src/chains.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 /// Formatting of chained expressions, i.e. expressions which are chained by
  12 /// dots: struct and enum field access, method calls, and try shorthand (?).
  13 ///
  14 /// Instead of walking these subexpressions one-by-one, as is our usual strategy
  15 /// for expression formatting, we collect maximal sequences of these expressions
  16 /// and handle them simultaneously.
  17 ///
  18 /// Whenever possible, the entire chain is put on a single line. If that fails,
  19 /// we put each subexpression on a separate, much like the (default) function
  20 /// argument function argument strategy.
  21 ///
  22 /// Depends on config options: `chain_indent` is the indent to use for
  23 /// blocks in the parent/root/base of the chain (and the rest of the chain's
  24 /// alignment).
  25 /// E.g., `let foo = { aaaa; bbb; ccc }.bar.baz();`, we would layout for the
  26 /// following values of `chain_indent`:
  27 /// Visual:
  28 /// ```
  29 /// let foo = {
  30 ///               aaaa;
  31 ///               bbb;
  32 ///               ccc
  33 ///           }
  34 ///           .bar
  35 ///           .baz();
  36 /// ```
  37 /// Inherit:
  38 /// ```
  39 /// let foo = {
  40 ///     aaaa;
  41 ///     bbb;
  42 ///     ccc
  43 /// }
  44 /// .bar
  45 /// .baz();
  46 /// ```
  47 /// Tabbed:
  48 /// ```
  49 /// let foo = {
  50 ///         aaaa;
  51 ///         bbb;
  52 ///         ccc
  53 ///     }
  54 ///     .bar
  55 ///     .baz();
  56 /// ```
  57 ///
  58 /// If the first item in the chain is a block expression, we align the dots with
  59 /// the braces.
  60 /// Visual:
  61 /// ```
  62 /// let a = foo.bar
  63 ///            .baz()
  64 ///            .qux
  65 /// ```
  66 /// Inherit:
  67 /// ```
  68 /// let a = foo.bar
  69 /// .baz()
  70 /// .qux
  71 /// ```
  72 /// Tabbed:
  73 /// ```
  74 /// let a = foo.bar
  75 ///     .baz()
  76 ///     .qux
  77 /// ```
  78
  79 use Shape;
  80 use rewrite::{Rewrite, RewriteContext};
  81 use utils::{wrap_str, first_line_width, last_line_width, mk_sp};
  82 use expr::rewrite_call;
  83 use config::IndentStyle;
  84 use macros::convert_try_mac;
  85
  86 use std::cmp::min;
  87 use std::iter;
  88 use syntax::{ast, ptr};
  89 use syntax::codemap::Span;
  90
  91 pub fn rewrite_chain(expr: &ast::Expr, context: &RewriteContext, shape: Shape) -> Option<String> {
  92     debug!("rewrite_chain {:?}", shape);
  93     let total_span = expr.span;
  94     let (parent, subexpr_list) = make_subexpr_list(expr, context);
  95
  96     // Bail out if the chain is just try sugar, i.e., an expression followed by
  97     // any number of `?`s.
  98     if chain_only_try(&subexpr_list) {
  99         return rewrite_try(&parent, subexpr_list.len(), context, shape);
 100     }
 101     let trailing_try_num = subexpr_list
 102         .iter()
 103         .take_while(|e| match e.node {
 104                         ast::ExprKind::Try(..) => true,
 105                         _ => false,
 106                     })
 107         .count();
 108
 109     // Parent is the first item in the chain, e.g., `foo` in `foo.bar.baz()`.
 110     let parent_shape = if is_block_expr(context, &parent, "\n") {
 111         match context.config.chain_indent() {
 112             IndentStyle::Visual => shape.visual_indent(0),
 113             IndentStyle::Block => shape.block(),
 114         }
 115     } else {
 116         shape
 117     };
 118     let parent_rewrite = try_opt!(parent.rewrite(context, parent_shape));
 119     let parent_rewrite_contains_newline = parent_rewrite.contains('\n');
 120     let is_small_parent = parent_rewrite.len() <= context.config.tab_spaces();
 121
 122     // Decide how to layout the rest of the chain. `extend` is true if we can
 123     // put the first non-parent item on the same line as the parent.
