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};
  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::{mk_sp, 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
 121     // Decide how to layout the rest of the chain. `extend` is true if we can
 122     // put the first non-parent item on the same line as the parent.
 123     let first_subexpr_is_try = match subexpr_list.last().unwrap().node {
 124         ast::ExprKind::Try(..) => true,
 125         _ => false,
 126     };
 127     let (nested_shape, extend) = if !parent_rewrite_contains_newline && is_continuable(&parent) {
 128         let nested_shape = if first_subexpr_is_try {
 129             parent_shape.block_indent(context.config.tab_spaces())
 130         } else {
 131             chain_indent(context, shape.add_offset(parent_rewrite.len()))
 132         };
 133         (nested_shape,
 134          context.config.chain_indent() == IndentStyle::Visual ||
 135          parent_rewrite.len() <= context.config.tab_spaces())
 136     } else if is_block_expr(context, &parent, &parent_rewrite) {
 137         match context.config.chain_indent() {
 138             // Try to put the first child on the same line with parent's last line
 139             IndentStyle::Block => (parent_shape.block_indent(context.config.tab_spaces()), true),
 140             // The parent is a block, so align the rest of the chain with the closing
 141             // brace.
 142             IndentStyle::Visual => (parent_shape, false),
 143         }
 144     } else if parent_rewrite_contains_newline {
 145         (chain_indent(context, parent_shape), false)
 146     } else {
 147         (shape.block_indent(context.config.tab_spaces()), false)
 148     };
 149
 150     let other_child_shape = nested_shape.with_max_width(context.config);
 151
 152     let first_child_shape = if extend {
 153         let overhead = last_line_width(&parent_rewrite);
 154         let offset = parent_rewrite.lines().rev().next().unwrap().trim().len();
 155         match context.config.chain_indent() {
 156             IndentStyle::Visual => try_opt!(parent_shape.offset_left(overhead)),
 157             IndentStyle::Block => try_opt!(parent_shape.block().offset_left(offset)),
 158         }
 159     } else {
 160         other_child_shape
 161     };
 162     debug!("child_shapes {:?} {:?}",
 163            first_child_shape,
 164            other_child_shape);
 165
 166     let child_shape_iter =
 167         Some(first_child_shape)
 168             .into_iter()
 169             .chain(::std::iter::repeat(other_child_shape).take(subexpr_list.len() - 1));
 170     let iter = subexpr_list.iter().rev().zip(child_shape_iter);
 171     let mut rewrites =
 172         try_opt!(iter.map(|(e, shape)| rewrite_chain_subexpr(e, total_span, context, shape))
 173                      .collect::<Option<Vec<_>>>());
 174
 175     // Total of all items excluding the last.
 176     let last_non_try_index = rewrites.len() - (1 + trailing_try_num);
 177     let almost_total = rewrites[..last_non_try_index]
 178         .iter()
 179         .fold(0, |a, b| a + first_line_width(b)) + parent_rewrite.len();
 180     let one_line_len = rewrites.iter().fold(0, |a, r| a + first_line_width(r)) +
 181                        parent_rewrite.len();
 182
 183     let one_line_budget = min(shape.width, context.config.chain_one_line_max());
 184     let veto_single_line = if one_line_len > one_line_budget {
 185         if rewrites.len() > 1 {
 186             true
 187         } else if rewrites.len() == 1 {
 188             context.config.chain_split_single_child() || one_line_len > shape.width
 189         } else {
 190             false
 191         }
 192     } else if context.config.take_source_hints() && subexpr_list.len() > 1 {
 193         // Look at the source code. Unless all chain elements start on the same
 194         // line, we won't consider putting them on a single line either.
