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                     ReturnIndent::WithWhereClauseOrArgs if where_clause.predicates.len() > 0 => {
  92                         indent + 4
  93                     }
  94                     // TODO we might want to check that using the arg indent doesn't
  95                     // blow our budget, and if it does, then fallback to the where
  96                     // clause indent.
  97                     _ => arg_indent,
  98                 };
  99
 100                 result.push('\n');
 101                 result.push_str(&make_indent(indent));
 102             } else {
 103                 result.push(' ');
 104             }
 105             result.push_str(&ret_str);
 106
 107             // Comment between return type and the end of the decl.
 108             let snippet_lo = fd.output.span().hi;
 109             if where_clause.predicates.len() == 0 {
 110                 let snippet_hi = next_span.lo;
 111                 let snippet = self.snippet(codemap::mk_sp(snippet_lo, snippet_hi));
 112                 let snippet = snippet.trim();
 113                 if snippet.len() > 0 {
 114                     result.push(' ');
 115                     result.push_str(snippet);
 116                 }
 117             } else {
 118                 // FIXME it would be nice to catch comments between the return type
 119                 // and the where clause, but we don't have a span for the where
 120                 // clause.
 121             }
 122         }
 123
 124         // Where clause.
 125         result.push_str(&self.rewrite_where_clause(where_clause, indent, next_span));
 126
 127         // Prepare for the function body by possibly adding a newline and indent.
 128         // FIXME we'll miss anything between the end of the signature and the start
 129         // of the body, but we need more spans from the compiler to solve this.
 130         if newline_brace {
 131             result.push('\n');
 132             result.push_str(&make_indent(self.block_indent));
 133         } else {
 134             result.push(' ');
 135         }
 136
 137         result
 138     }
 139
 140     fn rewrite_args(&self,
 141                     args: &[ast::Arg],
 142                     explicit_self: Option<&ast::ExplicitSelf>,
 143                     one_line_budget: usize,
 144                     multi_line_budget: usize,
 145                     arg_indent: usize,
 146                     ret_span: Span)
 147         -> String
 148     {
 149         let mut arg_item_strs: Vec<_> = args.iter().map(|a| self.rewrite_fn_input(a)).collect();
 150         // Account for sugary self.
 151         let mut min_args = 1;
 152         if let Some(explicit_self) = explicit_self {
 153             match explicit_self.node {
 154                 ast::ExplicitSelf_::SelfRegion(ref lt, ref m, _) => {
 155                     let lt_str = match lt {
 156                         &Some(ref l) => format!("{} ", pprust::lifetime_to_string(l)),
 157                         &None => String::new(),
 158                     };
 159                     let mut_str = match m {
 160                         &ast::Mutability::MutMutable => "mut ".to_string(),
 161                         &ast::Mutability::MutImmutable => String::new(),
 162                     };
 163                     arg_item_strs[0] = format!("&{}{}self", lt_str, mut_str);
 164                     min_args = 2;
 165                 }
 166                 ast::ExplicitSelf_::SelfExplicit(ref ty, _) => {
 167                     arg_item_strs[0] = format!("self: {}", pprust::ty_to_string(ty));
 168                 }
 169                 ast::ExplicitSelf_::SelfValue(_) => {
 170                     arg_item_strs[0] = "self".to_string();
 171                     min_args = 2;
 172                 }
 173                 _ => {}
 174             }
 175         }
 176
 177         // Comments between args
 178         let mut arg_comments = Vec::new();
 179         if min_args == 2 {
 180             arg_comments.push("".to_string());
 181         }
 182         // TODO if there are no args, there might still be a comment, but without
 183         // spans for the comment or parens, there is no chance of getting it right.
 184         // You also don't get to put a comment on self, unless it is explicit.
 185         if args.len() >= min_args {
 186             arg_comments = self.make_comments_for_list(arg_comments,
 187                                                        args[min_args-1..].iter(),
 188                                                        ",",
 189                                                        ")",
 190                                                        |arg| arg.pat.span.lo,
 191                                                        |arg| arg.ty.span.hi,
 192                                                        ret_span.lo);
 193         }
 194
 195         debug!("comments: {:?}", arg_comments);
 196
 197         // If there are // comments, keep them multi-line.
 198         let mut list_tactic = ListTactic::HorizontalVertical;
 199         if arg_comments.iter().any(|c| c.contains("//")) {
 200             list_tactic = ListTactic::Vertical;
 201         }
 202
 203         assert_eq!(arg_item_strs.len(), arg_comments.len());
 204         let arg_strs: Vec<_> = arg_item_strs.into_iter().zip(arg_comments.into_iter()).collect();
 205
 206         let fmt = ListFormatting {
 207             tactic: list_tactic,
 208             separator: ",",
 209             trailing_separator: SeparatorTactic::Never,
 210             indent: arg_indent,
 211             h_width: one_line_budget,
 212             v_width: multi_line_budget,
 213         };
 214
 215         write_list(&arg_strs, &fmt)
 216     }
 217
 218     // Gets comments in between items of a list.