 124     let first_subexpr_is_try = subexpr_list.last().map_or(false, is_try);
 125     let (nested_shape, extend) = if !parent_rewrite_contains_newline && is_continuable(&parent) {
 126         let nested_shape = if first_subexpr_is_try {
 127             parent_shape.block_indent(context.config.tab_spaces())
 128         } else {
 129             chain_indent(context, shape.add_offset(parent_rewrite.len()))
 130         };
 131         (nested_shape, context.config.chain_indent() == IndentStyle::Visual || is_small_parent)
 132     } else if is_block_expr(context, &parent, &parent_rewrite) {
 133         match context.config.chain_indent() {
 134             // Try to put the first child on the same line with parent's last line
 135             IndentStyle::Block => (parent_shape.block_indent(context.config.tab_spaces()), true),
 136             // The parent is a block, so align the rest of the chain with the closing
 137             // brace.
 138             IndentStyle::Visual => (parent_shape, false),
 139         }
 140     } else if parent_rewrite_contains_newline {
 141         (chain_indent(context, parent_shape), false)
 142     } else {
 143         (shape.block_indent(context.config.tab_spaces()), false)
 144     };
 145
 146     let other_child_shape = nested_shape.with_max_width(context.config);
 147
 148     let first_child_shape = if extend {
 149         let overhead = last_line_width(&parent_rewrite);
 150         let offset = parent_rewrite.lines().rev().next().unwrap().trim().len();
 151         match context.config.chain_indent() {
 152             IndentStyle::Visual => try_opt!(parent_shape.offset_left(overhead)),
 153             IndentStyle::Block => try_opt!(parent_shape.block().offset_left(offset)),
 154         }
 155     } else {
 156         other_child_shape
 157     };
 158     debug!("child_shapes {:?} {:?}",
 159            first_child_shape,
 160            other_child_shape);
 161
 162     let child_shape_iter =
 163         Some(first_child_shape)
 164             .into_iter()
 165             .chain(::std::iter::repeat(other_child_shape).take(subexpr_list.len() - 1));
 166     let iter = subexpr_list.iter().rev().zip(child_shape_iter);
 167     let mut rewrites = try_opt!(iter.map(|(e, shape)| {
 168                                              rewrite_chain_subexpr(e, total_span, context, shape)
 169                                          }).collect::<Option<Vec<_>>>());
 170
 171     // Total of all items excluding the last.
 172     let last_non_try_index = rewrites.len() - (1 + trailing_try_num);
 173     let almost_total = rewrites[..last_non_try_index]
 174         .iter()
 175         .fold(0, |a, b| a + first_line_width(b)) + parent_rewrite.len();
 176     let one_line_len = rewrites.iter().fold(0, |a, r| a + first_line_width(r)) +
 177                        parent_rewrite.len();
 178
 179     let one_line_budget = min(shape.width, context.config.chain_one_line_max());
 180     let veto_single_line = if one_line_len > one_line_budget {
 181         if rewrites.len() > 1 {
 182             true
 183         } else if rewrites.len() == 1 {
 184             context.config.chain_split_single_child() || one_line_len > shape.width
 185         } else {
 186             false
 187         }
 188     } else if context.config.take_source_hints() && subexpr_list.len() > 1 {
 189         // Look at the source code. Unless all chain elements start on the same
 190         // line, we won't consider putting them on a single line either.
 191         let last_span = context.snippet(mk_sp(subexpr_list[1].span.hi, total_span.hi));
 192         let first_span = context.snippet(subexpr_list[1].span);
 193         let last_iter = last_span.chars().take_while(|c| c.is_whitespace());
 194
 195         first_span.chars().chain(last_iter).any(|c| c == '\n')
 196     } else {
 197         false
 198     };
 199
 200     let mut fits_single_line = !veto_single_line && almost_total <= shape.width;
 201     if fits_single_line {
 202         let len = rewrites.len();
 203         let (init, last) = rewrites.split_at_mut(len - (1 + trailing_try_num));
 204         fits_single_line = init.iter().all(|s| !s.contains('\n'));
 205
 206         if fits_single_line {
 207             fits_single_line = match expr.node {
 208                 ref e @ ast::ExprKind::MethodCall(..) => {
 209                     if rewrite_method_call_with_overflow(e,
 210                                                          &mut last[0],
 211                                                          almost_total,
 212                                                          total_span,
 213                                                          context,
 214                                                          shape) {
 215                         // If the first line of the last method does not fit into a single line
 216                         // after the others, allow new lines.