 195         let last_span = context.snippet(mk_sp(subexpr_list[1].span.hi, total_span.hi));
 196         let first_span = context.snippet(subexpr_list[1].span);
 197         let last_iter = last_span.chars().take_while(|c| c.is_whitespace());
 198
 199         first_span.chars().chain(last_iter).any(|c| c == '\n')
 200     } else {
 201         false
 202     };
 203
 204     let mut fits_single_line = !veto_single_line && almost_total <= shape.width;
 205     if fits_single_line {
 206         let len = rewrites.len();
 207         let (init, last) = rewrites.split_at_mut(len - (1 + trailing_try_num));
 208         fits_single_line = init.iter().all(|s| !s.contains('\n'));
 209
 210         if fits_single_line {
 211             fits_single_line = match expr.node {
 212                 ref e @ ast::ExprKind::MethodCall(..) => {
 213                     if rewrite_method_call_with_overflow(e,
 214                                                          &mut last[0],
 215                                                          almost_total,
 216                                                          total_span,
 217                                                          context,
 218                                                          shape) {
 219                         // If the first line of the last method does not fit into a single line
 220                         // after the others, allow new lines.
 221                         almost_total + first_line_width(&last[0]) < context.config.max_width()
 222                     } else {
 223                         false
 224                     }
 225                 }
 226                 _ => !last[0].contains('\n'),
 227             }
 228         }
 229     }
 230
 231     // Try overflowing the last element if we are using block indent.
 232     if !fits_single_line && context.config.fn_call_style() == IndentStyle::Block {
 233         let (init, last) = rewrites.split_at_mut(last_non_try_index);
 234         let almost_single_line = init.iter().all(|s| !s.contains('\n'));
 235         if almost_single_line {
 236             let overflow_shape = Shape {
 237                 width: one_line_budget,
 238                 ..parent_shape
 239             };
 240             fits_single_line = rewrite_last_child_with_overflow(context,
 241                                                                 &subexpr_list[trailing_try_num],
 242                                                                 overflow_shape,
 243                                                                 total_span,
 244                                                                 almost_total,
 245                                                                 one_line_budget,
 246                                                                 &mut last[0]);
 247         }
 248     }
 249
 250     let connector = if fits_single_line && !parent_rewrite_contains_newline {
 251         // Yay, we can put everything on one line.
 252         String::new()
 253     } else {
 254         // Use new lines.
 255         format!("\n{}", nested_shape.indent.to_string(context.config))
 256     };
 257
 258     let first_connector = if subexpr_list.is_empty() {
 259         ""
 260     } else if extend || first_subexpr_is_try {
 261         // 1 = ";", being conservative here.
 262         if last_line_width(&parent_rewrite) + first_line_width(&rewrites[0]) + 1 <=
 263            context.config.max_width() {
 264             ""
 265         } else {
 266             &*connector
 267         }
 268     } else {
 269         &*connector
 270     };
 271
 272     wrap_str(format!("{}{}{}",
 273                      parent_rewrite,
 274                      first_connector,
 275                      join_rewrites(&rewrites, &subexpr_list, &connector)),
 276              context.config.max_width(),
 277              shape)
 278 }
 279
 280 // True if the chain is only `?`s.
 281 fn chain_only_try(exprs: &[ast::Expr]) -> bool {
 282     exprs.iter().all(|e| if let ast::ExprKind::Try(_) = e.node {
 283                          true
 284                      } else {
 285                          false
 286                      })
 287 }
 288
 289 // Try to rewrite and replace the last non-try child. Return `true` if
 290 // replacing succeeds.