 219     fn make_comments_for_list<T, I, F1, F2>(&self,
 220                                             prefix: Vec<String>,
 221                                             mut it: I,
 222                                             separator: &str,
 223                                             terminator: &str,
 224                                             get_lo: F1,
 225                                             get_hi: F2,
 226                                             next_span_start: BytePos)
 227         -> Vec<String>
 228         where I: Iterator<Item=T>,
 229               F1: Fn(&T) -> BytePos,
 230               F2: Fn(&T) -> BytePos
 231     {
 232         let mut result = prefix;
 233
 234         let mut prev_end = get_hi(&it.next().unwrap());
 235         for item in it {
 236             let cur_start = get_lo(&item);
 237             let snippet = self.snippet(codemap::mk_sp(prev_end, cur_start));
 238             let mut snippet = snippet.trim();
 239             let white_space: &[_] = &[' ', '\t'];
 240             if snippet.starts_with(separator) {
 241                 snippet = snippet[separator.len()..].trim_matches(white_space);
 242             } else if snippet.ends_with(separator) {
 243                 snippet = snippet[..snippet.len()-separator.len()].trim_matches(white_space);
 244             }
 245             result.push(snippet.to_string());
 246             prev_end = get_hi(&item);
 247         }
 248         // Get the last commment.
 249         // FIXME If you thought the crap with the commas was ugly, just wait.
 250         // This is awful. We're going to look from the last item span to the
 251         // start of the return type span, then we drop everything after the
 252         // first closing paren. Obviously, this will break if there is a
 253         // closing paren in the comment.
 254         // The fix is comments in the AST or a span for the closing paren.
 255         let snippet = self.snippet(codemap::mk_sp(prev_end, next_span_start));
 256         let snippet = snippet.trim();
 257         let snippet = &snippet[..snippet.find(terminator).unwrap_or(snippet.len())];
 258         let snippet = snippet.trim();
 259         result.push(snippet.to_string());
 260
 261         result
 262     }
 263
 264     fn compute_budgets_for_args(&self,
 265                                 result: &mut String,
 266                                 indent: usize,
 267                                 ret_str_len: usize,
 268                                 newline_brace: bool)
 269         -> (usize, usize, usize)
 270     {
 271         let mut budgets = None;
 272
 273         // Try keeping everything on the same line
 274         if !result.contains("\n") {
 275             // 3 = `() `, space is before ret_string
 276             let mut used_space = indent + result.len() + ret_str_len + 3;
 277             if !newline_brace {
 278                 used_space += 2;
 279             }
 280             let one_line_budget = if used_space > MAX_WIDTH {
 281                 0
 282             } else {
 283                 MAX_WIDTH - used_space
 284             };
 285
 286             // 2 = `()`
 287             let used_space = indent + result.len() + 2;
 288             let max_space = IDEAL_WIDTH + LEEWAY;
 289             debug!("compute_budgets_for_args: used_space: {}, max_space: {}",
 290                    used_space, max_space);
 291             if used_space < max_space {
 292                 budgets = Some((one_line_budget,
 293                                 max_space - used_space,
 294                                 indent + result.len() + 1));
 295             }
 296         }
 297
 298         // Didn't work. we must force vertical layout and put args on a newline.
 299         if let None = budgets {
 300             result.push('\n');
 301             result.push_str(&make_indent(indent + 4));
 302             // 6 = new indent + `()`
 303             let used_space = indent + 6;
 304             let max_space = IDEAL_WIDTH + LEEWAY;
 305             if used_space > max_space {
 306                 // Whoops! bankrupt.
 307                 // TODO take evasive action, perhaps kill the indent or something.
 308             } else {
 309                 // 5 = new indent + `(`
 310                 budgets = Some((0, max_space - used_space, indent + 5));
 311             }
 312         }
 313
 314         budgets.unwrap()
 315     }
 316
 317     fn newline_for_brace(&self, where_clause: &ast::WhereClause) -> bool {
 318         match FN_BRACE_STYLE {
 319             BraceStyle::AlwaysNextLine => true,
 320             BraceStyle::SameLineWhere if where_clause.predicates.len() > 0 => true,
 321             _ => false,
 322         }
 323     }
 324
 325     fn rewrite_generics(&self, generics: &ast::Generics, indent: usize, ret_span: Span) -> String {
 326         // FIXME convert bounds to where clauses where they get too big or if
 327         // there is a where clause at all.
 328         let mut result = String::new();
 329         let lifetimes: &[_] = &generics.lifetimes;
 330         let tys: &[_] = &generics.ty_params;
 331         if lifetimes.len() + tys.len() == 0 {
 332             return result;
 333         }
 334
 335         let budget = MAX_WIDTH - indent - 2;
 336         // TODO might need to insert a newline if the generics are really long
 337         result.push('<');
 338
 339         // Strings for the generics.
 340         let lt_strs = lifetimes.iter().map(|l| self.rewrite_lifetime_def(l));
 341         let ty_strs = tys.iter().map(|ty| self.rewrite_ty_param(ty));
 342
 343         // Extract comments between generics.