 217                         almost_total + first_line_width(&last[0]) < context.config.max_width()
 218                     } else {
 219                         false
 220                     }
 221                 }
 222                 _ => !last[0].contains('\n'),
 223             }
 224         }
 225     }
 226
 227     // Try overflowing the last element if we are using block indent.
 228     if !fits_single_line && context.use_block_indent() {
 229         let (init, last) = rewrites.split_at_mut(last_non_try_index);
 230         let almost_single_line = init.iter().all(|s| !s.contains('\n'));
 231         if almost_single_line {
 232             let overflow_shape = Shape {
 233                 width: one_line_budget,
 234                 ..parent_shape
 235             };
 236             fits_single_line = rewrite_last_child_with_overflow(context,
 237                                                                 &subexpr_list[trailing_try_num],
 238                                                                 overflow_shape,
 239                                                                 total_span,
 240                                                                 almost_total,
 241                                                                 one_line_budget,
 242                                                                 &mut last[0]);
 243         }
 244     }
 245
 246     let connector = if fits_single_line && !parent_rewrite_contains_newline {
 247         // Yay, we can put everything on one line.
 248         String::new()
 249     } else {
 250         // Use new lines.
 251         if context.force_one_line_chain {
 252             return None;
 253         }
 254         format!("\n{}", nested_shape.indent.to_string(context.config))
 255     };
 256
 257     let first_connector = choose_first_connector(context,
 258                                                  &parent_rewrite,
 259                                                  &rewrites[0],
 260                                                  &connector,
 261                                                  &subexpr_list,
 262                                                  extend);
 263
 264     if is_small_parent && rewrites.len() > 1 {
 265         let second_connector = choose_first_connector(context,
 266                                                       &rewrites[0],
 267                                                       &rewrites[1],
 268                                                       &connector,
 269                                                       &subexpr_list[0..subexpr_list.len() - 1],
 270                                                       false);
 271         wrap_str(format!("{}{}{}{}{}",
 272                          parent_rewrite,
 273                          first_connector,
 274                          rewrites[0],
 275                          second_connector,
 276                          join_rewrites(&rewrites[1..],
 277                                        &subexpr_list[0..subexpr_list.len() - 1],
 278                                        &connector)),
 279                  context.config.max_width(),
 280                  shape)
 281     } else {
 282         wrap_str(format!("{}{}{}",
 283                          parent_rewrite,
 284                          first_connector,
 285                          join_rewrites(&rewrites, &subexpr_list, &connector)),
 286                  context.config.max_width(),
 287                  shape)
 288     }
 289 }
 290
 291 fn is_extendable_parent(context: &RewriteContext, parent_str: &str) -> bool {
 292     context.config.chain_indent() == IndentStyle::Block &&
 293     parent_str.lines().last().map_or(false, |s| {
 294         s.trim()
 295             .chars()
 296             .all(|c| c == ')' || c == ']' || c == '}' || c == '?')
 297     })
 298 }
 299
 300 // True if the chain is only `?`s.
 301 fn chain_only_try(exprs: &[ast::Expr]) -> bool {
 302     exprs.iter().all(|e| if let ast::ExprKind::Try(_) = e.node {
 303                          true
 304                      } else {
 305                          false
 306                      })
 307 }
 308
 309 // Try to rewrite and replace the last non-try child. Return `true` if
 310 // replacing succeeds.
 311 fn rewrite_last_child_with_overflow(context: &RewriteContext,
 312                                     expr: &ast::Expr,
 313                                     shape: Shape,
 314                                     span: Span,
 315                                     almost_total: usize,
 316                                     one_line_budget: usize,
 317                                     last_child: &mut String)
 318                                     -> bool {
 319     if let Some(shape) = shape.shrink_left(almost_total) {
 320         if let Some(ref mut rw) = rewrite_chain_subexpr(expr, span, context, shape) {
 321             if almost_total + first_line_width(rw) <= one_line_budget {
 322                 ::std::mem::swap(last_child, rw);
 323                 return true;
 324             }
 325         }
 326     }
 327     false
 328 }
 329
 330 pub fn rewrite_try(expr: &ast::Expr,
 331                    try_count: usize,
 332                    context: &RewriteContext,
 333                    shape: Shape)
 334                    -> Option<String> {
 335     let sub_expr = try_opt!(expr.rewrite(context, try_opt!(shape.sub_width(try_count))));
 336     Some(format!("{}{}",
 337                  sub_expr,
 338                  iter::repeat("?").take(try_count).collect::<String>()))
 339 }
 340
 341 fn join_rewrites(rewrites: &[String], subexps: &[ast::Expr], connector: &str) -> String {
 342     let mut rewrite_iter = rewrites.iter();
 343     let mut result = rewrite_iter.next().unwrap().clone();
 344     let mut subexpr_iter = subexps.iter().rev();
 345     subexpr_iter.next();
 346
 347     for (rewrite, expr) in rewrite_iter.zip(subexpr_iter) {
 348         match expr.node {
 349             ast::ExprKind::Try(_) => (),
 350             _ => result.push_str(connector),
 351         };
 352         result.push_str(&rewrite[..]);
 353     }
 354
 355     result
 356 }
 357
 358 // States whether an expression's last line exclusively consists of closing
 359 // parens, braces, and brackets in its idiomatic formatting.