 291 fn rewrite_last_child_with_overflow(context: &RewriteContext,
 292                                     expr: &ast::Expr,
 293                                     shape: Shape,
 294                                     span: Span,
 295                                     almost_total: usize,
 296                                     one_line_budget: usize,
 297                                     last_child: &mut String)
 298                                     -> bool {
 299     if let Some(shape) = shape.shrink_left(almost_total) {
 300         if let Some(ref mut rw) = rewrite_chain_subexpr(expr, span, context, shape) {
 301             if almost_total + first_line_width(rw) <= one_line_budget {
 302                 ::std::mem::swap(last_child, rw);
 303                 return true;
 304             }
 305         }
 306     }
 307     false
 308 }
 309
 310 pub fn rewrite_try(expr: &ast::Expr,
 311                    try_count: usize,
 312                    context: &RewriteContext,
 313                    shape: Shape)
 314                    -> Option<String> {
 315     let sub_expr = try_opt!(expr.rewrite(context, try_opt!(shape.sub_width(try_count))));
 316     Some(format!("{}{}",
 317                  sub_expr,
 318                  iter::repeat("?").take(try_count).collect::<String>()))
 319 }
 320
 321 fn join_rewrites(rewrites: &[String], subexps: &[ast::Expr], connector: &str) -> String {
 322     let mut rewrite_iter = rewrites.iter();
 323     let mut result = rewrite_iter.next().unwrap().clone();
 324     let mut subexpr_iter = subexps.iter().rev();
 325     subexpr_iter.next();
 326
 327     for (rewrite, expr) in rewrite_iter.zip(subexpr_iter) {
 328         match expr.node {
 329             ast::ExprKind::Try(_) => (),
 330             _ => result.push_str(connector),
 331         };
 332         result.push_str(&rewrite[..]);
 333     }
 334
 335     result
 336 }
 337
 338 // States whether an expression's last line exclusively consists of closing
 339 // parens, braces, and brackets in its idiomatic formatting.
 340 fn is_block_expr(context: &RewriteContext, expr: &ast::Expr, repr: &str) -> bool {
 341     match expr.node {
 342         ast::ExprKind::Call(..) => {
 343             context.config.fn_call_style() == IndentStyle::Block && repr.contains('\n')
 344         }
 345         ast::ExprKind::Struct(..) |
 346         ast::ExprKind::While(..) |
 347         ast::ExprKind::WhileLet(..) |
 348         ast::ExprKind::If(..) |
 349         ast::ExprKind::IfLet(..) |
 350         ast::ExprKind::Block(..) |
 351         ast::ExprKind::Loop(..) |
 352         ast::ExprKind::ForLoop(..) |
 353         ast::ExprKind::Match(..) => repr.contains('\n'),
 354         ast::ExprKind::Paren(ref expr) |
 355         ast::ExprKind::Binary(_, _, ref expr) |
 356         ast::ExprKind::Index(_, ref expr) |
 357         ast::ExprKind::Unary(_, ref expr) => is_block_expr(context, expr, repr),
 358         _ => false,
 359     }
 360 }
 361
 362 // Returns the root of the chain and a Vec of the prefixes of the rest of the chain.
 363 // E.g., for input `a.b.c` we return (`a`, [`a.b.c`, `a.b`])
 364 fn make_subexpr_list(expr: &ast::Expr, context: &RewriteContext) -> (ast::Expr, Vec<ast::Expr>) {
 365     let mut subexpr_list = vec![expr.clone()];
 366
 367     while let Some(subexpr) = pop_expr_chain(subexpr_list.last().unwrap(), context) {
 368         subexpr_list.push(subexpr.clone());
 369     }
 370
 371     let parent = subexpr_list.pop().unwrap();
 372     (parent, subexpr_list)
 373 }
 374
 375 fn chain_indent(context: &RewriteContext, shape: Shape) -> Shape {
 376     match context.config.chain_indent() {
 377         IndentStyle::Visual => shape.visual_indent(0),
 378         IndentStyle::Block => shape.block_indent(context.config.tab_spaces()),
 379     }
 380 }
 381
 382 fn rewrite_method_call_with_overflow(expr_kind: &ast::ExprKind,
 383                                      last: &mut String,
 384                                      almost_total: usize,
 385                                      total_span: Span,
 386                                      context: &RewriteContext,
 387                                      shape: Shape)
 388                                      -> bool {
 389     if let &ast::ExprKind::MethodCall(ref method_name, ref types, ref expressions) = expr_kind {
 390         let shape = match shape.shrink_left(almost_total) {
 391             Some(b) => b,
 392             None => return false,
 393         };
 394         let mut last_rewrite = rewrite_method_call(method_name.node,
 395                                                    types,
 396                                                    expressions,
 397                                                    total_span,
 398                                                    context,
 399                                                    shape);
 400
 401         if let Some(ref mut s) = last_rewrite {
 402             ::std::mem::swap(s, last);
 403             true
 404         } else {
 405             false
 406         }
 407     } else {
 408         unreachable!();
 409     }
 410 }
 411
 412 // Returns the expression's subexpression, if it exists. When the subexpr
 413 // is a try! macro, we'll convert it to shorthand when the option is set.