 344         let lt_spans = lifetimes.iter().map(|l| {
 345             let hi = if l.bounds.len() == 0 {
 346                 l.lifetime.span.hi
 347             } else {
 348                 l.bounds[l.bounds.len() - 1].span.hi
 349             };
 350             codemap::mk_sp(l.lifetime.span.lo, hi)
 351         });
 352         let ty_spans = tys.iter().map(span_for_ty_param);
 353         let comments = self.make_comments_for_list(Vec::new(),
 354                                                    lt_spans.chain(ty_spans),
 355                                                    ",",
 356                                                    ">",
 357                                                    |sp| sp.lo,
 358                                                    |sp| sp.hi,
 359                                                    ret_span.lo);
 360
 361         // If there are // comments, keep them multi-line.
 362         let mut list_tactic = ListTactic::HorizontalVertical;
 363         if comments.iter().any(|c| c.contains("//")) {
 364             list_tactic = ListTactic::Vertical;
 365         }
 366
 367         let generics_strs: Vec<_> = lt_strs.chain(ty_strs).zip(comments.into_iter()).collect();
 368         let fmt = ListFormatting {
 369             tactic: list_tactic,
 370             separator: ",",
 371             trailing_separator: SeparatorTactic::Never,
 372             indent: indent + 1,
 373             h_width: budget,
 374             v_width: budget,
 375         };
 376         result.push_str(&write_list(&generics_strs, &fmt));
 377
 378         result.push('>');
 379
 380         result
 381     }
 382
 383     fn rewrite_where_clause(&self,
 384                             where_clause: &ast::WhereClause,
 385                             indent: usize,
 386                             next_span: Span)
 387         -> String
 388     {
 389         let mut result = String::new();
 390         if where_clause.predicates.len() == 0 {
 391             return result;
 392         }
 393
 394         result.push('\n');
 395         result.push_str(&make_indent(indent + 4));
 396         result.push_str("where ");
 397
 398         let comments = self.make_comments_for_list(Vec::new(),
 399                                                    where_clause.predicates.iter(),
 400                                                    ",",
 401                                                    "{",
 402                                                    |pred| span_for_where_pred(pred).lo,
 403                                                    |pred| span_for_where_pred(pred).hi,
 404                                                    next_span.lo);
 405         let where_strs: Vec<_> = where_clause.predicates.iter()
 406                                                         .map(|p| (self.rewrite_pred(p)))
 407                                                         .zip(comments.into_iter())
 408                                                         .collect();
 409
 410         let budget = IDEAL_WIDTH + LEEWAY - indent - 10;
 411         let fmt = ListFormatting {
 412             tactic: ListTactic::Vertical,
 413             separator: ",",
 414             trailing_separator: SeparatorTactic::Never,
 415             indent: indent + 10,
 416             h_width: budget,
 417             v_width: budget,
 418         };
 419         result.push_str(&write_list(&where_strs, &fmt));
 420
 421         result
 422     }
 423
 424     fn rewrite_return(&self, ret: &ast::FunctionRetTy) -> String {
 425         match *ret {
 426             ast::FunctionRetTy::DefaultReturn(_) => String::new(),
 427             ast::FunctionRetTy::NoReturn(_) => "-> !".to_string(),
 428             ast::FunctionRetTy::Return(ref ty) => "-> ".to_string() + &pprust::ty_to_string(ty),
 429         }
 430     }
 431
 432     // TODO we farm this out, but this could spill over the column limit, so we ought to handle it properly
 433     fn rewrite_fn_input(&self, arg: &ast::Arg) -> String {
 434         format!("{}: {}",
 435                 pprust::pat_to_string(&arg.pat),
 436                 pprust::ty_to_string(&arg.ty))
 437     }
 438 }
 439
 440 fn span_for_return(ret: &ast::FunctionRetTy) -> Span {
 441     match *ret {
 442         ast::FunctionRetTy::NoReturn(ref span) |
 443         ast::FunctionRetTy::DefaultReturn(ref span) => span.clone(),
 444         ast::FunctionRetTy::Return(ref ty) => ty.span,
 445     }
 446 }
 447
 448 fn span_for_ty_param(ty: &ast::TyParam) -> Span {
 449     // Note that ty.span is the span for ty.ident, not the whole item.
 450     let lo = ty.span.lo;
 451     if let Some(ref def) = ty.default {
 452         return codemap::mk_sp(lo, def.span.hi);
 453     }
 454     if ty.bounds.len() == 0 {
 455         return ty.span;
 456     }
 457     let hi = match ty.bounds[ty.bounds.len() - 1] {
 458         ast::TyParamBound::TraitTyParamBound(ref ptr, _) => ptr.span.hi,
 459         ast::TyParamBound::RegionTyParamBound(ref l) => l.span.hi,
 460     };
 461     codemap::mk_sp(lo, hi)
 462 }
 463
 464 fn span_for_where_pred(pred: &ast::WherePredicate) -> Span {
 465     match *pred {
 466         ast::WherePredicate::BoundPredicate(ref p) => p.span,
 467         ast::WherePredicate::RegionPredicate(ref p) => p.span,
 468         ast::WherePredicate::EqPredicate(ref p) => p.span,
 469     }
 470 }