 360 fn is_block_expr(context: &RewriteContext, expr: &ast::Expr, repr: &str) -> bool {
 361     match expr.node {
 362         ast::ExprKind::Mac(..) |
 363         ast::ExprKind::Call(..) => context.use_block_indent() && repr.contains('\n'),
 364         ast::ExprKind::Struct(..) |
 365         ast::ExprKind::While(..) |
 366         ast::ExprKind::WhileLet(..) |
 367         ast::ExprKind::If(..) |
 368         ast::ExprKind::IfLet(..) |
 369         ast::ExprKind::Block(..) |
 370         ast::ExprKind::Loop(..) |
 371         ast::ExprKind::ForLoop(..) |
 372         ast::ExprKind::Match(..) => repr.contains('\n'),
 373         ast::ExprKind::Paren(ref expr) |
 374         ast::ExprKind::Binary(_, _, ref expr) |
 375         ast::ExprKind::Index(_, ref expr) |
 376         ast::ExprKind::Unary(_, ref expr) => is_block_expr(context, expr, repr),
 377         _ => false,
 378     }
 379 }
 380
 381 // Returns the root of the chain and a Vec of the prefixes of the rest of the chain.
 382 // E.g., for input `a.b.c` we return (`a`, [`a.b.c`, `a.b`])
 383 fn make_subexpr_list(expr: &ast::Expr, context: &RewriteContext) -> (ast::Expr, Vec<ast::Expr>) {
 384     let mut subexpr_list = vec![expr.clone()];
 385
 386     while let Some(subexpr) = pop_expr_chain(subexpr_list.last().unwrap(), context) {
 387         subexpr_list.push(subexpr.clone());
 388     }
 389
 390     let parent = subexpr_list.pop().unwrap();
 391     (parent, subexpr_list)
 392 }
 393
 394 fn chain_indent(context: &RewriteContext, shape: Shape) -> Shape {
 395     match context.config.chain_indent() {
 396         IndentStyle::Visual => shape.visual_indent(0),
 397         IndentStyle::Block => shape.block_indent(context.config.tab_spaces()),
 398     }
 399 }
 400
 401 fn rewrite_method_call_with_overflow(expr_kind: &ast::ExprKind,
 402                                      last: &mut String,
 403                                      almost_total: usize,
 404                                      total_span: Span,
 405                                      context: &RewriteContext,
 406                                      shape: Shape)
 407                                      -> bool {
 408     if let &ast::ExprKind::MethodCall(ref method_name, ref types, ref expressions) = expr_kind {
 409         let shape = match shape.shrink_left(almost_total) {
 410             Some(b) => b,
 411             None => return false,
 412         };
 413         let mut last_rewrite = rewrite_method_call(method_name.node,
 414                                                    types,
 415                                                    expressions,
 416                                                    total_span,
 417                                                    context,
 418                                                    shape);
 419
 420         if let Some(ref mut s) = last_rewrite {
 421             ::std::mem::swap(s, last);
 422             true
 423         } else {
 424             false
 425         }
 426     } else {
 427         unreachable!();
 428     }
 429 }
 430
 431 // Returns the expression's subexpression, if it exists. When the subexpr
 432 // is a try! macro, we'll convert it to shorthand when the option is set.