 414 fn pop_expr_chain(expr: &ast::Expr, context: &RewriteContext) -> Option<ast::Expr> {
 415     match expr.node {
 416         ast::ExprKind::MethodCall(_, _, ref expressions) => {
 417             Some(convert_try(&expressions[0], context))
 418         }
 419         ast::ExprKind::TupField(ref subexpr, _) |
 420         ast::ExprKind::Field(ref subexpr, _) |
 421         ast::ExprKind::Try(ref subexpr) => Some(convert_try(subexpr, context)),
 422         _ => None,
 423     }
 424 }
 425
 426 fn convert_try(expr: &ast::Expr, context: &RewriteContext) -> ast::Expr {
 427     match expr.node {
 428         ast::ExprKind::Mac(ref mac) if context.config.use_try_shorthand() => {
 429             if let Some(subexpr) = convert_try_mac(mac, context) {
 430                 subexpr
 431             } else {
 432                 expr.clone()
 433             }
 434         }
 435         _ => expr.clone(),
 436     }
 437 }
 438
 439 // Rewrite the last element in the chain `expr`. E.g., given `a.b.c` we rewrite
 440 // `.c`.
 441 fn rewrite_chain_subexpr(expr: &ast::Expr,
 442                          span: Span,
 443                          context: &RewriteContext,
 444                          shape: Shape)
 445                          -> Option<String> {
 446     let rewrite_element = |expr_str: String| if expr_str.len() <= shape.width {
 447         Some(expr_str)
 448     } else {
 449         None
 450     };
 451
 452     match expr.node {
 453         ast::ExprKind::MethodCall(ref method_name, ref types, ref expressions) => {
 454             rewrite_method_call(method_name.node, types, expressions, span, context, shape)
 455         }
 456         ast::ExprKind::Field(_, ref field) => rewrite_element(format!(".{}", field.node)),
 457         ast::ExprKind::TupField(_, ref field) => rewrite_element(format!(".{}", field.node)),
 458         ast::ExprKind::Try(_) => rewrite_element(String::from("?")),
 459         _ => unreachable!(),
 460     }
 461 }
 462
 463 // Determines if we can continue formatting a given expression on the same line.
 464 fn is_continuable(expr: &ast::Expr) -> bool {
 465     match expr.node {
 466         ast::ExprKind::Path(..) => true,
 467         _ => false,
 468     }
 469 }
 470
 471 fn rewrite_method_call(method_name: ast::Ident,
 472                        types: &[ptr::P<ast::Ty>],
 473                        args: &[ptr::P<ast::Expr>],
 474                        span: Span,
 475                        context: &RewriteContext,
 476                        shape: Shape)
 477                        -> Option<String> {
 478     let (lo, type_str) = if types.is_empty() {
 479         (args[0].span.hi, String::new())
 480     } else {
 481         let type_list: Vec<_> =
 482             try_opt!(types.iter().map(|ty| ty.rewrite(context, shape)).collect());
 483
 484         let type_str = if context.config.spaces_within_angle_brackets() && type_list.len() > 0 {
 485             format!("::< {} >", type_list.join(", "))
 486         } else {
 487             format!("::<{}>", type_list.join(", "))
 488         };
 489
 490         (types.last().unwrap().span.hi, type_str)
 491     };
 492
 493     let callee_str = format!(".{}{}", method_name, type_str);
 494     let span = mk_sp(lo, span.hi);
 495
 496     rewrite_call(context, &callee_str, &args[1..], span, shape)
 497 }