps kill the indent or something.
 285             } else {
 286                 // 5 = new indent + `(`
 287                 budgets = Some((0, max_space - used_space, indent + 5));
 288             }
 289         }
 290
 291         budgets.unwrap()
 292     }
 293
 294     fn newline_for_brace(&self, where_clause: &ast::WhereClause) -> bool {
 295         match FN_BRACE_STYLE {
 296             BraceStyle::AlwaysNextLine => true,
 297             BraceStyle::SameLineWhere if where_clause.predicates.len() > 0 => true,
 298             _ => false,
 299         }
 300     }
 301
 302     fn rewrite_generics(&self, generics: &ast::Generics, indent: usize, ret_span: Span) -> String {
 303         // FIXME convert bounds to where clauses where they get too big or if
 304         // there is a where clause at all.
 305         let mut result = String::new();
 306         let lifetimes: &[_] = &generics.lifetimes;
 307         let tys: &[_] = &generics.ty_params;
 308         if lifetimes.len() + tys.len() == 0 {
 309             return result;
 310         }
 311
 312         let budget = MAX_WIDTH - indent - 2;
 313         // TODO might need to insert a newline if the generics are really long
 314         result.push('<');
 315
 316         // Strings for the generics.
 317         let lt_strs = lifetimes.iter().map(|l| self.rewrite_lifetime_def(l));
 318         let ty_strs = tys.iter().map(|ty| self.rewrite_ty_param(ty));
 319
 320         // Extract comments between generics.
 321         let lt_spans = lifetimes.iter().map(|l| {
 322             let hi = if l.bounds.len() == 0 {
 323                 l.lifetime.span.hi
 324             } else {
 325                 l.bounds[l.bounds.len() - 1].span.hi
 326             };
 327             codemap::mk_sp(l.lifetime.span.lo, hi)
 328         });
 329         let ty_spans = tys.iter().map(span_for_ty_param);
 330         let comments = self.make_comments_for_list(Vec::new(),
 331                                                    lt_spans.chain(ty_spans),
 332                                                    ",",
 333                                                    ">",
 334                                                    |sp| sp.lo,
 335                                                    |sp| sp.hi,
 336                                                    ret_span.lo);
 337
 338         // If there are // comments, keep them multi-line.
 339         let mut list_tactic = ListTactic::HorizontalVertical;
 340         if comments.iter().any(|c| c.contains("//")) {
 341             list_tactic = ListTactic::Vertical;
 342         }
 343
 344         let generics_strs: Vec<_> = lt_strs.chain(ty_strs).zip(comments.into_iter()).collect();
 345         let fmt = ListFormatting {
 346             tactic: list_tactic,
 347             separator: ",",
 348             trailing_separator: SeparatorTactic::Never,
 349             indent: indent + 1,
 350             h_width: budget,
 351             v_width: budget,
 352         };
 353         result.push_str(&write_list(&generics_strs, &fmt));
 354
 355         result.push('>');
 356
 357         result
 358     }
 359
 360     fn rewrite_where_clause(&self,
 361                             where_clause: &ast::WhereClause,
 362                             indent: usize,
 363                             next_span: Span)
 364         -> String
 365     {
 366         let mut result = String::new();
 367         if where_clause.predicates.len() == 0 {
 368             return result;
 369         }
 370
 371         result.push('\n');
 372         result.push_str(&make_indent(indent + 4));
 373         result.push_str("where ");
 374
 375         // TODO uncomment when spans are fixed
 376         //println!("{:?} {:?}", where_clause.predicates.iter().map(|p| self.snippet(span_for_where_pred(p))).collect::<Vec<_>>(), next_span.lo);
 377         // let comments = self.make_comments_for_list(Vec::new(),
 378         //                                            where_clause.predicates.iter(),
 379         //                                            ",",
 380         //                                            "{",
 381         //                                            |pred| span_for_where_pred(pred).lo,
 382         //                                            |pred| span_for_where_pred(pred).hi,
 383         //                                            next_span.lo);
 384         let comments = vec![String::new(); where_clause.predicates.len()];
 385         let where_strs: Vec<_> = where_clause.predicates.iter()
 386                                                         .map(|p| (self.rewrite_pred(p)))
 387                                                         .zip(comments.into_iter())
 388                                                         .collect();
 389
 390         let budget = IDEAL_WIDTH + LEEWAY - indent - 10;
 391         let fmt = ListFormatting {
 392             tactic: ListTactic::Vertical,
 393             separator: ",",
 394             trailing_separator: SeparatorTactic::Never,
 395             indent: indent + 10,
 396             h_width: budget,
 397             v_width: budget,
 398         };
 399         result.push_str(&write_list(&where_strs, &fmt));
 400
 401         result
 402     }
 403
 404     fn rewrite_return(&self, ret: &ast::FunctionRetTy) -> String {
 405         match *ret {
 406             ast::FunctionRetTy::DefaultReturn(_) => String::new(),
 407             ast::FunctionRetTy::NoReturn(_) => "-> !".to_string(),
 408             ast::FunctionRetTy::Return(ref ty) => "-> ".to_string() + &pprust::ty_to_string(ty),
 409         }
 410     }
 411
 412     // TODO we farm this out, but this could spill over the column limit, so we ought to handle it properly
 413     fn rewrite_fn_input(&self, arg: &ast::Arg) -> String {
 414         format!("{}: {}",
 415                 pprust::pat_to_string(&arg.pat),
 416                 pprust::ty_to_string(&arg.ty))
 417     }
 418 }
 419
 420 fn span_for_return(ret: &ast::FunctionRetTy) -> Span {
 421     match *ret {
 422         ast::FunctionRetTy::NoReturn(ref span) |
 423         ast::FunctionRetTy::DefaultReturn(ref span) => span.clone(),
 424         ast::FunctionRetTy::Return(ref ty) => ty.span,
 425     }
 426 }
 427
 428 fn span_for_ty_param(ty: &ast::TyParam) -> Span {
 429     // Note that ty.span is the span for ty.ident, not the whole item.
 430     let lo = ty.span.lo;
 431     if let Some(ref def) = ty.default {
 432         return codemap::mk_sp(lo, def.span.hi);
 433     }
 434     if ty.bounds.len() == 0 {
 435         return ty.span;
 436     }
 437     let hi = match ty.bounds[ty.bounds.len() - 1] {
 438         ast::TyParamBound::TraitTyParamBound(ref ptr, _) => ptr.span.hi,
 439         ast::TyParamBound::RegionTyParamBound(ref l) => l.span.hi,
 440     };
 441     codemap::mk_sp(lo, hi)
 442 }
 443
 444 fn span_for_where_pred(pred: &ast::WherePredicate) -> Span {
 445     match *pred {
 446         ast::WherePredicate::BoundPredicate(ref p) => p.span,
 447         ast::WherePredicate::RegionPredicate(ref p) => p.span,
 448         ast::WherePredicate::EqPredicate(ref p) => p.span,
 449     }
 450 }