 433 fn pop_expr_chain(expr: &ast::Expr, context: &RewriteContext) -> Option<ast::Expr> {
 434     match expr.node {
 435         ast::ExprKind::MethodCall(_, _, ref expressions) => {
 436             Some(convert_try(&expressions[0], context))
 437         }
 438         ast::ExprKind::TupField(ref subexpr, _) |
 439         ast::ExprKind::Field(ref subexpr, _) |
 440         ast::ExprKind::Try(ref subexpr) => Some(convert_try(subexpr, context)),
 441         _ => None,
 442     }
 443 }
 444
 445 fn convert_try(expr: &ast::Expr, context: &RewriteContext) -> ast::Expr {
 446     match expr.node {
 447         ast::ExprKind::Mac(ref mac) if context.config.use_try_shorthand() => {
 448             if let Some(subexpr) = convert_try_mac(mac, context) {
 449                 subexpr
 450             } else {
 451                 expr.clone()
 452             }
 453         }
 454         _ => expr.clone(),
 455     }
 456 }
 457
 458 // Rewrite the last element in the chain `expr`. E.g., given `a.b.c` we rewrite
 459 // `.c`.
 460 fn rewrite_chain_subexpr(expr: &ast::Expr,
 461                          span: Span,
 462                          context: &RewriteContext,
 463                          shape: Shape)
 464                          -> Option<String> {
 465     let rewrite_element = |expr_str: String| if expr_str.len() <= shape.width {
 466         Some(expr_str)
 467     } else {
 468         None
 469     };
 470
 471     match expr.node {
 472         ast::ExprKind::MethodCall(ref method_name, ref types, ref expressions) => {
 473             rewrite_method_call(method_name.node, types, expressions, span, context, shape)
 474         }
 475         ast::ExprKind::Field(_, ref field) => rewrite_element(format!(".{}", field.node)),
 476         ast::ExprKind::TupField(ref expr, ref field) => {
 477             let space = match expr.node {
 478                 ast::ExprKind::TupField(..) => " ",
 479                 _ => "",
 480             };
 481             rewrite_element(format!("{}.{}", space, field.node))
 482         }
 483         ast::ExprKind::Try(_) => rewrite_element(String::from("?")),
 484         _ => unreachable!(),
 485     }
 486 }
 487
 488 // Determines if we can continue formatting a given expression on the same line.
 489 fn is_continuable(expr: &ast::Expr) -> bool {
 490     match expr.node {
 491         ast::ExprKind::Path(..) => true,
 492         _ => false,
 493     }
 494 }
 495
 496 fn is_try(expr: &ast::Expr) -> bool {
 497     match expr.node {
 498         ast::ExprKind::Try(..) => true,
 499         _ => false,
 500     }
 501 }
 502
 503 fn choose_first_connector<'a>(context: &RewriteContext,
 504                               parent_str: &str,
 505                               first_child_str: &str,
 506                               connector: &'a str,
 507                               subexpr_list: &[ast::Expr],
 508                               extend: bool)
 509                               -> &'a str {
 510     if subexpr_list.is_empty() {
 511         ""
 512     } else if extend || subexpr_list.last().map_or(false, is_try) ||
 513               is_extendable_parent(context, parent_str) {
 514         // 1 = ";", being conservative here.
 515         if last_line_width(parent_str) + first_line_width(first_child_str) + 1 <=
 516            context.config.max_width() {
 517             ""
 518         } else {
 519             connector
 520         }
 521     } else {
 522         connector
 523     }
 524 }
 525
 526 fn rewrite_method_call(method_name: ast::Ident,
 527                        types: &[ptr::P<ast::Ty>],
 528                        args: &[ptr::P<ast::Expr>],
 529                        span: Span,
 530                        context: &RewriteContext,
 531                        shape: Shape)
 532                        -> Option<String> {
 533     let (lo, type_str) = if types.is_empty() {
 534         (args[0].span.hi, String::new())
 535     } else {
 536         let type_list: Vec<_> =
 537             try_opt!(types.iter().map(|ty| ty.rewrite(context, shape)).collect());
 538
 539         let type_str = if context.config.spaces_within_angle_brackets() && type_list.len() > 0 {
 540             format!("::< {} >", type_list.join(", "))
 541         } else {
 542             format!("::<{}>", type_list.join(", "))
 543         };
 544
 545         (types.last().unwrap().span.hi, type_str)
 546     };
 547
 548     let callee_str = format!(".{}{}", method_name, type_str);
 549     let span = mk_sp(lo, span.hi);
 550
 551     rewrite_call(context, &callee_str, &args[1..], span, shape)
 552 }